Stability of Deep Underground Openings Through Large Fault Zones in Argillaceous Rock

sustainability

Article Stability of Deep Underground Openings through Large Fault Zones in Argillaceous Rock

Deyu Qian 1,* ID , Nong Zhang 1,*, Dongjiang Pan 1 ID , Zhengzheng Xie 1, Hideki Shimada 2, Yang Wang 1,3, Chenghao Zhang 1 and Nianchao Zhang 4 1 Key Laboratory of Deep Coal Resource Mining, Ministry of Education of China, School of Mines, China University of Mining and Technology, Xuzhou 221116, China; [email protected] (D.P.); [email protected] (Z.X.); [email protected] (Y.W.); [email protected] (C.Z.) 2 Department of Earth Resources Engineering, Faculty of Engineering, Kyushu University, Fukuoka 819-0395, Japan; [email protected] 3 School of Public Policy and Urban Affairs, College of Social Sciences and Humanities, Northeastern University, Boston, MA 02115, USA 4 School of Earth Sciences, University of Queensland, St Lucia, QLD 4072, Australia; [email protected] * Correspondence: [email protected] (D.Q.); [email protected] (N.Z.)

Received: 11 November 2017; Accepted: 21 November 2017; Published: 22 November 2017

Abstract: The stability of underground openings is pivotal to sustainable safe mining in underground coal mines. To determine the stability and tunneling safety issues in 800-m-deep underground openings through large fault zones in argillaceous rocks in the Guqiao Coal Mine in East China, the pilot industrial test, laboratory experimentation, and field measurements were used to analyze the large deformations and failure characteristics of the surrounding rock, the influence factors of safe excavation and stability of underground openings, and to study the stability control countermeasures. The main factors influencing the stability and tunneling safety include large fault zones, high in situ stress, poor mechanical properties and engineering performance of the argillaceous rock mass, groundwater inrush and gas outburst. According to the field study, the anchor-ability of cables and the groutability of cement-matrix materials in the argillaceous rock in the large fault zones were extremely poor, and deformations and failure of the surrounding rock were characterized by dramatic initial deformation, high long-term creep rate, obviously asymmetric deformations and failure, rebound of roof displacements, overall loosened deformations of deep surrounding rock on a large scale, and high sensitivity to engineering disturbance and water immersion. Various geo-hazards occurred during the pilot excavation, including roof collapse, groundwater inrush, and debris flow. Control techniques are proposed and should be adopted to ensure tunneling safety and to control the stability of deep underground openings through large fault zones, including regional strata reinforcement technique such as ground surface pre-grouting, primary enhanced control measures, floor grouting reinforcement technique, and secondary enclosed support measures for long-term stability, which are critical for ensuring the sustainable development of the coal mine.

Keywords: deep underground opening; argillaceous rock; fault zones; coal mine; excavation; deformation; grouting; stability

1. Introduction Sustainable mining of coal resources will inevitably shift from shallow to deep within the earth’s crust in China. The shallow resources are limited and are being exhausted, as the demand for and dependence on energy resources stemming from China’s quick economic development and industrialization have caused the growth of coal production and consumption [1–4]. Coal accounted

Sustainability 2017, 9, 2153; doi:10.3390/su9112153 www.mdpi.com/journal/sustainability Sustainability 2017, 9, 2153 2 of 28 for 75.6% and 66.0% of China’s total energy production and consumption in 2013, respectively [5]. Coal has and will continue to occupy the dominant position in China’s long-term energy mix given the rich coal resources and poor oil and natural gas resources [6–8]. With the increasing demand for energy and mining intensity, the mining depth of underground coal mines in China has increased 8–12 m per year on average. Particularly, the mining depth in East China increases by 10–25 m/year on average [2]. Approximately 200 underground coal mines presently exist, the mining depths of which have exceeded 800 m in the mining areas of Huainan, Kailuan, Xinwen, Shenyang, Changguang, Jixi, Fushun, Fuxin, and Xuzhou. Moreover, 47 underground coal mines exist in China with mining depths of more than 1000 m. The kilometer-deep coal mines in China are mainly found in the North, East, and Northeast, 80.85% of which are in East China, including the Anhui, Jiangsu, and Shandong Provinces. Among these is the Guqiao Coal Mine, which has a maximum annual coal output of 12.3 million tons (Mt) in the Huainan mining area, and the Suncun Coal Mine, which has the greatest mining depth of 1501 m in the Xinwen mining area. These are the largest kilometer-deep coal mine and the deepest coal mine in Asia, respectively. Deep underground coal resource development is being demanded by the national energy strategy. The deep coal mines in the mining areas of East China have complex geological conditions, with thick Cenozoic loose strata, large overburden depth of coal seams, and Ordovician-confined aquifers at the bottom. The coal-series strata belong to a Carboniferous-Permian system sedimentary environment of the North China platform type. Over time, the coal seam situation and geological conditions of the coal-series strata have been affected by the Indosinian movement, Yanshan movement, Himalayan tectonic movement, and neo-tectonic movements. Faults and folds are well developed. For example, the Huainan mining area is a coalfield with the most complex geological conditions. Eighty-three large faults with throws greater than 50 m high, more than 4900 faults with throws greater than 5 m high, and many other small faults in the Huainan mining area have been found [9]. Faults are commonly encountered poor geological conditions during underground excavation [10]. Deformations and failure of an underground opening are prominently governed by adjacent faults [10,11]. In engineering practices, many instability problems, including underground openings during excavation and operation, are caused by these deformations and failures regardless of fault exposure or concealment during excavation [12,13]. Some experts and scholars have analyzed the surrounding rock stability of underground openings or tunnels affected by faults. Numerical and physical simulation analyses have revealed that the extent of deformation and the size of the plastic zone increased as the distance from a fault to the tunnel decreased, and the shear deformation occurred along the weak plane [14]. Numerical investigation using Universal Distinct Element Code (UDEC) software indicated that a fault affects the stability of an underground opening by increasing the plastic zones and displacements, and by causing asymmetrically distribution in rock masses adjacent to the excavation [12]. Using an articulated design for the lining was proposed for a motorway tunnel through an active fault zone in Turkey to mitigate the seismic risk [15]. The freezing construction method was used in the Guangzhou metro tunnel crossing the Qingquanjie fault [16]. Based on monitoring analysis of the main haulage roadway at a mining level of −648 m through a large fault, floor heave was an important factor for instability and failure of the roadway. The grouting tube and rock bolts at wall corners were used to resist the shear displacement at the floor corner with concentrated stress [10]. Support schemes of the surrounding rock, including 2–3 m-long advance pre-grouting, shotcrete, shedding, and bolts, were proposed to control the stability of a main roadway through a large aquitard normal fault F92 with 435 m-high throw in the Taoyuan Coal Mine in China [17]. Previous control techniques of the surrounding rock in underground engineering have mainly focused on a single fault fracture zone or fault zones at shallow depths. However, few studies have been performed on the stability control of deep underground openings through large fracture zones of fault groups (fault zones) in areas with high in situ stress. Currently, no completely successful engineering examples have reported safety and long-term stability of underground openings 800 m or deeper below the ground surface through large thick fault zones. When underground openings, Sustainability 2017, 9, 2153 3 of 28 such as tunnels, are excavated through large thick fault zones, construction accidents, such as the collapse of large rock mass volume into the opening, may suddenly and unexpectedly occur because of the extremely variable lithology, complexity, and mutability of geological conditions. This causes considerable difficulties for the construction and property losses but also seriously threatens the lives of workers. Using conventional surrounding rock control techniques, avoiding geo-hazards such as roof collapse, groundwater inrush, debris flow, etc., during excavation is difficult. Progressive instability and failure of the surrounding rock and support structure during operation may be a result of long-term creep and time-dependent behavior, especially in deep underground openings through large thick fault zones in argillaceous rock. The tunneling safety and stability of underground openings or gateroads are vital for ventilation, transportation and other essential services for sustainable safe mining of underground coal mines [18,19]. Based on the engineering background of underground openings at a depth of 800 m below the ground surface, through large fault zones in argillaceous rock in the Guqiao Coal Mine in the Huainan mining area, the pilot industrial test, laboratory experiment, and field measurements methods were used to analyze the deformation and failure characteristics of the surrounding rock, reveal the factors that influence safe excavation and underground opening stability, and study the proposed control countermeasures for safe excavation and stability. The originality of this study includes the minimum range of pre-grouting and post-grouting reinforcement for deep underground openings through large fault zones, pre-grouting and deep holes post-grouting with a novel polyurethane grouting material, and floor grouting reinforcement technique. The main objectives are to propose safe excavation and stability control techniques for deep underground opening through large fault zone in argillaceous rock. This study has practical referable significance for deep underground openings through large fault zones, especially in underground coal mines in East China, as well as other deep underground engineering scenarios with similarly complex geological conditions.

2. Geological Proﬁles of Deep Underground Openings in Large Fault Zones

2.1. Introduction to the Guqiao Coal Mine The Guqiao Coal Mine is in the Northwest of Huainan City, Anhui Province, 500 km from Shanghai City, China. It is one of the major coal mines owned by Huainan Mining (Group) Co., Ltd., Huainan, China, that provides an important energy source for the rapid sustainable economic growth of East China [20], producing an annual coal output of more than 11 million tons (Mt) since 2009, reaching a maximum of 12.3 Mt/year. The mine is expected to have a remaining service life of up to 85 years as of 2013. The coal mine is divided into four districts: central, eastern, northern, and southern. The recoverable reserves within the southern district are 392.7 million tons, accounting for 30.3% of the total recoverable reserves of 1297 million tons in the Guqiao Coal Mine.

2.2. Geological Profiles of Deep Underground Openings The south haulage and rail underground openings, with a horizontal width of 30–40 m in the first mining level of −780 m, connect the central mining district to the southern mining district as two key transportation corridors playing a pivotal role in the sustainable development of the Guqiao Coal Mine with high output. The south underground openings, with a length of 3000 m, inevitably pass through large geological anomaly fault zones within the southern “X” conjugate shear fault zones where many numerous fault structures exist that are extremely complex, as shown in Figure1. According to drill core logs and surface geological boreholes (SGB), the rock quality designation (RQD) values (Figure2) are generally less than 25%, and the RQD is zero within the fault fracture zones, reflecting that the fault zones and adjacent rock mass are extremely broken. The pilot underground excavation passing through fault FD108-1 also showed that small faults and fractures are well-developed, and the surrounding rock is generally broken. The lithology is mainly made of argillaceous rock mass. The rock mass contains dense fractures, most of which are filled with fault gouge and argillaceous infilling. Sustainability 2017, 9, 2153 4 of 29

According to drill core logs and surface geological boreholes (SGB), the rock quality designation (RQD) values (Figure 2) are generally less than 25%, and the RQD is zero within the fault fracture zones, reflecting that the fault zones and adjacent rock mass are extremely broken. The pilot underground excavation passing through fault FD108-1 also showed that small faults and fractures are well-developed, and the surrounding rock is generally broken. The lithology is mainly made of argillaceousSustainability 2017 rock, 9, 2153mass. The rock mass contains dense fractures, most of which are filled with4 offault 28 gouge and argillaceous infilling.

0m 3 -1 West d7 0 F H= Fd79 ∠65-70°H=40m 0° -7 60 ∠ South North Fd79 ∠65-70°H=0-40m Measurement points m 5 6 East 1 = - m H 8 5 m 0 0 ° = Collapse 7m C3 1 C1 C8 C7 C6 C5 C4 C2 0 C10 C11 C12 C13 C9 1C9 =1 D - 8 H F - ° 0 °H G5 0 7 5 -8 GA2 SJ57 SJ56 ∠ 7 70 ∠ 86m ∠ SJ52 Collapse 8-b South haulage 80°H=0-18m a 10

∠ - G5+46m F 5 G5+53m sealing 30m

8 underground opening 4 R

0 Fd78 H=35m R

C Fd77 1 C d F m S75S74 S73 S72 S71 S68 S67 S66 S76 S69

m ° Η=50 -770.724 B2 B1 South rail B6 B5 -85 B4 B3 FD108-1 underground opening =0 H 70-80 ∠ ∠

70° 70-80°H=5-65m ∠ FD108-1 08 Measurement points FD1

(a)

(b)

FigureFigure 1. ((aa)) Plan Plan of of the the geological profilesprofiles ofof thethe undergroundunderground openingsopenings andand field field measurement measurement pointspoints during during the pilot excavation ofof thethe GuqiaoGuqiao CoalCoal Mine.Mine. Note:Note: CR5:CR5: ConnectionConnection roadway roadway No. No. 5; 5; CR4:CR4: Connection Connection roadway No. 4; SJ52 and S68S68 areare twotwo geologicalgeological observationobservation points points at at the the interface interface betweenbetween the the geological geological anomaly fault zones andand normalnormal locationslocations inin thethe southsouth haulage haulage and and the the rail rail undergroundunderground openings, openings, respectively. (b) SectionSection ofof geologicalgeological profilesprofiles of of the the haulage haulage underground underground openingopening in in the Guqiao Coal Mine.Mine. Note:Note: GroundGround surfacesurface pre-groutingpre-grouting(GSPG) (GSPG) reinforcement reinforcement range range outlinedoutlined in in the the green box was completed afterafter thethe pilotpilotexcavation excavation and and before before re-excavation. re-excavation.

TheThe underground underground excavation excavation will will involve involve the the ge geologicalological anomaly anomaly fault fault zones zones consisting consisting of of a ◦ ◦ seriesa series of offaults faults from from the the north north to the to thesouth, south, incl includinguding FD108-1 FD108-1 (normal (normal faults, faults, dip angle: dip angle: 70–80°, 70 –80throw, heightthrow H height = 65 m, H =the 65 width m, the of width aperture of aperture with fillings with ﬁllingsof clay offault clay gouge fault W gouge = 4.3 W m), = 4.3FD108-b m), FD108-b (normal ◦ ◦ ◦ ◦ fault,(normal dip fault, angle: dip 70–80°, angle: H 70 = –8010 m),, H FD108 = 10 m), (normal FD108 fault, (normal dip fault,angle: dip 70–80°, angle: H 70= 37–80 m,, W H == 3712 m,m), ◦ ◦ FD108-aW = 12 m),(normal FD108-a fault, (normal dip angle: fault, 75°, dip H angle:= 5 m), 75Fd77, H (normal = 5 m), fault, Fd77 dip (normal angle: fault, 75°, H dip = 0–18 angle: m), 75 etc., TheH = structural 0–18 m), etc.form The in the structural section formis a large in the grab sectionen made is a largeup of grabenthe eight made main up step-shaped of the eight normal main step-shaped normal faults with an east–west (EW) direction on the strike and a dip in the south–north (SN) direction. The maximum combined drop of 140 m of the fault group is 670 m wide from north to south. The structures are well-developed in the fault zones. Moreover, the groundwater pressures within the large fault zones are high [21]. Sustainability 2017, 9, 2153 5 of 29 faults with an east–west (EW) direction on the strike and a dip in the south–north (SN) direction. The maximum combined drop of 140 m of the fault group is 670 m wide from north to south. The Sustainabilitystructures 2017are ,well-developed9, 2153 in the fault zones. Moreover, the groundwater pressures within5 of the 28 large fault zones are high [21].

Length Core Depth Thickness RQD Borehole of core extraction No. (m) (m) (%) Rock strata column (m) rate (%)

163 742.50

164 751.80 9.30 9.15 98 10 Sandy mudstone

165 755.10 3.30 2.90 88 30 Siltstone

166 756.85 1.75 1.45 83 0 Mudstone 167 757.65 0.80 0.80 100 Coal seam 16-2 168 758.20 0.55 0.55 100 50 Mudstone

169 759.80 1.60 1.50 94 0 Fine sandstone

170 761.80 2.00 2.00 100 15 Sandy mudstone

171 762.65 0.85 Coal seam 16-1

172 784.50 21.85 20.90 96 30 Sandy mudstone

173 785.50 1.00 0.90 90 10 Argillaceous rock

174 787.00 1.50 1.30 87 10 Sandy mudstone

175 796.00 9.00 8.30 92 30 Argillaceous rock

176 818.00 22.00 19.60 89 0 Sandy mudstone

177 819.00 1.00 1.00 100 0 Fine sandstone

178 821.50 2.50 2.40 96 0 Sandy mudstone

179 822.60 1.10 0.90 82 0 Fine sandstone

180 827.05 4.45 4.45 100 0 Mudstone

181 829.60 2.55 2.18 85 Coal seam 13-1

FigureFigure 2.2. Rock quality designation (RQD) Values and boreholeborehole corecore columncolumn ofof surfacesurface geologicalgeological boreholeborehole No.No. 1010 (SGB10).(SGB10).

3. Deformations, Failure Characteristics, and Factors Influencing Deep Underground Openings 3. Deformations, Failure Characteristics, and Factors Inﬂuencing Deep Underground Openings throughthrough LargeLarge FaultFault ZonesZones

3.1.3.1. ProﬁlesProfiles ofof IndustrialIndustrial TestTest ofof thethe PilotPilot ExcavationExcavation ofof DeepDeep UndergroundUnderground Openings Openings TheThe southsouth undergroundunderground openingopening withwith aa quadrantquadrant angleangle ofof NS178NS178°◦ (azimuth(azimuth ofof 358358°)◦) waswas excavatedexcavated along along an an uphill uphill slope slope of 3‰ of 3 at aat depth a depth of approximately of approximately 800 m 800below m the below ground the groundsurface. surface.Its cross-section Its cross-section has a semicircle-arch has a semicircle-arch crownh shape crown with shape a withstraight a straight sidewall. sidewall. The excavation The excavation cross- cross-section was 6000 mm wide and 4600 mm high, whereas the cross-section after the use of U-shaped steel sets and shotcrete support was 5600 mm wide and 4400 mm high. Many support schemes Sustainability 2017, 9, 2153 6 of 28 were used and optimized during the industrial testing of the pilot excavation of the underground openings through the large geological anomaly fault zones, such as the single pilot heading method (small cross-section: 4600 mm wide and 3500 mm high) and 35 m-long boreholes pre-grouting. However, various geo-hazards still occurred during the previous excavation, including roof collapse, groundwater inrush, and debris ﬂow, which seriously threatened tunneling safety in the deep underground openings. Several main optimization support schemes during the pilot excavation were used as follows.

(1) Scheme 1 (SJ52~SJ52 + 80 m, G5~G5 + 46 m in the south haulage underground opening; S68~Fault F108 in the south rail underground opening): Five 3 m-long advanced boreholes pre-grouting with rapid-hardening high-strength sulfoaluminate cement (with a strength grade of 52.5 MPa) and U29-shaped steel sets support with intervals of 500 mm, plus 19 high-strength bolts reinforcing each cross-section (array pitch was 1000 mm), primary shotcrete with a thickness of 70 to 100 mm and seven pre-stressed cables (length of 6300 mm and a diameter of 17.8 mm) supporting the roof and sidewalls (the array pitch was 1000 mm), and secondary shotcrete with a thickness of 50 mm, plus post-grouting (1.5 m-deep holes, 3 m-deep holes, and supplementary 8 m-deep holes post-grouting with ordinary Portland cement with a strength grade of 42.5 MPa). (2) Scheme 2 (SJ52 + 80 m~SJ52 + 150.8 m, G5~G5 + 46 m in the south haulage underground opening): Five 8 m-long advanced boreholes pre-grouting with sulfoaluminate cement, U29-shaped steel sets support with intervals of 500 mm, primary shotcrete with a thickness of 70–100 mm, 17 bolts and seven cables reinforcing each cross-section, secondary shotcrete with a thickness of 50 mm, and post-grouting (3 m-deep holes with ordinary Portland cement and 8 m-deep holes with superfine cement with a strength grade of 62.5 MPa). The specifications of the bolts were the same as those of Scheme 1. The interval and array pitch of the bolts were 800 mm and 1000 mm, respectively. The diameter and length of the cables were 21.8 mm and 6300 mm, respectively. The array pitch of the cables was 1000 mm. (3) Scheme 3 (SJ52 + 120 m~SJ52 + 150 m in the south haulage underground opening): 35 m-long borehole grouting (the grouting material was ordinary Portland cement with a strength grade of 52.5 MPa and sodium silicate), U36-shaped steel sets support with intervals of 500 mm, plus bolts and cables, shotcrete with a thickness of 70–100 mm, and post-grouting (3 m-deep hole with ordinary Portland cement and 8 m-deep hole with superfine cement). The parameters of the bolts, cables, and post-grouting were the same as those in Scheme 2. (4) Scheme 4 (Fault FD108 at SJ52 + 148.8 m~SJ52 + 154 m in the south haulage underground opening): Five advanced exploration boreholes (25–75 m long) and six gas and water drainage boreholes (46–49 m long), 30 m-long boreholes pre-grouting (the grouting material was ordinary Portland cement with a strength grade of 52.5 MPa and sodium silicate (3–5% by weight)), 15 m-long shed-pipe advanced pre-grouting support, 8 m-long boreholes pre-grouting with Gurit chemical material, U36-shaped steel sets support with intervals of 500 mm, shotcrete with a thickness of 70–100 mm and 3 m-deep holes post-grouting with ordinary Portland cement, plus cables, and 8 m-deep holes post-grouting with superfine cement. The parameters of the cables and post-grouting were the same as those in Scheme 2. (5) Scheme 5 (G5 + 46 m~G5 + 53 m in the south haulage underground opening and from Fault F108 at S68, and 200 m to the south in the south rail underground opening): 8 m-long boreholes pre-grouting with sulfoaluminate cement, single-pilot heading method with a small cross-section 4600 mm wide and 3500 mm high, U36-shaped steel sets with intervals of 500 mm, shotcrete with a thickness of 70–100 mm, 3 m-deep holes with high strength sulfoaluminate cement, 13 bolts and five cables supporting each cross-section (the bolts and cables had a diameter of 22 mm and a length of 2800 mm, and a diameter of 21.8 mm and a length of 7300 mm, respectively. The array pitches of the bolt and cable layouts were both 1000 mm), and 8 m-deep holes post-grouting with superfine cement. Sustainability 2017, 9, 2153 7 of 28 Sustainability 2017, 9, 2153 7 of 29 Sustainability 2017, 9, 2153 7 of 29 The roof collapse and debris flow occurred in the areas from SJ52 + 120 m to SJ52 + 150 m in The roof collapse and debris flow occurred in the areas from SJ52 + 120 m to SJ52 + 150 m in the the southThe roof haulage collapse underground and debris opening flow occurred when thein th tunnelinge areas from face SJ52 approached + 120 m faultto SJ52 FD108 + 150 under m in the the south haulage underground opening when the tunneling face approached fault FD108 under the southsupport haulage of Scheme underground 2. The instantaneous opening when volume the tunn ofeling debris face flow approached was up to fault 20 m 3FD108. The areasunder were the support of Scheme 2. The instantaneous volume of debris flow was up to 20 m3. The areas were then supportthen sealed, of Scheme and 88.75 2. The t sulfoaluminate instantaneous volume cement wasof debris used flow to infill was the up roof to 20 collapse m3. The space. areas were After then that, sealed, and 88.75 t sulfoaluminate cement was used to infill the roof collapse space. After that, Scheme sealed,Scheme and 3 was 88.75 used, t sulfoaluminate but the roof collapse cement andwas debrisused to flow infill occurred the roof oncecollapse more space. when After the tunneling that, Scheme face 3 was used, but the roof collapse and debris flow occurred once more when the tunneling face 3approached was used, faultbut the FD108. roof Afterward,collapse and Scheme debris 4flow was used.occurred However, once more the northern when the roof tunneling collapse face and approached fault FD108. Afterward, Scheme 4 was used. However, the northern roof collapse and approacheddebris flow occurredfault FD108. again. Afterward, Scheme 4 was used. However, the northern roof collapse and debris flow occurred again. debrisThe flow roof occurred collapse again. occurred in the south rail underground opening under support Scheme 1 when The roof collapse occurred in the south rail underground opening under support Scheme 1 when the tunnelingThe roof collapse face reached occurred fault in FD108. the south Scheme rail un 5,derground including theopening 8 m-long under borehole support pre-grouting Scheme 1 when and the tunneling face reached fault FD108. Scheme 5, including the 8 m-long borehole pre-grouting and thepilot tunneling heading face method, reached was fault then FD used108. in Scheme the south 5, railincluding underground the 8 m-long opening borehole from fault pre-grouting FD108 toward and pilot heading method, was then used in the south rail underground opening from fault FD108 toward pilotthe south. heading Nevertheless, method, was the then southern used in roofthe south collapse rail occurredunderground again opening when Scheme from fault 5 was FD108 used toward as the the south. Nevertheless, the southern roof collapse occurred again when Scheme 5 was used as the thetunneling south. Nevertheless, face approached the thesouthern G5 + 53 roof m areacollapse in the occurred south haulage again when underground Scheme 5 opening. was used The as roofthe tunneling face approached the G5 + 53 m area in the south haulage underground opening. The roof tunnelingcollapse in face the approached south underground the G5 + opening 53 m area is shownin the south in Figures haulage3 and underground4. opening. The roof collapse in the south underground opening is shown in Figures 3 and 4. collapse in the south underground opening is shown in Figures 3 and 4.

Figure 3. The debris flow and roof collapse at the tunneling face near fault FD108. FigureFigure 3. 3. TheThe debris debris flow ﬂow and and roof roof collapse collapse at at the the tunneling tunneling face face near near fault fault FD108. FD108.

Figure 4. The collapse section diagram of the south haulage underground opening. FigureFigure 4. 4. TheThe collapse collapse section section diagram diagram of of the the south south haulage haulage underground underground opening. opening. In addition, other geo-hazards were encountered, and special phenomena occurred during In addition, other geo-hazards were encountered, and special phenomena occurred during excavation.In addition, Orifice other flow geo-hazardsand groundwater were inflow encountered, occurred and while special drilling phenomena the advanced occurred exploration, during excavation. Orifice flow and groundwater inflow occurred while drilling the advanced exploration, excavation.gas, and groundwater Orifice flow drainage and groundwater boreholes. The inflow distance occurred of the while orifice drilling flow theincluding advanced coal, exploration, water, and gas, and groundwater drainage boreholes. The distance of the orifice flow including coal, water, and gas,gravel and from groundwater the borehole drainage was more boreholes. than 10 m. The The distance maximum of the orifice orifice flow flow from including a single coal, advanced water, gravel from the borehole was more than 10 m. The maximum orifice flow from a single advanced andexploration gravel from borehole the borehole was up wasto 14 more m3. The than maximum 10 m. The maximumgas concentration orifice flow in the from advanced a single geological advanced exploration borehole was up to 14 m3. The maximum gas concentration in the advanced geological explorationboreholes was borehole up to 10%. was The up tosticking, 14 m3. blocking, The maximum and jamming gas concentration of drill bits infrequently the advanced occurred geological during boreholes was up to 10%. The sticking, blocking, and jamming of drill bits frequently occurred during boreholesthe advanced was exploration up to 10%. Thedrilling sticking, process blocking, and pre-grouting and jamming boreholes. of drill bits frequently occurred during the advanced exploration drilling process and pre-grouting boreholes. the advanced exploration drilling process and pre-grouting boreholes. 3.2. Deformations and Failure Characteristics of Deep Underground Openings 3.2. Deformations and Failure Characteristics of Deep Underground Openings The pressure and deformation behaviors of the underground openings were changeable because The pressure and deformation behaviors of the underground openings were changeable because of the extremely complex and variable lithology in the large fault zones. Field measurements, such of the extremely complex and variable lithology in the large fault zones. Field measurements, such Sustainability 2017, 9, 2153 8 of 28

3.2. Deformations and Failure Characteristics of Deep Underground Openings

SustainabilityThe pressure 2017, 9, 2153 and deformation behaviors of the underground openings were changeable because8 of 29 of the extremely complex and variable lithology in the large fault zones. Field measurements, such as assurface surface displacements displacements using using the the M9579-YHJ-300J M9579-YHJ-300J (A) (A) laser laser distance distance measurement measurement instrument instrument with with the theaccuracySustainability accuracy of 1 2017of mm, 1, 9mm,, 2153 axial axial load load of of bolts bolts and and cables, cables, and and borehole borehole image image monitoring,monitoring, were performed8 of 29 during the pilot excavation to analyze the pres pressuresure on the support structure and deformation as surface displacements using the M9579-YHJ-300J (A) laser distance measurement instrument with behavior law of the surrounding rock and evaluate the effect and rationality of various support behaviorthe accuracy law ofof 1the mm, surro axialunding load of rockbolts and cables,evaluate and the borehole effect image and rationalitymonitoring, of were various performed support measures.during the The pilot layout excavation of the ﬁeldfield to measurementmeasurementanalyze the pres pointspointssure during duringon the the thesupport pilot pilot excavation excavationstructure and is is shown shown deformation in in Figure Figure 1. 1.The Thebehavior displacements displacements law of the of theof surro the surrounding undingsurrounding rock rock and rock at evaluate the at representativethe representative the effect measurementand measurementrationality points of variouspoints C3 at C3 SJ52support at +SJ52 24 m+ 24and measures.m C7 and at C7 SJ52 The at +SJ52 layout 104 + m 104 of are them graphically arefield graphically measurement presented presented points in Figures during in Figures5 the and pilot 65. and excavation 6. is shown in Figure 1. The displacements of the surrounding rock at the representative measurement points C3 at SJ52 + 3500 140 80 24 m and C7 at SJ52 +Measurement 104 m are point graphically C3 presented 1400in Figures 5 andMeasurement 6. point C3 3000 120 70 1200 3500 140 80 60 2500 adding 8-m-deep holes 100 14001000 Measurement point C3 Measurementpost-grouting point C3 with cement 3000 120 70 50 2000 80 1200800 60 40 2500 adding 8-m-deep holes 100 1000 1500 post-grouting with cement 60 600 50 D(sidewall-to-sidewall) D(left sidewall) 30 2000 80 800 D(roof-to-floor) 400 D(right sidewall) 40

1000 40 20 Velocity (mm/d) Velocity (mm/d) Velocity

V(sidewall-to-sidewall) Displacement (mm) V(left sidewall) Displacement (mm) Displacement 1500 60 600 30 V(roof-to-floor) D(sidewall-to-sidewall) 200 D(left V(right sidewall) sidewall) 10 500 20 D(roof-to-floor) 400 D(right sidewall)

1000 40 20 Velocity (mm/d) Velocity (mm/d) Velocity 0 V(sidewall-to-sidewall) Displacement (mm) V(left sidewall) 0 Displacement (mm) Displacement 0 0 V(roof-to-floor) 200 V(right sidewall) 10 500 20 -200 -10 0 50 100 150 200 250 300 0 0 50 100 150 200 2500 300 0 0 Time (day) Time (day) -200 -10 0 50 100(a) 150 200 250 300 0 50 100( 150b) 200 250 300 Time (day) Time (day) Measurement point C3 70 250 (a) 20 3000 Measurement(b) point C3 Floor dinting 60 250 Measurement point C3 20 30002500 Measurement point C3 70 200 15 Floor dinting 60 50 25002000 200 15 150 10 50 40 D(roof) 20001500 150 10 V(roof) D(floor) 40 100 5 30 D(roof) 1500 V(floor) 1000 D(floor) Velocity (mm/d) V(roof) Velocity (mm/d) 100 5 30 20 Displacement (mm) Displacement (mm) Displacement V(floor) 50 0 1000 Velocity (mm/d) 500 20 Velocity (mm/d) Displacement (mm) Displacement (mm) Displacement 10 50 0 500 0 -5 10 0 0 0 -5 0 0 0 50 100 150 200 250 300 0 50 100 150 200 250 300 0 50 100Time (day) 150 200 250 300 0 50 100Time 150 (day) 200 250 300 Time(c) (day) Time( (day)d) (c) (d) Figure 5. 5. CurvesCurves of displacements of displacements and velocities and velocities versus time versus at measurement time at measurement point C3: (a) pointsidewall- C3: Figure 5. Curves of displacements and velocities versus time at measurement point C3: (a) sidewall- to-sidewall(a) sidewall-to-sidewall and roof-to-floor; and roof-to-ﬂoor; (b) left and right (b) left sidewalls; and right (c sidewalls;) roof; and ((cd)) roof; floor. and (d) ﬂoor. to-sidewall and roof-to-floor; (b) left and right sidewalls; (c) roof; and (d) floor.

1200 100 180 1200 100 180 Measurement point C7 3500 Measurement point C7 Measurement point C7 3500 Measurement point C7 160 160 1000 3000 1000 80 3000 140 80 140 2500 120 800 2500 120 800 60 60 100 20002000 100 600600 80 1500 80 1500 D(left D(left sidewall) sidewall) 40 40 D(sidewall-to-sidewall) 60 D(right sidewall) D(sidewall-to-sidewall) 60 400400 D(right sidewall) 10001000 Velocity (mm/d) D(roof-to-floor) D(roof-to-floor) Velocity (mm/d) V(left sidewall) V(left sidewall) Velocity (mm/d) Velocity (mm/d) Displacement (mm) Displacement Displacement (mm) Displacement 40 Displacement (mm) V(sidewall-to-sidewall) V(sidewall-to-sidewall) Displacement (mm) V(right V(right sidewall) sidewall) 20 20 500 500 V(roof-to-floor) V(roof-to-floor) 20 200200 0 0 0 0 0 0 0 -500-500 -20-20 00 50 50 100 100 150 150 200 200 250 250 300 00 50 50 100 100 150 150 200 200 250 250 300 300 TimeTime (day) (day) TimeTime (day) (day) (a(a) ) (b()b) Figure 6. Cont. Sustainability 2017, 9, 2153 9 of 28 Sustainability 2017, 9, 2153 9 of 29

35 1200 100 Measurement point C7 500 Measurement point C7 30 1000 80 25 400 800 20 60 300 15 600 D(roof) 10 D(left sidewall) 40 200 V(roof) 400 D(right sidewall)

5 (mm/d) Velocity V(left sidewall) Velocity (mm/d) Displacement (mm) Displacement Displacement (mm) Displacement 100 V(right sidewall) 20 0 200

-5 0 0 0 -10 0 50 100 150 200 250 300 0 50 100 150 200 250 300 Time (day) Time (day) (c) (d)

FigureFigure 6. 6. CurvesCurves of displacements of displacements and velocities and velocities versus time versus at measurement time at measurement point C7: (a) sidewall- point C7: (a)to-sidewall sidewall-to-sidewall and roof-to-floor; and roof-to-ﬂoor; (b) left and right (b) left sidewalls; and right (c) sidewalls;roof; and (d (c)) floor. roof; and (d) ﬂoor.

3.2.1.3.2.1. Dramatic Dramatic Initial Initial Deformations Deformations TheThe sidewall-to-sidewall sidewall-to-sidewall andand roof roof-to-floor-to-floor displacements displacements were were severe severe at the at theearly early stage stage due to due a to a redistributionredistribution of of stresses stresses in in the the rock rock mass mass around around the opening the opening result resultinging from the from excavation the excavation [22]. The [ 22]. Thevisible visible macroscopic macroscopic deformations deformations and and support support structure structure damage damage occurred occurred half halfa month a month after after excavation.excavation. For For example, example, according according toto thethe monitoring results results of of measurement measurement point point C3, C3, the the maximum maximum displacementdisplacement velocities velocities of of sidewall-to-sidewall sidewall-to-sidewall andand roof-to-floor roof-to-floor were were 125 125 mm/day mm/day and and 75 75mm/day, mm/day, respectivelyrespectively (Figure (Figure5a). 5a). Sixteen Sixteen days days later, later, thethe sidewall-to-sidewallsidewall-to-sidewall and and roof-to-floor roof-to-floor displacements displacements werewere 1000 1000 mm mm andand 675 675 mm, mm, respectively, respectively, and and the co therresponding corresponding displacement displacement velocities velocities were 58.33 were mm/day and 41.53 mm/day, respectively. 58.33 mm/day and 41.53 mm/day, respectively. Similarly, according to the monitoring results of measurement point C7, the maximum velocities Similarly, according to the monitoring results of measurement point C7, the maximum velocities of sidewall-to-sidewall and roof-to-floor displacement were 160 mm/day and 80 mm/day, of sidewall-to-sidewall and roof-to-floor displacement were 160 mm/day and 80 mm/day, respectively respectively (Figure 6a). Fifteen days later, the sidewall-to-sidewall and roof-to-floor displacements (Figurewere6 995a). Fifteenmm and days 1170 later,mm, therespectively, sidewall-to-sidewall and the corre andsponding roof-to-floor displacement displacements velocities werewere 995up to mm and48 1170 mm/day mm, and respectively, 79 mm/day, and respectively. the corresponding displacement velocities were up to 48 mm/day and 79 mm/day,The duration respectively. of the dramatic initial deformation stage was approximately 70 days. Seventy days later,The the duration sidewall-to-sidewall of the dramatic and initial roof-to-floor deformation displacements stage was and approximately velocities at measurement 70 days. Seventy point days later,C3 thewere sidewall-to-sidewall 1740 mm and 2128 mm, and 5 roof-to-floor mm/day and displacements10 mm/day, respectively and velocities (Figure at 5a). measurement Likewise, the point C3corresponding were 1740 mm displacements and 2128 mm, and 5velocities mm/day at andmeasurement 10 mm/day, point respectively C7 were 1427 (Figure mm and5a). 2460 Likewise, mm, the5 correspondingmm/day and 11 displacements mm/day, respectively and velocities (Figure at 6a). measurement point C7 were 1427 mm and 2460 mm, 5 mm/day and 11 mm/day, respectively (Figure6a). 3.2.2. High Long-Term Creep Rate 3.2.2. High Long-Term Creep Rate The surrounding rock tended to deform gently and smoothly after the stress redistribution disturbanceThe surrounding and relatively rock rapid tended initial to deform deformation. gently According and smoothly to the aftermonitoring the stress at measurement redistribution disturbancepoint C3 and and construction relatively rapidinformation initial on deformation. site, the supplementary According 8 tom-deep the monitoring holes post-grouting at measurement with pointcement C3 and in Scheme construction 1 was further information completed on site, on the the 143rd supplementary day, when the 8 m-deep sidewall-to-sidewall holes post-grouting and floor with cementcreep inrates Scheme were 12.17 was mm/day further and completed 8.33 mm/day, on the 143rdrespectively, day, when which the then sidewall-to-sidewall dropped to 0.6 mm/day and floor creepand rates 2.60 weremm/day, 2.17 mm/dayrespectively, and on 8.33 the mm/day, 148th day respectively, (Figure 5a,d). which The then8 m-deep dropped holes to 0.6post-grouting mm/day and 2.60reinforced mm/day, the respectively, surrounding on rock the 148thand improved day (Figure the5 ana,d).chor The effect 8 m-deep of the cables holes post-groutingto some extent, reinforced which thedecreased surrounding the deformation rock and improved creep rates. the anchor effect of the cables to some extent, which decreased the deformationHowever, creepa significant rates. time-dependent creep behavior of argillaceous surrounding rock still occurred,However, which a significant would lead time-dependentto the progressive creep damage behavior and delayed of argillaceous failure that undermine surrounding the rocklong- still occurred,term stability which of would underground lead to openings the progressive [23]. The damage effect of andthe 8 delayed m-deep failureholes post-grouting that undermine with the long-termcement was stability limited. of undergroundSpecifically, a total openings of 277 [ 23days]. The later, effect the creep of the rates 8 m-deep of sidewall-to-sidewall, holes post-grouting roof- with cementto-floor, was the limited. left sidewall, Specifically, the right a sidewall, total of 277the roof, days and later, the the floor creep at measurement rates of sidewall-to-sidewall, point C3 were 0.50 mm/day, 1.50 mm/day, 0.43 mm/day, 0.07 mm/day, 0 mm/day, and 1.50 mm/day, respectively. roof-to-floor, the left sidewall, the right sidewall, the roof, and the floor at measurement point The total corresponding displacements were 2045 mm, 3015 mm, 1360 mm, 685 mm, 180 mm, and C3 were 0.50 mm/day, 1.50 mm/day, 0.43 mm/day, 0.07 mm/day, 0 mm/day, and 1.50 mm/day, 2835 mm, respectively (Figure 5). respectively. The total corresponding displacements were 2045 mm, 3015 mm, 1360 mm, 685 mm, 180 mm, and 2835 mm, respectively (Figure5). Sustainability 2017, 9, 2153 10 of 28 Sustainability 2017, 9, 2153 10 of 29

WithWith respect respect toto measurementmeasurement pointpoint C7, the totaltotal displacements of of 1852 1852 mm, mm, 3259 3259 mm, mm, 752 752 mm, mm, 11001100 mm,mm, 358358 mm,mm, andand 29012901 mmmm werewere recordedrecorded for sidewall-to-sidewall, r roof-to-floor,oof-to-floor, the the left left sidewall,sidewall, the the rightright sidewall,sidewall, thethe roof,roof, and the floor, floor, respectively, for a monitoring monitoring period period of of 261 261 days days after excavation. The corresponding creep rates were 1.85 mm/day, 3.49 mm/day, 0.56 mm/day, 1.28 after excavation. The corresponding creep rates were 1.85 mm/day, 3.49 mm/day, 0.56 mm/day, mm/day, −0.18 mm/day, and 3.67 mm/day, respectively (Figure 6). The creep deformation of the deep 1.28 mm/day, −0.18 mm/day, and 3.67 mm/day, respectively (Figure6). The creep deformation underground openings in argillaceous rock could be perpetual and last as long as the opening exists of the deep underground openings in argillaceous rock could be perpetual and last as long as the or even after full closure occurs. The high long-term creep rate indicates that support schemes 1 and opening exists or even after full closure occurs. The high long-term creep rate indicates that support 2 do not meet the requirements for long-term stability of the underground openings. The obvious schemes 1 and 2 do not meet the requirements for long-term stability of the underground openings. creep and time-dependent behavior of deep underground openings in argillaceous rock are due to The obvious creep and time-dependent behavior of deep underground openings in argillaceous rock the solid–liquid–gas-temperature coupling effect of deep rock mass and the interaction with the are due to the solid–liquid–gas-temperature coupling effect of deep rock mass and the interaction with underground openings, which is a complex issue that should be further investigated. the underground openings, which is a complex issue that should be further investigated. 3.2.3. Obviously Asymmetric Deformations 3.2.3. Obviously Asymmetric Deformations The northern 150 m-long pilot excavation of the south haulage underground opening was The northern 150 m-long pilot excavation of the south haulage underground opening was between between the large faults FD108-1 and FD108. Moreover, two strike faults, Fd78 and Fd79, were the large faults FD108-1 and FD108. Moreover, two strike faults, Fd78 and Fd79, were approximately approximately parallel to the opening axis direction that were on the east and west sides of the parallel to the opening axis direction that were on the east and west sides of the opening, respectively. opening, respectively. The deformations and failure of the surrounding rock showed significant asymmetry on the The deformations and failure of the surrounding rock showed significant asymmetry on the same cross-section along the axis direction due to the influence of the fault group. More precisely, same cross-section along the axis direction due to the influence of the fault group. More precisely, the the deformation of the left sidewall (1360 mm) was greater than that of the right sidewall (685 mm), deformation of the left sidewall (1360 mm) was greater than that of the right sidewall (685 mm), which which accounted for 67% of the sidewall-to-sidewall closure (2045 mm) in the area from SJ52 to accounted for 67% of the sidewall-to-sidewall closure (2045 mm) in the area from SJ52 to SJ52 + 80 m SJ52 + 80 m (Figure5a,b). Conversely, the deformation of the right sidewall (1100 mm) was greater (Figure 5a,b). Conversely, the deformation of the right sidewall (1100 mm) was greater than that of than that of the left sidewall (752 mm), representing 59% of the sidewall-to-sidewall closure (1852 mm) the left sidewall (752 mm), representing 59% of the sidewall-to-sidewall closure (1852 mm) in the area infrom the areaSJ52 from+ 80 m SJ52 to +SJ52 80 m+ 150 to SJ52 m (Figure + 150 m 6a,b). (Figure The6 a,b).floor The deformations floor deformations at measurement at measurement points C3 points and C3C7 and accounted C7 accounted for 94% for and 94% 89% and of 89%the corresponding of the corresponding roof-to-floor roof-to-floor convergenc convergences,es, respectively, respectively, which whichwere much were muchgreater greater than that than of that sidewall-to-sidewa of sidewall-to-sidewall,ll, which whichwas much was muchlarger largerthan that than ofthat the ofroof. the roof.The asymmetric The asymmetric failure failure of the of surrounding the surrounding rock and rock support and support structure structure are shown are shown in Figure in Figure 7. 7.

Figure 7. The asymmetric failure of the surrounding rock and support structure: (a) left sidewall from Figure 7. The asymmetric failure of the surrounding rock and support structure: (a) left sidewall from SJ52 to SJ52 + 80 m; (b) right sidewall from SJ52 + 80 m to SJ52 + 150 m; and (c) severe floor heave. SJ52 to SJ52 + 80 m; (b) right sidewall from SJ52 + 80 m to SJ52 + 150 m; and (c) severe floor heave. 3.2.4. Rebound Phenomenon of Roof Displacements 3.2.4. Rebound Phenomenon of Roof Displacements The rebound phenomenon of roof displacements occurred 30 days after the pilot excavation (FiguresThe rebound5c and 6c). phenomenon For instance, the of roofroof displacementsdisplacement velocity occurred at measurement 30 days after point the pilotC3 experienced excavation (Figuresa fluctuation5c and between6c). For instance,−5.0 mm/day the roof and displacement 0 mm/day from velocity 30 days at measurement to 70 days after point excavation C3 experienced (Figure a5c). fluctuation Afterward, between the roof−5.0 displacement mm/day and tended 0 mm/day to be fromstable. 30 This days is to perhaps 70 days because after excavation many developing (Figure5c). Afterward,fissures and the pore roof spaces displacement exist in the tended roof torock be ma stable.ss. The This roof is perhaps experienced because an upward many developing movement fissures trend andunder pore the spaces squeezing exist in action the roof of rockhigh mass.horizontal The roof tectonic experienced stress and an upwardthe large movement sidewall-to-sidewall trend under thedeformations. squeezing action of high horizontal tectonic stress and the large sidewall-to-sidewall deformations.

3.2.5.3.2.5. High High SensitivitySensitivity toto EngineeringEngineering DisturbanceDisturbance and Water Immersion AccordingAccording to to the the construction construction information information and continuousand continuous monitoring, monitoring, the displacement the displacement velocities increasedvelocities dueincreased to the due ﬂoor to the dinting, floor thedinting, adjacent the adjacent excavation, excavati groundwateron, groundwater or construction or construction water Sustainability 2017, 9, 2153 11 of 28

SustainabilitySustainability 2017 2017, 9, ,2153 9, 2153 1111 of of29 29 immersion, and blasting operation. The curve of the displacement velocities showed an obvious fluctuationwaterwater immersion, immersion, during excavation and and blasting blasting due op tooperation. engineeringeration. TheThe curve disturbancecurve ofof thethe anddisplacement water immersion velocitiesvelocities(Figures showed showed5 anand an 6 ) . Forobvious example,obvious fluctuation fluctuation the floor during dintingduring excava excava aroundtiontion measurementdue due to to engineering engineering point disturbancedisturbance C3 occurred andand on water water the immersion 38th immersion day and (Figures (Figures 59th day, 5 and 6). For example, the floor dinting around measurement point C3 occurred on the 38th day and when5 and the 6). For displacement example, the velocities floor dinting of thearound floor measurement were 15 mm/day point C3 andoccurred 13 mm/day, on the 38th respectively. day and 59th59th day, day, when when the the displacement displacement velocities velocities of of the the floor floor were were 1515 mm/day andand 13 13 mm/day, mm/day, respectively. respectively. In contrast, the displacement velocities suddenly accelerated to 30 mm/day on the 39th day and In contrast,In contrast, the the displacement displacement velocities velocities suddenly suddenly accelerated accelerated to 30 mm/day onon the the 39th 39th day day and and 21 21 21 mm/day on the 63rd day (Figure5d). mm/daymm/day on onthe the 63rd 63rd day day (Figure (Figure 5d). 5d). 3.2.6. Overall Loosened Deformations of Deep Surrounding Rock on a Large Scale 3.2.6.3.2.6. Overall Overall Loosened Loosened Deformations Deformations of of Deep Deep Surrounding Surrounding Rock on aa LargeLarge Scale Scale Multiple-pointMultiple-point borehole borehole extensometers extensometers were were installed installed in both in sidewalls both sidewalls (Figure 8(Figure) at measurement 8) at Multiple-point borehole extensometers were installed in both sidewalls (Figure 8) at pointmeasurement B2 in the south point rail B2 underground in the south rail opening underground to obtain opening the to displacements obtain the displacements of the deep of surroundingthe deep measurement point B2 in the south rail underground opening to obtain the displacements of the deep rock mass.surrounding rock mass. surrounding rock mass.

21m14m 9m 4m Left Right 3m 8m 13m 18m 25m 21m14m 9m 4m Left Right 3m 8m 13m 18m 25m 7m 5m 5m 4m 3m 5m 5m 5m 7m 7m 5m 5m 4m 3m 5m 5m 5m 7m Figure 8. Layout of multiple-point borehole extensometers at measurement point B2. Figure 8. Layout of multiple-point borehole extensometers at measurement point B2. Figure 8. Layout of multiple-point borehole extensometers at measurement point B2. The absolute displacements of the 4 m-deep point, 9 m-deep point, and 14 m-deep point within The absolute displacements of the 4 m-deep point, 9 m-deep point, and 14 m-deep point within theThe left absolute sidewall displacements were 93, 52, and of 14 the mm, 4 m-deep respectively, point, which 9 m-deep accounted point, forand 61%, 14 m-deep 34%, and point 9% of within the the left sidewall were 93, 52, and 14 mm, respectively, which accounted for 61%, 34%, and 9% of the totalleft sidewall displacement were of93, 153 52, mm and between 14 mm, 0respectively, m and the 21-m-deep which accounted point, respectively for 61%, 34%, (Figure and 9a).9% ofThe the the total displacement of 153 mm between 0 m and the 21-m-deep point, respectively (Figure9a). totalabsolute displacement displacements of 153 ofmm the between 3 m-deep, 0 8m m-deep, and the 13 21-m-deep m-deep, and point, 18-m-deep respectively points within(Figure the 9a). right The Theabsolute absolutesidewall displacements displacementsclose to the southof the of haulage 3 the m-deep, 3 m-deep, underground 8 m-deep, 8 m-deep, 13op eningm-deep, 13 were m-deep, and 79, 18-m-deep 57, and 49, 18-m-deep and points 29 mm, within points respectively, the within right the rightsidewallwhich sidewall close accounted close to the to for thesouth 41%, south haulage 30%, haulage 26%, underground and underground 15% of optheening total opening displacementwere were 79, 57, 79, 49, 57,of 191 and 49, mm and 29 mm,between 29 mm, respectively, respectively,the 0 m whichwhichand accounted accounted the 25 m-deep for for 41%, 41%,point, 30%,30%, respectively 26%,26%, and (Figure 15% of of9b). the the total total displacement displacement of of 191 191 mm mm between between the the 0 m 0 m The displacements were mainly concentrated in the area from the surface (0 m) to 8–9 m deep in andand the the 25 25 m-deep m-deep point, point, respectively respectively (Figure(Figure 99b).b). the surrounding rock mass. More precisely, the displacement within the 0–9 m-deep rock mass (101 TheThe displacements displacements were were mainly mainly concentrated concentrated in the in area the from area the from surface the surface(0 m) to 8–9 (0 m) m deep to 8–9 in m mm = 153 mm − 52 mm) occupied 66% of the total (153 mm) of the left sidewall. Similarly, the deepthe surrounding in the surrounding rock mass. rock More mass. precisely, More the precisely, displacement the within displacement the 0–9 m-deep within rock the mass 0–9m-deep (101 displacement within the 0–8 m-deep rock mass (134 mm = 191 mm − 57 mm) accounted for 70% of rockmm mass = 153 (101 mm mm − 52 = mm) 153 mmoccupied− 52 66% mm) of occupied the total 66%(153 ofmm) the of total the (153left sidewall. mm) of theSimilarly, left sidewall. the the total (191 mm) at the right sidewall. Therefore, the deep holes post-grouting should be used to Similarly,displacementimprove the the displacement within strength the and 0–8 within intactness m-deep the rock 0–8of 8–9 m-deepmass m-deep (134 rock surrounding mm mass = 191 (134 mm rock mm − mass. 57 = 191mm) mm accounted− 57 mm) for accounted70% of forthe 70% total of (191 the total mm) (191 at the mm) right at thesidewall. right sidewall.Therefore, Therefore, the deep holes the deep post-grouting holes post-grouting should be used should to be usedimprove to improve the strength the strengthMeasurement and intactness point and B2 intactness- Left of sidewall 8–9 m-deep of 8–9 m-deepsurrounding surrounding rock mass. rock mass. 160 Measurement point B2-right sidewall 200

140 Measurement0 m point B2 - Left sidewall 0 mMeasurement point B2-right sidewall 160 120 14 m 200150 18m 9 m 13m 140 100 4 m 0 m 08m m 120 80 3m 14 m 150100 18m 9 m 13m 100 60 4 m 8m 40

80 (mm) Displacement Displacement (mm) Displacement 3m 10050

60 20

0 40 0 Displacement (mm) Displacement

Displacement (mm) Displacement 50 -20 20 0 50 100 150 200 250 0 50 100 150 200 250 0 Time (day) 0 Time (day) -20 (a) (b) 0 50 100 150 200 250 0 50 100 150 200 250 Time (day) Figure 9. Displacements of deep surrounding rock at measurement point B2,Time 19 (day)m away from fault FD108-1: (a) left sidewall;(a) and (b) right sidewall. (b)

FigureFigureHowever, 9. 9.Displacements Displacements the deep ofdisplacementsof deepdeep surrounding of the rock rockinner at at su measurement measurementrrounding rock point point were B2, B2, 19also 19m mevidentlyaway away from from large, fault fault 49 FD108-1:mmFD108-1: at the (a ( )a13) left left m-deep sidewall; sidewall; point andand and ((bb)) rightright29 mm sidewall. at the 18 m-deep point. The loosened range of the inner

However,However, the the deep deep displacements displacements of of the the inner inner surrounding surrounding rock rock were were also also evidently evidently large, large, 49 49 mm atmm the 13at m-deepthe 13 m-deep point and point 29 mmand at29 the mm 18 at m-deep the 18 point.m-deep The point. loosened The rangeloosened of therange inner of surroundingthe inner Sustainability 2017, 9, 2153 12 of 28 rock, i.e., the excavation damaged zone (EDZ) [24], due to stress redistribution after excavation, was over ﬁve times larger than the equivalent excavation radius (3 m) of the underground opening. The monitoring results indicated that the displacement of the inner surrounding rock was characterized by overall deformations on a large scale. The minimum pre-reinforcement range around the proposed opening should be 13–18 m. In addition, the deep displacements within the right sidewall were much larger than those within the left sidewall. According to the construction and continuous monitoring, the deep displacement velocities suddenly accelerated twofold due to the delayed excavation of the south haulage underground opening. The monitoring indicates that subsequent excavation affects the stability of the south rail underground opening previously excavated, although the space between those two underground openings is approximately 30–40 m.

3.3. Factors Inﬂuencing Safe Excavation and the Stability of Deep Underground Openings

3.3.1. High In Situ Stress The in-situ stress in the south underground opening was measured by hydraulic fracturing experiments performed in two long horizontal and vertical boreholes in the 800 m-deep connection roadway No. 5, where the rock mass was hard and intact. According to the results of the in-situ stress measurements, the magnitudes of the vertical stress and the maximum and minimum principal horizontal stresses were 28.78 MPa (σH), 16.34 MPa (σh), and 18.08 MPa (σv), respectively. The horizontal-to-vertical stress coefﬁcient (λ = σH/σv = 1.6) was more than 1.0. The in-situ stress ﬁeld was dominated by horizontal tectonic stress. The south underground openings are in an extremely high-stress area. The orientation of the maximum horizontal stress is nearly in the EW direction. The directions of the maximum and minimum principal horizontal stresses are approximately perpendicular to and parallel to the south underground opening axis, respectively. The higher the in-situ stress, the larger the deviator stress after excavation. The radial stress σrr decreases to 0 at the surface of the opening, whereas the tangential stress σθθ increases after excavation [25], resulting in a contradiction between the high stress and low rock mass strength and will inevitably lead to the rapid degradation of the surrounding rock mass after excavation. This is an important factor for deformations, failure, and instability of the deep underground opening through the large fault zones.

3.3.2. Large Fault Zones The southern shear fault zones are large geological anomaly fault zones consisting of many large faults and small fractures, which are multi-period active fault zones that have undergone several tectonic movements including the Indosinian movement, Yanshan movement, and the neo-tectonic movement, that trend in the North–West–West (NWW) direction. The coal measure strata are frequently ruptured by faults, and the strata attitude varies strongly, leading to extremely complex geological conditions. The pilot underground excavation, passing through large fault FD108-1 to the south, showed that the surrounding rock mass was generally very loose and broken. The excavation-induced stress increase ahead of the tunneling face on the large fault would possibly cause the slip behavior of the large fault, affecting the excavation safety. In addition, the large deformations of the underground openings may also cause the delayed reactivation of faults, resulting in a wide range of rock mass instability. The fault reactivation will seriously threaten the tunneling safety and stability of the deep underground openings during excavation and operation. Engineering practices showed that the roof collapse still occurred many times as the tunneling face approached the large fault FD108, even though 30 m-long pre-grouting boreholes and 15 m-long shed-pipe advanced pre-grouting supports were used. The pre-grouting reinforcement, such as ground surface pre-grouting (GSPG) should be used to improve the mechanical properties, including cohesion and internal frictional angle, of the large faults and regional engineering rock mass on a large scale. Sustainability 2017, 9, 2153 13 of 29 28

3.3.3. Poor Physical-Mechanical Properties and Engineering Performance of the Surrounding Rock3.3.3. PoorMass Physical-Mechanical Properties and Engineering Performance of the Surrounding Rock Mass • Phase Composition Analysis by X-ray Diffraction (XRD)(XRD) Six argillaceous rockrock specimensspecimens werewere collected collected from from the the south south haulage haulage underground underground openings openings in inthe the large large fault fault zones zones in in the the Guqiao Guqiao Coal Coal Mine Mine to to analyze analyze the the mineral mineral compositioncomposition ofof thethe rock mass using the D/Max-3B XRD XRD instrument instrument (Rigaku (Rigaku Corporation, Corporation, Tokyo, Tokyo, Japan). Qualitative andand quantitative quantitative analyses analyses showed showed that that the rockthe massrock mainlymass mainly consisted consisted of clay minerals. of clay Theminerals. quantitative The quantitative results are results illustrated are illustrated in Table1 and in Table Figure 1 and10. Figure 10.

Table 1. Results of quantitative analysis of rock specimens’ minerals (weight percentage). Table 1. Results of quantitative analysis of rock specimens’ minerals (weight percentage).

No.No. Description Description Q Q F F K K I I/S I/S S S C C L L P P D D O O SJ52 + 75 m 4 SJ52 + 75 m 11.8 1.3 56.1 1.6 22.5 2.9 2.1 Other 4 11.8 1.3 56.1 1.6 22.5 2.9 2.1 Other RoofRoof SJ52 + 77 m 5 SJ52 + 77 m 13.7 0.8 55.9 2.9 18.6 4.3 1.4 Other 5 13.7 0.8 55.9 2.9 18.6 4.3 1.4 Other RoofRoof SJ52 + 77 m 6 SJ52 + 77 m 15.4 4.8 45.2 9.2 13.3 4.2 4.1 1.6 0.5 0.3 Other 6 Floor 15.4 4.8 45.2 9.2 13.3 4.2 4.1 1.6 0.5 0.3 Other Floor Note: Q—Quartz: SiO2; F—Feldspar: (Na,Ca)AlSi3O8/(Na,K)AlSi3O8; K—Kaolinite: Al4(OH)8Si4O10, Note: Q—Quartz: SiO2; F—Feldspar: (Na,Ca)AlSi3O8/(Na,K)AlSi3O8; K—Kaolinite: Al4(OH)8Si4O10, 2 2 4 10 0.7 4 4 8 20 2 I—Illite: KAl KAl2(OH)(OH)2(AlSi)(AlSi)4O10O; S—Smectite:; S—Smectite: (Na,Ca) (Na,Ca)0.7(Al,Mg)(Al,Mg)4(OH)4(OH)(SiAl)8(SiAl)O20·nH O2O;·nH I/S—IlliteO; I/S—Illite and smectite and smectiteinterstratiﬁed interstratified minerals; L—Siderite: minerals; FeCO L—Siderite:3; P—Pyrite: FeCO FeS23;; C—Calcite:P—Pyrite: CaCO FeS23; ; D—Dolomite:C—Calcite: CaCO (Ca, Mg)CO3; D—3, and O—Other. Dolomite: (Ca, Mg)CO3, and O—Other.

Q 600 800 Q

Specimen 5 Specimen 6 Q K 600 K Q 400 K K C K K OS K 400 I/S Q K F F Q Q 200 I K Q Q K Q F K Q F K F K K L Q P Q Q O K K O Q 200 I C K C Q Q I O P K P K S Q OP KK K K I/S O F K C Q OO K DC Q K O D CK C D LK I P DP K PKK O Intensity (counts per second) per (counts Intensity Intensity (countsIntensity per second) 0 0 -100 -100 3 10 20 30 40 50 60 3 10 20 30 40 50 60 Diffraction angle (degree) Diffraction angle (degree) (a) (b)

Figure 10. X-ray diffraction patterns of specimens: ( a) Specimen 5; and ( b) Specimen 6.

The Illite, Smectite, and Illite-Smectite interstratified minerals content in Specimens 4, 5, and 6 The Illite, Smectite, and Illite-Smectite interstratiﬁed minerals content in Specimens 4, 5, and 6 were 27%, 25.8%, and 26.7%, respectively. The kaolinite content in Specimens 4, 5, and 6 was 56.1%, were 27%, 25.8%, and 26.7%, respectively. The kaolinite content in Specimens 4, 5, and 6 was 56.1%, 55.9%, and 45.2%, respectively. Therefore, the rock surrounding the south underground openings 55.9%, and 45.2%, respectively. Therefore, the rock surrounding the south underground openings through the large fault zones consist of more than 70% clay minerals. The argillaceous rock contains through the large fault zones consist of more than 70% clay minerals. The argillaceous rock contains substantial amounts of water-sensitive clay minerals and undergoes argillization when it is subjected substantial amounts of water-sensitive clay minerals and undergoes argillization when it is subjected to water. to water. • Argillization Experiment of Rock Mass Specimens withwith WaterWater ImmersionImmersion Eight rock specimens (Table 2 2)) werewere collectedcollected fromfrom thethe southsouth haulagehaulage undergroundunderground openingopening inin large faultfault zoneszones toto conductconduct an an argillization argillization experiment experiment with with water water immersion, immersion, as as shown shown in Figurein Figure 11. 11.Some Some parts parts of the of saturated the saturated rock specimens rock specimens were taken were out taken and driedout and naturally dried tonaturally analyze weatheringto analyze weatheringand disintegration and disintegration of rock specimens. of rock Thespecimens. weathering The andweathering disintegration and disi ofntegration saturated of argillaceous saturated argillaceousrock specimens rock are specimens shown in are Figure shown 12. in Figure 12.

Sustainability 2017, 9, 2153 14 of 29 SustainabilitySustainability2017 2017, ,9 9,, 2153 2153 1414 of of 29 28

Table 2. Description of rock specimens with water immersion. Table 2. Description of rock specimens with water immersion. Specimen No. Rock Specimen Description Notes 1 Argillaceous rock from the left sidewall at SJ52 + 150 m Specimen No. Rock Specimen Description Notes 2 Argillaceous rock from the right sidewall at SJ52 + 150 m 3 1 Argillaceous Argillaceous rock rock from from the the left roof sidewall at SJ52 at SJ52 + 150 + 150m m 2 Argillaceous rock from the right sidewall at SJ52 + 150 m 4 Argillaceous sandstone from tunneling face at SJ52 + 150 m Indoor temperature was 3 Argillaceous rock from the roof at SJ52 + 150 m 5 Argillaceous rock from the floor at SJ52 + 150 m around 20 °C. 6 4 Argillaceous Sandstone sandstone from the from sidewall tunneling at SJ52 face + at 140 SJ52 m + 150 m Indoor temperature was 6 5 Sandstone Argillaceous from rock the from sidewall the ﬂoor at atSJ52 SJ52 + 140 + 150 m m around 20 ◦C. 7 Argillaceous rock from the roof at SJ52 + 140 m 7 6 Argillaceous Sandstone rock from from the sidewall the roof at at SJ52 SJ52 + + 140 140 m m 8 7 Argillaceous Argillaceous rock rock from from the the floor roof at SJ52 ++ 140140 mm 8 Argillaceous rock from the ﬂoor at SJ52 + 140 m

(a)

(b)

(c)

FigureFigure 11. 11.Argillization Argillization experimentexperiment processprocess of rock specimens with water water immersion: immersion: (a (a) )condition condition of of specimensspecimens before before water water immersion; immersion; (b ()b conditions) conditions of of specimens specimens with with water water immersion immersion half half a day a day later; andlater; (c )and condition (c) condition of specimens of specimens with water with water immersion immersion one day one later. day later.

Figure 12. Weathering and disintegration of saturated argillaceous rock. FigureFigure 12.12. Weathering and disintegration of saturated argillaceous argillaceous rock. rock. As shown in Figures 11 and 12, argillaceous rock specimens were in full argillization after one AsAs shownshown inin FiguresFigures 1111 andand 1212,, argillaceousargillaceous rock specimens were were in in full full argillization argillization after after one one day with water immersion, except Specimens 4 and 6, indicating that argillaceous rock containing dayday withwith waterwater immersion,immersion, exceptexcept SpecimensSpecimens 4 and 6, indicating that that argi argillaceousllaceous rock rock containing containing substantial amounts of water-sensitive clay minerals will undergo evident softening, argillization, substantialsubstantial amountsamounts ofof water-sensitivewater-sensitive clay minerals will will undergo undergo evident evident softening, softening, argillization, argillization, swelling, dissolution, and weakening when in contact with water and will easily disintegrate and swelling,swelling, dissolution,dissolution, andand weakeningweakening when in contact with with water water and and will will easily easily disintegrate disintegrate and and weather after air drying. The experimental results show that the argillaceous rock, in the south weatherweather afterafter airair drying.drying. The experimental results results show show that that the the argillaceous argillaceous rock, rock, in in the the south south underground openings through large fault zones, is hydrophilic swelling soft rock, sensitive to undergroundunderground openingsopenings throughthrough largelarge fault zones, is hydrophilic swelling swelling soft soft rock, rock, sensitive sensitive to to disintegrating and weathering, with a high erosion rate. Groundwater seepage and construction disintegratingdisintegrating and and weathering, weathering, with with a higha high erosion erosion rate. rate. Groundwater Groundwater seepage seepage and constructionand construction water water should be a focus during excavation and support. shouldwater should be a focus be a during focus during excavation excavation and support. and support. SustainabilitySustainability 20172017,, 99,, 21532153 1515 ofof 2929 Sustainability 2017, 9, 2153 15 of 28

•• LowLow RockRock MassMass StrengthStrength LowTheThe excavationexcavation Rock Mass waswas Strength subjectedsubjected toto aa seriesseries ofof faulfaultsts fromfrom northnorth toto southsouth inin thethe deepdeep undergroundunderground openings.openings.The excavation TheThe smallsmall was faultsfaults subjected andand fracturesfractures to a series developeddeveloped of faults wellwell from withwith north argillaceousargillaceous to south in gougegouge the deep infilling.infilling. underground TheThe rockrock openings.massmass waswas extremely Theextremely small broken faultsbroken and inin geologicalgeological fractures developed anomalyanomaly fafa wellultult zones.zones. with argillaceous TheThe strengthstrength gouge ofof thethe infilling. surroundingsurrounding The rockrock massisis extremelyextremely was extremely low.low. TheThe broken roofroof collapsescollapses in geological cancan anomalybebe easilyeasily fault attributedattributed zones. toto The thethe strength brokenbroken ofsoftsoft the rockrock surrounding massmass withoutwithout rock isstand-upstand-up extremely timetime low. afterafter The excavation.excavation. roof collapses AccordingAccording can be toto easilythethe clasclas attributedsificationsification of toof surrounding thesurrounding broken soft rockrock rock inin rockrock mass roadwaysroadways without stand-upforfor coalmines,coalmines, time afterthethe classificationclassification excavation. Accordingofof thethe surroundinsurroundin to the classificationgg rockrock ofof thethe south ofsouth surrounding undergroundunderground rock openingsopenings in rock roadways throughthrough forthethe coalmines,faultfault zoneszones the isis categorycategory classification VV [26–28].[26–28]. of the TheThe surrounding compressivcompressiv rockee strengthstrength of the south ofof rockrock underground massmass waswas generallygenerally openings lessless through thanthan the1.61.6 MPa. faultMPa. zones is category V [26–28]. The compressive strength of rock mass was generally less than 1.6 MPa. •• PoorPoor EngineeringEngineering PerformancePerformance ofof RockRock MassMass Poor Engineering Performance of Rock Mass BoreholeBorehole imageimage monitoringmonitoring waswas completedcompleted toto dedetecttect thethe fracturefracture conditionsconditions andand analyzeanalyze thethe Borehole image monitoring was completed to detect the fracture conditions and analyze the qualityquality ofof thethe groutinggrouting effecteffect inin thethe roofroof afterafter popost-grouting.st-grouting. TheThe fractures,fractures, especiallyespecially withinwithin 4–84–8 m-m- quality of the grouting effect in the roof after post-grouting. The fractures, especially within 4–8 m-deep deepdeep surroundingsurrounding rock,rock, remainedremained extremelyextremely developeddeveloped afterafter 33 m-deepm-deep andand 88 m-deepm-deep holesholes post-post- surrounding rock, remained extremely developed after 3 m-deep and 8 m-deep holes post-grouting groutinggrouting withwith cementcement (Figures(Figures 1313 andand 14).14). TheThe boboreholerehole imageimage monitoringmonitoring resultsresults indicatedindicated thatthat thethe with cement (Figures 13 and 14). The borehole image monitoring results indicated that the groutability groutabilitygroutability ofof thethe cement-matricement-matrixx groutgrout materialsmaterials waswas extremelyextremely poorpoor inin thethe argillaceousargillaceous rockrock of the cement-matrix grout materials was extremely poor in the argillaceous rock containing substantial containingcontaining substantialsubstantial amountsamounts ofof clayclay minerals,minerals, duedue toto theirtheir lowlow permeabilitypermeability andand self-sealingself-sealing amounts of clay minerals, due to their low permeability and self-sealing properties, as argillaceous properties,properties, asas argillaceousargillaceous rockrock swellsswells whenwhen itit meetsmeets water,water, thusthus closingclosing fracturesfractures [29–31].[29–31]. TheThe rock swells when it meets water, thus closing fractures [29–31]. The common cement-matrix grout commoncommon cement-matrixcement-matrix groutgrout cancan onlyonly penetratepenetrate frfracturesactures ofof porespores widerwider thanthan 0.10.1 mmmm duedue toto itsits can only penetrate fractures of pores wider than 0.1 mm due to its large particle size [32]. Chemical largelarge particleparticle sizesize [32].[32]. ChemicalChemical materialsmaterials shouldshould bebe furtherfurther adoptedadopted forfor deepdeep holesholes post-groutingpost-grouting materials should be further adopted for deep holes post-grouting reinforcement. reinforcement.reinforcement.

FigureFigure 13.13. BoreholeBorehole imageimage monitoringmonitoring inin thethe roofroof afterafter 33 m-deepm-deep holesholes post-groutingpost-grouting withwith PortlandPortland Figure 13. Borehole image monitoring in the roof after 3 m-deep holes post-grouting with Portland cement. cement.cement.

FigureFigure 14.14. BoreholeBorehole imageimage monitoringmonitoring inin thethe roofroof afterafter 88 m-deepm-deep holesholes post-groutingpost-grouting withwith superfinesuperfine Figure 14. Borehole image monitoring in the roof after 8 m-deep holes post-grouting with superﬁne cement. cement.cement.

FigureFigure 15 15 presents presents thethethe curvecurvecurve ofofof thethe axialaxial loadsloads ofofof cablescables atat SJ52SJ52 ++ 92 m during during re-excavation whenwhen cablecable installationinstallationinstallation occurred occurredoccurred before beforebefore shotcrete shotcreteshotcrete and andand 3 m-deep 33 m-deepm-deep holes holesholes post-grouting. post-grouting.post-grouting. The axial TheThe loadsaxialaxial ofloadsloads cables ofof ﬁrstcablescables increased firstfirst increasedincreased but then butbut suddenly thenthen suddenlysuddenly decreased. decreased.decreased. The axial loadsTheThe axialaxial of the loadsloads cables ofof underwent thethe cablescables plummeting underwentunderwent andplummetingplummeting unloading andand phenomena. unloadingunloading The phenomena.phenomena. anchor-ability TheThe of cablesanchor-abilityanchor-ability within argillaceous ofof cablescables surrounding withinwithin argillaceousargillaceous rock was extremelysurroundingsurrounding poor. rockrock waswas extremelyextremely poor.poor. BecauseBecause ofof thethe gapgap andand thethe broken broken rockrock massmass behindbehind thethe anchoranchor cablecable plates,plates, thethe high high pre-tension pre-tension forceforce waswas difﬁcultdifficultdifficult toto preloadpreload toto thethe cablescables thatthat werewere installedinstalled before before shotcrete shotcrete and and post-grouting. post-grouting. CablesCables werewere notnot ableable toto effectivelyeffectively reinforcereinforce thethe rockrorockck massmass inin timetime becausebecause ofof thethe lowlow pre-tensionpre-tension andand Sustainability 2017, 9, 2153 16 of 28

Sustainability 2017, 9, 2153 16 of 29 broken rock mass. Because the argillaceous surrounding rock mass mainly consists of water-sensitive broken rock mass. Because the argillaceous surrounding rock mass mainly consists of water-sensitive clay minerals and excessive frequent groundwater inﬂow, the cables were often installed and anchored clay minerals and excessive frequent groundwater inflow, the cables were often installed and in the soft broken surrounding rock. The low pre-tension of the cables and the failure of rock mass anchored in the soft broken surrounding rock. The low pre-tension of the cables and the failure of around cable boreholes led to the plummet and unloading phenomena of the axial loads of cables. rock mass around cable boreholes led to the plummet and unloading phenomena of the axial loads Theof strengthcables. The and strength bearing and capacity bearing of capacity argillaceous of argillaceous rock mass rock around mass undergroundaround underground openings openings with bolt andwith cable bolt support and cable would support be would signiﬁcantly be significantly additionally additionally lower duringlower during its argillization its argillization process process due to groundwaterdue to groundwater seepage seepage [33]. This [33]. would This would result result in the in failure the failure of the of bolting-reinforcedthe bolting-reinforced structure structure and seriouslyand seriously threaten threaten the long-term the long-term stability stability of the of underground the underground openings. openings.

3-m-deep holes post-grouting 1# Left sidewall 200 2# Left arch abutment 8-m-deep holes 3# Left shoulder post-grouting with cement 4# Arch crown 150 5# Right shoulder 6# Right arch abutment 7# Right sidewall

100 8-m-deep holes post-grouting with Marithan Axial load (KN) load Axial 50

-10 0 10 20 30 40 50 60 70 80 Time (day) Figure 15.FigureAxial 15. loads Axial of loads cables of installedcables installed before shotcretebefore shotcrete and 3 m-deepand 3 m-deep holes post-grouting holes post-grouting during during re-excavation. re-excavation. 3.3.4. Groundwater Inrush and Coal and Gas Outburst 3.3.4. Groundwater Inrush and Coal and Gas Outburst The aquifer in the water-bearing Cenozoic loose strata on the bedrock that was dislocated by The aquifer in the water-bearing Cenozoic loose strata on the bedrock that was dislocated by faults is rich aqueous. If the main faults, acting as groundwater inrush channels, are reactivated under faults is rich aqueous. If the main faults, acting as groundwater inrush channels, are reactivated under thethe dynamic dynamic pressure pressure resulting resulting from from the the excavation, excavation, the groundwaterthe groundwater inrush inrush from from the Cenozoicthe Cenozoic aquifer willaquifer threaten will tunnelingthreaten tunneling safety during safety excavation. during excavation. DuringDuring the the pilot pilot excavation, excavation, excessive excessive groundwater groundwate inflow,r inflow, frequently frequently associated associated with with faults faults and 3 fractures,and fractures, often often occurred. occurred. The The groundwater groundwater inrush inrush inflow inflow of of 10 10 m m3/h/h or or more more occurred occurred more more than than 3 ◦ 1515 times. times. The The maximum maximum water water inflow inflow waswas upup toto 60 m3/h/h with with a atemperature temperature of ofapproximately approximately 42 42°C. C. 3 TheThe normal normal water water inflow inflow of of the the complete complete excavationexcavation reachedreached 5 m3/h./h. The The excessive excessive groundwater groundwater inflowinflow and and seepage seepage not not only only threatensthreatens tunnelingtunneling sa safetyfety during during excavation excavation but but also also continues continues to to deterioratedeteriorate the the strength strength and and deformation deformation characteristics characteristics of of the the rock rock mass mass over over time, time, and and decreases decreases the stabilitythe stability of deep of undergrounddeep underground openings openings in argillaceous in argillaceous rock [rock34]. [34]. The influenceThe influence of groundwater of groundwater on the argillaceouson the argillaceous rock contains rock two contains main aspects:two main the mechanicalaspects: the actionmechanical of water action on the of surrounding water on the rock, includingsurrounding the hydrostatic rock, including pressure the ofhydrostatic the effective pressu forcere andof the the effective dynamic force water and scouring the dynamic effect, water and the physicalscouring and effect, chemical and the action physical of water and chemical on the rock action mass, of water including on the softening, rock mass, argillization, including softening, dissolution, andargillization, swelling [35 dissolution,,36]. and swelling [35,36]. InIn addition, addition, the the phenomenon phenomenon ofof gasgas emissionemission exis existsts in in advanced advanced geological geological boreholes boreholes ahead ahead of of thethe tunneling tunneling face, face, and and thethe maximum gas gas concentration concentration was was up upto 10%. to 10%. Owing Owing to the to influence the influence of the of faults, the excavation will pass through multiple coal seams, including coal seam 13-1 with coal and the faults, the excavation will pass through multiple coal seams, including coal seam 13-1 with coal gas outburst risk and coal seam 11-2 with high rich gas [37], which also seriously threaten the and gas outburst risk and coal seam 11-2 with high rich gas [37], which also seriously threaten the accomplishment of a safe excavation. accomplishment of a safe excavation. 4. Control Countermeasures for Deep Underground Openings through Large Fault Zones in 4. Control Countermeasures for Deep Underground Openings through Large Fault Zones inArgillaceous Argillaceous Rock Rock Because of the geo-hazards encountered and potential fault slip behavior during deep Because of the geo-hazards encountered and potential fault slip behavior during deep underground excavation in large fault zones, providing adequate support or reinforcement to the underground excavation in large fault zones, providing adequate support or reinforcement to the rock Sustainability 2017, 9, 2153 17 of 28 mass with sufficient speed after excavation is almost impossible. Reinforcing the rock mass in advance of excavation should be practical and adopted. In addition, extra reinforcement should be provided as part of the normal cycle, in anticipation of higher stresses being imposed on the rock at a later stage during the service life of the opening. Many underground support schemes, such as the single-pilot heading method and long boreholes pre-grouting, were used during the industrial test of the pilot excavation of the deep underground openings through the large geological anomaly fault zones. However, various geological disasters still occurred during previous excavations, such as roof collapse, water inrush and debris flow. Engineering practices have shown that the geological conditions of underground openings are extremely complex. According to the deformations and failure characteristics of the surrounding rock, the factors influencing safe excavation, underground opening stability, and geo-hazards encountered during the pilot excavation, a coordinated control technique method, including improvement of regional lithology, such as GSPG, primary enhanced control measures of the surrounding rock, and secondary enclosed support, should be adopted to ensure tunneling safety and the long-term stability of deep underground openings through large fault zones in argillaceous rock.

4.1. Regional Strata Reinforcement Technique—GSPG GSPG involves injection of cement, or clay-cement, chemical liquid grouting materials into faults, fractures or dissolution cavities within water-bearing strata using mechanical methods [38]. The purposes of grouting are to block water-bearing conduits, control groundwater inﬂow, improve the regional engineering rock mass stability, and ensure safety during excavation and operation of deep underground openings. GSPG should be used to reinforce the regional engineering rock mass between the northern roof collapse location close to fault FD108 and the southern collapse. Boreholes are usually inside and/or outside the proposed excavated diameter of the south haulage underground opening. The detailed parameters and the reinforcement effect of GSPG and its inﬂuence on the stability of deep underground openings have been previously studied [21]. After the quality assessment of the GSPG effect, it is determined whether the proposed excavated zone pre-reinforcement technique, with underground long boreholes and shed-pipe advanced grouting support, should still be used. Short cycle chemical grouting pre-reinforcement should still be performed to prevent the roof and the tunneling face from collapsing during excavation. In addition, gas and water drainage exploration must be implemented to eliminate gas outbursts, groundwater inrush, and ensure tunneling safety.

4.2. Primary Enhanced Control Measures of the Surrounding Rock after Excavation Rock mass is very broken in geological anomaly fault zones. The strength of the surrounding rock is extremely low. The roof collapses easily due to the broken soft rock mass not having stand-up time after excavation. Owing to the extremely dramatic initial deformations and complex geological conditions, enclosed support measures cannot be constructed immediately at the tunneling face after excavation. Based on regional strata reinforcement, pre-grouting reinforcement, etc., completing primary enhanced control measures of the surrounding rock (heavy U36-shaped steel sets (36 kg/m steel), shallow holes post-grouting with superfine cement, bolts and long cables, and deep holes post-grouting with chemical material) should be aligned with the short cycle construction steps to control the dramatic initial deformations after excavation. The U36-shaped steel sets are used first to ensure roof safety after excavation. Shotcrete lining and shallow holes post-grouting with cement should then be applied to seal the rock surface, inhibit weathering processes, fill the pore space behind the steel sets, and reinforce the shallow rock mass. Afterward, the high strength and pre-stressed thread steel bolt support system, combined with the long pre-stressed anchor cables, are installed. After that, deep holes post-grouting with chemical material, such as a novel polyurethane grouting material like the Marithan® polyurethane strata injection system [39,40], should be used to block fracture water from seeping, improve the intactness of SustainabilitySustainability 20172017, ,99, ,2153 2153 1818 of of 29 28 of rock mass, and prevent the deep argillaceous surrounding rock mass from argillization. Marithan® isrock a flexible mass, andpolyurethane prevent the product deep argillaceous consisting of surrounding resin grout rock and masscatalyst, from particularly argillization. well-suited Marithan ®foris thea flexible reinforcement polyurethane of fractured product consistingrock mass, of resinthe stabilization grout and catalyst, of water-bearing particularly strata, well-suited and forwater the stoppage.reinforcement The product of fractured has rockhigh mass,adhesive the stabilizationstrength, outstanding of water-bearing mechanical strata, properties, and water and stoppage. good flexibility,The product creating has high an excellent adhesive bond strength, with rock outstanding mass, which mechanical is maintained properties, through and the good service flexibility, life of thecreating workplace. an excellent According bond withto laboratory rock mass, experiment which is maintainedation, the average through uniaxial the service compressive life of the workplace. strength, tensileAccording strength, to laboratory shear strength, experimentation, and cohesion the average are 65.8 uniaxial MPa, compressive41.5 MPa, 29.7 strength, MPa, tensileand 10.2 strength, MPa, respectivelyshear strength, [28]. and cohesion are 65.8 MPa, 41.5 MPa, 29.7 MPa, and 10.2 MPa, respectively [28]. TheThe particle particle size size distribution distribution of ofMarithan Marithan® grout® grout was wasobserved observed by using by using a Mastersizer a Mastersizer 2000 mercury2000 mercury porosimeter, porosimeter, as shown as shown in Figure in Figure 16. The 16. average The average particle particle sizes sizesof Marithan of Marithan® resin® resinand catalystand catalyst are 2.95 are nm 2.95 and nm 825.6 and nm, 825.6 respectively. nm, respectively. The maximum The maximum frequency frequency size of Marithan size of® Marithan resin and® catalystresin and ( d catalyst ) are (d2.69max )nm are and 2.69 615.14 nm and nm, 615.14 respectively, nm, respectively, while the while particle the particlesizes of sizes the grout of the cumulativegrout cumulative distribution distribution curve corresponding curve corresponding to 95% to (d 95%) for (d95 resin) for and resin catalyst and catalyst are 3.62 are nm 3.62 and nm 824.99and 824.99 nm, respectively. nm, respectively. According According to the to groutabili the groutabilityty principle principle of fracture of fracture or porous or porous mediums, mediums, the widththe width of the of thefractures fractures or pores or pores the thegrout grout could could be beinjected injected into into is isbigger bigger than than triple triple the the grouting grouting max materialmaterial particleparticle sizesize [ 41[41].]. The The particle particle sizes sizes over over triple triple the d theand d d95 onand the d cumulative on the cumulative distribution × × distributioncurve of Marithan curve ®ofresin Marithan are 8 nm® resin (R3 aredmax 8 )nm and (R 11× nm ()R and3 d95 11), respectively.nm (R×), Therefore,respectively. the Therefore, Marithan® thegrout Marithan can be® injectedgrout can into be injected fine fractures into fine or fractures pores of or 11 pores nm in of width, 11 nm thein width, groutability the groutability of which of is whichobviously is obviously higher than higher cement-matrix than cement-matrix grout (≥ grout0.1 mm). (≥0.1 When mm). MarithanWhen Marithan® is injected® is injected into the into strata, the strata,the low-viscosity the low-viscosity mixture mixture remains remains in a liquid in a state liquid for state several for seconds,several seconds, penetrates penetrates small fine small fractures fine fracturesand expands, and expands, thus effectively thus effectively reinforcing reinforcing and sealing and the sealing area[ the42]. area [42].

35 100 30 80 25

Marithan resin 60 20 Marithan catalyst Marithan resin Marithan catalyst 15 40

10 20 Percentage(%) Cumulative distribution(%) Cumulative 5 0 0 0 1 2 3 4 5 6 10-1 100 101 102 103 104 105 106 10 10 10 10 10 10 10 Particle size (nm) Particle size(nm) (a) (b)

FigureFigure 16. (a) ParticleParticle sizesize distribution; distribution; and and (b )( cumulativeb) cumulative particle particle size distributionsize distribution of Marithan of Marithan® grout.® grout. 4.3. Floor Grouting Reinforcement Technique with Pressurization and Progressive Depths 4.3. Floor Grouting Reinforcement Technique with Pressurization and Progressive Depths The floor heave of the underground openings is critical. Field measurements during the pilot excavationThe floor indicated heave of that the theunderground displacement openings and velocityis critical. of Field the floormeasurements were up toduring 2901 the mm pilot and excavation80 mm/day, indicated respectively. that the The displacement floor must be and reinforced velocity given of the the floor destructive were up floor to 2901 heave. mm However, and 80 mm/day,the holes respectively. drilled in the The floor floor are must always be subjected reinforced to given collapse the becausedestructive of the floor soft heave. broken However, argillaceous the holesrock massdrilled and in itsthe argillization. floor are always The subjected bolts and to cables collapse cannot because be installed of the soft in the broken floor. argillaceous rock mass Basedand its onargillization. the industrial The testingbolts and of cables the floor cannot reinforcement be installed in in the the south floor. haulage underground opening,Based we on proposed the industrial the floor testing grouting of the reinforcement floor reinforcement technique in with the pressurizationsouth haulage and underground progressive opening,depths in we argillaceous proposed rock. the Grouting floor grouting depths in re theinforcement floor successively technique increased with frompressurization shallow to deep,and progressiveand the corresponding depths in argillaceous grouting pressure rock. Grouting also progressively depths in the increased floor successively (Figure 17). increased The array from pitch shallowand the to water-to-cement deep, and the corresponding ratio for 2.5 m-deep, grouting 4.5 pr m-deep,essure also and progressively 6.5 m-deep holes increased grouting (Figure were 17). all The1600 array mm andpitch 1:1, and respectively. the water-to-cement The array pitch ratio of for 8 m-deep 2.5 m-deep, holes with4.5 m-deep, grouting and with 6.5 chemical m-deep material holes grouting(Marithan were®) was all 20001600 mm.mm and The 1:1, earlier respectively. shallow holes The groutingarray pitch not of only 8 m-deep reinforces holes the with shallow grouting rock ® withmass chemical but also formsmaterial a stop-grouting (Marithan ) layer was for2000 subsequent mm. The deeper earlier drilling shallow holes holes grouting grouting and solvesnot only the reinforces the shallow rock mass but also forms a stop-grouting layer for subsequent deeper drilling holes grouting and solves the problem of wall collapse in deeper holes. The 8 m-deep holes with Sustainability 2017, 9, 2153 19 of 28

Sustainability 2017, 9, 2153 19 of 29 Sustainability 2017, 9, 2153 19 of 29 problem of wall collapse in deeper holes. The 8 m-deep holes with grouting with chemical material ® ® grouting(Marithangrouting withwith) reinforces chemicalchemical the materialmaterial deep rock(Marithan(Marithan mass® in)) reinforcesreinforces the floor and thethe formsdeepdeep rockrock a large massmass joint inin bearingthethe floorfloor ring andand with formsforms the aa largereinforcedlarge jointjoint bearing deepbearing rock ringring mass withwith in the thethe reinforced roofreinforced and sidewalls. deepdeep rorockck This massmass technique inin thethe roofroof effectively andand sidewalls.sidewalls. strengthens ThisThis the techniquetechnique floor in effectivelytheeffectively large faults strengthensstrengthens in argillaceous thethe floorfloor rock. inin the Thethe largelarge displacement faultsfaults inin velocityargillaceousargillaceous of the rock.rock. floor TheThe decreased displacementdisplacement to 0.7 mm/day velocityvelocity on ofof theaverage,the floorfloor providing decreaseddecreased a to foundationto 0.70.7 mm/daymm/day forsecondary onon average,average, enclosed providingproviding support aa foundationfoundation measures for forfor the secondarysecondary long-term enclosedenclosed stability supportofsupport the surrounding measuresmeasures forfor rock. thethe long-termlong-term stabilitystability ofof thethe surroundingsurrounding rock.rock.

Over-excavation of 400mm, Concrete floor 200-mm-thickOver-excavation concrete of 400mm floor, Concrete floor 200-mm-thick concrete floor

2.5-m-deep holes Grouting pressure was 1 MPa. 2.5-m-deep holes Grouting pressure was 1 MPa.

4.5-m-deep holes Grouting pressure was 3 MPa. 4.5-m-deep holes Grouting pressure was 3 MPa.

6.5-m-deep holes Grouting pressure was 5 MPa. 6.5-m-deep holes Grouting pressure was 5 MPa.

8-m-deep holes Grouting pressure was 6 MPa. 8-m-deep holes Grouting pressure was 6 MPa. FigureFigure 17.17. IndustrialIndustrial testtest processprocess diagramdiagram ofof floorfloor groutinggrouting reinforcement.reinforcement. Figure 17. Industrial test process diagram of floor grouting reinforcement. 4.4.4.4. SecondarySecondary EnclosedEnclosed SupportSupport 4.4. Secondary Enclosed Support GivenGiven thethe significantsignificant creepcreep behaviorbehavior ofof thethe deformationsdeformations andand thethe long-termlong-term stabilitystability ofof thethe deepdeep Given the significant creep behavior of the deformations and the long-term stability of the undergroundunderground openingsopenings inin thethe largelarge faultsfaults inin arargillaceousgillaceous rock,rock, thethe secondarysecondary enclosedenclosed supportsupport deep underground openings in the large faults in argillaceous rock, the secondary enclosed support measures,measures, suchsuch asas enclosedenclosed heavyheavy U36-shapedU36-shaped steelsteel setssets andand precastprecast reinforcedreinforced steelsteel plateplate concreteconcrete measures, such as enclosed heavy U36-shaped steel sets and precast reinforced steel plate concrete segments,segments, shouldshould bebe used.used. TheThe bufferbuffer spacespace betwbetweeneen thethe secondarysecondary enclosedenclosed supportsupport structurestructure andand segments, should be used. The buffer space between the secondary enclosed support structure and the thethe primaryprimary enhancedenhanced controlcontrol measuresmeasures shouldshould bebe filledfilled withwith backfillingbackfilling materialsmaterials toto enableenable thethe primary enhanced control measures should be filled with backfilling materials to enable the pressure pressurepressure toto evenlyevenly actact onon thethe backfibackfillinglling layerlayer andand thethe supportsupport structure.structure. to evenly act on the backfilling layer and the support structure. 5.5. Re-ExcavationRe-Excavation ofof DeepDeep UndergroundUnderground OpeningsOpenings throughthrough LargeLarge FaultFault ZonesZones andand 5. Re-Excavation of Deep Underground Openings through Large Fault Zones and Field Measurements FieldField MeasurementsMeasurements 5.1. Support Schemes 5.1.5.1. SupportSupport SchemesSchemes The deformations and failure of the deep underground openings before re-excavation were The deformations and failure of the deep underground openings before re-excavation were extremelyThe deformations serious (Figure and 18 ).failure of the deep underground openings before re-excavation were extremelyextremely seriousserious (Figure(Figure 18).18).

Figure 18. Failure of the deep underground openings through large fault zones in argillaceous rock. Figure 18. Failure of the deep underground openings throughthrough largelarge faultfault zoneszones inin argillaceousargillaceous rock.rock.

2 TheThe areasareas ofof thethe residualresidual cross-sectionscross-sections werewere lessless thanthan 44 mm2.. MostMost cross-sectionscross-sections ofof thethe deepdeep The areas of the residual cross-sections were less than 4 m2. Most cross-sections of the undergroundunderground openingsopenings inin thethe largelarge faultfault zoneszones werewere closed.closed. TheThe undergroundunderground openingopening waswas re-re- deep underground openings in the large fault zones were closed. The underground opening was excavatedexcavated byby handhand airair drill.drill. TheThe optimizedoptimized supportsupport measuresmeasures duringduring re-excavationre-excavation areare illustratedillustrated asas re-excavated by hand air drill. The optimized support measures during re-excavation are illustrated follows.follows. as follows.

Sustainability 2017, 9, 2153 20 of 29

5.1.1.Sustainability Short2017 Cycle, 9, 2153Chemical Grouting Pre-Reinforcement 20 of 28

® ShortSustainability cycle 2017 pre-grouting, 9, 2153 with chemical material (Marithan ) was performed to further20 reinforce of 29 fractured5.1.1. Short rock Cycle mass Chemical and prevent Grouting the Pre-Reinforcement tunneling face from collapsing (Figure 19). The lengths of grouting5.1.1. boreholes Short Cycle and Chemical pipes were Grouting 8000 Pre-Reinforcement mm and 6000 mm, respectively. The diameter of the grouting Short cycle pre-grouting with chemical material (Marithan®) was performed to further reinforce boreholes was 42 mm. The grouting pressure was 1–3 MPa. ® fractured rockShort masscycle andpre-grouting prevent with the tunneling chemical material face from (Marithan collapsing) was (Figure performed 19). The to further lengths reinforce of grouting fractured rock mass and prevent the tunneling face from collapsing (Figure 19). The lengths of boreholes and pipes were 8000 mm and 6000 mm, respectively. The diameter of the grouting boreholes grouting boreholes and pipes were 8000 mm and 6000 mm, respectively. The diameter of the grouting was 42 mm. The grouting pressure was 1–3 MPa. boreholes was 42 mm. The grouting pressure was 1–3 MPa. 00 80

00 80

3 0 °

0 3 ° 0 °

3 5600 0

° 1600

5600 1600

30°

Figure 19. Layout diagram of short cycle chemical grouting pre-reinforcement. Figure 19. Layout diagram of short cycle chemical grouting pre-reinforcement. Figure 19. Layout diagram of short cycle chemical grouting pre-reinforcement. 5.1.2. U36-Shaped Steel Sets 5.1.2. U36-Shaped Steel Sets 5.1.2. U36-Shaped Steel Sets U36-shapedU36-shaped steel steel sets sets with with intervals intervals of of 400 400 mmmm were installedinstalled after after excavation. excavation. The The net cross-net cross- sectionU36-shapedsection of the of steel the steelsteel sets setssets was withwas 5600 5600 intervals mm mm in in width of width 400 mman andd were44004400 mmmm installed in in height. height. after Two excavation. Two high-strength high-strength The netthread cross-sectionthread steel steel leg-lockerof theleg-locker steel bolts sets bolts was were 5600were installed mminstalled in widthin intime time and to to 4400fix fix the the mm legleg in of height. thethe steelsteel Two set set high-strength in in the the corner. corner. threadThe The diametersteel diameter leg-locker and and lengthboltslength were of the installedof bolts the bolts were in were time 22 mm22 to mm ﬁx and theand 2800 leg2800 ofmm, mm, the respectively. respectively. steel set in the The The corner. torque torque of The ofeach each diameter bolt bolt was was and not lengthnotless thanless of than the 200bolts Nm.200 were Nm. 22 mm and 2800 mm, respectively. The torque of each bolt was not less than 200 Nm.

5.1.3. 5.1.3.Cable Cable Beams Beams in Sidewalls in Sidewalls Pre-stressed anchor cable beams (Figure 20) composed of cables and strips of I-steel No. 11 were Pre-stressed anchor cable beams (Figure(Figure 2020)) composed of cables andand strips of I-steel No. 11 were installed in the sidewalls after four U-shaped steel sets were finished. The diameter and length of the installed in in the the sidewalls sidewalls after after four four U-shaped U-shaped steel steel sets sets were were finished. ﬁnished. The The diameter diameter and and length length of the of cables were 21.8 mm and 8200 mm, respectively. The pre-tension force of 100 kN was preloaded to cablesthe cablescables were were to 21.8 achieve 21.8 mm mm highand and 8200pre-stress 8200 mm, mm, to respectively. reinforce respectively. the Thsidewallse The pre-tension pre-tension and restrict force force the of deformations100 of 100 kN kN was was ofpreloaded the preloaded U- to cablesto cablesshaped to achieve to steel achieve sets. high high pre-stress pre-stress to reinforce to reinforce the thesidewalls sidewalls and and restrict restrict the thedeformations deformations of the of theU- shapedU-shaped steel steel sets. sets. I I

Cables Φ21.8×L8200 Cables Φ21.8×L8200 1000 1000

I Section I-I 1000 1000 Figure 20. Layout diagram of I steel cable beams duringSection re-excavation. I-I I Figure 20. LayoutLayout diagram of I steel cable beams during re-excavation. Sustainability 2017, 9, 2153 21 of 28

Sustainability 2017, 9, 2153 21 of 29 5.1.4. Primary Shotcrete 5.1.4. Primary Shotcrete PrimarySustainability shotcrete 2017, 9, 2153 was performed up to the tunneling face to seal the rock surface and21 of 29 fill the pore spacePrimary behind shotcrete the steel was sets performed after every up fiveto the U-shaped tunneling steel face sets to seal were the finished. rock surface The and thickness fill the was 5.1.4. Primary Shotcrete 50–70pore mm. space The behind shotcrete the steel was sets composed after every of five ordinary U-shaped Portland steel sets cement, were finished. sand, and The gravel thickness mixed was with water.50–70 The mm.Primary weight The shotcrete shotcrete ratio of cement,was was performed composed sand, andup of toordinary gravel the tunnelin was Portland 1:2:2,g face andcement, to theseal water-to-cementsand,the rock and surface gravel and mixed ratio fill was thewith 45%. pore space behind the steel sets after every five U-shaped steel sets were finished. The thickness was Thewater. strength The gradeweight of ratio the of ordinary cement, Portlandsand, andcement gravel was was 1:2:2, 42.5 and MPa. the water-to-cement ratio was 45%. The50–70 strength mm. Thegrade shotcrete of the ordinary was composed Portland of ordinarycement was Portland 42.5 MPa. cement, sand, and gravel mixed with 5.1.5.water. Shallow The Holesweight Post-Grouting ratio of cement, withsand, Superfineand gravel Cementwas 1:2:2, and the water-to-cement ratio was 45%. 5.1.5.The Shallowstrength Holesgrade ofPost-Grouting the ordinary withPortland Superfine cement Cement was 42.5 MPa. Shallow holes post-grouting with superfine cement was completed after shotcrete (Figure 21). Shallow holes post-grouting with superfine cement was completed after shotcrete (Figure 21). The lengths5.1.5. Shallow of the Holes grouting Post-Grouting pipes and with boreholes Superfine were Cement 2000 mm and 3000 mm, respectively, and the The lengths of the grouting pipes and boreholes were 2000 mm and 3000 mm, respectively, and the array pitch was 3200 mm. Grouting pressure was generally not more than 3 MPa. The strength of the array pitchShallow was holes 3200 post-groutingmm. Grouting with pressure superfine was genecementrally was not completed more than after 3 MPa. shotcrete The strength (Figure of21). the superfinesuperfineThe lengths cement cement of was the was grouting 62.5 62.5 MPa. MPa. pipes The The and water-to-cement water-to-cement boreholes were ratio ratio2000 was wasmm 0.8–1.0. and 0.8–1.0. 3000 The Themm, distance distance respectively, of shallow of shallow and holes the holes post-groutingpost-groutingarray pitch relative was relative 3200 to mm.to the the tunnelingGrouting tunneling pressure face face waswas was lessless gene thanrally 6 m.not m. more than 3 MPa. The strength of the superfine cement was 62.5 MPa. The water-to-cement ratio was 0.8–1.0. The distance of shallow holes post-grouting relative to the tunneling face was less than 6 m. 4 3 5 3 4 1 7 5 170 0 2 0 0 1 7 170 0 2 0 0 6 6 5600

5 °

° 5600 5 2

5 °

° 5 1 600 2 7

1 600 7 FigureFigure 21. 21.Pipe Pipe layout layout diagram diagram ofof 33 m-deepm-deep hole holess post-grouting post-grouting during during re-excavation. re-excavation. Figure 21. Pipe layout diagram of 3 m-deep holes post-grouting during re-excavation. 5.1.6.5.1.6. High-Strength High-Strength and and Pre-Stressed Pre-Stressed Bolts Bolts 5.1.6.Seventeen High-Strength high-strength and Pre-Stressed pre-stressed Bolts bolts (left-hand twist and IV class thread steel HRB500) Seventeen high-strength pre-stressed bolts (left-hand twist and IV class thread steel HRB500) were were usedSeventeen to reinforce high-strength each cross-section pre-stressed (Figure bolts (left- 22).hand The diametertwist and andIV class length thread of the steel bolts HRB500) were 22 used to reinforce each cross-section (Figure 22). The diameter and length of the bolts were 22 mm and mmwere and used 2800 to mm, reinforce respectively. each cross-section The interval (Figure and array22). The pitch diameter of the boltsand length were 800 of the mm bolts and were 800 mm, 22 2800 mm, respectively. The interval and array pitch of the bolts were 800 mm and 800 mm, respectively. respectively.mm and 2800 The mm, torque respectively. of each bolt The wasinterval not lessand thanarray 200 pitch Nm. of the bolts were 800 mm and 800 mm, The torquerespectively. of each The bolt torque was of not each less bolt than was 200 notNm. less than 200 Nm.

Bolts Φ22×L2800 Bolts Φ22×L2800 800

800 ° 0 3 ° 0 3

Figure 22. Layout of bolts. Figure 22. Layout of bolts. Figure 22. Layout of bolts. 5.1.7. Pre-Stressed Cables 5.1.7. Pre-Stressed Cables 5.1.7. Pre-StressedSeven pre-stressed Cables cable beams (Figure 23), consisting of cables and T steel strips, were applied Seven pre-stressed cable beams (Figure 23), consisting of cables and T steel strips, were applied installed perpendicular to the roadway axis direction. The diameter of the cables was 21.8 mm. The Seveninstalled pre-stressed perpendicular cable to the beams roadway (Figure axis 23directio), consistingn. The diameter of cables of andthe cables T steel was strips, 21.8 weremm. The applied installedlengthlength perpendicularof of the the cables cables with with to thean an exposedexposed roadway lengthlength axis ofof direction. approximately The diameter200200 mmmm waswas of 8200 the8200 cablesmm. mm. A A washigh high 21.8pre- pre- mm. The length of the cables with an exposed length of approximately 200 mm was 8200 mm. A high Sustainability 2017, 9, 2153 22 of 28 Sustainability 2017, 9, 2153 22 of 29 Sustainability 2017, 9, 2153 22 of 29 pre-tensiontension force force of of approximately approximately 100 100 kN kN should should be be pr preloadedeloaded to tocables cables to toachieve achieve the the high high pre-stress pre-stress tension force of approximately 100 kN should be preloaded to cables to achieve the high pre-stress duringduring post-excavation post-excavation installation. installation. The The delaying delaying distance distance of cable of installationcable installation relative relative to the tunnelingto the during post-excavation installation. The delaying distance of cable installation relative to the facetunneling was less face than was 8 m. less than 8 m. tunneling face was less than 8 m. I I

Cables Φ21.8×CablesL8200 Φ21.8×L8200

0 240 0 240 400 400 1600 1600 400 400 1600 1600 I Section I-I Section I-I I FigureFigure 23.23. LayoutLayout diagram of of the the cable cable beams. beams. Figure 23. Layout diagram of the cable beams. 5.1.8. Secondary Shotcrete 5.1.8.5.1.8. Secondary Secondary Shotcrete Shotcrete Secondary shotcrete was used to seal the deformation-induced fractures and pore space of the SecondarySecondary shotcrete shotcrete was was used used to to seal seal thethe deformation-induceddeformation-induced fractures fractures and and pore pore space space of the of the boreholes after cable installation. The thickness was 50–70 mm. The shotcrete materials were the same boreholesboreholes after after cable cable installation. installation. The The thickness thickness waswas 50–70 mm. mm. The The shotcrete shotcrete materials materials were were the thesame same as those of primary shotcrete. The distance of the secondary shotcrete relative to the tunneling face as thoseas those of primaryof primary shotcrete. shotcrete. The The distance distance ofof thethe secondary shotcrete shotcrete relative relative to tothe the tunneling tunneling face face was less than 10 m. waswas less less than than 10 10 m. m.

5.1.9.5.1.9.5.1.9. Deep Deep Deep Holes Holes Holes Post-Grouting Post-Grouting Post-Grouting with withwith Chemical ChemicalChemical MaterialMaterial Deep holes post-grouting with Marithan® were bored after secondary shotcrete (Figure 24). The DeepDeep holes holes post-grouting post-grouting with Marithan Marithan® ®werewere bored bored after after secondary secondary shotcrete shotcrete (Figure(Figure 24). The 24). lengths of grouting pipes and boreholes were 6000 mm and 8000 mm, respectively. The array pitch Thelengths lengths of of grouting grouting pipes pipes and and bo boreholesreholes were were 6000 6000 mm mm and and 8000 8000 mm, mm, respectively. respectively. The The array array pitch pitch was 3200 mm. The grouting pressure was 6–8 MPa. waswas 3200 3200 mm. mm. The The grouting grouting pressure pressure was was 6–8 6–8 MPa.MPa. 3 22 4 240 400

5600

2 2 ° 5 ° 5 5 ° 5 ° 2 2 600 11 600 55 FigureFigureFigure 24. 24. 24.Pipe Pipe Pipe layout layout layout diagram diagramdiagram of ofof 888 m-deepm-deep hole holess post-grouting post-grouting duringduring during re-excavation.re-excavation. re-excavation.

ToTo improveimprove thethe groutinggrouting effect,effect, deepdeep post-grouting was conducted byby aa repeatedrepeated groutinggrouting To improve the grouting effect, deep post-grouting was conducted by a repeated grouting method methodmethod with with alternating alternating intervals;intervals; i.e.,i.e., thethe odd array holes grouting waswas firstfirst completedcompleted along along the the with alternating intervals; i.e., the odd array holes grouting was first completed along the opening openingopening axis axis direction. direction. Afterward, Afterward, thethe groutinggrouting of the remaining eveneven arrayarray holesholes was was conducted. conducted. In In axis direction. Afterward, the grouting of the remaining even array holes was conducted. In addition, addition,addition, the the deep deep holes holes post-grouting post-grouting sequencessequences at the same cross-section werewere from from holes holes No. No. 1 1 and and theNo.No. deep 5 5 in holesin the the corners, post-groutingcorners, thenthen holesholes sequences No.No. 22 andand at the No. same 4 in cross-sectionthe shoulders, were toto thethe from lastlast holesholehole No.No. No. 33 1in in and the the No.arch arch 5 in thecrown.crown. corners, then holes No. 2 and No. 4 in the shoulders, to the last hole No. 3 in the arch crown. 5.1.10. Secondary Enclosed Support 5.1.10.5.1.10. Secondary Secondary Enclosed Enclosed Support Support TheTheThe floor floorfloor grouting groutinggrouting reinforcement reinforcementreinforcement technique techniquetechnique with pressurizationwith pressurization and progressive andand progressiveprogressive depth parameters depthdepth wereparametersparameters the same were were as those the the same insame Section asas thosethose4. The inin SectionSection secondary 4. The enclosed secondary support enclosed should supportsupport be further shouldshould designed be be further further and implementeddesigneddesigned and and after implemented implemented floor grouting after after reinforcement floorfloor groutinggrouting reinfo to ensurercement the to long-term ensureensure thethe stability long-termlong-term of thestability stability underground of of the the openings through large fault zones in argillaceous rock, given the creep and time-dependent behavior. Sustainability 2017, 9, 2153 23 of 29 Sustainability 2017, 9, 2153 23 of 28 underground openings through large fault zones in argillaceous rock, given the creep and time- dependent behavior. 5.2. Field Measurements 5.2. Field Measurements To analyze the reliability of the support parameters for the deep underground opening during To analyze the reliability of the support parameters for the deep underground opening during re-excavation, field measurements such as surface displacements, bedding separation of roof strata, re-excavation, field measurements such as surface displacements, bedding separation of roof strata, axial load monitoring of cables, and borehole image monitoring were recorded, discussed and axial load monitoring of cables, and borehole image monitoring were recorded, discussed and comparedcompared with with the the monitoring monitoring results results during during thethe pilotpilot excavation. 5.3. Results and Discussion 5.3. Results and Discussion •Surface Surface Displacements Displacements TheThe field field measurements measurements confirmed confirmed that that cablecable reinforcementreinforcement after after shotcrete shotcrete and and 3 m-deep 3 m-deep holes holes post-groutingpost-grouting could could reduce reduce the the displacements displacements ofof thethe surrounding rock. rock. For For example, example, thethe maximum maximum sidewall-to-sidewallsidewall-to-sidewall and and roof-to-floor roof-to-floor displacementdisplacement velocities were were 25 25 mm/day mm/day and and 46 46mm/day, mm/day, respectively,respectively, on theon the first first day day after after re-excavation. re-excavation. TheThe corresponding displace displacementment velocities velocities visibly visibly decreaseddecreased to 13 to mm/day13 mm/day on on the the seventh seventh dayday andand 15 mm/day mm/day on on the the ninth ninth day, day, respectively, respectively, after after the the cablescables around around the measurementthe measurement point point at SJ52 at SJ52 + 24 m+ 24 were m installedwere installed on the on sixth the daysixth after day re-excavation after re- (Figureexcavation 25). (Figure 25).

300 18 Cables 1200 8-m-deep holes post-grouting with 50 16 Marithan 250 1000 14 D(sidewall-to-sidewall) 40 D(roof-to-floor) 200 12 800 V(sidewall-to-sidewall) V(roof-to-floor) 30 10 150 600 Floor grouting 8-m-deep holes grouting 8 with Marithan for floor 20 D(left sidwall) 6 400 100 D(right sidewall) Velocity (mm/d) Velocity (mm/d) Displacement (mm) V(left sidwall) Displacement (mm) Displacement 4 10 200 50 V(right sidewall) 2

0 0 0 0

-20 0 20 40 60 80 100 120 140 160 180 -2 -20 0 20 40 60 80 100 120 140 160 180 Time (day) Time (day) (a) (b) 6

25 1200 5 50

4 1000 20 D(floor) 40 3 V(floor) D(roof) 800 15 V(roof) 30 2 Floor grouting 600 8-m-deep holes 1 grouting with Marithan 10 for floor was finished 20 400 Velocity (mm/d) 0 Velocity (mm/d) Displacement (mm) Displacement (mm) Displacement 5 10 -1 200

-2 0 0 0

-3 -20 0 20 40 60 80 100 120 140 160 180 -20 0 20 40 60 80 100 120 140 160 180 Time (day) Time (day) (c) (d)

FigureFigure 25. Curves25. Curves of displacements of displacements and and velocities velocities versus versus time time during during re-excavation: re-excavation: (a) sidewall-to-sidewall (a) sidewall-to- andsidewall roof-to-ﬂoor; and roof-to-floor; (b) left and ( rightb) left sidewalls; and right sidewalls; (c) roof; and (c) roof; (d) ﬂoor.and (d) floor.

® TheThe 8 m-deep 8 m-deep holes holes post-grouting, post-grouting, reinforced reinforced with chemicalwith chemical material material (Marithan (Marithan®) for the) for sidewalls the sidewalls and the roof around the monitoring point, were installed on the 35th day and finished on and the roof around the monitoring point, were installed on the 35th day and finished on the 38th day the 38th day after re-excavation, further reducing the displacement velocities. For instance, the after re-excavation, further reducing the displacement velocities. For instance, the sidewall-to-sidewall sidewall-to-sidewall and roof-to-floor displacement velocities were 4.5 mm/day and 11 mm/day on and roof-to-floor displacement velocities were 4.5 mm/day and 11 mm/day on the 35th day, respectively, which then decreased to 1 mm/day and 6 mm/day on the 38th day, respectively. Thirty-eight days later, the sidewall-to-sidewall and roof-to-floor displacements were 344 mm and 770 mm, respectively. Afterward, the deformations of the surrounding rock were rheological (creep and time-dependent), but the displacement creep rate of the left sidewall, right sidewall, and roof were Sustainability 2017, 9, 2153 24 of 28 less than 1Sustainability mm/day. 2017 Deep, 9, 2153 holes post-grouting reinforced with chemical material played24 of an 29 important role in thethe stability 35th day, of therespectively, deep underground which then decrease opening.d to 1 mm/day and 6 mm/day on the 38th day, The floorrespectively. grouting Thirty-eight reinforcement days later, techniquethe sidewall-to-sidewall with pressurization and roof-to-floor and displacements progressive were depths was started on344 the mm 35th and day 770 andmm, finishedrespectively. on Afterward, the 99th day.the deformations The floor displacementof the surrounding velocity rock were experienced rheological (creep and time-dependent), but the displacement creep rate of the left sidewall, right dramatic fluctuationssidewall, and roof between were less 0 and than 23.5 1 mm/day. mm/day Deep during holes post-grouting the floor grouting reinforced due with to chemical the construction disturbancematerial of the played drilling an important boreholes. role Ninety-nine in the stability daysof the later,deep underground the floor displacement opening. velocity decreased to below 1 mm/dayThe floor withgrouting an reinforcement average of 0.7technique mm/day. with pressurization The floor grouting and progressive reinforcement depths was technique provides astarted foundation on the 35th for day secondary and finished enclosed on the 99th support day. The measures floor displacement for the velocity long-term experienced stability of the dramatic fluctuations between 0 and 23.5 mm/day during the floor grouting due to the construction surroundingdisturbance rock. of the drilling boreholes. Ninety-nine days later, the floor displacement velocity A totaldecreased of 158 daysto below later, 1 mm/day according with to an Figure average 25 ,of the 0.7 creepmm/day. rates The of floor sidewall-to-sidewall, grouting reinforcementroof-to-floor, the left sidewall,technique provides the right a foundation sidewall, for secondary the roof, enclosed and the support floor measures were for 0.36 the mm/day,long-term stability 0.71 mm/day, 0.21 mm/day,of the surrounding 0.14 mm/day, rock. 0 mm/day, and 0.71 mm/day, respectively. The total corresponding A total of 158 days later, according to Figure 25, the creep rates of sidewall-to-sidewall, roof-to- displacementsfloor, the were left sidewall, 413 mm, the 1142right sidewall, mm, 257 the r mm,oof, and 156 the mm,floor were 3 mm, 0.36 mm/day, and 1139 0.71 mm,mm/day, respectively. In addition,0.21 the mm/day, displacements 0.14 mm/day, showed 0 mm/day, asymmetry and 0.71 mm/day, during respectively. re-excavation. The total The corresponding displacements of the left sidewalldisplacements (257 mm) were and 413 the mm, floor 1142 (1139 mm, mm) 257 mm, were 156 much mm, larger3 mm, and than 1139 those mm, of respectively. the roof and In the right sidewall, whichaddition, represented the displacements 62% showed and 99% asymmetry of the during roof-to-floor re-excavation. (1142 The mm) displacements and sidewall-to-sidewall of the left sidewall (257 mm) and the floor (1139 mm) were much larger than those of the roof and the right (413 mm)sidewall, deformations, which represented respectively. 62% and Compared 99% of the toroof-to-floor the displacements (1142 mm) and during sidewall-to-sidewall the pilot excavation, the displacements(413 mm) deformations, decreased considerablyrespectively. Compared during to re-excavation. the displacements Compared during the withpilot excavation, the displacements of sidewall-to-sidewallthe displacements (1852 decreased mm) considerably and roof-to-floor during re-excavation. (3259 mm) Compared at measurement with the displacements point C7 during the pilotof excavation, sidewall-to-sidewall the displacements (1852 mm) and roof-to-floor decreased (3259 considerably mm) at measurement by 78% point and C7 during 65%, the respectively, pilot excavation, the displacements decreased considerably by 78% and 65%, respectively, during re- during re-excavation.excavation. The The support support effect is effect shown is in shown Figure 26. in Figure 26.

® Figure 26.FigureSupport 26. Support effect effect after after 8 8 m-deep m-deep holes holes post-grouting post-grouting with Marithan with Marithan. ®. • Borehole Image Monitoring BoreholeCompared Image Monitoring to the grouting effect of 3 m-deep holes post-grouting with cement and 8 m-deep Comparedholes post-grouting to the grouting with superfine effect of cement 3 m-deep in the holesroof (Figures post-grouting 13 and 14), borehole with cement image andmonitoring 8 m-deep holes showed that fractures were significantly reduced after 8 m-deep post-grouting with Marithan® post-grouting with superﬁne cement in the roof (Figures 13 and 14), borehole image monitoring showed (Figure 27), indicating that the chemical material is much better and more suitable for reinforcing ® that fracturesargillaceous were signiﬁcantlysurrounding rock reduced mass than after cement 8 m-deep grouting. post-groutingDeep holes post-grouting with Marithan with chemical(Figure 27), indicatingmaterial that the Marithan chemical® could material improve the ismuch intactness better of argillaceous and more rock suitable mass. for reinforcing argillaceous surrounding rock mass than cement grouting. Deep holes post-grouting with chemical material Marithan® could improve the intactness of argillaceous rock mass. Sustainability 2017, 9, 2153 25 of 29

Figure 27. Borehole image monitoring in the roof after 8 m-deep holes post-grouting with Marithan®. Figure 27. Borehole image monitoring in the roof after 8 m-deep holes post-grouting with Marithan®. • Axial Load Monitoring of Cables

The 8 m-deep holes post-grouting with chemical material (Marithan®) around the monitoring cross-section of cables at SJ52 + 54 m were installed the 23rd and the 25th day, and were finished on the 46th day, after re-excavation. Compared to the anchor-ability of installed before shotcrete and the 3 m-deep holes post-grouting (Figure 15), the anchor-ability of cables within argillaceous surrounding rock was greatly improved when the cables were installed after shotcrete and 3 m-deep holes post-grouting (Figure 28). The 8 m-deep holes post-grouting with Marithan® reinforced the rock mass and further improved the anchor-ability of the cables.

180 8-m-deep holes post-grouting with marithan

160

140

120

100

60 Axial load (KN) load Axial 1# Left sidewall 40 2# Left arch abutment 3# Left shoulder 4# Arch crown 20 5# Right shoulder 6# Right arch abutment 0 7# Right sidewall

-10 0 10 20 30 40 50 60 70 Time (day) Figure 28. Axial loads of cables installed after shotcrete and 3 m-deep holes post-grouting during re- excavation using 8 m-deep holes post-grouting with Marithan®.

6. Conclusions and Research Prospects The stability of deep underground openings during operation determines the sustainable safety production in underground coal mines. This work was a case study on the stability control of 800 m- deep underground openings in large fault zones in argillaceous rock that play a pivotal role in the sustainable development of the Guqiao Coal Mine in East China. The results were based on the analysis of long-term field measurements and engineering practices that provide valuable practical guidance for the stability control of deep underground openings in other coal mines with similar geological conditions, such as the Gubei and Panyidong Coal Mines in East China. Some conclusions and research prospects are summarized below.

Sustainability 2017, 9, 2153 25 of 29

Sustainability 2017, 9, 2153 25 of 28 Figure 27. Borehole image monitoring in the roof after 8 m-deep holes post-grouting with Marithan®.

• AxialAxial Load Load Monitoring Monitoring of of Cables Cables The 8 m-deep holes post-grouting with chemical material (Marithan®) around the monitoring The 8 m-deep holes post-grouting with chemical material (Marithan®) around the monitoring cross-section of cables at SJ52 + 54 m were installed the 23rd and the 25th day, and were ﬁnished cross-section of cables at SJ52 + 54 m were installed the 23rd and the 25th day, and were finished on onthe the 46th 46th day, day, after after re-excavation. re-excavation. Compared Compared to the toanchor-ability the anchor-ability of installed of installedbefore shotcrete before and shotcrete the and3 them-deep 3 m-deep holes holespost-grouting post-grouting (Figure (Figure 15), 15the), theanchor-ability anchor-ability of ofcables cables within within argillaceous argillaceous surroundingsurrounding rock rock was was greatly greatly improved improved whenwhen the ca cablesbles were were installed installed after after shotcrete shotcrete and and 3 m-deep 3 m-deep ® holesholes post-grouting post-grouting (Figure (Figure 28 28).). The The 88 m-deepm-deep holes post-grouting post-grouting with with Marithan Marithan® reinforcedreinforced the the rock rock massmass and and further further improved improved the the anchor-ability anchor-ability ofof the cables.

180 8-m-deep holes post-grouting with marithan

160

140

120

100

60 Axial load (KN) load Axial 1# Left sidewall 40 2# Left arch abutment 3# Left shoulder 4# Arch crown 20 5# Right shoulder 6# Right arch abutment 0 7# Right sidewall

-10 0 10 20 30 40 50 60 70 Time (day) FigureFigure 28. 28.Axial Axial loadsloads of cables installed installed after after shotcrete shotcrete and and 3 m-deep 3 m-deep holes holes post-grouting post-grouting during during re- re-excavationexcavation using using 8 8m-deep m-deep holes holes post-grouting post-grouting with with Marithan Marithan®. ®.

6.6. Conclusions Conclusions and and Research Research Prospects Prospects TheThe stability stability of of deep deep underground underground openingsopenings during operation operation determines determines the the sustainable sustainable safety safety productionproduction in in underground underground coal coal mines. mines. This This work work was wasa case a study case studyon the stability on the stabilitycontrol of control 800 m- of deep underground openings in large fault zones in argillaceous rock that play a pivotal role in the 800 m-deep underground openings in large fault zones in argillaceous rock that play a pivotal role in sustainable development of the Guqiao Coal Mine in East China. The results were based on the the sustainable development of the Guqiao Coal Mine in East China. The results were based on the analysis of long-term field measurements and engineering practices that provide valuable practical analysis of long-term ﬁeld measurements and engineering practices that provide valuable practical guidance for the stability control of deep underground openings in other coal mines with similar guidance for the stability control of deep underground openings in other coal mines with similar geological conditions, such as the Gubei and Panyidong Coal Mines in East China. Some conclusions geologicaland research conditions, prospects such areas summarized the Gubei andbelow. Panyidong Coal Mines in East China. Some conclusions and research prospects are summarized below.

6.1. Deformation and Failure Characteristics Engineering practices and ﬁeld measurements indicated that deformations and failure of the surrounding rock of deep underground openings in large fault zones are characterized by dramatic initial deformation, high long-term creep rate, obviously asymmetric deformations and failure, rebound of roof displacements, overall loosened deformations of deep surrounding rock mass on a large scale, and high sensitivity to engineering disturbance and water immersion.

6.2. Minimum Range of Pre-Grouting and Post-Grouting Reinforcement for Deep Underground Openings through Large Fault Zones According to ﬁeld measurements, the minimum pre-reinforcement range around the proposed deep underground opening through the large fault zones should be 13–18 m. Moreover, the minimum reinforcement range of deep holes post-grouting should be completed to improve the strength and intactness of the 8–9 m-deep surrounding rock mass. Sustainability 2017, 9, 2153 26 of 28

6.3. Inﬂuencing Factors The main factors inﬂuencing safe excavation and the stability of deep underground openings include large fault zones, high in situ stress, poor mechanical properties and engineering performance of the argillaceous surrounding rock mass, groundwater inrush, and gas outburst. The risks, including large fault reactivation, coal and gas outbursts, and groundwater inrush, seriously threaten tunneling safety during excavation. Ground surface pre-grouting (GSPG) should be completed to reinforce the regional engineering rock mass around the large fault FD108, between the northern and southern collapses, and eliminate fault reactivation and groundwater inrush hazards, as well as underground long advanced boreholes pre-grouting. The detection and drainage of groundwater and gas in advance, as well as strengthening management of groundwater and construction water should be conducted.

6.4. Pre-Grouting and Deep Holes Post-Grouting with a Novel Polyurethane Grouting Material The experimental results show that the argillaceous rock consisting of over 70% clay minerals will undergo softening, argillization, disintegrating, and swelling when in contact with water seepage. Engineering practices indicate that the anchor-ability of cables before shotcrete and post-grouting, and groutability with cement-matrix materials in the argillaceous rock mass is extremely poor. Shotcrete should be applied to seal and support the rock surface to inhibit weathering processes after excavation. Pre-grouting and deep holes post-grouting with a novel polyurethane grouting material (Marithan®) should be used to block fracture water from seeping, and prevent the deep argillaceous rock mass from argillization. Field measurements during re-excavation indicated that deep holes post-grouting with Marithan® were not only able to improve the intactness of deep rock mass and prevent the argillaceous rock from argillization, but also improves the anchor-ability of cables in the fractured argillaceous rock mass.

6.5. Suggestions of Coordinated Control Techniques According to the deformations and failure characteristics of the surrounding rock, the factors inﬂuencing the safe excavation and the stability and geo-hazards encountered during the pilot excavation, coordinated control techniques, including regional strata reinforcement technique such as GSPG, primary enhanced control measures of the surrounding rock, ﬂoor grouting reinforcement technique with pressurization and progressive depths, and secondary enclosed support are proposed and should be adopted to ensure the tunneling safety and long-term stability of deep underground openings through large fault zones in argillaceous rock.

6.6. Research Prospects The inﬂuence of creep and time-dependent behavior on the stability of 800 m-deep underground openings was obtained in this study by only using ﬁeld measurements. However, the obvious creep and time-dependent behavior of deep underground openings in argillaceous rock that results from the solid–liquid–gas-temperature coupling effect of deep rock mass, as well as the interaction with the underground openings is a complex issue that should be further investigated in the future using other methods such as numerical simulation.

Acknowledgments: This work was financially supported by the National Key Research and Development Program of China (Grant No. 2017YFC0603001), the National Natural Science Foundation of China (Grant No. 51704277), and the Project funded by China Postdoctoral Science Foundation (Grant No. 2017M621874). The authors would like to express appreciation to Liang YUAN in the Anhui University of Science and Technology, Quansheng LIU in the Institute of Rock and Soil Mechanics (Wuhan), Chinese Academy of Sciences and the staff at the Guqiao Coal Mine for their assistance during the field measurements. We also thank MDPI English Editing Service for improving the English text of this manuscript. Author Contributions: All of the authors contributed extensively to the work. Deyu Qian proposed key ideas and wrote the manuscript. Nong Zhang provided some ideas and practice guidance in the research process. Dongjiang Pan, Zhengzheng Xie, Hideki Shimada, Yang Wang, Chenghao Zhang and Nianchao Zhang modified the manuscript. Conflicts of Interest: The authors declare no conflict of interest. Sustainability 2017, 9, 2153 27 of 28

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