Research on Supporting Method for High Stressed Soft Rock Roadway in Gentle Dipping Strata of Red Shale

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Article Research on Supporting Method for High Stressed Soft Rock Roadway in Gentle Dipping Strata of Red Shale

Chunde Ma 1,2, Jiaqing Xu 1,* , Guanshuang Tan 1, Weibin Xie 1 and Zhihai Lv 1

1 School of Resources and Safety Engineering, Central South University, Changsha 410083, China; [email protected] (C.M.); [email protected] (G.T.); [email protected] (W.X.); [email protected] (Z.L.) 2 Advanced Research Center, Central South University, Changsha 410083, China * Correspondence: [email protected]; Tel.: +86-15904920851

Abstract: Red shale is widely distributed among the deep mine areas of Kaiyang Phosphate Mine, which is the biggest underground phosphate mine of China. Because of the effect of various factors, such as high stress, ground water and so on, trackless transport roadways in deep mine areas were difficult to effectively support for a long time by using traditional supporting design methods. To deal with this problem, some innovative works were carried out in this paper. First, mineral composition and microstructure, anisotropic, hydraulic mechanical properties and other mechanical parameters of red shale were tested in a laboratory to reveal its deformation and failure characteristics from the aspect of lithology. Then, some numerical simulation about the failure process of the roadways in layered red shale strata was implemented to investigate the change regulation of stress and strain in the surrounding rock, according to the real rock mechanical parameters and in-situ stress data. Therefore, based on the composite failure law and existing support problems of red shale roadways, some effective methods and techniques were adopted, especially a kind of new wave-type bolt that was used to relieve rock expansion and plastic energy to prevent concentration of stress and excess Citation: Ma, C.; Xu, J.; Tan, G.; Xie, deformation. The field experiment shows the superiorities in new techniques have been verified and W.; Lv, Z. Research on Supporting successfully applied to safeguard roadway stability. Method for High Stressed Soft Rock Roadway in Gentle Dipping Strata of Keywords: high stressed soft rock roadway; wave-type bolt; support technology Red Shale. Minerals 2021, 11, 423. https://doi.org/10.3390/min11040423

Academic Editor: Abbas Taheri 1. Introduction As the mining depth increases, the in-situ stress increases rapidly, the original support Received: 15 March 2021 technology and measures are invalid, the roadway repair rate is high and there are frequent Accepted: 13 April 2021 Published: 16 April 2021 roof falls, slabs, bottom heaves, etc. [1–3] after permanent roadway support, which requires multiple maintenances. With reinforcement, maintenance workload and high support cost

Publisher’s Note: MDPI stays neutral have a serious impact on the normal and safe mining of the mine in Kaiyang Phosphate with regard to jurisdictional claims in Mine. The large deformation of the roadway severely restricts the production of soft rock published maps and institutional afﬁl- mines [4–6]. Roadway support is a crucial step in the mining process, and it is also the iations. direction that many scholars have been studying [7–9]. The traditional support method of bolts, cables and steel supports do not distinguish between soft and hard rock. At the same time, the current internationally popular New Austrian Tunnelling Method (NATM) does not clearly answer the question of what the support object is [10,11]. Therefore, it is particularly critical to ensure the safety of roadways in deep inclined rock formations. Copyright: © 2021 by the authors. Licensee MDPI, Basel, Switzerland. Before supporting, it is necessary to clarify the failure mechanism of surrounding This article is an open access article rock. The failure mechanism of the surrounding rock of roadway has been extensively distributed under the terms and investigated in recent years. Wu et al. [12] studied the deformation mechanism of soft conditions of the Creative Commons rock roadway through in-situ monitoring technology, and the study pointed out that high Attribution (CC BY) license (https:// ground pressure and low rock strength are the main factors that cause large roadway creativecommons.org/licenses/by/ deformation. Li et al. [13] used an exploratory physical model, numerical simulation and 4.0/). ﬁeld measurements to evaluate the deformation and failure modes of soft rock roadways.

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He et al. [14] believe that deep underground support engineering should mainly consider how to counteract dynamic impact and retain the suitable rock mass deformation. Li et al. [15] discovered that the surrounding rock stress gradually decreases, meanwhile the deformation and failure mainly occur to the center of the roadway roof. Yang et al. [16] conducted a study on the failure mechanism of deep soft rock roadways in Xin’an Coal Mine, Gansu, China and found that the failure was first caused by high deviator stress caused by excavation, and then the damage expanded upon the deep part. At the same time, various damage phenomena in the shallow part were analyzed as tensile. Guo et al. [17] observed that the deformation of the soft rock roadway started from the roof and then led to the destruction of the entire support system. They believed that the cause of the failure was the uncoupling of the support mechanism and the surrounding rock. In addition, many scholars have discovered different failure mechanisms of surrounding rocks and analyzed the reasons for a targeted manner [18–20]. In response to the above problems, researchers have developed some theories and techniques for soft rock support. In order to solve the serious initial deformation of the soft rock roadway in Xiaokang Coal Mine, Wang et al. [21] designed a set of circular fully enclosed combined support systems, including high-strength prestressed bolts, a “W”-type strong anchor cable and U-shaped yielding steel. Chang et al. [22] used hydraulic expansion bolts to solve the problem of the floor heave of the soft rock roadway and overcome the adverse effects of residual rock powder in the bolt holes. Wang et al. [23] developed a confined concrete support system, using high-strength arch supports to ensure safe mining in Liangjia Coal Mine. Shreedharan et al. [24] used discrete element simulation software to analyze the stability of tunnels with different cross-sections under high stress, which provided a reference for the shape and support of the tunnel. Yu et al. [25] investigated a combined support methodology and optimized the support parameters by analysis of the field structure of weak surrounding rock to ensure the safety of the roadway. Although scholars work together to attempt to ensure safe production of deep stopes, there are still hidden safety hazards in some soft roadways. The support technique for highly stressed soft rock roadways still needs further development and study [26,27], especially when the roadway lays in a gently dipped layered soft rock mass with the typical bedding structure, which is a challenge to the control of soft rock with great deformation failure and rheological property [28]. In this paper, the failure mechanisms of the typical soft rock (red shale) have been investigated by testing for mineral composition and microstructure, anisotropic and hydraulic mechanical properties and ground stress and analyzing of evaluation on existing support and numerical simulation on layered strata. Based on the failure mechanism, the approved version of the shotcrete rock bolt mesh technique is proposed to new-designed wave-type bolt layout installed at different angles for controlling the bedding structure. Besides, other helpful engineering suggestions were proposed. Finally, in-site industrial experiments results have validated the new support technique’s reasonableness.

2. Mechanical Properties of Red Shale In Kaiyang Phosphate Mine, most of the main development roadways are arranged in the footwall (red shale rock strata), which presents an inclination angle close to 31 degrees as shown in Figure1. The effect of rock mechanical properties on roadway stability is obvious, and the mineral components of rock have a decisive inﬂuence on rock mechanical properties. To investigate the failure mechanisms of the deep red shale rock roadways, a series of laboratory tests have been completed to learn the special physical and mechanical characteristics of red shale, including mineral composition and microstructure test, hydraulic mechanical properties, creep characteristic and anisotropic test.

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a microscope. The main mineral compositions were ﬁgured out as shown in Table1: its components of debris are quartz, orthoclase, sericite, muscovite and little zircon. And Minerals 2021, 11, x 3 of 18 the interstitial materials are composed of calcite, quartz, sericite, clay-type mud and ferruginous cementation. Clay-type mud accounted for 35% of mineral composition. Figure 1. The red shale inclined bedding structure around roadway cross section.

2.1. Mineral Composition and Microstructure Test The red shale sample was taken from a new heading face of main haulage roadway in No.640 middle level in Kaiyang Phosphate Mine, then cut into slices and tested using a microscope. The main mineral compositions were figured out as shown in Table 1: its components of debris are quartz, orthoclase, sericite, muscovite and little zircon. And the interstitial materials are composed of calcite, quartz, sericite, clay-type mud and ferruginous cementation. Clay-type mud accounted for 35% of mineral composition. FigureFigure 1. 1.The The red red shale shale inclined inclined bedding bedding structure structure around around roadway roadway cross section. cross section. Table 1. The main mineral composition and its content of red shale. Table 1. The main mineral composition and its content of red shale. 2.1. Mineral Composition andMineral Microstructure Name Test Content % The red shaleMineral sample NameClay-type was taken mud from a new heading Content face of % main 35 haulage roadway in No.640 middleClay-type level in mud KaiyangQuartz Phosphate Mine, then cut into 35 slices20 and tested using a microscope. The mainQuartz mineralOrthoclase compositions were figured out 20 as shown15 in Table 1: its OrthoclaseSericite 15 12 components of debris are quartz, orthoclase, sericite, muscovite and little zircon. And the SericiteMuscovite 12 8 Muscovite 8 interstitial materials are composedCalcite of calcite, quartz, sericite, clay-type5 mud and ferruginous cementation. Clay-typeCalcite mud accounted for 35% of mineral 5 composition. FerruginousFerruginous cementation cementation 5 5 ZirconZircon Little Little Table 1. The main mineral composition and its content of red shale. The red shale was observed with a polarizing microscope, and the result is shown in The red shale was observed with a polarizing microscope, and the result is shown in FigureMineral 2. A muddyName layer distributed among the main part Content of the rock % can be observed in Figure2. A muddy layer distributed among the main part of the rock can be observed in theClay-type slice’s border, mud which is made up of 85% interstitial material 35 and 15% chippings. Based the slice’s border, which is made up of 85% interstitial material and 15% chippings. Based on the microstructure graph under polarizing filters and mineral composition, red shale on the microstructureQuartz graph under polarizing ﬁlters and mineral composition,20 red shale can can Orthoclasebe classified as amaranth shale with pelitic and aleuritic textures15 and bedding struc- be classiﬁed as amaranthture. shale with pelitic and aleuritic textures and bedding structure. Sericite 12 Muscovite 8 Calcite 5 Ferruginous cementation 5 Zircon Little

The red shale was observed with a polarizing microscope, and the result is shown in Figure 2. A muddy layer distributed among the main part of the rock can be observed in the slice’s border, which is made up of 85% interstitial material and 15% chippings. Based on the microstructure graph under polarizing filters and mineral composition, red shale can be classified as amaranth shale with pelitic and aleuritic textures and bedding struc- Figure Figure2.ture. Red shale’s 2. Red polarizing shale’s polarizing microscope microscope graph. Note: graph. (a) Note:plane (polarizeda) plane polarizedlight; (b) perpendicular light; (b) perpendicular polarized light. polarized light.

Figure 2. Red shale’s polarizing microscope graph. Note: (a) plane polarized light; (b) perpendicular polarized light.

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2.2. Hydraulic Mechanical Properties Test From the above investigation into mineral composition, clay-type mud is the main ingredient of red shale. Therefore, groundwater and humid air have a great impact on rock strength and roadway stability. In order to clarify the failure mechanism of roadways arranged in red shale, it is necessary to conduct detailed research on various engineering mechanical properties of this rock. Uniaxial compressive strength experiments, rock expansion experiments and creep experiments under the influence of water were set up to investigate its hydraulic mechanical properties. Rock samples all came from the same drill Minerals 2021, 11, 423 hole. As shown in Figure 3, the dip angle of all rock samples was completely4 of 17 the same: about 31° perpendicular to loading direction. The length of the drill hole was more than 50 m so that the effect of blast vibration and other factors from mining could be neglected. drill hole. As shown in Figure3, the dip angle of all rock samples was completely the Accordingsame: aboutto the 31◦ standardperpendicular testing to loading method direction. of The ISRM length (International of the drill hole was Society more for Rock Me- chanics),than rock 50 m somass that thewas effect processed of blast vibration to standard and other rock factors samples from mining with an could L/D be ratio of 2 with an averageneglected. diameter According of to 50 the mm standard and testingremaining method average of ISRM (Internationalnatural water Society content for less than 1% Rock Mechanics), rock mass was processed to standard rock samples with an L/D ratio of sealed.2 with an average diameter of 50 mm and remaining average natural water content less than 1% sealed.

Figure 3. Schematic diagram of red shale joints and the orientation of the load.

2.2.1. Uniaxial Compressive Strength Experiment Figure 3. Schematic diagram of red shale joints and the orientation of the load. The rock samples soaked for different times or drying on drying box had their uniaxial compressive strength tested on the Instron 1342 testing machine (Instron, UK). The loading 2.2.1. patternUniaxial was Compressive set to displacement Strength control Experiment with the rate of 0.3 mm/min. Three samples were selected for the uniaxial compression test for each immersion time. The uniaxial Thecompressive rock samples strength ofsoaked the rock for samples different with the times same or immersion drying time on wasdrying averaged. box had their uniaxial compressiveAll results are shown strength in Figure tested4. When on the immersion Instron time 1342 was testing less than machine two hours, (Instron, the UK). The loadinguniaxial pattern compressive was set strength to displacement of the rock samples control sharply with decreased the rate from of 22.220.3 mm/min. MPa to Three sam- 7.94 MPa. The uniaxial compressive strength of rock samples soaking for over 24 h was ples wereonly 5.04 selected MPa, equivalent for the uniaxial to a quarter compression of a rock sample’s test strength for each in natural immersion state. When time. The uniaxial compressiveimmersion strength time exceeded of the 72 h,rock water-saturated samples rockwith samples the same partly immersion disintegrated beforetime was averaged. All resultsloading are and theshown uniaxial in compressive Figure 4. strengthWhen isimmersion the lowest one time and only was about less 1.56 than MPa. two hours, the uniaxial compressive strength of the rock samples sharply decreased from 22.22 MPa to 7.94 MPa. The uniaxial compressive strength of rock samples soaking for over 24 h was only 5.04 MPa, equivalent to a quarter of a rock sample’s strength in natural state. When

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Figure 4. The relation of uniaxial compressive strength and immersion time.

2.2.2. Expansion Experiment The rock expansion experiment under water swelling was been implemented by using a digital rock free swelling ratio test device that is made up of a height adjustable metal support, three high-precision displacement sensors and a data collection system. Its measure precision can reach 0.001 mm with real-time gathering data onto frequency of 100 Hz. Lab measures scene is shown as Figure5. As shown in Figure6, in the first hour, the axial and lateral displacements increased rapidly at the same time. One hour later, the lateral displacement exceeded the axial displacement and increased rapidly in the next six hours, while the axial displacement reduced the growth rate at this time to a slow increase, and then the lateral displacement growth rates decreased and stabilized. The axial displacement kept increasing slowly from the second hour to the end of the experiment. It is worth mentioning that the sample disintegrated at the twenty-sixth hour of the experiment, resulting in a sudden increase in displacement, but then the displacement of the sample continued to stabilize, and finally the axial and lateral displacement reached 0.15 mm and 0.13 mm, respectively. It can be clearly seen that the axial and lateral deformation of red shale increased significantly with the increase of water immersion time, and was most significant in the first two hours.

Water also affects red shale’s creep rupture strength a lot. Red shale’s creep displacement in water saturated state is apparently larger than natural moisture states. Meanwhile, its macroscopic failure can be seen after 3500 s, so red shale’s creep rupture strength also declined a lot in its water saturated state. When loading is less than the critical load of Minerals 2021, 11, x softening, red shale is within stable deformation state. Red shale’s plastic deformation will 6 of 18 happen to the critical load of softening. As learned from the creep experiment, red shale’s critical load of softening is only about 70–80% of uniaxial compression strength in natural moisture state and 30–50% of uniaxial compression strength in water saturated state.

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Figure 5. Digital measure device for rock free swelling ratio. FigureFigure 5. Digital 5. Digital measure device measure for rock free device swelling for ratio. rock free swelling ratio.

Figure 6. 6.Red Red shale’s shale’s expansion expansion displacement displacement in vertical in andvertical lateral and direction lateral within direction sixty hours.within sixty hours.

2.2.3. Creep Characteristic Test Red shale creep experiments were implemented by an Instron test machine. Most of the loading condition was respectively set as 10%, 20%, 30%, 50%, 70% and 80% of the uniaxial compressive strength. Rock samples were in natural moisture state except that one rock sample of loading with 50% UCS (Uniaxial Compressive Strength) in water sat- uratedFigure state. 6. AsRed shown shale’s in Figure expansion 7, red shal displacemente’s displacement in isvertical increased and while lateral load rais-direction within sixty hours. ing so that creep behavior is clear. When the loading reached 80% for the rock sample, macroscopic failure was obviously happening. It can be concluded that red shale’s creep rupture2.2.3. strength Creep is Characteristic only about 70%–80% Test of its uniaxial compression strength in its natural moisture state. Water also affects red shale’s creep rupture strength a lot. Red shale’s creep displacementRed inshale water creep saturated experiments state is apparently were larger implemented than natural moisture by an states.Instron test machine. Most of Meanwhile,the loading its macroscopic condition failure was can respectively be seen after 3500s, set soas red 10%, shale’s 20%, creep 30%, rupture 50%, 70% and 80% of the strengthuniaxial also declinedcompressive a lot in its strength. water saturated Rock state. samples When loading were is lessin thannatural the crit- moisture state except that ical load of softening, red shale is within stable deformation state. Red shale’s plastic de- formationone rock will sample happen to of the loading critical load with of softening. 50% UCS As learned (Uniaxial from the Compressive creep experi- Strength) in water sat- ment,urated red shale’sstate. critical As shown load of softeningin Figure is only 7, redabout shal 70–80%e’s ofdisplacement uniaxial compression is increased while load rais- strengthing so in that natural creep moisture behavior state and 30–50%is clear. of uniaxialWhen compression the loading strength reached in water 80% for the rock sample, saturated state. macroscopic failure was obviously happening. It can be concluded that red shale’s creep rupture strength is only about 70%–80% of its uniaxial compression strength in its natural moisture state. Water also affects red shale’s creep rupture strength a lot. Red shale’s creep displacement in water saturated state is apparently larger than natural moisture states. Meanwhile, its macroscopic failure can be seen after 3500s, so red shale’s creep rupture strength also declined a lot in its water saturated state. When loading is less than the critical load of softening, red shale is within stable deformation state. Red shale’s plastic deformation will happen to the critical load of softening. As learned from the creep experiment, red shale’s critical load of softening is only about 70–80% of uniaxial compression strength in natural moisture state and 30–50% of uniaxial compression strength in water saturated state.

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Figure 7. 7.Red Red shale’s shale’s creep creep experiments experiments result result in different in different constant constant loading andloading water and effect. water effect. 2.3. Anisotropic Mechanical Properties Test 2.3. Anisotropic Mechanical Properties Test The bedding structure can affect structure stability a lot [29]. By the means of mi- crostructureThe bedding analysis structure and appearance can affect morphology structure survey, stability it can a be lot found [29]. thatBy the red shalemeans is of micro- apparentlystructure analysis thin layered and bedding appearance structure morphology spacing from survey, micron it to can millimeter. be found Therefore, that red shale is theapparently anisotropic thin mechanical layered bedding properties structure have been spacing investigated from in micron this section. to millimeter. Rock mass Therefore, taken from ﬁeld was processed into standard rock samples of different states with parallel, the anisotropic mechanical properties have been investigated in this section. ◦Rock mass verticaltaken from and oblique field was bedding processed (i.e., splitting into standard into different rock dip samples angles of respectively different ofstates about with 0 , parallel, 30◦, 45◦, 60◦ and 90◦). Then, the standard uniaxial compressive, tensile and shear strength testsvertical were and carried oblique out on bedding the Instron (i.e., 1342 splitting electro-hydraulic into different servo dip controlling angles materialrespectively test- of about ing0°, machine.30°, 45°, As60° the and results 90°). show Then, in Figure the 8standa, red shalerd uniaxial has typical compressive, thin bedding structuretensile and shear

Minerals 2021, 11and,strength x apparently tests were anisotropic carried mechanical out on the feature. Instron Red1342 shale’s electro-hydraulic mechanical properties servo8 of controlling18 are ma- differentterial testing as with machine. different As dip the angles results of bedding show in structure. Figure 8, red shale has typical thin bedding structure and apparently anisotropic mechanical feature. Red shale’s mechanical properties are different as with different dip angles of bedding structure.

Figure 8. Cont.

Figure 8. The graphs of red shale’s mechanical properties in different dip angles. Note: (a) Uniaxial Compressive Strength and Elastic modulus in different dip angles; (b) Tensile strength and Shear strength in different dip angles.

The uniaxial compressive, tensile and shear strength are highest in vertical bedding. The strength index is the last one while the dip angle is 30°. Elastic modulus is the highest

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Figure 8. TheFigure graphs 8. ofThe red shale’s graphs mechanical of red shale’s properties mechanical in different propertiesdip angles. Note: in different (a) Uniaxial dip Compressive angles. Note: Strength (a ) Uniaxial and Elastic modulus in different dip angles; (b) Tensile strength and Shear strength in different dip angles. Compressive Strength and Elastic modulus in different dip angles; (b) Tensile strength and Shear strength in differentThe dip uniaxial angles. compressive, tensile and shear strength are highest in vertical bedding. The strength index is the last one while the dip angle is 30°. Elastic modulus is the highest The uniaxial compressive, tensile and shear strength are highest in vertical bedding. The strength index is the last one while the dip angle is 30◦. Elastic modulus is the highest in parallel bedding. Shear strength of sample rock in parallel bedding is obviously lower in comparison to vertical beddings.

3. Validation of Numerical Simulation on Layered Strata 3.1. Numerical Model In order to determine the displacement field change and the distribution law of the plastic zone, the 3DEC numerical analysis software (4.10) was used to simulate and analyze the main haulage roadway with 640 levels in the deep. In order to ensure the authenticity of the data of the simulation experiment, before the numerical simulation experiment, the in-situ stress measurement was carried out by borehole strain over-coring method, and the distribution and change law of the three-dimensional in-situ stress field in Kaiyang Phosphate Mine were obtained. The numerical simulation model size was 200 × 200 × 200 m, and the dip angle of red shale was 31◦. The surrounding rock is red shale, and different colors were used in the model to reflect the dip angle. The model is shown in Figure9. The Drucker-Prager criterion was adopted in the simulation. The left and right, front and back boundaries and bottom boundary of the model adopted fixed boundary displacements. A vertical compressive stress of 13.2MPa was applied to the upper surface of the model. The calculated area size was 15 m × 15 m × 15 m. The model calculation parameters are shown in Table2.

3.2. Analysis of Numerical Simulation The contour diagrams of stress and displacement in the vertical and horizontal directions have been saved as Figure 10. Numerical simulation results have verified some phenomenon observed from field detection. After roadway excavation, the roadway displacement and effect zone around bedding direction are larger than other directions, and the floor deformation is the largest in other parts of the cross section. Learned from Figure 10a, there are stress concentrations in the sides and roof corners approaching the roadway’s surface after excavation. The maximum value of tensile stress is about 0.38 MPa. For roadway stability, the presence of tensile stress concentration in Minerals 2021, 11, x 9 of 18

in parallel bedding. Shear strength of sample rock in parallel bedding is obviously lower in comparison to vertical beddings.

3. Validation of Numerical Simulation on Layered Strata 3.1. Numerical Model In order to determine the displacement field change and the distribution law of the plastic zone, the 3DEC numerical analysis software (4.10) was used to simulate and analyze the main haulage roadway with 640 levels in the deep. In order to ensure the authen-

Minerals 2021, 11, 423 ticity of the data of the simulation experiment, before9 of 17the numerical simulation experiment, the in-situ stress measurement was carried out by borehole strain over-coring method, and the distribution and change law of the three-dimensional in-situ stress field this area is very bad. Learned from Figure 10b the stress concentration region in a vertical directionin Kaiyang can be classed Phosphate as an X-type Mine shape on were the axial obtained. line of roadway. The A tensile numerical stress of simulation model size was 200 about 0.30 MPa is generated at the top and bottom plates, and the range of tensile stress concentration× 200 × 200 almost m, covers and the the entire dip top and angle bottom of plates. red Affected shale by beddingwas 31°. structure, The surrounding rock is red shale, theand vertical different stress is not colors completely were symmetrically used distributedin the model on the sides to of reflect roadway. Thethe dip angle. The model is shown effect range perpendicular to the bedding direction is larger than in other directions. in LearnedFigure from 9. Figure The 10 c,Drucker-Prager rock strata’s bedding direction criterion apparently was affects adopted the defor- in the simulation. The left and mationright, distribution front and in horizontal back direction.boundaries The displacement and bottom on the sides boundary and floor of theof the model adopted fixed bound- roadway is larger than in other parts. And the displacement on the left side is larger than theary other displacements. sides. The high stress squeezesA vertical roadway compressive sides with the free face. stress From Figure of 13.2MPa 10d was applied to the upper insurface vertical direction, of the most model. of the deformation The calculated is from floor heavearea besides size roofwas collapse. 15 m The × 15 m × 15 m. The model calcula- phenomenon observed from the field also verified the above analysis. tionAfter parameters roadway excavation are shown without immediate in Table support, 2. the plastic zones tend to expand and break, and the broken rock’s deformation is larger than the rock mass in the plastic zone. The floor heave is the main part of surrounding rock deformation, which exceeds other parts.Table The bedding 2. The direction model affects calculation ground stress parameters. distribution and roadway’s displacement a lot. Roadway’s displacement along the bedding direction is so large that Normal Stiffness Shear Stiffnessthe plastic zone is small. Vertical to theInternal bedding direction, Friction the above-mentioned Tensile parameters Elastic Modulus Poisson’s are just opposite,Cohesion/MPa so it is easy for them to cause support failure. Therefore, it is better that (GPa/m) (GPa/M)the water ditch is set on the right bottomAngle/(°) corner and strengthening Strength/MPa support on the left (GPa) Ratio shoulder corner. The deep in-suit stress concentrates on the bottom corners, which is going 5.2 2.63to enlarge and squeeze1.05 the roadway and lead30° to large floor heaves so that 1.5 the roadway 9 0.24 floor’s support has to be reinforced.

FigureFigure 9. The 9. calculation The calculation model. model.

3.2. Analysis of Numerical Simulation The contour diagrams of stress and displacement in the vertical and horizontal directions have been saved as Figure 10. Numerical simulation results have verified some phenomenon observed from field detection. After roadway excavation, the roadway displacement and effect zone around bedding direction are larger than other directions, and the floor deformation is the largest in other parts of the cross section.

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Table 2. The model calculation parameters.

Normal Stiffness Shear Stiffness Internal Friction Tensile Elastic Modulus Poisson’s Minerals 2021, 11,(GPa/m) x (GPa/M) Cohesion/MPa Angle/(◦) Strength/MPa (GPa) Ratio 10 of 18

5.2 2.63 1.05 30◦ 1.5 9 0.24

Figure 10.Figure The 10.stressThe contour stress contour diagrams diagrams and and displacement displacement contour contour diagramsdiagrams in in the the vertical vertical and and horizontal horizontal direction. direction. Note: Note: (a) Horizontal(a) Horizontal stress distribution; stress distribution; (b) vertical (b) vertical stress stress distribution; distribution; (c) ( cHorizontal) Horizontal displacement displacement distribution; distribution; (d )(d vertical) vertical dis- placementdisplacement distribution. distribution. 3.3. Analysis of Numerical Simulation Learned from Figure 10a, there are stress concentrations in the sides and roof corners Through laboratory analysis and numerical simulation verification, it can be con- approachingcluded that the red roadway’s shale is not surface engineered after softexcava rocktion. in the The traditional maximum sense. valu Itse of uniaxial tensile stress is aboutcompressive 0.38 MPa. strengths For roadway parallel to andstability, perpendicular the presence to the bedding of tensile all exceed stress 25 concentration MPa, and in this areaexhibit is brittlenessvery bad.under Learned low from stress. Figure The deformation 10b the stress is a characteristic concentration of rock, region but it in will a vertical directionundergo can obvious be classed brittle-ductile as an X-type transformation shape on under the high axial stress line conditions of roadway. and significant A tensile stress of aboutplastic 0.30 deformation MPa is generated will occur, at showing the top obviousand bottom engineered plates, soft and rock the properties,range of tensile with stress concentrationreduced long-term almost strengthcovers the and entire enhanced top rheological and bottom characteristics. plates. Affected Because by its bedding mineral struc- composition contains clay-like components, it will swell and soften significantly when ture,exposed the vertical to water, stress which is not significantly completely deteriorates symmetrically its engineering distributed mechanical on the properties. sides of roadway.So, The red effect shale deformationrange perpendicular characteristics to canthe bebedd drawning as direction three deformation is larger mechanisms than in other of directions.weathering collapse after water absorption, destruction under high stress and uniformed destructionLearned from of bedding Figure structure. 10c, rock After strata’s exposure bedding to excavation, direction red shaleapparently is easy toaffects soften, the de- formationswells withdistribution water, and in weathering horizontal causes direction. its poor The performance displaceme ofnt debris on the and sides interstitial and floor of material, then its engineering mechanical behavior and strength quickly weaken. When the the roadway is larger than in other parts. And the displacement on the left side is larger stress levels that the roadway sustains exceeds critical softening loading, including tectonic thanstress, the other gravity sides. stress, The secondary high stress stress squeezes adjustment roadway and mining sides induced with the influence, free face. plastic From Fig- ure 10d in vertical direction, most of the deformation is from floor heave besides roof collapse. The phenomenon observed from the field also verified the above analysis. After roadway excavation without immediate support, the plastic zones tend to expand and break, and the broken rock’s deformation is larger than the rock mass in the plastic zone. The floor heave is the main part of surrounding rock deformation, which exceeds other parts. The bedding direction affects ground stress distribution and roadway’s displacement a lot. Roadway’s displacement along the bedding direction is so large that the plastic zone is small. Vertical to the bedding direction, the above-mentioned parameters are just opposite, so it is easy for them to cause support failure. Therefore, it is better that the water ditch is set on the right bottom corner and strengthening support on the left shoulder corner. The deep in-suit stress concentrates on the bottom corners, which is going to enlarge and squeeze the roadway and lead to large floor heaves so that the roadway floor’s support has to be reinforced.

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deformation of red shale sharply increases and softens. The roadway is seriously squeezed by large deformation and rheo-destruction. Under high stress, the layered red shale tends to wrinkle to free face on the roadway floor. It has to consider the influence of bedding direction to the stress level and displacement on surrounding rock. The interaction and influence of the three deformation mechanisms keep the support cost high and affects the normal production of the stope.

4. New Support Scheme With mining depth increasing in the Kaiyang Phosphate Mine area, the ground stress is higher than in shallow parts. The existing bolt-mesh-grouting technique cannot adapt to the high ground stress environment in deep parts. Especially, the deformation features of layered soft rock have not been taken seriously. Original roadways support has not been strengthened to limit nonlinear large deformation. So, there are many roadways destruction phenomenon, like rock collapse, bolt retracting and ﬂoor cracks, shown in Figure 11. Some roadways even cannot keep a regular working state and personnel safety. Therefore, we proposed a new support design to meet support requirements in new excavation roadway. In view of red shale compound failure mechanisms analysis, it is reasonable to apply coupled support methods to simplify roadway failure mechanisms. Then, the Minerals 2021, 11, x 12 of 18 support scheme for shotcrete rock bolt mesh technique is proposed to new-designed wave-type bolts.

Figure 11.Figure The different 11. The roadways different failure roadways phenomenon failure phenomenonin Kaiyang Phosphate in Kaiyang Mine Phosphate area. Note: Mine (a) roof area. collapse; Note: (b) floor cracks; (c) wall collapse; (d) bolt retracting. (a) roof collapse; (b) floor cracks; (c) wall collapse; (d) bolt retracting. 4.1. Wave-Type Bolts4.1. Wave-Type Support Bolts Support Because of surroundingBecause rockof surrounding compound rock features compound of strength features weakness of strength and expansionweakness and expan- rheology, the existingsion rheology, support the technique existing support of shotcrete technique rock of boltshotcrete cannot rock effectively bolt cannot take effectively take control of surroundingcontrol of rock surrounding loosening rock region. loosening Support region for.soft Support rock for roadways soft rock needs roadways to needs to allow the existenceallow of athe plastic existence circle of releasing a plastic thecircle surrounding releasing the rock surrounding deformation rock energy deformation to energy safeguard rock strength.to safeguard The rock support strength. system The mustsupport provide system enough must provide support enough resistance support to resistance limit the plasticto circle limit region the plastic and circle prevent region rock and collapse. prevent Meanwhile, rock collapse. it Meanwhile, should be flexibleit should be flexible and easy to adaptand to easy the nonlinearto adapt to deformation the nonlinear for deformation rock expansion for rock of expansion coupled stress of coupled field. stress field. The deformation energy and support loading can be controlled after several adjustments of stress and strain. Finally, the interaction between the roadway support and surrounding rocks come into being a synergetic bearing system. Therefore, scholars have developed a new bolt and named it energy-absorbing bolt. The traditional energy-absorbing bolt’s functions just meet the support materials’ requirements about strength and flexibility [29]. Therefore, a new type of bolt is proposed, which has high strength and large deformation ability. As shown in Figures 12 and 13, for accommodating large rock dilations of roadways surrounding rock under high stress, like in Kaiyang mine area, the new energy- absorbing bolt has been created with an anchor section. The energy-absorbing anchor section is processed into a sine wave shape. Through calculation, the arc length is set to 119.883 mm and the chord length is set to 113.097 mm, so the maximum elongation is 6.786 mm. When the bolt completely has stretched straight by rock mass, the accumulated deformation can reach 53 mm. The setting of the energy- absorbing section means that the borehole diameter needs to be enlarged. These increments are insignificant compared to the spacing of the anchor rods. In order to avoid water vapor corrosion, the swelling sponge will be used to block the orifice during anchoring. In in-site experiments, the wave-type bolt will not break as its drawing force can reach 150 kN. When the deep soft rock needs to relieve plastic energy, the wave-type bolt can coordinate deformation to store huge energy, avoiding rock mass collapse. In key sections of

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The deformation energy and support loading can be controlled after several adjustments

Mineralsof 2021 stress, 11, x and strain. Finally, the interaction between the roadway support and surrounding13 of 18 rocks come into being a synergetic bearing system. Therefore, scholars have developed

Minerals 2021, 11, x a new bolt and named it energy-absorbing bolt. The traditional energy-absorbing bolt’s 13 of 18 functions just meetroadway the support (proof, materials’ floor, sides, requirements arch corner and about bottom strength corner), and the ﬂexibility rigid support [29 ].trans- Therefore, a new typeformed of bolt into isflexible proposed, support which adopted has by high the newly strength designed and largewave-type deformation bolts layout, as ability. As shown inshown Figures in Figure12 and 13. 13 , for accommodating large rock dilations of roadways surrounding rockroadway under (proof, high stress, floor, likesides, in Kaiyangarch corner mine and area, bottom the new corner), energy-absorbing the rigid support trans- bolt has beenformed created withinto flexible an anchor support section. adopted by the newly designed wave-type bolts layout, as shown in Figure 13.

Figure 12. The wave-type bolt’s construction diagram. 1—Prolonged anchor section, 2—Sine-wave structure section, 3— Pallet, 4—Fastening nut, 5—Threaded section, 6—Stirring wing. Note: (a) The wave-type bolt; (b) Sine-wave structure section.

The wave-type section is a high-strength spiral steel bar processed as sine-wave type by heat-treatment technology. The other components, like pallet, fastening nut and threaded section, are completely the same with the straight-rod spiral steel bolt. The stir- Figure 12. TheFigure wave-type 12. The bolt’s wave-type constructionring wing bolt’s is construction diagram.two steel 1—Prolongedreinforcing diagram. rods 1—Prolonged anchor with asection, length anchor of2—Sine-wave 50 section,mm and 2—Sine-wave diameterstructure of section, 6 mm 3— Pallet, 4—Fasteningstructure nut, section, 5—Threaded 3—Pallet,welded section, 4—Fastening on the top6—Stirring of the nut, lengthening 5—Threaded wing. Note: anchor section,(a) seThection, wave-type 6—Stirring which enhance bolt; wing. (theb Note:) Sine-waveability (a) of The stirring structure section. wave-type bolt; (b) Sine-wavefor strengthening structure resin section. anchor effect. The wave-type section is a high-strength spiral steel bar processed as sine-wave type by heat-treatment technology. The other components, like pallet, fastening nut and threaded section, are completely the same with the straight-rod spiral steel bolt. The stirring wing is two steel reinforcing rods with a length of 50 mm and diameter of 6 mm welded on the top of the lengthening anchor section, which enhance the ability of stirring for strengthening resin anchor effect.

FigureFigure 13. 13.The The wave-type wave-type bolt’s bolt’s construction construction diagram. diagram. 1—surrounding 1—surrounding rock, 2—borehole, rock, 2—borehole, 3—wave-type 3—wave- bolt. type bolt. The prolonged anchor section at one end is past on the borehole’s surface rock. An- other end is anchored on surrounding rock by a pallet and fastening nut, which can pro- The energy-absorbingvide a pre-stress anchor on section the anchor is processed rod body. In into the ahigh sine stress wave state, shape. there Throughis compression calculation, the arcdeformation length is set for to free 119.883 face from mm the and surrounding the chord soft length rock; the is reacting set to 113.097force for mm,surround- so the maximum elongationing rock gradually is 6.786 increases mm. When for the the wave-type bolt completely bolt. Then, the has eight stretched anchors straightsection begins by rock mass, the accumulatedto gradually stretch deformation and assimilates can reachdeformation 53 mm. energy The from setting the surrounding of the energy- rock. Sim- absorbing section meansultaneously, that the the borehole wave-type diameter bolt also needsmakes toa reacting be enlarged. force to These limit rock increments deformation. When the deformation of surrounding rock is going to increase, there will be a stronger are insignificant comparedreacting force to the to spacing the straight-rod of the anchorfor rock rods.squeezing. In order As the to wave-type avoid water section vapor relieves Figurecorrosion, 13. The wave-type the swelling bolt’smuch spongeconstruction more energy will diagram. beleading used to to1—s large blockurrounding deformation, the orifice rock, the during higher2—borehole, reacting anchoring. 3—wave-type force from In in-site wave-type bolt. experiments, the wave-typebolts is generated bolt willto limit not deformation break as itsfrom drawing rock mass. force After can the reachwave-type 150 section kN. is When the deep softThestretched rock prolonged needs to be to completely relieveanchor plasticsection straight, energy, at the one rod theend body wave-type is sustains past on the boltthe maximal borehole’s can coordinate pressure surface in sur- rock. An- deformation toother store end huge is anchored energy, avoiding on surrounding rock mass rock collapse. by a pallet In key and sections fastening of roadway nut, which can pro- (proof, floor, sides,vide a archpre-stress corner on and the bottom anchor corner), rod body. the In rigid the supporthigh stress transformed state, there into is compression flexible supportdeformation adopted byfor thefree newlyface from designed the surrounding wave-type soft bolts rock; layout, the reacting as shown force in for surround- Figure 13. ing rock gradually increases for the wave-type bolt. Then, the eight anchors section begins The wave-typeto gradually section stretch is a and high-strength assimilates spiral deformation steel bar energy processed from the as sine-wavesurrounding rock. Sim- type by heat-treatmentultaneously, technology. the wave-type The other bolt components,also makes a likereacting pallet, force fastening to limit nut rock and deformation. When the deformation of surrounding rock is going to increase, there will be a stronger reacting force to the straight-rod for rock squeezing. As the wave-type section relieves much more energy leading to large deformation, the higher reacting force from wave-type bolts is generated to limit deformation from rock mass. After the wave-type section is stretched to be completely straight, the rod body sustains the maximal pressure in sur-

Minerals 2021, 11, 423 13 of 17

threaded section, are completely the same with the straight-rod spiral steel bolt. The stirring wing is two steel reinforcing rods with a length of 50 mm and diameter of 6 mm welded on the top of the lengthening anchor section, which enhance the ability of stirring for strengthening resin anchor effect. The prolonged anchor section at one end is past on the borehole’s surface rock. An- other end is anchored on surrounding rock by a pallet and fastening nut, which can provide a pre-stress on the anchor rod body. In the high stress state, there is compression deformation for free face from the surrounding soft rock; the reacting force for surrounding rock gradually increases for the wave-type bolt. Then, the eight anchors section begins to gradually stretch and assimilates deformation energy from the surrounding rock. Simulta- neously, the wave-type bolt also makes a reacting force to limit rock deformation. When the deformation of surrounding rock is going to increase, there will be a stronger reacting force to the straight-rod for rock squeezing. As the wave-type section relieves much more energy leading to large deformation, the higher reacting force from wave-type bolts is generated to limit deformation from rock mass. After the wave-type section is stretched to be completely straight, the rod body sustains the maximal pressure in surrounding rock like a high-strength rigid bolt. In time and space, the wave-type bolts coordinate the rock mass’s deformation so that the internal pressures can be relieved moderately to limit excessive deformation.

4.2. Bolt-Net-Anchor Coupling Support and Controlling of Sidewalls and Corner The full cross-section bolt-net-anchor coupling support is used to strengthen support strength. For bedding structure of the layered red shale and plastic deformation, the moving displacement of layered rock leads to uncoordinated deformation of surrounding rock and support materials in some weak sections and it is easy to lose system stability. Therefore, the long steel bolts and grouting immediately is used to strengthen support in the roof section of the roadway intersection and broken rock strata. For the inﬂuence of bedding structure, the stress is asymmetrically distributed over the horizontal direction of the roadway so that the water ditch is set on the right hand for the small horizontal displacement and it is easy to maintain its original shape. The stress concentration on the left arch corner and right bottom corner is serious so the roadway supports need to be strengthened by means of increasing the long steel bolt’s amount of left arch corner or reducing the bolts spacing and masonry reinforcement on the right bottom corner. In consideration of the anisotropic mechanical properties, the support design should ensure the maximization of the installation angle of the bolt direction and the bedding orientations to give full play to the strength of the surrounding rock. While the bolt’s parallel to bedding, it should readjust the installing angles of bolts on bedding directions.

4.3. Groundwater Controlling and Secondary Support After roadways excavation, metallic net must immediately be laid to increase toughness, then concrete cement sprayed to seal the ﬂat land ﬂoor to avoid water erosion weakening rock strength. In the intersection of roadways, the anchor cable for support should be lengthened and the surrounding rock should be pre-grouted in the fracture zone to strengthen before support work. After ground stress redistribution and roadway maintaining stability, the function-losing bolts should be replaced, adapted to secondary intensifying support in key sections and grouted to protect broken rock mass.

4.4. Support Parameter Many successful support cases show that the combined support of anchor net and shotcrete is a common and mature method. By referring to the similar soft rock mine support plan, the anchor rod is still used as the main support. From the previous analysis, it can be seen that because it is perpendicular to the bedding structure, the stress concentration on the left corner and the right bottom corner is more obvious, so the left corner is appropriate. Reducing the bolt spacing and setting the water ditch at the right bottom Minerals 2021, 11, 423 14 of 17

corner is more conducive to roadway support. The row and column spacing of the bolts is 800 mm × 1000 mm. At the same time, wave-type bolts are used at several key points of the roadway to control the deformation of the soft rock roadway. The bottom corners of both sides are made of thick round steel to enhance the support of the bottom plate. The bottom plate is made of poured concrete. The support is enclosed by the ground, and a Minerals 2021, 11layer, x of metal mesh is laid on the ground to increase the toughness. Figure 14 is a sketch of 15 of 18

the new roadway support schemes.

Figure 14. Sketch of theFigure new roadway14. Sketch support of the new schemes. roadway support schemes.

It should be notedIt should that the be supportingnoted that the method supporting mainly method adopts mainly full-section adopts full-section support support with bolt and shotcretewith bolt net, and while shotcrete strengthening net, while strength the controlening of the the control bottom of drum.the bottom When drum. When constructing theconstructing anchor rods the at theanchor left rods bottom at the corner left bottom and the corner right and arch the corner, right arch the drillcorner, the drill holes of the anchorholes rods of cannotthe anchor be parallel rods cannot to the be bedding parallel direction.to the bedding Thestress direction. concentration The stress concentra- is more obvious attion the is left more arch obvious corner at and the right left arch bottom corner corner and perpendicularright bottom corner to the perpendicular bedding to the bedding direction, and support should be strengthened near these positions. After the direction, and support should be strengthened near these positions. After the excavation excavation of the roadway, the initial spraying and sealing of the floor should be carried of the roadway, the initial spraying and sealing of the floor should be carried out as early out as early as possible, and fiber materials should be added to the concrete to enhance its as possible, and fiber materials should be added to the concrete to enhance its plasticity. plasticity. Thick-diameter round steel is used at the bottom corner of the roadway to con- Thick-diameter roundtrol the steel floor is heave, used at the the long bottom anchor corner cable of is the added roadway at the to roadway control intersection the floor and the heave, the long anchorsurrounding cable isrock added is reinforced at the roadway by pre-grouting intersection before and the the support surrounding at the local rock broken sec- is reinforced by pre-groutingtion or fault location. before the support at the local broken section or fault location.

4.5. Field Experiments4.5. Field Experiments Based on the newBased support on the scheme, new support the in-site scheme, industrial the in-site experiments industrial experiments about roadway about roadway deformation monitoringdeformation are implemented monitoring are in implemented three months in with three SWJ-IV months tunnel with convergence SWJ-IV tunnel conver- gauge. Four differentgence supportgauge. Four plans different have beensupport designed plans have to test been the designed support to performance. test the support perfor- The test site is locatedmance. on The the test 100 site m regionis located of 640on the middle 100 m levels region in of the 640 Kaiyang middlemine levels area. in the Kaiyang As shown inmine Table area.3, roadway deformation monitoring for different support plans starts simultaneouslyAs in shown different in Table locations, 3, roadway but the deformation displacement monitoring of roadway for excavateddifferent support a plans long time ago is stillstarts larger simultaneously than the new in different excavated locations, roadway but that the adopteddisplacement the new of roadway support excavated a plan. The monitoringlong time result ago has is still veriﬁed larger the than superiority the new excavated in newsupport roadway designs, that adopted as shown the new support in Figure 15. Theplan. new The plan monitoring can sharply result reduce has verified the displacement the superiority of roadways.in new support Especially, designs, as shown the sides’ displacementin Figuredeclined 15. The new from plan 50% can and sharply roof reduce and ﬂoor the displacement displacement of decreasedroadways. Especially, about 78% in comparisonthe sides’ displacement to the original declined support. from Plan 50% I andand IVroof with and original floor displacement support is decreased excavated beforeabout plans 78% II and in comparison III, and especially to the original plan IV support. is excavated Plan I a and long IV time with ago. original The support is excavated before plans II and III, and especially plan IV is excavated a long time ago. The roadway displacement of support plans II and III is obviously smaller than support plan I and IV’s. The displacement of floor is predominant in parts with the displacement of vertical direction for four support plans. Meanwhile, the displacement of roadway of plan

Minerals 2021, 11, x 16 of 18

Minerals 2021, 11, 423 15 of 17

II in a horizontal direction and a vertical direction respectively declined about 78% and roadway displacement of support plans II and III is obviously smaller than support plan I50% and IV’s. in comparison The displacement to of ﬂoorplan is predominantI and IV’s in so parts that with improved the displacement roadway of stability. vertical direction for four support plans. Meanwhile, the displacement of roadway of plan IITable in a horizontal 3. The directionconvergence and a vertical deformation direction respectively of different declined support about 78%plans and in three months. 50% in comparison to plan I and IV’s so that improved roadway stability.

TableThe 3. NumberThe convergence of deformation the of different support plans inExcavating three months. Support Method Floor Control TheSupport Number of thePlan Time Support Method Excavating Time Floor Control SupportPlan Plan one Original Lately New floor spraying concrete cement New floor spraying Plan one Original Lately Plan two New Latelyconcrete cement Floor with metallic net Plan two New Lately Floor with metallic net New floor spraying PlanPlan three three NewNew Lately Lately New floor spraying concrete cement concrete cement Plan four four OriginalOriginal EarlyEarly Original floor Original floor

FigureFigure 15. The15. new The support new scheme support and support scheme parameters. and support parameters. Plan II has a good performance in control of roadway deformation. According to in-site observation in deformation monitoring experiment, the appearance and morphology of the roadwayPlan II surface has a is smoothgood andperformance straight and surrounding in control rock of does roadway not crack to deformation. According to in- failuresite observation and even to be slump in deformation block. monitoring experiment, the appearance and morphology 5.of Conclusions the roadway surface is smooth and straight and surrounding rock does not crack to failure(1) According and even to the labto testbe of slump red shale, block. the mineral composition and microstructure, anisotropic and hydraulic mechanical properties of red shale have been investigated. According to laboratory experiments analysis and validation of numerical simulation, red5. Conclusions shale deformation characteristics can be drawn as three deformation mechanisms of weathering collapse after water absorption, destruction under high stress and uniformed destruction(1) distributionAccording for bedding to the structure. lab test The of multi-reaction red shale, of the water mineral and rock mass composition and microstructure, leads to rock crack and collapse and bolt retraction to damage roadway stability, and the layeredanisotropic rock moves and to destruction hydraulic and localmechanical deformation properties on roof. Numerical of simulationred shale have been investigated. Ac- cording to laboratory experiments analysis and validation of numerical simulation, red shale deformation characteristics can be drawn as three deformation mechanisms of weathering collapse after water absorption, destruction under high stress and uniformed destruction distribution for bedding structure. The multi-reaction of water and rock mass leads to rock crack and collapse and bolt retraction to damage roadway stability, and the layered rock moves to destruction and local deformation on roof. Numerical simulation analysis has verified the deformation phenomenon in field. Also bedding structure is affected a lot under stress distribution. (2) Based on deep analysis of compound failure mechanisms, the coupled support method is applied to transfer mechanisms. Then, the approved version of shotcrete rock bolt mesh technique was proposed to new-designed wave-type bolts layout. The wave- type bolts can relieve roadway supports loading and controlling excess deformation. The layout of wave-type bolts and regular bolts were used to adjust the uneven stress distribution and strengthen some parts’ support. The installing angle of bolts is sufficiently considered in the influence of bedding orientations. Meanwhile, the shotcrete rock bolt mesh technique can guarantee enough support of rigidity and strength to relieve the uneven support loading on weak parts of roadway.

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analysis has verified the deformation phenomenon in field. Also bedding structure is affected a lot under stress distribution. (2) Based on deep analysis of compound failure mechanisms, the coupled support method is applied to transfer mechanisms. Then, the approved version of shotcrete rock bolt mesh technique was proposed to new-designed wave-type bolts layout. The wave-type bolts can relieve roadway supports loading and controlling excess deformation. The layout of wave-type bolts and regular bolts were used to adjust the uneven stress distribution and strengthen some parts’ support. The installing angle of bolts is sufficiently considered in the influence of bedding orientations. Meanwhile, the shotcrete rock bolt mesh technique can guarantee enough support of rigidity and strength to relieve the uneven support loading on weak parts of roadway. (3) The result of the study is applied to 640 levels in the Kaiyang mine area. Four support plans of in-site industrial experiments about roadway deformation monitoring are implemented in three months with SWJ-IV tunnel convergence gauge. The consequences have verified the new support design’s superiority. Afterwards, the new support technolo- gies have been applied to Kaiyang mine area and behave well.

Author Contributions: Writing-review and editing: C.M., J.X. and G.T.; Experimental test: W.X., Z.L.; Numerical simulation: G.T. All authors have read and agreed to the published version of the manuscript. Funding: This research was funded by the Open Sharing Fund for the Large-scale Instruments and Equipments of Central South University (number CSUZC202133), National Natural Science Foundation of China (52074352). Conﬂicts of Interest: The authors declare no conﬂict of interest.

References 1. Lin, P.; Li, S.C.; Xu, Z.H.; Wang, J.; Huang, X. Water Inflow Prediction during Heavy Rain While Tunneling through Karst Fissured Zones. Int. J. Géoméch. 2019, 19, 04019093. [CrossRef] 2. Chen, Y.; Meng, Q.; Xu, G.; Wu, H.; Zhang, G. Bolt-grouting combined support technology in deep soft rock roadway. Int. J. Min. Sci. Technol. 2016, 26, 777–785. [CrossRef] 3. Chen, X.; Guo, H.; Zhao, P.; Peng, X.; Wang, S. Numerical modeling of large deformation and nonlinear frictional contact of excavation boundary of deep soft rock tunnel. J. Rock Mech. Geotech. Eng. 2011, 3, 421–428. [CrossRef] 4. Cao, R.; Cao, P.; Lin, H. Support technology of deep roadway under high stress and its application. Int. J. Min. Sci. Technol. 2016, 26, 787–793. [CrossRef] 5. Shen, B. Coal Mine Roadway Stability in Soft Rock: A Case Study. Rock Mech. Rock Eng. 2014, 47, 2225–2238. [CrossRef] 6. He, M.; Xie, H.; Peng, S.; Jiang, Y. Study on rock mechanics in deep mining engineering. Chin. J. Rock Mech. Eng. 2005, 16, 2803–2813. (in Chinese). 7. Li, G.; Ma, F.; Guo, J.; Zhao, H.; Liu, G. Study on deformation failure mechanism and support technology of deep soft rock roadway. Eng. Geol. 2020, 264, 105262. [CrossRef] 8. Tian, S.; Xu, X.; Li, Z. Disaster-inducing mechanism in a roadway roof near the driving face and its safety-control criteria. Saf. Sci. 2019, 115, 208–214. [CrossRef] 9. Yang, H.; Cao, S.; Li, Y.; Sun, C.; Guo, P. Soft Roof Failure Mechanism and Supporting Method for Gob-Side Entry Retaining. Minerals 2015, 5, 707–722. [CrossRef] 10. Kovaˇcević,M.S.; Baˇcić,M.; Gavin, K.; Stipanović,I. Assessment of long-term deformation of a tunnel in soft rock by utilizing particle swarm optimized neural network. Tunn. Undergr. Space Technol. 2021, 110, 103838. [CrossRef] 11. Golser, J. The New Austrian Tunneling Method (NATM), Theoretical Background & Practical Experiences. In Proceedings of the 2nd Shotcrete Conference, Easton, PA, USA, 4–8 October 1976. 12. Wu, L.; Cui, C.; Geng, N.; Wang, J. Remote sensing rock mechanics (RSRM) and associated experimental studies. Int. J. Rock Mech. Min. Sci. 2000, 37, 879–888. [CrossRef] 13. Li, Y.; Zhang, D.; Fang, Q.; Yu, Q.; Xia, L. A physical and numerical investigation of the failure mechanism of weak rocks surrounding tunnels. Comput. Geotech. 2014, 61, 292–307. [CrossRef] 14. He, M.; Gong, W.; Wang, J.; Qi, P.; Tao, Z.; Du, S.; Peng, Y. Development of a novel energy-absorbing bolt with extraordinarily large elongation and constant resistance. Int. J. Rock Mech. Min. Sci. 2014, 67, 29–42. [CrossRef] 15. Li, S.; Wang, Q.; Wang, H.; Jiang, B.; Wang, D.; Zhang, B.; Li, Y.; Ruan, G. Model test study on surrounding rock deformation and failure mechanisms of deep roadways with thick top coal. Tunn. Undergr. Space Technol. 2015, 47, 52–63. [CrossRef] 16. Yang, S.-Q.; Chen, M.; Jing, H.-W.; Chen, K.-F.; Meng, B. A case study on large deformation failure mechanism of deep soft rock roadway in Xin’An coal mine, China. Eng. Geol. 2017, 217, 89–101. [CrossRef] Minerals 2021, 11, 423 17 of 17

17. Guo, P.; He, M.; Wang, J. Study on Coupling Support Technique in the Roadway of Hecaogou No. 2 Coal Mine with Soft Roadway of Large Deformation. Geotech. Geol. Eng. 2017, 1–13. [CrossRef] 18. Wang, Q.; Jiang, B.; Pan, R.; Li, S.-C.; He, M.-C.; Sun, H.-B.; Qin, Q.; Yu, H.-C.; Luan, Y.-C. Failure mechanism of surrounding rock with high stress and confined concrete support system. Int. J. Rock Mech. Min. Sci. 2018, 102, 89–100. [CrossRef] 19. Meng, B.; Jing, H.; Chen, K.; Su, H. Failure mechanism and stability control of a large section of very soft roadway surrounding rock shear slip. Int. J. Min. Sci. Technol. 2013, 23, 127–134. [CrossRef] 20. Jia, P.; Tang, C. Numerical study on failure mechanism of tunnel in jointed rock mass. Tunn. Undergr. Space Technol. 2008, 23, 500–507. [CrossRef] 21. Wang, Z.; Wang, C.; Wang, X. Research on High Strength and Pre-stressed Coupling Support Technology in Deep Extremely Soft Rock Roadway. Geotech. Geol. Eng. 2018, 36, 3173–3182. [CrossRef] 22. Chang, Q.; Zhou, H.; Xie, Z.; Shen, S. Anchoring mechanism and application of hydraulic expansion bolts used in soft rock roadway floor heave control. Int. J. Min. Sci. Technol. 2013, 23, 323–328. [CrossRef] 23. Wang, Q.; Pan, R.; Jiang, B.; Li, S.; He, M.; Sun, H.; Wang, L.; Qin, Q.; Yu, H.; Luan, Y. Study on failure mechanism of roadway with soft rock in deep coal mine and confined concrete support system. Eng. Fail. Anal. 2017, 81, 155–177. [CrossRef] 24. Shreedharan, S.; Kulatilake, P.H.S.W. Discontinuum–Equivalent Continuum Analysis of the Stability of Tunnels in a Deep Coal Mine Using the Distinct Element Method. Rock Mech. Rock Eng. 2016, 49, 1903–1922. [CrossRef] 25. Yu, K.; Ren, F.; Puscasu, R.; Lin, P.; Meng, Q. Optimization of combined support in soft-rock roadway. Tunn. Undergr. Space Technol. 2020, 103, 103502. [CrossRef] 26. Qu, G.L.; Wang, J.; Liu, G.L. Research on Supporting Theory of Pressure-Bearing Ring and Yield Supporting Technology in Extremely Soft Rock Roadway. Appl. Mech. Mater. 2013, 395–396, 536–543. [CrossRef] 27. Ran, J.Q.; Passaris, E.K.S.; Mottahed, P. Shear sliding failure of the jointed roof in laminated rock mass. Rock Mech. Rock Eng. 1994, 27, 235–251. [CrossRef] 28. Wu, G.; Chen, W.; Jia, S.; Tan, X.; Zheng, P.; Tian, H.; Rong, C. Deformation characteristics of a roadway in steeply inclined formations and its improved support. Int. J. Rock Mech. Min. Sci. 2020, 130, 104324. [CrossRef] 29. Varden, R.; Lachenicht, R.; Player, J.; Thompson, A.; Villaescusa, E. Development and Implementation of the Garford Dynamic Bolt at the Kanowna Belle Mine. Australas. Inst. Mining Metall. Publ. Ser. 2008, 10, 95–102.