Study on Mechanical Mechanism and Stability of Surrounding Rock in Fault Structure Roadway

： In order to study the deformation and failure mechanism of the fault passage, this paper 7 makes a series of research on the fault passage through theoretical analysis, field investigation and 8 numerical simulation. Firstly, the mechanical characteristics of the fault structure and the 9 deformation and failure characteristics of the surrounding rock passing through the fault are 10 summarized. Then, the numerical analysis is carried out before and after the tunnel passing 11 through the fault. The results show that the original support scheme has large deformation and 12 failure in the surrounding rock of the fault section, and the deterioration and expansion of the 13 plastic zone leads to the failure of the support. Finally, the comprehensive support scheme and 14 principle of "bolt + anchor cable + metal mesh + grouting" is put forward, and the support for the 15 broken tunnel passing through the fault is strengthened. The calculation results show that the 16 support scheme can keep the tunnel passing through the fault in a stable deformation range, which 17 is conducive to the long - term stability of the surrounding rock. 18


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China's coal resources in the past 20 years with a relatively stable growth rate, with the 22 improvement of mining technology, as well as the consumption of shallow resources, China's coal 23 is gradually entering deep mining. In this context, China's new roadways can reach 10,000 24 kilometers per year [1] . Many roadways in the deep high stress, roadway support difficulties, large 25 deformation, fluid damage is increasingly prominent. At present, there are many coal seam mining 26 lanes often can not avoid some complex tectonic geological con-ditions, such as faults, broken 27 belt and so on [2][3][4] . After the roadway crosses the fault, it is generally affected by large tectonic 28 stress. On the one hand, the maximum main stress direction of the laneway is deflected, on the 29 other hand, it will weaken the strength of the rock body around the laneway and make the rock 30 formations have no continuous distribu-tion [5] . Therefore, once the roadway is faced with the 31 geological structure of large faults, if not to take effective support measures or in accordance with 32 the normal construction rules to deal with the roadway fault zone, once the roadway under high 33 tectonic stress, it is easy to occur support difficulties, roadways can not be used normally. In order 34 to meet the demand and safety requirements, roadways often re-quire secondary or multiple 35 repairs to main-tain the stability of the surrounding rock, which brings many outstanding 36 problems to mining safety and efficiency. Therefore, many scholars pay attention to the 37 deformation and destruction mechanism of this kind of fault roadway, and have made some 38 research results in theory, indoor test and field application. For example, Zhang Mingzhong and so 39 on [2] studi-ed the characteristics of the deep roadway through the large fault broken surrounding 40 rock, and compared the situation of the no-fault formation roadway surrounding rock, established 41 a suitable for the oversteed fault roadway support principle and method; Zhang Mingqiang [9] put 42 forward a comprehensive support means of anchor net rope and slurry when the top plate is 43 broken and sunk when the roadway is close to the fault, and the support effect is obvious. Meng 44 Zhaoping and others [10] carried out detailed indoor laboratory tests on coal rocks near faults, and 45 carried out numerical tests to systematically reveal the effects of positive faults on the physical 46 and physical properties of coal and the distribution of mineral pressure. At present, many roadway 47 fault support means or follow the traditional design methods as a reference, and these support 48 means can not meet the support re-quirements [11][12][13][14] . There is no more in-depth and systematic 49 research on the influence of the fault roadway on the range of surrounding rock plastic area, the 50 support structure and the optimization of the support mode. Therefore, this paper analyzes the 51 characteristics of fault laneways through theory, and establishes the extended forces model of 52 hidden faults and the critical model of burst water. According to the actual roadway fault as the 53 engineering background, using Flac 3D numerical simula-tion software to explore the deformation 54 of the cross fault lane, consider the impact of the support design on the stability of the roadway, 55 and carry out optimization research, for such a fault roadway stability and deformation of the 56 understanding of a certain reference and re-ference.

Fault breaking banding characteristics 59
After the rock formation breaks, a relative slip surface is produced, which causes the rock 60 layer to be in a state of indesemination, and this face refers to the fault plane. Figure 1   In the process of disorting and squeezing the upper and lower parts of the fault, a large 71 number of fissures will occur in the rock body within the fault range, and the fault rock will be 72 divided into discrete block structures. Therefore, according to the integrity degree of the rock body, 73 fault rock can be divided into broken belt and crack development zone (Figure 2), and the fault 74 breaking zone will form a process of temperature, pressure and fracture development from high to 75 low evolution, the corresponding structure and stress environment complex and variable.

Stability criterion of faults 82
As shown in Figure 2, if the fault reaches a stable condition, the ratio of maximum and 83 minimum principal stress is [15] : 84 Where:  is the angle between the direction of the fracture surface and the direction of the 5 The change of K value is related to fault dip  and fault friction angle . If the fault dip  88 value is fixed, the K value decreases as the fault friction angle  increases. If the fault friction 89 angle  value is fixed, the K value increases as the fault dip  increases. (1) indicates that the 90 maximum and minimum principal stress ratio K has a critical value of 1, that is, when K is greater 91 than 1, 1>3, then vertical stress is regarded as the maximum principal stress; on the contrary, 92 horizontal stress is considered to be the maximum principal stress. 93 The roadway crossing the broken zone of the fault structure will cause the change of the 94 direction of its principal stress, which will affect the change of the principal stress value, literature 95 [16][17][18][19] shows that the change of the middle principal stress of the roadway is mainly related to the 96 ratio of the maximum and minimum principal stress before and after the active of the large fault or 97 hidden fault. The greater the ratio of the two, the greater the intermediate principal stress. Among 98 them, the main stress changes of normal faults before and after the formation of the fault structural 99 zone are shown in Table 1. Table 1 Main stress change of normal fault 100

Item
Before the fault After the fault Normal fault

The mechanism of hydraulic inrush activation by hidden faults 101
At present, domestic coal mines are gradually entering deep mining, and disasters such as 102 high water pressure and high gas pressure in the depths occur frequently. Excessive faults in the 103 roadway will cause difficulties in support; in addition, many hidden small faults and small 104 structures are under the action of mining and confined water, which pose a prominent threat to 105 coal production. Current prevention and control methods are often unable to effectively predict 106 and prevent. The activation mechanics of hidden faults plays an important role in understanding 107 problems such as water inrush caused by fault activation. 108 For this reason, we think that the structure of the hidden fault can be regarded as a crack with 109 some frictional effect, so that the active equivalent of the hidden fault with mining can be a crack 110 expansion force model, as shown in Figure 3. The stress intensity factor at the tip of a hidden fault 6 can be superimposed on each other to obtain the composite stress intensity factor of the hidden 113 fault tip extension. Among them, there is the following relationship between the propagation stress 114 G and the intensity factor K of the hidden fault crack [20][21] : 115 Where: p K  is the stress intensity factor of confined water; n K   is the normal stress 117 intensity factor; n K   is the shear stress intensity factor; E is the elastic modulus. 118 Where: l is the length of the concealed fault crack; n  and n  are the principal stress and In the formula, l  is the activation length of the fracture crack.  production requirements, and it needs to be repaired and strengthened many times. It can be observed that the surrounding rock fragmentation can be divided into severe, medium, 197 and minor damage zones from the inside to the outside. When the roadway crosses a fault or 198 structural zone, the surrounding rock fragmentation range is relatively large, the range of the 199 minor damage zone can reach 4.88m, the range of the medium damage zone is 3.70m, and the 200 range of the severe damage zone is 2.28m. Therefore, the failure area is mainly distributed around 201 the plastic zone of the roadway, and in the fault fracture zone, the degree of broken surrounding 202 rock shows irregular expansion and development, specifically the character-istics of left 203 side>right side>roof [22] .  The cross section of the on-site roadway is a trapezoidal roadway, with a width of 4.6 m, 4.45 225 m on the left side and 3.3 m on the right side. The original support scheme is a combined support 226 of bolts and cables, as shown in Figure 7. Among them, the diameter of the anchor rod is 22× 227 2400 mm, and the distance between rows is 700×600 mm; the anchor cable is 22×7300 mm in 228 diameter and the distance between rows is 1600×800 mm. In addition, in the numerical process, a

Control countermeasures and support optimization of roadway crossing fault 251
When the roadway passes through the fault, the rock mass is severely broken and the stress 252 changes greatly. As shown in Figure 9, the plastic zone of the roadway crossing the fault has 253 obvious malignant expansion, presenting a similar "butterfly" plastic zone range. Large 254 deformation failure occurs in the mining roadway, the essence of which is that the stress failure 255 zone of the roadway is irregular, and the support means cannot control the malignant development 256 Roof of the plastic zone, es-pecially for the "butterfly" failure theory [25][26] . The original support plan of 257 the roadway was within the "butterfly" plastic zone, and the support structure failed. The original 258 support method cannot maintain the stability of the roadway well at this time, the uneven 259 deformation of the surrounding rock of the roadway continues to increase, the full section of the 260 roadway shrinks seriously, and the displacement convergence of the roof and floor and the two 261 sides can reach nearly 6,000 mm. Generally speaking, in addition to the impact of the stress disturbance on the roadway, the 283 more important thing is that the 284 roadway is broken, which reduces the integrity of the surrounding rock, and the support 285 system and the surrounding rock cannot jointly bear the broken deformation of the surrounding 286 rock. In order to better control the deformation and failure of extremely broken surrounding rocks 287 when such roadways pass through faults, according to the numerical calculation results, in order to 288 reduce the extent of the roadway plastic zone, the emphasis is on strengthening the corners of the 289 roadway "butterfly" zone. Therefore, comprehensively considering the characterist-ics of the 290 plastic zone of the fault-broken roadway, a joint optimization support scheme considering the 291 strengthening of the roadway angle is proposed: when the roadway crosses the fault, the roadway 292 angle is densified or the bolts and cables are lengthened; for special fractures The surrounding 293 rock of the roadway considers strengthening the support, and cooperates with the grouting 294 reinforcement, the partial damage is serious, and the full-section support reinforcement is carried 295 out. 296 Figure 10 shows the numerical calculation results of the reinforced support scheme for the 297 roadway crossing the fault. It can be found that after the roadway plastic zone is strengthened, the 298 "butterfly" plastic zone area is reduced, and the anchor cables and bolts are outside the plastic 299 zone. The malignant development of the plastic zone is well controlled. The long-term 300 displacement of the surrounding rock of the roadway has been well controlled (when the exceed 70mm; the distance between the roof and floor does not exceed 280mm). And judging 303 from the maximum shear stress diagram, the concentrated stress around the roadway is also 304 relatively small. Therefore, the proposed "bolt, anchor cable, grouting" combined support scheme 305 has good stability for the support of extremely broken roadways through faults, and ensures the 306 stability and long-term use of the roadways.

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(1) The mechanical characteristics and failure characteristics of the fault fracture zone are 320 summarized, and the mining activation mechanism of concealed small faults and small structures 321 is explored through fracture mechanics theory, and the critical value of water inrush due to floor 322 failure caused by fault activation is obtained. 323 (2) The fault fracture zone has the characteristics of plastic faults, resembling a "butterfly" 324 distribution. The internal structure of the rock mass is obviously different, and the mechanical 325 unity of the rock formation is reduced within a certain range. 326 The data used to support the findings of this study are available from the corresponding 349 authors upon request.      Numerical calculation results of the optimal support scheme for roadway passing through faults: (a) plastic zone; (b) contour of total displacement; (c) maximum shear stress; (d) convergence curve of monitoring points