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Mechanism and technology study of collaborative support with long and short bolts in large-deformation roadways
International Journal of Mining Science and Technology 25 (2015) 587–593
Contents lists available at ScienceDirect
International Journal of Mining Science and Technology journal homepage: www.elsevier.com/locate/ijmst
Mechanism and technology study of collaborative support with long and short bolts in large-deformation roadways Yu Hui ⇑, Niu Zhiyong, Kong Linggen, Hao Caicheng, Cao Peng School of Resources and Safety Engineering, China University of Mining and Technology, Beijing 100083, China
a r t i c l e
i n f o
Article history: Received 18 November 2014 Received in revised form 3 January 2015 Accepted 6 February 2015 Available online 25 June 2015 Keywords: Collaborative support with long and short bolt Docking long bolt Numerical analysis Similarity simulation
a b s t r a c t Common short bolts of equal length are widely used to support the roofs of roadways in coal mines. However, they are insufficient to keep the roof stable against large deformations, so docking long bolts with high levels of elongation that can adapt to large deformations of the surrounding rock have been adopted. This paper proposes a collaborative support method that uses long and short bolts. In this study, the mechanism of docking long bolts and collaborative support was studied. Numerical simulation, similarity simulation, and field testing were used to analyze the distribution law of the displacement, stress, and plastic failure in the surrounding rock under different support schemes. Compared with the equal-length short bolt support, the collaborative support changed the maximum principal stress of the shallow roof from tensile stress to compressive stress, and the minimum principal stress of the roof significantly increased. The stress concentration degree of the anchorage zone clearly increased. The deformation of the roof and the two sides was greatly reduced, and the subsidence shape of the shallow roof changed from serrated to a smooth curve. The roof integrity was enhanced, and the roof moved down as a whole. Plastic failure significantly decreased, and the plastic zone of the roof was within the anchorage range. The similarity simulation results showed that, under the maximum mining stress, the roof collapsed with the equal-length short bolt support but remained stable with the collaborative support. The collaborative support method was successfully applied in the field and clearly improved the stability of the surrounding rock for a large deformation roadway. Ó 2015 Published by Elsevier B.V. on behalf of China University of Mining & Technology.
1. Introduction Bolt support has been a key method of roadway support in coal mine operations. At present, the common short bolt is the primary support component used in support systems of coal roadways. Since the common bolt is too short, it cannot meet the support requirements of large-deformation roadways. Therefore, the anchor cable is widely used at this time. However, the cables have a small extension capacity and are prone to breaking due to roof convergence. They therefore cannot form an effective support system on the roof and cannot adapt to the large-deformation conditions of the roadway. Therefore, the docking long bolt with a high elongation capability that can adapt to large deformations of the surrounding rock is adopted and a collaborative support method with both long and short bolts is proposed under large rock deformation conditions. Bolts with different lengths play different roles in roadway support, strengthening the links between shallow and
⇑ Corresponding author. Tel.: +86 15201323411. E-mail address: [email protected] (H. Yu).
deep surrounding rock and making bolt support more functional and hierarchical. Substantial studies of the collaborative support method with long and short bolts have been conducted at home and abroad. After studying the mechanism of the full-size grouted bolt, Wang proposed a support scheme comprised of full-size grouted long and short bolts in the tunnel support and explained how it works as well as presenting the equations that describe the internal stress [1,2]. Using numerical modeling, Wang optimized the composite support of the long and short bolt, greatly improving the safety factor of slopes [3,4]. He concluded that the collaborative support of long and short bolts can effectively improve the antiknock ability of the anchoring tunnels [5]. Chen conducted industrial testing in a high-stress soft rock tunnel, achieving good results [6]. Foreign scholars have also carried out research on composite support with long and short bolts [7–13]. Yeung carried out computer simulations, concluding that arranging the long and short bolts in an alternating pattern is important for forming a highly stable supporting structure [14]. The short bolt can reinforce the shallow rock to form the bearing arch structure and the long bolt can anchor the bearing arch structure to deep rock. Therefore, the
http://dx.doi.org/10.1016/j.ijmst.2015.05.011 2095-2686/Ó 2015 Published by Elsevier B.V. on behalf of China University of Mining & Technology.
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collaborative support can effectively control the large deformations of the roadway, providing an important engineering reference for roadway support design. 2. Geological conditions and characteristics of roof movement The Tunlan mining area is located in the central part of Shanxi province and has complex geological conditions. Undulating folds and faults have developed as a result of several tectonic movements. In the mining area, the 12,501 working face is being mined. The haulage roadway of 12,501 currently uses the equal length short bolt support scheme. During roadway excavation, the support method meets the requirements of keeping the roof stable. However, roof subsidence is severe during working face excavation, with the roof collapsing in local areas (Fig. 1), seriously affecting roadway use. The 12,501 haulage roadway is located in the 2# coal seam of the south panel at the +750 m level. It has a large cross section and passes through geological tectonic regions such as faults. The distance from the coal seam to the ground is approximately 612.5–650.3 m, with an average distance of 626 m. The thickness of the coal seam is 3.8–5.2 m, with an average thickness of 4.25 m. The hardness coefficient of the coal seam is less than 0.8. The coal seam has a simple structure and a relatively developed fracture, belonging to a relatively stable thick seam. It is a nearly horizontal seam with an average inclination of 2.5°, with a maximum of 6°. The immediate roof of this coal seam consists of carbonaceous mudstone and sandy mudstone. The basic roof is composed of siltstone and fine sandstone. The immediate floor is black sandy mudstone and the basic floor is mainly composed of fine sandstone (Fig. 2). 3. Mechanism of collaborative support and optimization of support scheme
support method with long and short bolts was proposed and the mechanism of the docking long bolt and collaborative support were studied. The collaborative support scheme was compared with the equal-length short bolt support scheme. The two kinds of support scheme were analyzed using numerical simulations, similarity simulations, and field testing. 3.1. Mechanism and parameters of docking long bolt (1) The docking long bolt is a kind of steel resin bolt, as shown in Fig. 3. The tail nut and tray of the docking long bolt are the same as those of a common bolt and it is easily installed by a roof bolter. According to the height of the roadway and the designed bolt length, the bolt is processed into two or more segments connected by screw bolts. The two parts are connected together by a roof bolter. The strength of connecting joint is much greater than the anchorage force and no less than 90% of the ultimate tensile strength. Therefore, the lengthening of the bolt can guarantee that the anchorage force will not decrease. (2) The docking long bolt is made of screw steel with no longitudinal ribs, a yield strength of more than 335 MPa, a tensile strength of no less than 490 MPa, and dimensions that must comply with the requirements of dedicated screw steel for bolts. The elongation of the bolt is greater than 15% and its straightness is less than 2 mm/m. The bolt diameter is 20 mm, the anchorage force is greater than 105 kN, a tail thread diameter based on the M22 thread, and a strength of no less than 105 kN. The diameter and length of the connecting joint is 26.5 ± 5 mm and 50 mm, respectively. The connecting bolt size is based on the M18 2 and the connector strength is greater than 139 kN. The tray strength is no less than 105 kN and the tail thread strength is greater than 105 kN. 3.2. Mechanism of collaborative support with long and short bolt
To keep the roof of a large deformation roadway stable, a docking long bolt with high elongation that can adapt to the large deformations of the surrounding rock was adopted. The collaborative
Fig. 1. Deformation and failure of the roof in the 12,501 haulage roadway.
In the collaborative support system, bolts of different lengths play different roles in roadway support, making the support more functional and hierarchical. After roadway excavation, the shallow surrounding rock inevitably enters the plastic state and interacts with the short bolt to form a reinforced arch structure with a certain bearing capacity. This changes the stress state of the surrounding rock from two-dimensional to three-dimensional, improving the overall strength and limiting the plastic deformation of the surrounding rock. Furthermore, the short bolt can reduce the mutual dislocation between rock formations and the shear stress of the long bolt in shallow rock to avoid shear failure. Furthermore, the long bolt can control the deformation of the deep surrounding rock and can be anchored into the elastic zone, thus suspending the
Fig. 2. Characteristics of roof-floor at the 12,501 haulage roadway.
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established using the FLAC numerical simulation software [15– 19] based on the geological conditions of the Tunlan mine and the characteristics of mining engineering problems. The roadway cross-section is a rectangle with dimensions 4.8 m 3.5 m and the length of working face is 120 m. Considering boundary effects, the size of the model is 160 m 100 m 60 m and the Mohr– Coulomb elastic–plastic constitutive model is adopted. The gravity stress of the overlying strata was estimated to be 8 MPa and was applied at the top boundary of the model. The coefficient of horizontal pressure was approximately 2.0 and a horizontal stress of approximately 16 MPa was applied on the sides of the model. At the bottom of the model, the displacement was restricted in three directions. Using the numerical simulations, the characteristics of deformation and internal stress of the surrounding rock with different support schemes were analyzed.
Fig. 3. Components of docking long bolt.
reinforced arch structure in deep stable rock. The shallow and deep surrounding rocks interact with each other to reach a compatible deformation. In summary, the collaborative support mechanism in large-deformation roadways is closely related to different functional orientations and the different roles of the long and short bolts. 3.3. Optimization of support scheme Based on the collaborative support mechanism, the collaborative support scheme with long and short bolts is proposed, as shown in Fig. 4b. It is compared with the original support scheme utilizing equal-length short bolts, shown in Fig. 4a. (1) Equal length short bolt support scheme (original support): Ö22 2400 mm common short bolt in the roof, row and line space of 900 900 mm, six bolts for each row of complete anchorage form, Ö20 1800 mm steel bolt in the two sides, and row and line space for 1000 900 mm. (2) Collaborative support scheme with long and short bolt (optimized support): Ö22 2400 mm common short bolt and Ö20 5000 mm docking long bolt in the roof, row and line space of 900 1800 mm for both short bolt and long bolts in a staggered arrangement, Ö20 1800 mm steel bolt in the two sides, and row & line space for 1000 900 mm. The two support systems were analyzed using numerical simulation, similarity simulation, and field testing. 4. Numerical analysis of roadway stability with different support schemes In order to simulate roadway deformation, as well as the internal stress of the surrounding rock with the different support schemes during working face excavation, a numerical analysis model was
4.1. Analysis of the plastic zone in the surrounding rock The distribution of the plastic zone in the surrounding rock under the influence of working face excavation is shown in Fig. 5. Severe plastic failure has occurred with the equal length short bolt support (Fig. 5a) and the range of the plastic zone has exceeded 3.0 m, which is beyond the anchorage range of the short bolt, suggesting that the short bolt fails to anchor the roof to the stable strata. Shear failure occurs in the deep roof, while the shallow roof has both shear failure and tensile failure that result in significant deformation. The two sides exhibit a lower extent of plastic failure, with the range of plastic zone being less than the length of the bolt. Compared with the original scheme, the collaboration support scheme exhibits greater control of the plastic zone development, as shown in Fig. 5b. Plastic failure of the roadway significantly decreases and the plastic zone of the roof is within the anchorage range of the short bolt. Only limited shear failure occurs in the roof without tensile failure, making the shallow roof more stable and the failure of two sides also decreases to a limited extent. This suggests that the change of support scheme has a small influence on the plastic zone of the two sides but a significant influence on the plastic zone of the roof. 4.2. Analysis of stress in surrounding rock The stress distribution in the surrounding rock under the influence of working face excavation, is shown in Fig. 6. The stress distribution of the surrounding rock is significantly different after applying the long bolt support. The maximum principal stress of the shallow roof changes from tensile stress to compressive stress, suggesting that a strong anchorage force has been applied to the roof. The anchorage effect has improved and a strong compressive stress prevents the roof from tensile failure. The minimum Docking long bolt
ϕ 20, L=5000 mm
900 900 900 900 900
150
Screw steel bolt ϕ 20, L=1800 mm150
Common short bolt ϕ 22, L=2400 mm 900 900 900 900 900 150
3500
Screw steel bolt 150 ϕ 20, L=1800 mm
1200 1000 1000 300 3500
Common short bolt ϕ 22, L=2400 mm
4800
(a) Equal length short bolt support
4800
(b) Collaborative support with long and short bolt Fig. 4. Optimization of support scheme.
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with only short bolt support exhibits severe destruction, with the subsidence shape of the shallow roof appearing serrated. The subsidence of roof between two bolts is significantly larger than that of the anchorage zone, indicating that the anchorage scope of the short bolt is very limited and the roof cannot be anchored as a whole. The integrity of the roof has been compromised and the maximum roof subsidence reaches up to 0.6 m. After the application of collaborative support with long and short bolts, roof subsidence significantly decreases, with a maximum subsidence of only 0.16 m. The roof sinks as a whole, which indicates that the long bolt has a larger anchorage scope and a stronger anchorage effect. The long and short bolts effects are superimposed, which results in the collaborative effect. As the roof remains stable, the force of the roof on the two sides reduces greatly, lowering the horizontal displacement between the two sides to a large extent.
None Shear-n shear-p Shear-n shear-p tension-p Shear-p Shear-p tension-p
(a) With original support
5. Similarity simulation analysis of the roadway stability with different support schemes
None Shear-n shear-p Shear-p Shear-p tension-p
(b) With optimized support Fig. 5. Plastic zone distribution of the surrounding rock with different support schemes.
principal stress of the roof significantly increases, with the stress concentration degree of the anchorage zone increasing significantly, which suggests that the long bolt’s clamping action has radically reduced the probability of roof separation. The integrity of the roof has been strengthened and the strength of the roof itself has been fully utilized to ensure roof stability. 4.3. Analysis of displacement in the surrounding rock The displacement distribution in the surrounding rock under the influence of working face excavation is shown in Fig. 7. The roof
Smax (MPa) -1 -3 -5 -7 -9 -11
Smax (MPa) 2 -2 -6 -10
With original support
With optimized support
(a) Maximum principal stress
In order to simulate roadway deformation and failure with different support schemes during working face excavation, the 12,501 haulage roadway was used as a prototype for the similarity simulation experiment. At the top of the model, the load is applied by hydraulic jacks to simulate the mining influence. Two roadways are arranged with different support schemes: the original support scheme on the right and the optimized support scheme on the left. 5.1. Building the model for the similarity simulation experiment The model frame requires sufficient rigidity and width to ensure the stability of the model. A two-dimensional laboratory bench with dimensions of 1800 mm 160 mm 1300 mm at the China University of Mining and Technology was used. The common short bolt and docking long bolt in this model were made with different types of iron wire to simulate the actual short bolt and the long bolt. The polyvinyl acetate emulsion,
Smin (MPa) -4 -8 -12 -16 -20 -24 -28
Smin (MPa) -2 -10 -18 -26 -34 -42
With original support
With optimized support
(b) Minimum principal stress
Fig. 6. Stress distribution in the surrounding rock with different support schemes.
Zdisp (m) 0.05 -0.05 -0.15 -0.25 -0.35 -0.45 -0.55
With original support
Zdisp (m) 0.06 0.02 -0.02 -0.06 -0.10 -0.14
With optimized support
(a) Z-displacement contour
Xdisp (m) 0.7 0.5 0.3 0.1 -0.1 -0.3 -0.5 -0.7
Xdisp (m) 0.9 0.5 0.1 -0.3 -0.7
With original support
With optimized support
(b) X-displacement contour
Fig. 7. Displacement distribution in the surrounding rock with different support schemes.
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plaster, and water are blended to make the anchoring agent. The anchor plate is simulated using a thin iron sheet and the metal mesh is simulated using a plastic net. The similarity simulation experimental model is shown in Fig. 8.
Both kinds of support scheme can make the roadway stable. With the original support scheme of common short bolt, the roof subsidence was approximately 2.3 mm. The roof subsidence was approximately 0.4 mm with the collaborative support system. (2) Under a load of 0.8 MPa
5.2. Similarity material ratio According to the similarity principle of similarity simulation experiments [20–23], the geometric, time, density, and stress similarity ratios are 10:1, 3.16:1, 1.6:1, 16:1, respectively. Based on the mechanical parameters of the computed model, cementing materials are selected to conduct the combination experiment. In order to accurately select the ratio in accordance with calculation parameters, a number of matching experiments were performed. The material ratios that meet the test requirements are summarized in Table 1. 5.3. Analysis of roof movement and failure characteristics Stress was applied on the model using a hydraulic jack. First, the model was loaded to the initial rock stress state. Based on the geological conditions around the simulated roadway, the gravity stress of the overlying strata was estimated to be 8 MPa and applied on the top of the model. As the stress similarity ratio was 16:1, when the model is in the initial rock stress state, a gravity stress of 0.5 MPa was applied to the overlying strata in the model. On this basis, the load is gradually increased in order to simulate the deformation and failure of the roadway roof affected by the working face excavation. According to the actual value of mine pressure monitoring during the working face excavation, the maximum coefficient of increasing mining stress is approximately 3.0 and thus the maximum applied load was set to 1.5 MPa. The load was increased in steps of 0.1 MPa. When the applied load reached a certain value, the failure characteristics appeared in the roof of the two roadways, as shown in Fig. 9. Four representative images were selected to analyze the process of roadway failure. (1) Under a load of 0.5 MPa The load on the top of the model was first increased to 0.5 MPa. As shown in Fig. 9a, the roadway was not affected by the working face excavation and the roof was in the initial rock stress state.
The roadway deformation due to the working face excavation is readily observed. As the load applied was increased to 0.8 MPa, the roof with the original support scheme begins to separate (Fig. 9b). At the same time, roof subsidence of the optimized support scheme also has a larger increase. Roof subsidence of the original support scheme was approximately 9.3 mm and the bed separation occurs to a lesser extent at a position 300 mm from the roof. The fracture spacing was approximately 3.5 mm and the cracks appear at the shoulder of the roadway with a tendency to expand further. Therefore, this poses the risk of the roof falling with the original support scheme. The roof subsidence of the optimized support scheme is 1.7 mm, meeting the demand of roof support. (3) Under a load of 1.2 MPa With the mining influence gradually increasing, the deformation and failure of the roof becomes more serious. As the load applied was increased to 1.2 MPa, the roof of the original support scheme was seriously damaged (Fig. 9c). Although the expansion of roof separation was not obvious, the degree of bending of the overlying strata increases. The surface rock of the roof collapses and the common short bolt support completely fails, with further development of the cracks at the shoulder of the roadway. However, the roof subsidence of the optimized support scheme was only 2.6 mm and the roof continued to be stable. (4) Under a load of 1.5 MPa As the load on the top of the model was increased to the maximum mining stress, the overlying strata with the original support scheme fully collapses and the bolt support completely fails (Fig. 9d). The upper boundary of the collapsed overlying strata was in the original roof separation position and the height of the collapsed strata was approximately 320 mm. The angle of collapse was the same as the top of the roadway. For the optimized support scheme, the roof separation occurred 49 mm away from the roof and the separation spacing was approximately 2.7 mm. The overlying strata had bent down for only 4.0 mm, suggesting that the optimized support scheme can meet the support requirements.
6. Field observations of surrounding rock deformation In order to test the effect of the collaborative support with the long and short bolts, the surface displacement of the roadway was monitored. The deformation characteristics of the roof and the two sides are shown in Fig. 10. The maximum subsidence of the roof was less than 180 mm and the maximum displacement
Fig. 8. Similarity simulation experimental model.
Table 1 Material ratios of the similarity simulation experiment. Lithology
Simulated density (g/cm3)
Simulated compressive strength (MPa)
Ratio
Material composition
Carbonaceous mudstone Fine sandstone Sandy mudstone Siltstone 2# Coal
1.416 1.638 1.552 1.613 0.938
1.124 5.148 2.685 4.181 0.381
6:3:3 9:6:4 6:2:2 9:8:2 8:7:3
Sand:lime:plaster
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Bed separation
Minimal subsidence
Roof subsidence
(a) Under a 0.5 MPa load
(b) Under a 0.8 MPa load
Flexural subsidence
Bed separation
Original separation position
Overall collapse Surface collapse
(c) Under a 1.2 MPa load
(d) Under a 1.5 MPa load
Fig. 9. Roof failure characteristics under different loads.
Deformation velocity (mm/d)
Cumulative displacement (mm)
250 Roof Two sides
200 150 100 50 0
20
40
60
80
100
120
Distance from measuing point to face (m) (a) Cumulative displacement of surrounding rock with face advancing
12 10 8 6 4 2 0
20
40
60
80
100
120
Distance from measuing point to face (m) (b) Deformation velocity of surrounding rock with face advancing
Fig. 10. Deformation characteristics of the roof and the two sides.
of the two sides was less than 200 mm. When the working face advances to a distance of 10–35 m from the monitoring point in front, the deformation rate of the surrounding rock generally increases because of the effect of the advancing support pressure in front of the working face. Overall, the surrounding rock has a small deformation and tends to be stable, suggesting that the collaborative support system can effectively control the deformation of the surrounding rock and meet the support requirements. 7. Conclusions This study proposes the collaborative support method with long and short bolts and the docking long bolt with high elongation capability that could adapt to the large deformations of surrounding rock. Using numerical simulations, similarity simulations, and field testing, the distributions of displacement and stress in the surrounding rock with different support schemes were analyzed.
stress. The minimum principal stress of the roof significantly increased, with the stress concentration in the anchorage zone increasing significantly. The deformation of the roof and the two sides was greatly reduced, with the subsidence shape of the shallow roof changing from a serrated to a smooth curve. The plastic failure of the roadway significantly decreases and the plastic zone of the roof was within the anchorage range of the short bolt. (2) The similarity simulation experiments show that under the maximum mining stress, the roof collapses with the equal-length short bolt support while remaining stable with the collaborative support. (3) The collaborative support method with long and short bolts was successful in field applications, improving the stability of the surrounding rock for the large-deformation roadway.
Acknowledgments (1) Compared with the equal-length short bolt support, the collaborative support system changed the maximum principal stress of the shallow roof from tensile stress to compressive
This work was supported by the State Key Program of National Natural Science Foundation of China (No. 51234005) and the State
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Key Program of National Natural Science Foundation-Coal Joint Fund (No. 51134018). References [1] Wang MS. Combined effect of long and short bolt. J China Coal Soc 1983;20(1):27–9. [2] Wang MS. Anchoring mechanism research of full length bolt. J China Coal Soc 1983;20(1):40–6. [3] Wang J. Stability analysis of layered rock slope with long and short bolts. N China Inst Water Conserv Hydroelectr Power 2009;30(1):87–9. [4] Wang J. Finite difference analysis of the Marlite slope’s stability reinforced by long and bolt. Fujian Architecture Constr 2009;27(1):59–60. [5] Wang GY. Technical measures study of enhancing anchoring tunnel’s antiknock ability. Hefei: China University of Science and Technology; 2009. [6] Chen YJ. Study on mechanical characteristics and application of half-rigidity shell sprayed anchor structure. Huainan: Anhui University of Science and Technology; 2005. [7] Wagner H, Herget, Vongpaisal. Design and underground excavation in highly stressed rock. In: Proceedings of the 6th International congress on rock mechanics. Canada; 1987. p. 1433–1456. [8] Aset MR, Reddish DJ, Lloyd PW. Rock support interaction analysis based on numerical modeling. Geotech Geol Eng 2000;19(3):23–7. [9] Zhang DM, Qi XH, Yin GZ, Zheng BB. Coal and rock fissure evolution and distribution characteristics of multi-seam mining. Int J Min Sci Technol 2013;23(6):835–40. [10] Zhou HW, Peng RD, Li ZD. Application of steel fibre-reinforced sprayed concrete to a deep tunnel in weak rocks. J Coal Sci Eng 2002;18(2):49–54. [11] Yue C, Esaki Tetsuro. An analytical model to predict axial load in grouted rock bolt for soft rock tunneling. Tunnel Underground Space Technol 2004;19(6):607–18.
593
[12] Kim Sang-Hwan. Interaction behaviors between parallel tunnels in soft ground. Tunnel Underground Space Technol 2004;19(9):78–83. [13] Ou SB, Wang LG, Wang PP, Wang ZS, Huang JH, Zhou DL. Numerical analysis of seepage flow characteristic of collapse column under the influence of mining. Int J Min Sci Technol 2012;22(4):559–65. [14] Yamsguchi I, Yamazaki I, Kiritani Y. Study of ground-tunnel interactions of four shield tunnels driven in close proximity in relation to design and construction of parallel shield tunnel. Tunnel Underground Space Technol 1998;13(3):289–304. [15] Zhou HW, Liu JF, Xue DJ, Yi HY, Xue JH. Numerical simulation of gas flow process in mining-induced crack network. Int J Min Sci Technol 2012;22(6):793–9. [16] Xin YJ, Gou PF, Ge FD. Analysis of stability of support and surrounding rock in mining top coal of inclined coal seam. Int J Min Sci Technol 2014;24(1):63–8. [17] Wang DC, Yang YJ, Wang K, Zhao NN. Numerical simulation of study on rupture development rules of overburden strata in repeated mining. Adv Mater Res 2012;433–440:1933–9. [18] Xiao TQ, Wang XY, Zhang ZG. Stability control of surrounding rocks for a coal roadway in a deep tectonic region. Int J Min Sci Technol 2014;24(2):171–6. [19] Zuo F. Experimental analysis and numerical simulation on the deformation of surrounding rock at deep mining roadway. Huainan: Anhui University of Science and Technology; 2011. [20] Wei XJ, Gao MZ, Lv YC, Shi XC, Gao HL, Zhou HW. Evolution of a mining induced fracture network in the overburden strata of an inclined coal seam. Int J Min Sci Technol 2012;22(6):779–83. [21] Yan S, Bai JB, Li WF, Chen JG, Li L. Deformation mechanism and stability control of roadway along a fault subjected to mining. Int J Min Sci Technol 2012;22(4):559–65. [22] Hou CJ, Xie SH, Zhang J. Simulation experiment of shallow seam mining under thick soil surface. Xi’an Min Inst 2003;23(4):357–61. [23] Qiao WG, Meng QB. Bolting technology and similar simulation study on deep high stress soft rock roadway. Min Metall Eng 2011;31(2):24–8.
Contents lists available at ScienceDirect
International Journal of Mining Science and Technology journal homepage: www.elsevier.com/locate/ijmst
Mechanism and technology study of collaborative support with long and short bolts in large-deformation roadways Yu Hui ⇑, Niu Zhiyong, Kong Linggen, Hao Caicheng, Cao Peng School of Resources and Safety Engineering, China University of Mining and Technology, Beijing 100083, China
a r t i c l e
i n f o
Article history: Received 18 November 2014 Received in revised form 3 January 2015 Accepted 6 February 2015 Available online 25 June 2015 Keywords: Collaborative support with long and short bolt Docking long bolt Numerical analysis Similarity simulation
a b s t r a c t Common short bolts of equal length are widely used to support the roofs of roadways in coal mines. However, they are insufficient to keep the roof stable against large deformations, so docking long bolts with high levels of elongation that can adapt to large deformations of the surrounding rock have been adopted. This paper proposes a collaborative support method that uses long and short bolts. In this study, the mechanism of docking long bolts and collaborative support was studied. Numerical simulation, similarity simulation, and field testing were used to analyze the distribution law of the displacement, stress, and plastic failure in the surrounding rock under different support schemes. Compared with the equal-length short bolt support, the collaborative support changed the maximum principal stress of the shallow roof from tensile stress to compressive stress, and the minimum principal stress of the roof significantly increased. The stress concentration degree of the anchorage zone clearly increased. The deformation of the roof and the two sides was greatly reduced, and the subsidence shape of the shallow roof changed from serrated to a smooth curve. The roof integrity was enhanced, and the roof moved down as a whole. Plastic failure significantly decreased, and the plastic zone of the roof was within the anchorage range. The similarity simulation results showed that, under the maximum mining stress, the roof collapsed with the equal-length short bolt support but remained stable with the collaborative support. The collaborative support method was successfully applied in the field and clearly improved the stability of the surrounding rock for a large deformation roadway. Ó 2015 Published by Elsevier B.V. on behalf of China University of Mining & Technology.
1. Introduction Bolt support has been a key method of roadway support in coal mine operations. At present, the common short bolt is the primary support component used in support systems of coal roadways. Since the common bolt is too short, it cannot meet the support requirements of large-deformation roadways. Therefore, the anchor cable is widely used at this time. However, the cables have a small extension capacity and are prone to breaking due to roof convergence. They therefore cannot form an effective support system on the roof and cannot adapt to the large-deformation conditions of the roadway. Therefore, the docking long bolt with a high elongation capability that can adapt to large deformations of the surrounding rock is adopted and a collaborative support method with both long and short bolts is proposed under large rock deformation conditions. Bolts with different lengths play different roles in roadway support, strengthening the links between shallow and
⇑ Corresponding author. Tel.: +86 15201323411. E-mail address: [email protected] (H. Yu).
deep surrounding rock and making bolt support more functional and hierarchical. Substantial studies of the collaborative support method with long and short bolts have been conducted at home and abroad. After studying the mechanism of the full-size grouted bolt, Wang proposed a support scheme comprised of full-size grouted long and short bolts in the tunnel support and explained how it works as well as presenting the equations that describe the internal stress [1,2]. Using numerical modeling, Wang optimized the composite support of the long and short bolt, greatly improving the safety factor of slopes [3,4]. He concluded that the collaborative support of long and short bolts can effectively improve the antiknock ability of the anchoring tunnels [5]. Chen conducted industrial testing in a high-stress soft rock tunnel, achieving good results [6]. Foreign scholars have also carried out research on composite support with long and short bolts [7–13]. Yeung carried out computer simulations, concluding that arranging the long and short bolts in an alternating pattern is important for forming a highly stable supporting structure [14]. The short bolt can reinforce the shallow rock to form the bearing arch structure and the long bolt can anchor the bearing arch structure to deep rock. Therefore, the
http://dx.doi.org/10.1016/j.ijmst.2015.05.011 2095-2686/Ó 2015 Published by Elsevier B.V. on behalf of China University of Mining & Technology.
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collaborative support can effectively control the large deformations of the roadway, providing an important engineering reference for roadway support design. 2. Geological conditions and characteristics of roof movement The Tunlan mining area is located in the central part of Shanxi province and has complex geological conditions. Undulating folds and faults have developed as a result of several tectonic movements. In the mining area, the 12,501 working face is being mined. The haulage roadway of 12,501 currently uses the equal length short bolt support scheme. During roadway excavation, the support method meets the requirements of keeping the roof stable. However, roof subsidence is severe during working face excavation, with the roof collapsing in local areas (Fig. 1), seriously affecting roadway use. The 12,501 haulage roadway is located in the 2# coal seam of the south panel at the +750 m level. It has a large cross section and passes through geological tectonic regions such as faults. The distance from the coal seam to the ground is approximately 612.5–650.3 m, with an average distance of 626 m. The thickness of the coal seam is 3.8–5.2 m, with an average thickness of 4.25 m. The hardness coefficient of the coal seam is less than 0.8. The coal seam has a simple structure and a relatively developed fracture, belonging to a relatively stable thick seam. It is a nearly horizontal seam with an average inclination of 2.5°, with a maximum of 6°. The immediate roof of this coal seam consists of carbonaceous mudstone and sandy mudstone. The basic roof is composed of siltstone and fine sandstone. The immediate floor is black sandy mudstone and the basic floor is mainly composed of fine sandstone (Fig. 2). 3. Mechanism of collaborative support and optimization of support scheme
support method with long and short bolts was proposed and the mechanism of the docking long bolt and collaborative support were studied. The collaborative support scheme was compared with the equal-length short bolt support scheme. The two kinds of support scheme were analyzed using numerical simulations, similarity simulations, and field testing. 3.1. Mechanism and parameters of docking long bolt (1) The docking long bolt is a kind of steel resin bolt, as shown in Fig. 3. The tail nut and tray of the docking long bolt are the same as those of a common bolt and it is easily installed by a roof bolter. According to the height of the roadway and the designed bolt length, the bolt is processed into two or more segments connected by screw bolts. The two parts are connected together by a roof bolter. The strength of connecting joint is much greater than the anchorage force and no less than 90% of the ultimate tensile strength. Therefore, the lengthening of the bolt can guarantee that the anchorage force will not decrease. (2) The docking long bolt is made of screw steel with no longitudinal ribs, a yield strength of more than 335 MPa, a tensile strength of no less than 490 MPa, and dimensions that must comply with the requirements of dedicated screw steel for bolts. The elongation of the bolt is greater than 15% and its straightness is less than 2 mm/m. The bolt diameter is 20 mm, the anchorage force is greater than 105 kN, a tail thread diameter based on the M22 thread, and a strength of no less than 105 kN. The diameter and length of the connecting joint is 26.5 ± 5 mm and 50 mm, respectively. The connecting bolt size is based on the M18 2 and the connector strength is greater than 139 kN. The tray strength is no less than 105 kN and the tail thread strength is greater than 105 kN. 3.2. Mechanism of collaborative support with long and short bolt
To keep the roof of a large deformation roadway stable, a docking long bolt with high elongation that can adapt to the large deformations of the surrounding rock was adopted. The collaborative
Fig. 1. Deformation and failure of the roof in the 12,501 haulage roadway.
In the collaborative support system, bolts of different lengths play different roles in roadway support, making the support more functional and hierarchical. After roadway excavation, the shallow surrounding rock inevitably enters the plastic state and interacts with the short bolt to form a reinforced arch structure with a certain bearing capacity. This changes the stress state of the surrounding rock from two-dimensional to three-dimensional, improving the overall strength and limiting the plastic deformation of the surrounding rock. Furthermore, the short bolt can reduce the mutual dislocation between rock formations and the shear stress of the long bolt in shallow rock to avoid shear failure. Furthermore, the long bolt can control the deformation of the deep surrounding rock and can be anchored into the elastic zone, thus suspending the
Fig. 2. Characteristics of roof-floor at the 12,501 haulage roadway.
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established using the FLAC numerical simulation software [15– 19] based on the geological conditions of the Tunlan mine and the characteristics of mining engineering problems. The roadway cross-section is a rectangle with dimensions 4.8 m 3.5 m and the length of working face is 120 m. Considering boundary effects, the size of the model is 160 m 100 m 60 m and the Mohr– Coulomb elastic–plastic constitutive model is adopted. The gravity stress of the overlying strata was estimated to be 8 MPa and was applied at the top boundary of the model. The coefficient of horizontal pressure was approximately 2.0 and a horizontal stress of approximately 16 MPa was applied on the sides of the model. At the bottom of the model, the displacement was restricted in three directions. Using the numerical simulations, the characteristics of deformation and internal stress of the surrounding rock with different support schemes were analyzed.
Fig. 3. Components of docking long bolt.
reinforced arch structure in deep stable rock. The shallow and deep surrounding rocks interact with each other to reach a compatible deformation. In summary, the collaborative support mechanism in large-deformation roadways is closely related to different functional orientations and the different roles of the long and short bolts. 3.3. Optimization of support scheme Based on the collaborative support mechanism, the collaborative support scheme with long and short bolts is proposed, as shown in Fig. 4b. It is compared with the original support scheme utilizing equal-length short bolts, shown in Fig. 4a. (1) Equal length short bolt support scheme (original support): Ö22 2400 mm common short bolt in the roof, row and line space of 900 900 mm, six bolts for each row of complete anchorage form, Ö20 1800 mm steel bolt in the two sides, and row and line space for 1000 900 mm. (2) Collaborative support scheme with long and short bolt (optimized support): Ö22 2400 mm common short bolt and Ö20 5000 mm docking long bolt in the roof, row and line space of 900 1800 mm for both short bolt and long bolts in a staggered arrangement, Ö20 1800 mm steel bolt in the two sides, and row & line space for 1000 900 mm. The two support systems were analyzed using numerical simulation, similarity simulation, and field testing. 4. Numerical analysis of roadway stability with different support schemes In order to simulate roadway deformation, as well as the internal stress of the surrounding rock with the different support schemes during working face excavation, a numerical analysis model was
4.1. Analysis of the plastic zone in the surrounding rock The distribution of the plastic zone in the surrounding rock under the influence of working face excavation is shown in Fig. 5. Severe plastic failure has occurred with the equal length short bolt support (Fig. 5a) and the range of the plastic zone has exceeded 3.0 m, which is beyond the anchorage range of the short bolt, suggesting that the short bolt fails to anchor the roof to the stable strata. Shear failure occurs in the deep roof, while the shallow roof has both shear failure and tensile failure that result in significant deformation. The two sides exhibit a lower extent of plastic failure, with the range of plastic zone being less than the length of the bolt. Compared with the original scheme, the collaboration support scheme exhibits greater control of the plastic zone development, as shown in Fig. 5b. Plastic failure of the roadway significantly decreases and the plastic zone of the roof is within the anchorage range of the short bolt. Only limited shear failure occurs in the roof without tensile failure, making the shallow roof more stable and the failure of two sides also decreases to a limited extent. This suggests that the change of support scheme has a small influence on the plastic zone of the two sides but a significant influence on the plastic zone of the roof. 4.2. Analysis of stress in surrounding rock The stress distribution in the surrounding rock under the influence of working face excavation, is shown in Fig. 6. The stress distribution of the surrounding rock is significantly different after applying the long bolt support. The maximum principal stress of the shallow roof changes from tensile stress to compressive stress, suggesting that a strong anchorage force has been applied to the roof. The anchorage effect has improved and a strong compressive stress prevents the roof from tensile failure. The minimum Docking long bolt
ϕ 20, L=5000 mm
900 900 900 900 900
150
Screw steel bolt ϕ 20, L=1800 mm150
Common short bolt ϕ 22, L=2400 mm 900 900 900 900 900 150
3500
Screw steel bolt 150 ϕ 20, L=1800 mm
1200 1000 1000 300 3500
Common short bolt ϕ 22, L=2400 mm
4800
(a) Equal length short bolt support
4800
(b) Collaborative support with long and short bolt Fig. 4. Optimization of support scheme.
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with only short bolt support exhibits severe destruction, with the subsidence shape of the shallow roof appearing serrated. The subsidence of roof between two bolts is significantly larger than that of the anchorage zone, indicating that the anchorage scope of the short bolt is very limited and the roof cannot be anchored as a whole. The integrity of the roof has been compromised and the maximum roof subsidence reaches up to 0.6 m. After the application of collaborative support with long and short bolts, roof subsidence significantly decreases, with a maximum subsidence of only 0.16 m. The roof sinks as a whole, which indicates that the long bolt has a larger anchorage scope and a stronger anchorage effect. The long and short bolts effects are superimposed, which results in the collaborative effect. As the roof remains stable, the force of the roof on the two sides reduces greatly, lowering the horizontal displacement between the two sides to a large extent.
None Shear-n shear-p Shear-n shear-p tension-p Shear-p Shear-p tension-p
(a) With original support
5. Similarity simulation analysis of the roadway stability with different support schemes
None Shear-n shear-p Shear-p Shear-p tension-p
(b) With optimized support Fig. 5. Plastic zone distribution of the surrounding rock with different support schemes.
principal stress of the roof significantly increases, with the stress concentration degree of the anchorage zone increasing significantly, which suggests that the long bolt’s clamping action has radically reduced the probability of roof separation. The integrity of the roof has been strengthened and the strength of the roof itself has been fully utilized to ensure roof stability. 4.3. Analysis of displacement in the surrounding rock The displacement distribution in the surrounding rock under the influence of working face excavation is shown in Fig. 7. The roof
Smax (MPa) -1 -3 -5 -7 -9 -11
Smax (MPa) 2 -2 -6 -10
With original support
With optimized support
(a) Maximum principal stress
In order to simulate roadway deformation and failure with different support schemes during working face excavation, the 12,501 haulage roadway was used as a prototype for the similarity simulation experiment. At the top of the model, the load is applied by hydraulic jacks to simulate the mining influence. Two roadways are arranged with different support schemes: the original support scheme on the right and the optimized support scheme on the left. 5.1. Building the model for the similarity simulation experiment The model frame requires sufficient rigidity and width to ensure the stability of the model. A two-dimensional laboratory bench with dimensions of 1800 mm 160 mm 1300 mm at the China University of Mining and Technology was used. The common short bolt and docking long bolt in this model were made with different types of iron wire to simulate the actual short bolt and the long bolt. The polyvinyl acetate emulsion,
Smin (MPa) -4 -8 -12 -16 -20 -24 -28
Smin (MPa) -2 -10 -18 -26 -34 -42
With original support
With optimized support
(b) Minimum principal stress
Fig. 6. Stress distribution in the surrounding rock with different support schemes.
Zdisp (m) 0.05 -0.05 -0.15 -0.25 -0.35 -0.45 -0.55
With original support
Zdisp (m) 0.06 0.02 -0.02 -0.06 -0.10 -0.14
With optimized support
(a) Z-displacement contour
Xdisp (m) 0.7 0.5 0.3 0.1 -0.1 -0.3 -0.5 -0.7
Xdisp (m) 0.9 0.5 0.1 -0.3 -0.7
With original support
With optimized support
(b) X-displacement contour
Fig. 7. Displacement distribution in the surrounding rock with different support schemes.
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plaster, and water are blended to make the anchoring agent. The anchor plate is simulated using a thin iron sheet and the metal mesh is simulated using a plastic net. The similarity simulation experimental model is shown in Fig. 8.
Both kinds of support scheme can make the roadway stable. With the original support scheme of common short bolt, the roof subsidence was approximately 2.3 mm. The roof subsidence was approximately 0.4 mm with the collaborative support system. (2) Under a load of 0.8 MPa
5.2. Similarity material ratio According to the similarity principle of similarity simulation experiments [20–23], the geometric, time, density, and stress similarity ratios are 10:1, 3.16:1, 1.6:1, 16:1, respectively. Based on the mechanical parameters of the computed model, cementing materials are selected to conduct the combination experiment. In order to accurately select the ratio in accordance with calculation parameters, a number of matching experiments were performed. The material ratios that meet the test requirements are summarized in Table 1. 5.3. Analysis of roof movement and failure characteristics Stress was applied on the model using a hydraulic jack. First, the model was loaded to the initial rock stress state. Based on the geological conditions around the simulated roadway, the gravity stress of the overlying strata was estimated to be 8 MPa and applied on the top of the model. As the stress similarity ratio was 16:1, when the model is in the initial rock stress state, a gravity stress of 0.5 MPa was applied to the overlying strata in the model. On this basis, the load is gradually increased in order to simulate the deformation and failure of the roadway roof affected by the working face excavation. According to the actual value of mine pressure monitoring during the working face excavation, the maximum coefficient of increasing mining stress is approximately 3.0 and thus the maximum applied load was set to 1.5 MPa. The load was increased in steps of 0.1 MPa. When the applied load reached a certain value, the failure characteristics appeared in the roof of the two roadways, as shown in Fig. 9. Four representative images were selected to analyze the process of roadway failure. (1) Under a load of 0.5 MPa The load on the top of the model was first increased to 0.5 MPa. As shown in Fig. 9a, the roadway was not affected by the working face excavation and the roof was in the initial rock stress state.
The roadway deformation due to the working face excavation is readily observed. As the load applied was increased to 0.8 MPa, the roof with the original support scheme begins to separate (Fig. 9b). At the same time, roof subsidence of the optimized support scheme also has a larger increase. Roof subsidence of the original support scheme was approximately 9.3 mm and the bed separation occurs to a lesser extent at a position 300 mm from the roof. The fracture spacing was approximately 3.5 mm and the cracks appear at the shoulder of the roadway with a tendency to expand further. Therefore, this poses the risk of the roof falling with the original support scheme. The roof subsidence of the optimized support scheme is 1.7 mm, meeting the demand of roof support. (3) Under a load of 1.2 MPa With the mining influence gradually increasing, the deformation and failure of the roof becomes more serious. As the load applied was increased to 1.2 MPa, the roof of the original support scheme was seriously damaged (Fig. 9c). Although the expansion of roof separation was not obvious, the degree of bending of the overlying strata increases. The surface rock of the roof collapses and the common short bolt support completely fails, with further development of the cracks at the shoulder of the roadway. However, the roof subsidence of the optimized support scheme was only 2.6 mm and the roof continued to be stable. (4) Under a load of 1.5 MPa As the load on the top of the model was increased to the maximum mining stress, the overlying strata with the original support scheme fully collapses and the bolt support completely fails (Fig. 9d). The upper boundary of the collapsed overlying strata was in the original roof separation position and the height of the collapsed strata was approximately 320 mm. The angle of collapse was the same as the top of the roadway. For the optimized support scheme, the roof separation occurred 49 mm away from the roof and the separation spacing was approximately 2.7 mm. The overlying strata had bent down for only 4.0 mm, suggesting that the optimized support scheme can meet the support requirements.
6. Field observations of surrounding rock deformation In order to test the effect of the collaborative support with the long and short bolts, the surface displacement of the roadway was monitored. The deformation characteristics of the roof and the two sides are shown in Fig. 10. The maximum subsidence of the roof was less than 180 mm and the maximum displacement
Fig. 8. Similarity simulation experimental model.
Table 1 Material ratios of the similarity simulation experiment. Lithology
Simulated density (g/cm3)
Simulated compressive strength (MPa)
Ratio
Material composition
Carbonaceous mudstone Fine sandstone Sandy mudstone Siltstone 2# Coal
1.416 1.638 1.552 1.613 0.938
1.124 5.148 2.685 4.181 0.381
6:3:3 9:6:4 6:2:2 9:8:2 8:7:3
Sand:lime:plaster
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Bed separation
Minimal subsidence
Roof subsidence
(a) Under a 0.5 MPa load
(b) Under a 0.8 MPa load
Flexural subsidence
Bed separation
Original separation position
Overall collapse Surface collapse
(c) Under a 1.2 MPa load
(d) Under a 1.5 MPa load
Fig. 9. Roof failure characteristics under different loads.
Deformation velocity (mm/d)
Cumulative displacement (mm)
250 Roof Two sides
200 150 100 50 0
20
40
60
80
100
120
Distance from measuing point to face (m) (a) Cumulative displacement of surrounding rock with face advancing
12 10 8 6 4 2 0
20
40
60
80
100
120
Distance from measuing point to face (m) (b) Deformation velocity of surrounding rock with face advancing
Fig. 10. Deformation characteristics of the roof and the two sides.
of the two sides was less than 200 mm. When the working face advances to a distance of 10–35 m from the monitoring point in front, the deformation rate of the surrounding rock generally increases because of the effect of the advancing support pressure in front of the working face. Overall, the surrounding rock has a small deformation and tends to be stable, suggesting that the collaborative support system can effectively control the deformation of the surrounding rock and meet the support requirements. 7. Conclusions This study proposes the collaborative support method with long and short bolts and the docking long bolt with high elongation capability that could adapt to the large deformations of surrounding rock. Using numerical simulations, similarity simulations, and field testing, the distributions of displacement and stress in the surrounding rock with different support schemes were analyzed.
stress. The minimum principal stress of the roof significantly increased, with the stress concentration in the anchorage zone increasing significantly. The deformation of the roof and the two sides was greatly reduced, with the subsidence shape of the shallow roof changing from a serrated to a smooth curve. The plastic failure of the roadway significantly decreases and the plastic zone of the roof was within the anchorage range of the short bolt. (2) The similarity simulation experiments show that under the maximum mining stress, the roof collapses with the equal-length short bolt support while remaining stable with the collaborative support. (3) The collaborative support method with long and short bolts was successful in field applications, improving the stability of the surrounding rock for the large-deformation roadway.
Acknowledgments (1) Compared with the equal-length short bolt support, the collaborative support system changed the maximum principal stress of the shallow roof from tensile stress to compressive
This work was supported by the State Key Program of National Natural Science Foundation of China (No. 51234005) and the State
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Key Program of National Natural Science Foundation-Coal Joint Fund (No. 51134018). References [1] Wang MS. Combined effect of long and short bolt. J China Coal Soc 1983;20(1):27–9. [2] Wang MS. Anchoring mechanism research of full length bolt. J China Coal Soc 1983;20(1):40–6. [3] Wang J. Stability analysis of layered rock slope with long and short bolts. N China Inst Water Conserv Hydroelectr Power 2009;30(1):87–9. [4] Wang J. Finite difference analysis of the Marlite slope’s stability reinforced by long and bolt. Fujian Architecture Constr 2009;27(1):59–60. [5] Wang GY. Technical measures study of enhancing anchoring tunnel’s antiknock ability. Hefei: China University of Science and Technology; 2009. [6] Chen YJ. Study on mechanical characteristics and application of half-rigidity shell sprayed anchor structure. Huainan: Anhui University of Science and Technology; 2005. [7] Wagner H, Herget, Vongpaisal. Design and underground excavation in highly stressed rock. In: Proceedings of the 6th International congress on rock mechanics. Canada; 1987. p. 1433–1456. [8] Aset MR, Reddish DJ, Lloyd PW. Rock support interaction analysis based on numerical modeling. Geotech Geol Eng 2000;19(3):23–7. [9] Zhang DM, Qi XH, Yin GZ, Zheng BB. Coal and rock fissure evolution and distribution characteristics of multi-seam mining. Int J Min Sci Technol 2013;23(6):835–40. [10] Zhou HW, Peng RD, Li ZD. Application of steel fibre-reinforced sprayed concrete to a deep tunnel in weak rocks. J Coal Sci Eng 2002;18(2):49–54. [11] Yue C, Esaki Tetsuro. An analytical model to predict axial load in grouted rock bolt for soft rock tunneling. Tunnel Underground Space Technol 2004;19(6):607–18.
593
[12] Kim Sang-Hwan. Interaction behaviors between parallel tunnels in soft ground. Tunnel Underground Space Technol 2004;19(9):78–83. [13] Ou SB, Wang LG, Wang PP, Wang ZS, Huang JH, Zhou DL. Numerical analysis of seepage flow characteristic of collapse column under the influence of mining. Int J Min Sci Technol 2012;22(4):559–65. [14] Yamsguchi I, Yamazaki I, Kiritani Y. Study of ground-tunnel interactions of four shield tunnels driven in close proximity in relation to design and construction of parallel shield tunnel. Tunnel Underground Space Technol 1998;13(3):289–304. [15] Zhou HW, Liu JF, Xue DJ, Yi HY, Xue JH. Numerical simulation of gas flow process in mining-induced crack network. Int J Min Sci Technol 2012;22(6):793–9. [16] Xin YJ, Gou PF, Ge FD. Analysis of stability of support and surrounding rock in mining top coal of inclined coal seam. Int J Min Sci Technol 2014;24(1):63–8. [17] Wang DC, Yang YJ, Wang K, Zhao NN. Numerical simulation of study on rupture development rules of overburden strata in repeated mining. Adv Mater Res 2012;433–440:1933–9. [18] Xiao TQ, Wang XY, Zhang ZG. Stability control of surrounding rocks for a coal roadway in a deep tectonic region. Int J Min Sci Technol 2014;24(2):171–6. [19] Zuo F. Experimental analysis and numerical simulation on the deformation of surrounding rock at deep mining roadway. Huainan: Anhui University of Science and Technology; 2011. [20] Wei XJ, Gao MZ, Lv YC, Shi XC, Gao HL, Zhou HW. Evolution of a mining induced fracture network in the overburden strata of an inclined coal seam. Int J Min Sci Technol 2012;22(6):779–83. [21] Yan S, Bai JB, Li WF, Chen JG, Li L. Deformation mechanism and stability control of roadway along a fault subjected to mining. Int J Min Sci Technol 2012;22(4):559–65. [22] Hou CJ, Xie SH, Zhang J. Simulation experiment of shallow seam mining under thick soil surface. Xi’an Min Inst 2003;23(4):357–61. [23] Qiao WG, Meng QB. Bolting technology and similar simulation study on deep high stress soft rock roadway. Min Metall Eng 2011;31(2):24–8.