Key Construction Technology of Shield Tunneling Crossing Underneath a Railway

infrastructures

Article Key Construction Technology of Shield Tunneling Crossing underneath a Railway

Jinjin Ge 1,*, Ying Xu 2 and Weiwei Cheng 1 1 School of Civil Engineering and Architecture, Anhui University of Science and Technology, Huainan 232001, China; [email protected] 2 Key Lab of Coal Deep-Well Structural Technique, Huaibei 235000, China; [email protected] * Correspondence: [email protected]; Tel.: +86-554-666-8652

Academic Editors: Higinio González-Jorge and Pedro Arias-Sánchez Received: 14 August 2016; Accepted: 4 November 2016; Published: 10 November 2016

Abstract: The shield tunnel of the Kunming subway crosses beneath the Kun-Shi Railway. Due to the high requirements of railway track for settlement control, this article proposes the following technical measures for controlling the settlement based on the analysis of risks arising from the shield crossing railway: (1) Reinforcing the stratum of the region crossed by the shield in advance to achieve high stability; (2) Using a reinforced segment for the shield tunnel and increasing reserved grouting holes for construction; (3) Reasonably conﬁguring resources, optimizing construction parameters, strengthening monitoring and information management during the shield crossing. In strict accordance with the construction plan, the shield successfully and safely crossed beneath the Kun-Shi Railway; this provides experience that can be used in similar projects in the future.

Keywords: subway tunnel; crossing railway; shield method; construction technology

1. Introduction Common tunneling methods include: open-cut method, cover and cut (top-down) method, spray anchor subsurface excavation method and shield method. However, subway lines always pass beneath the downtown areas with heavy traffic and many economic activities, so it is necessary to reduce the impact of tunnel construction on the ground. Compared to other methods, shield construction does not affect ground traffic and underground pipelines, so the shield method is often used for subway tunnel excavation [1–6]. The history of tunnel construction with the shield method goes back more than 150 years. The first study was conducted by French engineer Marc Isambard Brunel [7,8]. In 1818, he began to study the construction of the shield method. In 1825, with a rectangular shield, he built the world’s first underwater tunnel (11.4 m wide, 6.8 m high) under the Thames in London. Although there are some unavoidable disadvantages in the shield method, such as: (1) Poor adaptability in the changing of section size; (2) Expensive purchase cost of the new shield, meaning the engineering of a short section construction is uneconomic; (3) Poor working environment of the workers, it is widely used because of its obvious advantages, such as: (1) Adequate construction safety for excavation and lining operation under the protection of the shield; (2) Underground construction not affecting the ground transportation and construction at the bottom of the river not affecting river navigation; (3) The construction operation not affected by climatic conditions; (4) The vibration and noise caused by the shield harming the environment less; (5) Small influence on the ground buildings and underground pipelines. The shield tunneling method was used for tunnel excavation in Kunming Rail Transit Line 3, which needed to cross beneath the running Kun-Shi Railway during the construction process. The Kun-Shi Railway was one of the first railway lines built in China, and it has greatly contributed

Infrastructures 2016, 1, 4; doi:10.3390/infrastructures1010004 www.mdpi.com/journal/infrastructures Infrastructures 2016, 1, 4 2 of 10 Infrastructures 2016, 1, 4 2 of 10 Kun-Shi Railway was one of the first railway lines built in China, and it has greatly contributed to the research of the development of China’s railways. It is classified as a Grade I Cultural Relic in toYunnan the research province. of the Therefore, development the railway of China’s tracks railways. were required It is classified to be protected as a Grade during I Culturalthe construction Relic in Yunnanof shield province. crossing, Therefore, greatly increasing the railway the tracks difficulty were of required construction. to be protectedIn addition, during risks the existing construction in the ofconstruction shield crossing, of shield greatly crossing increasing included: the difficulty(1) Large uplift of construction. and settlement In addition, of ground risks surface existing resulting in the constructionin uneven subgrade of shield which crossing caused included: traffic(1) accidents; Large uplift (2) Impact and settlement of train runnin of groundg on the surface annular resulting tunnel; in uneven(3) High-risk subgrade ground which monitoring; caused traffic (4) Uplift accidents; and settl (2)ement Impact of ofground train runningsurface caused on the by annular interruption tunnel; (3)of High-riskshield tunneling. ground To monitoring; ensure the (4) safety Uplift of and the settlementrailway and of shield ground tunnel surface during caused construction by interruption and ofoperation, shield tunneling. a rigorous To reinforcement ensure the safety scheme of the was railway prepared and prior shield totunnel shield duringtunneling construction based on the and operation,domestic research a rigorous and reinforcement analysis of settlement scheme was cont preparedrol [9–15]. prior Facts to shieldproved tunneling that this basedscheme on was the domesticfeasible. research and analysis of settlement control [9–15]. Facts proved that this scheme was feasible. ThisThis article article introduces introduces thethe keykey constructionconstruction technologytechnology of shield crossing railway railway based based on on the the successfulsuccessful construction construction of of a shielda shield crossing crossing for thefor Kun-Shithe Kun-Shi Railway Railway to provide to provide a reference a reference for relevant for engineeringrelevant engineering practice. practice.

2.2. ProjectProject Overview 2.1. Project Introduction 2.1. Project Introduction TwoTwo Komatsu Komatsu single-circular, single-circular, mudding mudding typetype EarthEarth Pressure Balanced (EPB) [16] [16] shield shield machines machines φ ofof φ6.34 6.34 m m were were used used for for tunneling tunneling in the in westthe west section section of Mianshan of Mianshan Station-Shagouwei Station-Shagouwei Station-Xiyuan Station- LijiaoXiyuan Station Lijiao section Station of section Kunming of Kunming Rail Transit Rail LineTransi 3.t TheLinenormal 3. The normal line spacing line spacing was 13.4 was m. 13.4 The m. tunnel The liningtunnel was lining designed was designed with an with external an external diameter diameter of 6.2 of m, 6.2 internal m, internal diameter diameter of 5.5of 5.5 m andm and ring ring width width of 1.2of m.1.2 Them. The shield shield crossed crossed beneath beneath the the Kun-Shi Kun-Shi Railway Railway in in the the section section of of YCK9 YCK9 + 030–060.+ 030–060. ThisThis project project started started fromfrom thethe MianshanMianshan StationStation near the Dian Ren Association south south of of Renmin Renmin WestWest Road Road and and advanced advanced towards towards the the easteast alongalong RenminRenmin WestWest Road.Road. The section of YCK9 + + 030–060 030–060 ◦ crossedcrossed thethe Kun-ShiKun-Shi RailwayRailway byby 3434° throughthrough the crossing of Renmin West West Road Road and and Changyuan Changyuan MiddleMiddle RoadRoad to the the Shaweigou Shaweigou Station Station near near the the Yunnan Yunnan Ruidian Ruidian Economic Economic and Trade and Trade Co., Ltd. Co., Both Ltd. Bothshield shield machines machines were were transferred transferred at the at theShaweigou Shaweigou Station. Station. Starting Starting from from the theend endwell well in the in theeast east of ofShaweigou Shaweigou Station, Station, the the two two shield shield machines machines advanc advanceded towards towards the east the along east alongthe Renmin the Renmin West Road West Roadand passed and passed Dongjiagou Dongjiagou and Haiyuan and Haiyuan River Rivercourse, course, finally ﬁnally arriving arriving at the atXiyuan the Xiyuan Lijiao LijiaoStation Station near nearLianyuan Lianyuan Filling Filling Station. Station. TheThe central central section section ofof thethe railwayrailway throughthrough whichwhich thethe shieldshield tunneled was YCK9 + 032. 032. The The section section withinwithin 30 30 m m before before and and after after thethe junctionjunction ofof thethe railwayrailway andand tunneltunnel was affected by by the construction construction withwith about about 10 10 days days of of shield shield crossing.crossing. TheThe shieldshield machinemachine tunneled through the the left left line line from from 1 1 February February toto 1010 FebruaryFebruary and tunneled tunneled through through the the right right lin linee from from 1 March 1 March to 10 to March 10 March at a low at a speed. low speed. The Therelationship relationship between between the shield the shield tunnel tunnel and Ku andn-Shi Kun-Shi Railway Railway is shown is shown in Figures in Figures 1 and 12. and 2.

y wa ail i R Sh n- Ku

Re nmin West Road

Shield hanging out well

FigureFigure 1.1. Kun-shiKun-shi railwayrailway and subway tunnel location. InfrastructuresInfrastructures2016 2016, 1,, 1 4, 4 3 of3 10 of 10

Kun-Shi Railway

Interval left line Interval right line

Figure 2. Figure 2.Kun-Shi Kun-Shirailway railway andand the subway tunnel tunnel cross cross section section relationship. relationship.

2.2.2.2. Geological Geological Conditions Conditions of of the the Railway Railway RegionRegion TheThe surface surface layer layer affectedaffected byby thethe projectproject alongalong the the line line was was plain plain filling filling soil, soil, composed composed of of QuaternaryQuaternary (Q4al (Q4al + + l) l) mud mud clay,clay, clay,clay, siltysilty clay,clay, silty sand and and peaty peaty soil soil at at the the upper upper part, part, Quaternary Quaternary (Q3al(Q3al + + l) l) clay, clay, silty silty clay,clay, peaty soil, soil, silty silty soil, soil, silty silty sand sand and and medium medium sand sandat the atmid-lower the mid-lower part. The part. Theoverlaying overlaying layer layer was was more more than than50 m 50thick. m thick.The soils The of soilseach oflayer each showed layer multiple showed crossed multiple tailing- crossed tailing-outout settlement, settlement, with withgreat great variation variation of burial of burial depth depth and and thickness thickness as well as well as asuneven uneven mechanical mechanical properties.properties. The The soils soils within within the the exploration exploration depthdepth can be divided divided into: into: (1-1) miscellaneous fill, including the roadbed fill and soil fill, loose to slightly close; (1-1)(2-1) miscellaneous silty clay, plastic, fill, includingthe basic bear theing roadbed capacity fill of and the soil soil fill, is 135 loose KPa; to slightly close; (2-1)(4-2) silty organic clay, soil, plastic, flow the to basicthe soft bearing plastic, capacity the basic of bearing the soil capacity is 135 KPa; of soil is 50 KPa; (4-2)(4-3) organic clay, plastic, soil, flow the tobasic the bearing soft plastic, capacity the of basic the bearingsoil is 120 capacity KPa; of soil is 50 KPa; (4-3)(4-3-1) clay, clay, plastic, soft theplastic, basic the bearing basic bearing capacity capacity of the soilof the is soil 120 is KPa; 90 KPa; (4-3-1)(4-4-1) clay, silty soft clay, plastic, the basic the bearing basic bearing capacity capacity of the soil of the is 100 soil KPa; is 90 KPa; (4-4-1)(9-3) silty clay, plastic, the basic the bearing basic bear capacitying capacity of the of soil the is soil 100 is KPa; 135 KPa; (9-4) peat soil, plastic, the basic bearing capacity of the soil is 80 KPa; (9-3) silty clay, plastic, the basic bearing capacity of the soil is 135 KPa; (9-6) powder sand, slightly to medium density, the basic bearing capacity of the soil is 180 KPa; (9-4) peat soil, plastic, the basic bearing capacity of the soil is 80 KPa; (12-1) silty clay, hard to plastic, the basic bearing capacity of soil 150 kPa. (9-6) powder sand, slightly to medium density, the basic bearing capacity of the soil is 180 KPa; 2.3.(12-1) Overview silty of clay, the Shield hard toMachine plastic, the basic bearing capacity of soil 150 kPa. Two Komatsu single-circular mudding type earth-pressure balanced shield machines of φ 6.34 m 2.3. Overview of the Shield Machine were used in the section. The shield machine is mainly composed of shield housing, excavation mechanism,Two Komatsu thrust single-circular mechanism, du muddingmp mechanism, type earth-pressure assembly mechan balancedism shieldand accessory machines devices. of φ 6.34 It m werecan usedbe widely in the used section. for construction The shield under machine the geolog is mainlyical composedconditions of of alluvial shield housing,clay, diluvial excavation clay, mechanism,sandy soil, thrust sand, mechanism,gravel and pebble dump without mechanism, separation assembly devices mechanism and more and area. accessory The overlaying devices. soil It can becan widely be relatively used for thin construction when it is used under for the construc geologicaltion. The conditions construction of alluvial of the earth-pressure clay, diluvial balanced clay, sandy soil,shield sand, can gravel effectively and pebble control without the uplift separation and settlement devices of andthe ground more area. surface The and overlaying has been soil widely can be relativelyapplied thinin many when subways it is used in forChina. construction. The construction of the earth-pressure balanced shield can effectivelyAs the monitoring control the system uplift mounted and settlement on the ofshield the groundmachine surface adopts andthe world’s has been latest widely PLC appliedcontrol in manytechnology, subways sensor in China. technology, automatic fault detection system and anti-misoperation system, the shieldAs themachine monitoring can achieve system a clear mounted monitoring on the pict shieldure, machineeasy operation, adopts accurate the world’s and fast latest data PLC control technology, sensor technology, automatic fault detection system and anti-misoperation system, Infrastructures 2016, 1, 4 4 of 10 the shield machine can achieve a clear monitoring picture, easy operation, accurate and fast data collection and processing as well as remote construction information transfer, so the central control room on the ground can keep track of the operation of shield machines. The shield machine adopts the measurement and guidance system integrated with target, total station, PLC and computer for simple, intuitive and accurate operation.

3. Key Construction Technology

3.1. Analysis of the Technical Difﬁculties When a subway tunnel crosses underneath a railway, mutual impact would occur between the subway and the railway. The ground surface settlement during the shield construction would affect the safety of railway operation while the dynamic load of the railway would affect the safety of the subway structure [17]. The impacts are described as follows:

(1) When the shield machine passes under the railway, the soil mechanical properties would be greatly disturbed, resulting in uneven ground surface settlement which would produce gaps, dislocation, steps and bevels at rail joints, seriously affecting the safety of train operation. (2) When a train is running, the dynamic stress which it produces on the subgrade soil gradually decreases with the depth. The degree of the decrease is related to the mechanical properties of soil and dynamic load of the train. Generally, the depth which dynamic stress can reach is about 4–7 m. However, when there is a structure underneath the subgrade, the propagation of dynamic stress is increased. (3) Shield construction leads to track settlement and irregularity, which increases the impact force between the wheel and rail, so the dynamic stress in the subgrade and soil dynamic load are increased; thus, the load applied on the subway tunnel segment is increased, affecting subway tunnel safety. (4) The increase in the travel speed of trains on the Kun-Shi Railway would also lead to an increase of dynamic load of the train, which inevitably leads to the increase of dynamic stress of the subgrade surface.

3.2. Reinforcement Measures According to the results of risk assessment [18], grouting pipes were required to be embedded in the affected region of the railway (within 15 m mileage before and after track central line and 3 m beyond the outline of section tunnel) before the shield crossing. Then the shield advanced to the region, pre-grouting was performed through the grouting holes of the head of the shield machine and tracing grouting was performed through the grouting holes reserved on the ground according to the railway monitoring values. Under the guarantee of the above measures, the shield continued to advance and cross the railway region.

3.2.1. Reinforcement Scheme During the shield construction, when the shield machine head reached the affected region of Kun-Shi Railway (YCK9 + 030), grouting was performed for reinforcement (reinforcement by double grouting with construction mix proportion of cement grout:sodium silicate =1:1) through the grouting holes reserved at the machine head. After each segment was assembled, grouting was performed and its volume was adjusted according to the monitoring data.

3.2.2. Reinforcement Region The shield machine tunneled beneath the section of YCK9 + 030–060 between Mianshan Station and Shaweigou Station of the Kun-Shi Railway; the site which the shield machines crossed was located at the Renmin West Road, crossing the Kun-Shi Railway by 34◦, with about 11 m of overlaying layer. Infrastructures 2016, 1, 4 5 of 10

The reinforcement region is shown in Figure3 on the layout of reinforcement region where the shield crossedInfrastructures underneath 2016 the, 1, 4 railway. 5 of 10

Infrastructures 2016, 1, 4 5 of 10

3 46 30

. 3 6 5 4 2

Shield h 8 anging . out well

3 5

Shield hanging out well 3 Explanation: the shadow part of the figure is grouting reinforcement area of the shield through the railway Explanation: the shadow part of the figure is grouting reinforcement FigureFigure 3. Layout 3. Layout of reinforcementof reinforcement area for for shield shield areatunneling tunneling of the shieldunder under through railway. railway.the railway 3.3. Tracing Grouting 3.3. Tracing Grouting Figure 3. Layout of reinforcement area for shield tunneling under railway. Before the shield crossed beneath the region, six grouting holes were drilled in the ground. BeforeAlong3.3. Tracing the the shielddirection Grouting crossed of shield beneath tunneling, the grouting region, holes six were grouting arranged holes at the position were drilled 3 m away in from the ground. Along thethe directionrailway. Inof the shield direction tunneling, vertical to grouting the tunnel, holes grouting were pipes arranged were arranged at the 3 position m away from 3 m awaythe from Before the shield crossed beneath the region, six grouting holes were drilled in the ground. the railway.outside In of the the direction tunnel. Grouting vertical pipes to thewere tunnel, 5 m deep grouting under the pipes ground. were The arrangedlayout of grouting 3 m away holes from the isAlong shown the in direction Figure 4. of shield tunneling, grouting holes were arranged at the position 3 m away from outside ofthethe railway. tunnel. In the Grouting direction pipes vertical were to the 5 mtunnel, deep grouting under pipes the ground. were arranged The layout 3 m away of grouting from the holes is shown inoutside Figure of 4the. tunnel. Grouting pipes were 5 m deep under the ground. The layout of grouting holes is shown in Figure 4.

Grouting hole1 Grouting hole2

3 Grouting ho Grou le1 Grout ting hole3 3 ing hole2

Grouting hole4 3

Grou 3 Shield hanging ting hole33 3 out Grouting hole5 3 well Grouting hole4 Grouting hole6 3 Shield hanging 3 out Grouting hole5 3 well Grouting hole6

Figure 4. Layout of grouting hole.

Grouting holes were drilled and grouting pipes were laid in the ground prior to shield construction according to the layoutFigureFigure of grouting 4. 4.Layout Layout holes. of of grouting grouting When hole. the hole. shield advanced within the area of the railway line, construction parameters were selected according to the monitoring results on the ground.Grouting Double holes grouts were were drilled used and for tracinggrouting gr pipesouting. were Grouting laid involume the ground and parameters prior to shield were Groutingadjustedconstruction holes and accordingthe were values drilled to of the uplift and layout and grouting ofsettlement grouting pipes ofholes. track were When face laid were the in theshield monitored ground advanced in prior real within time. to shield the area construction of accordingthe torailway the layout line, construction of grouting parameters holes. When were selected the shield according advanced to the monitoring within the results area ofon thethe railway line, constructionground. Double parameters grouts were were used selected for tracing according grouting. toGrouting the monitoring volume and resultsparameters on were the ground. adjusted and the values of uplift and settlement of track face were monitored in real time. Double grouts were used for tracing grouting. Grouting volume and parameters were adjusted and the values of uplift and settlement of track face were monitored in real time. Infrastructures 2016, 1, 4 6 of 10

3.4. Measurements for Shield Construction The key to the reduction of the shield construction’s disturbance of the surrounding soil was to maintain the stability of the shield excavation face and to ensure timely ﬁlling of the tail void when the segment left the shield tail. The stability of the excavation face of the shield tunnel was controlled by optimizing the excavation parameters and the ﬁlling of the tail void was achieved by synchronous grouting and secondary grouting. To ensure the safety and successfulness of crossing the Kun-Shi Railway, the following measures were taken:

(1) Monitoring points were arranged in advance in the affected region of the railway. Shield construction test sections were set and construction parameters of shield advance speed, cutter rotation speed, earth chamber positive pressure, excavated volume and synchronous grouting volume were adjusted. (2) Earth pressure values at rest were set at reasonable levels. The set values of balanced earth pressure for construction were reasonably adjusted according to shield buried depth, current soil conditions, tunnel construction of previous test section and monitoring data. Excavated volume was strictly controlled and excessive or inadequate excavation was avoided. Excavated volume was reasonably adjusted according to the monitoring results on the ground and in the tunnel and adjusted according to the data. The soil loss due to excavation was controlled within 5‰. (3) Advance speed was strictly controlled and adjusted. The shield machine slowed down when it reached the site 30 m away from the railway. The advance speed was controlled at around 4–5 cm/min. The shield machine slowed down again when it reached the site 20 m away from the railway. The advance speed was controlled at around 3–4 cm/min. During the crossing construction, construction data were analyzed and summarized in a timely manner to determine new parameters to guide the construction. (4) The shield construction axis was strictly controlled. Changes in shield posture should not be too large and frequent to reduce the loss of soil and disturbance to the surrounding soil. The deviation of the shield advancing axis should be controlled within ±20 mm. Before the shield machine crossed the region, the shield postures were perfectly adjusted. An automatic measuring system of shield posture was adopted for automatically measuring the deviation of shield postures every 20 cm to send the measurement data to the axis control system in a timely manner so as to ensure that the shield could successfully cross the railway. (5) Shield rectification was strictly controlled. Operators of the shield machine strictly executed the instructions and corrected the initial small deviations in a timely manner to prevent the shield machine from advancing in a serpentine way. They controlled the correction amount within a limit range each time to reduce the disturbance to stratum and create good conditions for segment assembly. The deviation of the shield advancing axis was corrected by adjusting the shield jacks: we decreased the operating pressure of the jacks in the place opposite the direction of deviation resulting in a path difference between the jacks in two regions so as to correct the deviation. The correction of the shield’s serpentine advancing was slowly performed in a long distance with one correction of less than 3 mm. (6) Synchronous grouting volume and quality were strictly controlled. For synchronous grouting, the voids between tail segment and soil could be filled in a timely manner to reduce the soil deformation during construction. Grout which can be hardened was used with consistency of 9.5–11.5 cm. Grouting pressure and volume were controlled based on the dynamic monitoring data when tunneling. Grouting volume was adjusted based on the monitoring of the railway tunnel. Preliminary grouting volume should be 3.0 M3/ring. Grouting pressure should be reasonably controlled to perform filling rather than splitting. The soil layer outside the segment would be disturbed by grout due to large grouting pressure, resulting in great settlement and grout loss; small grouting pressure would lead to slow filling. Large deformation would also Infrastructures 2016, 1, 4 7 of 10

Infrastructuresbe caused 2016, by 1, 4 inadequate ﬁlling. Grouting pressure should be controlled by 1.1–1.2 times earth7 of 10 pressure at rest. (7)(7) Segment assembly was strictly controlled. The jack was used as much asas possiblepossible forfor segmentsegment assembly andand waswas not not allowed allowed to to stand stand idle. idle. The The jack jack was was retracted retracted as little as aslittle possible as possible after shield after shieldtunneling tunneling to meet to segment meet segment assembly assembly so as to preventso as to the prevent jack from the retraction jack from and retraction disturbance and disturbanceto soil. The jackingto soil. forceThe jacking of the jackforce was of the adjusted jack was in a adjusted timely manner in a timely after manner segment after assembly segment to assemblyprevent abrupt to prevent changes abrupt in shield changes posture. in shield posture. (8)(8) In order to prevent groundwater and synchronoussynchronous grout from rushingrushing intointo thethe tunneltunnel fromfrom thethe shield tail duringduring thethe shield’sshield’s advance, advance, grease grease was was applied applied onto onto the the wire wire brush brush of of the the shield shield tail tail to toensure ensure that that the voidsthe voids between between shield tailshield and tail segment and weresegment ﬁlled were with filled grease with during grease construction during constructionto seal the shield. to seal the shield. (9)(9) Secondary groutinggrouting was was performed performed in a timelyin a ti mannermely manner to control to thecontrol post-construction the post-construction settlement. settlement.After shield After crossing, shield the long-termcrossing, tracingthe long-ter groutingm tracing was conducted grouting in was a timely conducted manner in on a thetimely soil mannersurrounding on the the tunnelsoil surrounding beneath the the railway tunnel section bene crossedath the by railway shield accordingsection crossed to the monitoring by shield accordingof the tunnel to the and monitoring ground track. of the tunnel and ground track.

3.5.3.5. Monitoring SchemeScheme

3.5.1.3.5.1. Arrangement ofof MonitoringMonitoring PointsPoints MonitoringMonitoring pointspoints ofof settlementsettlement andand displacementdisplacement werewere arrangedarranged alongalong bothboth sidessides ofof the railway subgradesubgrade accordingaccording to to the the layout layout in Figurein Figure5; four 5; rows four of rows settlement of settlement monitoring monitoring points were points arranged were alongarranged the along direction the direction of the shield’s of the advanceshield’s advance with a row with spacing a row spacing of 5 m andof 5 am lineand spacinga line spacing of 15 m;of two15 m; rows two of rows displacement of displacement monitoring monitoring points werepoints arranged were arranged on the railon inthe the rail direction in the direction of the shield’s of the advanceshield’s advance with a line with spacing a line of spacing 7.5 m; aof precision 7.5 m; a levelprecision instrument level instrument was used for was settlement used for monitoring settlement andmonitoring a total station and a total instrument station wasinstrument used for was displacement used for displacement measurement. measurement.

Interval left line

Interval right line

Settlement monitoring point Displacement monitoring points

FigureFigure 5.5. Layout ofof monitoringmonitoring pointspoints (m).(m).

Infrastructures 2016, 1, 4 8 of 10

3.5.2. Control Standards (1) Monitoring accuracy The monitoring accuracy is shown in Table1.

Table 1. Monitoring accuracy of shield crossing railway.

Number Monitoring Project Alarm per Two Hour Rate Cumulative Change Alarm 1 Surface subsidence 3 mm/times Settlement 30 mm; uplift 10 mm 2 Line settlement 3 mm/times ±20 mm 3 Line horizontal displacement 2 mm/times 8 mm 4 Pipeline settlement 2 mm/times 10 mm 5 Uneven settlement of rail surface 2 mm/times 10 mm

(2) Monitoring and controlling indexes According to the design requirements, the settlement of ground surface and national track face caused by the shield’s crossing railway was controlled within ±10 mm. The height difference between two tracks of each railway line was not greater than 4 mm. At the same time, 70% of the above limit values were taken as the values for the monitoring alarm.

3.5.3. Monitoring Content (1) Ground surface settlement Nine monitoring sections of ground surface settlement were respectively set at both sides of the railway line where the shield crossed underneath, along the vertical direction of the shield’s advance.

(2) Track settlement Deformation monitoring points were ﬁrst arranged on the ground prior to the shield’s advance. Five monitoring sections (one section was set in the centers of railway line respectively and one section was set at the edge of the track bed on either side of the railway line) of transverse settlement were set in the crossed region; the monitoring points on the monitoring section of transverse settlement were arranged in the same way as the ground surface settlement.

(3) Uneven settlement between rail face Monitoring points of settlement were arranged on the rail face corresponding to the section in the region affected by construction.

3.5.4. Monitoring Method, Technical Requirements and Monitoring Frequency (1) Leveling survey Settlement monitoring was conducted according to the national Grade II leveling speciﬁcations. Two or three bench marks were set at about 100 m beyond the construction region at the beginning of the reckoning. Each monitoring point and bench marks formed a closed or annexed leveling line. The average of the two measured values was taken as the initial leveling value. An S1 (Geodetic level) level instrument was used for measurement with a per kilometer round-trip error (accuracy) of less than or equal to 1 mm. This is mainly used for the national secondary level precision leveling measurement. Infrastructures 2016, 1, 4 9 of 10

(2) Measuring method A precise level instrument was used for the measurement. Initial leveling measurements were acquired jointly at working bench marks and bench marks nearby. Each tolerance should be strictly controlled when monitoring. The tolerance at each monitoring point should not exceed 0.5 mm. One monitoring station should have fewer than three monitoring points which were not on the leveling line. If exceeded, the measurements at post monitoring should be accented for veriﬁcation. Monitoring should be conducted twice at the monitoring point for the ﬁrst time. The difference between the two leveling values should be less than ±0.1 mm and the average should be taken as the initial value.

(3) Uneven settlement between rail face

1) Monitoring point embedment Monitoring points of the rail face were set in the bolt shaft of the rail fastening. 2) Measuring method Uneven settlement between the rail face was determined through level measurement.

3.5.5. Monitoring Frequency All monitoring points were observed when the shield advanced to the site 30 m away from the railway for collecting original values. When the shield advanced to the site 20 m away from the railway, monitoring was continuously conducted. The monitoring frequency was required to be adjusted again after the shield crossed underneath according to the changes in measurement data. The monitoring frequency of the shield’s crossing railway is shown in Table2.

Table 2. Monitoring the frequency of the shield crossing railway.

Number Construction Condition Monitoring Frequency 1 Excavation face distance from the railway line 30 m Initial value 2 20 m ≤ Excavation face distance from the railway line ≤ 30 m 1 times/day 3 Excavation face distance from the railway line ≤ 20 m 1 times/rings 4 Shield machine shield tail after crossing the railway line 3 times/day 5 Shield machine shield tail over rail line more than 50 m 1 times/day 6 Settlement tends to be stable 1 times/week 7 Settling stability 1 times/month

4. Conclusions In this paper, the key technology of the construction of a shield tunnel crossing a railway is described in detail within the context of Kunming Rail Transit Line 3 crossing the Kun-Shi Railway. The shield crossed Kun-Shi Railway safely because the process followed these methods: (1) reinforcing the stratum of the region crossed by the shield in advance to achieve high stability; (2) accurately setting the front earth-pressure and controlling the driving speed; (3) strengthening synchronous grouting, reasonably controlling grouting quantity and the quality of grouting; (4) setting the parameters of shield tunneling by monitoring data, maintaining information construction; (5) strengthening the shield tail seal; (6) controlling shield tunneling attitude, gently rectiﬁcating, minimizing the disturbance of the front and the surrounding soil by shield tunneling. Monitoring data shows that, during the period of reinforcement, the maximum cumulative uplift on the railway line was 2.2 mm; during the period of shield crossing, the maximum cumulative uplift on the railway line was 3.1 mm, the maximum settlement was 4.3 mm and the maximum single settlement was 1.2 mm. Seen from the construction process control and monitoring results, the use of appropriate construction parameters after stratum reinforcement could control the uplift and settlement of the rail face within a 5 mm range, far smaller than the alarm values. After the shield Infrastructures 2016, 1, 4 10 of 10 crosses the railway, according to the late settlement, secondary grouting must be carried out in time to control the late settlement.

Acknowledgments: We extend our gratitude to the National Natural Science Foundation, China (51374012), Anhui Province Science and Technology Project, China (1501041123). Those supports are gratefully acknowledged. Author Contributions: Jinjin Ge wrote the manuscript. Ying Xu provided guidance and suggestions. Weiwei Cheng provided related pictures. Conﬂicts of Interest: The authors declare no conﬂict of interest.

References

1. Liu, J.H.; Hou, X.Y. Shield Tunnel; China Railway Press: Beijing, China, 1991. (In Chinese) 2. Qian, Q.H. Meeting the development climax of urban underground space in China. Chin. J. Geotech. Eng. J. 1998, 20, 112–113. (In Chinese) 3. Japanese Civil Society; Liu, T.X., Translators; Standard Specification and Explanation of Japan Tunnel; Southwest Jiao Tong University Press: Chengdu, China, 1993. (In Chinese) 4. Gao, B.L.; Ren, J.X. Safety risk assessment for adjacent underground pipelines in metro construction. Mod. Tunn. Technol. J. 2016, 53, 118–123. (In Chinese with English abstract) 5. Masahiro, M.; Kotaro, K. Use of compact shield tunneling method in urban underground construction. Tunn. Undergr. Space Technol. J. 2005, 20, 159–166. 6. He, C.; Feng, K.; Fang, Y. Review and prospects on constructing technologies of metro tunnels using shield tunnelling method. J. Southwest Jiaotong Univ. J. 2015, 50, 97–109. (In Chinese with English abstract) 7. Desmond, T.D. Henry Marc Brunel: The first submarine geological survey and the invention of the gravity corer. Mar. Geol. J. 1967, 5, 5–14. 8. Nick, M.; Mike, B. Tunnel vision? Brunel’s Thames Tunnel and project narratives. Int. J. Proj. Manag. J. 2013, 31, 692–704. 9. Guo, H.Y.; Gu, Z.W. Construction technique for tunnel excavation with large TSM under Huhang railway line. Build. Construct. J. 2006, 28, 767–768, 771. (In Chinese with English abstract) 10. Liu, Y.C. Tunnel boring across underneath high-speed rail ways by shield machines. Tunn. Construct. J. 2006, 26, 47–49. (In Chinese with English abstract) 11. Zhang, S.R.; Tian, X.X.; Wang, G. 3D numerical simulation of excavation of shield tunnel in softground. Chin. J. Undergr. Space Eng. J. 2012, 8, 807–814. (In Chinese with English abstract) 12. Ye, Y.D.; Ju, J.; Wang, R.L. Discussion on construction technology during passing of shield through the operating metro tunnel. Construct. Technol. J. 2005, 34, 67–68. (In Chinese with English abstract) 13. Guo, M. Influencing factors and control technologies for ground surface settlement induced by shield tunneling when shield bores slowly/shield stop. Tunn. Construct. J. 2016, 36, 701–708. (In Chinese with English abstract) 14. Peng, B.; Yang, Z.Y. Construction application of shield tunnel through railroad group. J. Maoming Univ. J. 2007, 17, 74–77. (In Chinese) 15. Liu, J.H. Numerical simulation of surface settlement caused by soil pressure in shield-tunneling. Tunn. Construct. J. 2007, 27, 30–32. (In Chinese with English abstract) 16. Zhang, Q.; Hou, Z.D.; Huang, G.Y. Mechanical characterization of the load distribution on the cutterhead–ground interface of shield tunneling machines. Tunn. Undergr. Space Technol. J. 2015, 47, 106–113. [CrossRef] 17. Hu, Z.; Shao, X.; Yao, H.Y. Mechanics analysis of shield construction traversing adjacently under existing urban tunnel. J. Sichuan Univ. (Eng. Sci. Ed.) 2016, 48, 52–59. (In Chinese with English abstract) 18. Zhang, J.; Jia, M.C.; Zhang, J. Analysis of risks in overall process during the construction period of metro shield tunnel construction. Highw. Eng. J. 2013, 38, 38–56. (In Chinese with English abstract)

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