Numerical simulation study of the failure evolution process and failure mode of surrounding rock in deep soft rock roadways

Numerical simulation study of the failure evolution process and failure mode of surrounding rock in deep soft rock roadways

International Journal of Mining Science and Technology 26 (2016) 209–221 Contents lists available at ScienceDirect International Journal of Mining S...

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International Journal of Mining Science and Technology 26 (2016) 209–221

Contents lists available at ScienceDirect

International Journal of Mining Science and Technology journal homepage: www.elsevier.com/locate/ijmst

Numerical simulation study of the failure evolution process and failure mode of surrounding rock in deep soft rock roadways Meng Qingbin a,b,⇑, Han Lijun a, Xiao Yu a, Li Hao a, Wen Shengyong a, Zhang Jian a a b

State Key Laboratory for Geomechanics and Deep Underground Engineering, China University of Mining and Technology, Xuzhou 221116, China Shandong Provincial Key Laboratory of Depositional Mineralization & Sedimentary Minerals, Shangdong University of Science and Technology, Qingdao 266590, China

a r t i c l e

i n f o

Article history: Received 18 July 2015 Received in revised form 17 September 2015 Accepted 5 October 2015 Available online 20 January 2016 Keywords: Deep soft rock roadway Evolutionary process Failure model Numerical simulation Model recognition

a b s t r a c t Based on the safety coefficient method, which assigns rock failure criteria to calculate the rock mass unit, the safety coefficient contour of surrounding rock is plotted to judge the distribution form of the fractured zone in the roadway. This will provide the basis numerical simulation to calculate the surrounding rock fractured zone in a roadway. Using the single factor and multi-factor orthogonal test method, the evolution law of roadway surrounding rock displacements, plastic zone and stress distribution under different conditions is studied. It reveals the roadway surrounding rock burst evolution process, and obtains five kinds of failure modes in deep soft rock roadway. Using the fuzzy mathematics clustering analysis method, the deep soft surrounding rock failure model in Zhujixi mine can be classified and patterns recognized. Compared to the identification results and the results detected by geological radar of surrounding rock loose circle, the reliability of the results of the pattern recognition is verified and lays the foundations for the support design of deep soft rock roadways. Ó 2016 Published by Elsevier B.V. on behalf of China University of Mining & Technology.

1. Introduction With increasing mining depth, deep rock is in a complex mechanics environment of ‘three high and one disturbance’ [1–3], and the combination of factors determine the stability of the surrounding rock of deep soft rock roadways. The deep geological environment is complicated, so the destruction of the surrounding rock of a roadway shows a diversity of characteristics. The surrounding rock has different failure modes so support of the roadway should also be changed. Scientific and reasonable support design schemes and parameters would more effectively control the deformation of the surrounding rock and reduce support costs. Engineering practice shows that the failure modes of the surrounding rock of tunnels or roadways in underground projects differ [4,5] under different engineering and geological conditions. Xiang et al. [6] set up a failure mode classification method for the surrounding rock in large-scale underground cavities. In this method, the large size, large aspect ratio and cavity interaction characteristics in large the cavern group are fully considered. Based on three levels: controlling factors, damage mechanism and occurrence conditions, 18 kinds of typical failure mode of the surround⇑ Corresponding author. Tel.: +86 13951468390.

ing rock were summarized. Wu et al. [7] established the failure mode classification method for hard surrounding rock in deep tunnels. The failure phenomenon in deep hard rock tunnels can be divided into 3 categories and 9 kinds of typical failure mode. Using this system, the mechanism of various failure modes, forms, and control strategies were analyzed. Studying the stress field distribution which was formed by underground mining in Jinchuan, Gansu province, Zhao et al. [8] pointed out that the deformation and failure characteristics of the rock surrounding a roadway showed gradual changes at different stages and at different locations. It was shown that the deformation and failure mode characteristics of a roadway could be explained by the surrounding rock deformation characteristics. Based on a rock model which can describe multi-joint behavior, Cui et al. [9] used numerical simulation technology to study the effect of joint angle and lateral pressure coefficient on the failure mode of a tunnel in jointed rock. Using two kinds of typical geological materials, including sand, Fang et al. [10] carried out a model test, and systematically studied the failure mode of a tunnel in surrounding rock which is considered to be a continuum. Using the rock failure process analysis software RFPA2D, Zhang et al. [11] analyzed the deformation and nonlinear gradual failure characteristics surrounding a round hole, as well as the stress variation in the key parts surrounding the roadway. Using RFPA2D, Yuan et al. [12] studied the effect of unloading confining pressure on the failure mode of pillars. Based on the rock

E-mail address: [email protected] (Q. Meng). http://dx.doi.org/10.1016/j.ijmst.2015.12.006 2095-2686/Ó 2016 Published by Elsevier B.V. on behalf of China University of Mining & Technology.

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failure process analysis system, Zhao et al. [13] used numerical simulation to study the failure form in tunnels of different section. Citing test data from 30 cases, Zhu and Xu [14] analyzed the surrounding rock mass with clastic structure by the method of fuzzy clustering. Using the standard model, the failure mode of 8 test samples was predicted. Gao et al. [15] put forward a new kind of evolutionary neural network (ENN) model in which new structures and weights evolved at the same time. It was applied to the identification of the failure mode of surrounding rock. In conclusion, experts and scholars at home and aboard have researched the failure mode of surrounding rock in underground engineering, with some useful conclusions being obtained. However, the related research into the rock burst evolution process and failure mode of the surrounding rock in deep soft rock roadways has not been studied. Based on the research of a deep soft rock roadway project in Zhujixi mine, Huainan, the failure modes of the surrounding rock of deep soft rock roadway are discussed, and the damage evolution process of deep soft rock roadway surrounding rock revealed. Finally, this paper provides a reference for the improvement in support technology in deep mines. 2. Numerical simulation of the damage evolution process and failure mode of surrounding rock in deep soft rock roadway under the condition of single factor effect A FLAC 3D simulation was established, having length, width and height of 60 m, 50 m and 50 m respectively. The displacement of the model base is 0. According to the buried depth of the roadway,

gravity stress was applied on the upper surface. On the basis of the lateral pressure coefficient, different horizontal stresses were applied. According to the rock testing results, numerical simulation parameters were taken, as shown in Table 1. Using the Mohr–Coulomb failure criteria, the deformation characteristics of the rock surrounding the roadway and the evolutionary regularity of the plastic zone under different conditions were revealed. 2.1. Results of numerical simulation under the conditions of different buried depth (1) Evolution law of surrounding rock displacement Eight depths of burial were used: h = 500 m, 600 m, 700 m, 800 m, 900 m, 1000 m, 1100 m and 1200 m, and the lateral pressure coefficient was taken as k = 0.8. In the model of the roadway, a monitoring line was set up along the vertical direction in the center of the roadway roof, floor and sides, in order to monitor the displacement of the roadway roof, floor and two sides [16–19]. The roadway surrounding rock displacement curves under different burial depths are shown in Fig. 1 and the numerical values are given in Table 2. Fig. 1 and Table 2 show that the amount of roof sag, floor heave and side extrusion have a linear relationship: Vroof = 0.4564h 106.7 and R2 = 0.997, Vfloor = 0.5943h 164.93 and R2 = 0.993, Vsides = 0.5768h 200.97 and R2 = 0.993. With increasing burial depth, the amount of roof sag, floor heave and side extrusion also increase, but the deformation amplitude of the surrounding rock decreases. This demonstrates the following rule: ‘‘the increase in

Table 1 Physical and mechanical properties test results of bed plate roadway of track crossheading and haulage gate. Roadway

Lithology

c (g/cm3)

rt (MPa)

rc (MPa)

E (GPa)

l

c (MPa)

u (°)

Bed plate roadway of track crossheading

Fine standstone Siltstone Mudstone

2.53 2.62 2.34

7.60 5.77 3.56

97.386 66.622 45.165

70.5 59.7 55.1

0.212 0.252 0.315

9.52 5.67 2.51

49.51 45.36 51.44

Bed plate roadway of haulage gate

Fine standstone Siltstone Mudstone

2.48 2.60 2.31

7.67 5.85 3.67

94.233 66.850 43.476

70.3 57.2 52.8

0.218 0.254 0.310

9.33 5.42 2.39

48.13 46.09 51.89

400 300 200 100 0

4

8

12

16

20

24

28

600

600

500

500

Displacement (mm)

Duried depth 500 m Duried depth 600 m Duried depth 700 m Duried depth 800 m Duried depth 900 m Duried depth 1000 m Duried depth 1100 m Duried depth 1200 m

Displacement (mm)

Displacement (mm)

500

400 300 200 100 0

Distance to the roof (m) (a) Roof convergence

4

8 12 16 20 Distance to the sides (m) (b) Sides extrusion

24

28

400 300 200 100 0

4

8

12

16

20

24

28

Distance to the floor (m)

(c) Floor heaves

Fig. 1. Roadway surrounding rock displacement curves under different buried depths.

Table 2 Roadway surrounding rock displacement under different buried depths. Buried depth (m)

500 600 700 800 900 1000 1100 1200

Roof convergence and increment (mm)

Floor heaves and increment (mm)

Sides extrusion and increment (mm)

Convergence

Increment

Amplitude (%)

Floor heaves

Increment

Amplitude (%)

Extrusion

Increment

Amplitude (%)

130.3 168.6 208.3 251.5 298.7 347.0 395.6 449.6

0.0 38.3 39.7 43.2 47.2 48.3 48.6 54.0

0.00 22.72 19.06 17.18 15.80 13.91 12.29 12.01

152.1 192.0 242.0 297.1 358.6 423.3 491.9 564.5

0.0 39.9 50.0 55.1 61.5 64.7 68.6 72.6

0.00 20.78 20.66 18.55 17.15 15.29 13.95 12.86

105.6 146.1 193.9 247.7 307.8 371.0 436.7 505.7

0.0 40.5 47.8 53.8 60.1 63.2 65.7 69.0

0.00 27.72 24.65 21.72 19.53 17.04 15.05 13.65

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floor heave is greater than the increase in side extrusion, which is larger than that of roof sinkage”. Under the condition of the same burial depth, the rule is: ‘‘the amount of floor heave is greater than the side extrusion, which is greater than that of roof sinkage”. (2) Analysis of the fracture evolution process and failure mode of the surrounding rock. The distribution of the plastic zone of the surrounding rock at different burial depths is shown in Fig. 2. Fig. 2 shows that, with increasing roadway burial depth (or stress level), the plastic zone of the surrounding rock extends from the surface to greater depth. The range and magnitude of the plastic zone also increases. After excavation, the evolution of the failure process in the surrounding rock develops gradually, eventually forming a zone of macroscopic deformation damage. The fracture evolution process in the surrounding rock was studied, with a burial depth of h = 1000 m, and the lateral pressure coefficient was

(a) h=500 m

(b) h=600 m

k = 0.8. After roadway excavation, the data was used to calculate the unit safety coefficient in the order of calculation [20]. A contour of damage in the surrounding rock area was drawn using surfer software, which will help define the scope of the surrounding rock damage area of the roadway. In turn, the fracture development of the roadway surrounding rock is revealed, as shown in Fig. 3. Fig. 3 shows that the destruction of a semicircular arched, straight wall roadway first occurs in both sides of the vault and the upper spandrel in the surrounding rock. Thereafter, the failure zones in the vaults of the surrounding rock run through and connect with each other. At the same time, the floor also begins to fail. The process of failure of the two sides is aggravated when the failure level of the floor develops. Failure zones in the rock around the roadway run through and begin to present the development of diamond patterns which shows that the floor failure depth is large. Numerical calculation results show that the effect of burial depth (or stress level) of a roadway on the failure pattern of the surrounding rock is not obvious. Although corners exist at the edge

(c) h=700 m

(d) h=800 m

None Shear-n shear-p Shear-n shear-p tension-p Shear-p Shear-p tension-p Tension-p (e) h=900 m

(f) h=1000 m

(g) h=1100 m

(h) h=1200 m

2.5

2.5

2.5

2.5

Fig. 2. Roadway surrounding rock plastic zone under different buried depth.

2.5

(c) Step 50

2

1.75

2

1.75

1.5

1.75

1.5

2

1.75

1.5

(d) Step 100

1.5

(b) Step 25

1.5

(a) Step 5

1.75

2

(e) Step 200

(f) Step 800

1.5 2

(g) Step 3000

Fig. 3. Failure process of surrounding rock (h = 1000 m).

2

(h) Step 12000

1.5

1

1.5

1

1.5

1 1.5

2

2 2.5

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of the failure area in the surrounding rock, failure behavior is similar to that of a circular excavation shape.

exceed the strength of the rock which thereby causes damage at this stress level. Hence, there is a relatively large area of surrounding rock failure.

(3) Analysis of stress evolution in the surrounding rock The surrounding stress will redistribute after the roadway is excavated and leads to the development of stress concentration regions. If the value of stress exceeds the strength of the surrounding rock, the rock mass will fail. To reflect the degree of stress concentration caused by roadway excavation, a stress concentration factor in the surrounding rock is defined as: k = rmax/rzz (where rmax is the maximum stress in the surrounding rock, and rzz is the initial stress). Rock stress distribution at different burial depths is shown in Fig. 4 and the maximum stress and the stress concentration factor at different burial depths is given in Table 3. Fig. 4 and Table 3 show that, with increasing of burial depth of a roadway, the value of maximum stress and the range of surrounding rock will increase, while the stress concentration coefficient will reduce. But with increasing burial depth of the roadway, the low stress zone increases with excavation of the surrounding rock and causes surrounding rock failure, and the high stress zone of deep surrounding rock also increases. This causes the stress to

(a) h=500 m

2.2. Numerical simulation results with different lateral pressure coefficients (1) Evolution analysis of displacement of surrounding rock Eight values of lateral pressure coefficient were considered: k = 0.6, 0.8, 1.0, 1.2, 1.4, 1.6, 1.8 and 2.0. The depth of the roadway was taken as h = 1000 m. For the arrangement of a survey line, the displacement curve of surrounding rock with different lateral pressure coefficients was used, as shown in Fig. 5. Displacement of the surrounding rock with different lateral pressure coefficients is shown in Table 4. Fig. 5 and Table 4 show that, with increasing lateral pressure coefficient (or stress state), roof sag, floor heave and side extrusion have a linear increase relationship: Vroof = 440.38k + 6.8548 and R2 = 0.98, Vfloor = 798.1k 207.32 and R2 = 0.98, Vsides = 377.17k + 57.813 and R2 = 0.965. Under the condition of the same lateral pressure coefficient (or stress state), when k 6 1.0, the rule is: ‘‘the amount of floor heave is greater than the side extrusion”.

(c) h=700 m

(b) h=600 m

(d) h=800 m

-4.1908e+007 -4.0000e+007 -3.5000e+007 -3.0000e+007 -2.5000e+007 -2.0000e+007 -1.5000e+007 -1.0000e+007 -5.0000e+006 0 (e) h=900 m

(g) h=1100 m

(f) h=1000 m

(h) h=1200 m

Fig. 4. Roadway surrounding rock stress distribution under different burial depths.

Table 3 Roadway surrounding rock maximum stress and the stress concentration coefficients under different burial depths. Buried depth (m)

500

600

700

800

900

1000

1100

1200

Maximum stress (MPa) Stress concentration factor

21.79 1.74

23.24 1.55

25.33 1.45

28.60 1.43

32.03 1.42

35.37 1.42

38.60 1.40

41.91 1.40

600 400 200 0

4

8 12 16 20 Distance to the roof (m) (a) Roof convergence

24

28

Displacement (mm)

800

Displacement (mm)

Displacement (mm)

1000

Coefficient of lateral pressure 0.6 Coefficient of lateral pressure 0.8 Coefficient of lateral pressure 1.0 Coefficient of lateral pressure 1.2 Coefficient of lateral pressure 1.4 Coefficient of lateral pressure 1.6 Coefficient of lateral pressure 1.8 Coefficient of lateral pressure 2.0

1000

800 600 400 200 0

4

8 12 16 20 Distance to the sides (m) (b) Side extrusion

24

28

1600 1400 1200 1000 800 600 400 200 0

4

8

12

16

20

Distance to the floor (m) (c) Floor heave

Fig. 5. Roadway surrounding rock displacement curves under different lateral pressure coefficients.

24

28

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Q. Meng et al. / International Journal of Mining Science and Technology 26 (2016) 209–221 Table 4 Roadway surrounding rock displacement under different lateral pressure coefficients. Lateral pressure coefficient

0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0

Roof subsidence and increment (mm)

Floor heaves and increment (mm)

Sides extrusion and increment (mm)

Subsidence

Increment

Amplitude (%)

Floor heaves

Increment

Amplitude (%)

Extrusion

Increment

Amplitude (%)

329.4 347.0 411.9 505.1 607.2 712.0 809.3 912.9

0.0 17.6 64.9 93.2 102.1 104.8 97.3 103.6

0.00 5.07 15.76 18.45 16.82 14.72 12.02 11.35

368.5 423.3 538.3 685.3 864.2 1070.0 1257.0 1435.0

0.0 54.8 115.0 147.0 178.9 205.8 187.0 178.0

0.00 12.95 21.36 21.45 20.70 19.23 14.88 12.40

325.3 371.0 423.5 480.2 545.3 630.5 741.3 868.0

0.0 45.7 52.5 56.7 65.1 85.2 110.8 126.7

0.00 12.32 12.40 11.81 11.94 13.51 14.95 14.60

(a) λ=0.6

(b) λ=0.8

(c) λ=1.0

(d) λ=1.2

None Shear-n shear-p Shear-n shear-p tension-p Shear-p Shear-p tension-p Tension-p

(e) λ=1.4

(f) λ=1.6

(g) λ=1.8

(h) λ=2.0

Fig. 6. Roadway surrounding rock plastic zone distribution under different lateral pressure coefficients.

When k > 1.0, the rule is: ‘‘the amount of floor heave is greater than roof sag, which is greater than that of the two sides”. (2) Analysis of the evolution process and failure mode of the surrounding rock The distribution of the plastic zone in the surrounding rock with different lateral pressure coefficients is shown in Fig. 6. Fig. 6 shows that, with increasing lateral pressure coefficient, the value and the range of the plastic zone in the roof and floor of the surrounding rock also increases, and the value and scope of the plastic zone in the two sides reduces. The shape of the distribution of plastic zone changes is from ‘flat’ to ‘tall’ [16]. (1) Analysis of the rock failure evolution process of a roadway with its trend parallel to the maximum horizontal principal stress As described in the above research methods, for a roadway burial depth of h = 1000 and a lateral pressure coefficient k = 1.2, the rock failure evolution process of a roadway with its trend parallel to the maximum horizontal principal stress is as shown in Fig. 7. Fig. 7 shows that, when the trend is parallel to the maximum horizontal principal stress, the rock fracture development process is the same as the conditions where the buried depth h = 1000 m and in the condition of a semi-circular arch wall section. When the lateral pressure coefficient increases, the depth and the

deformation of the damage area in the surrounding rock also increases. But the impact on the failure pattern of the roadway surrounding rock is not obvious. Overall, the failure modes form an approximate circular shape. This shows that the failure pattern of the roadway surrounding rock varies with lateral pressure coefficient. Overall, the failure modes form an approximate circular shape. (2) Analysis of the rock failure evolution process of a roadway with its trend perpendicular to the maximum horizontal principal stress Fig. 8 shows that, when the roadway axis has a trend perpendicular to the maximum horizontal principal stress, development of the failure evolution process of the surrounding rock also starts from the sides of the vault, but its speed of development is relatively fast. The failure of the two sides and floor occurs almost at the same time. After the failure zone of the surrounding rock is connected, the failure pattern is in diamond-shaped. This shows that the failure zone in the floor and roof develops quickly and the depth of failure is large. When the trend of the roadway is perpendicular to the direction of maximum horizontal principal stress, the change in lateral pressure coefficient of the roadway has a great influence on the surrounding rock failure pattern. When the value of the lateral pressure coefficient is larger than before, the shape of the plastic zone of the surrounding rock is characterized by ‘tall’. The failure

2.5

2.5

2.5

Q. Meng et al. / International Journal of Mining Science and Technology 26 (2016) 209–221

2.5

214

2.5

(c) Step 50

1

1.75

1.75

1

1 1.5

2

2

2.5

2 (e) Step 200

(f) Step 800

1

1.5

1.5

1.75

1.75

1.75

2

1.75

1

1.75 1.5

1.5

1.5

1.5

1.75

2

(d) Step 100

1.75

(b) Step 25

1.5

(a) Step 5

1.75

(g) Step 3000

(h) Step 12000

2.5

2.5

Fig. 7. Distribution of failure area when roadway parallel to the direction of maximum horizontal principal stress.

2 2.5

(c) Step 50

1

1.75

2

1.75

2

3

2

3

2.5

1.

1

2

5

5

1.

1.75

2

5 2 1.7 1.5

2.5

(d) Step 100

1.5

(b) Step 25

1.5 1.75

(a) Step 5

2

2.5

2

1 1.5

1

1

1.5 (e) Step 200

(f) Step 800

(g) Step 3000

1.5 (h) Step 12000

Fig. 8. Distribution of failure area when roadway perpendicular to the direction of maximum horizontal principal stress.

pattern of the roadway surrounding rock varies with the lateral pressure coefficient. Overall, the failure modes perform an approximate ellipse. (3) Analysis of surrounding rock stress evolution The stress distribution of the surrounding rock under different lateral pressure coefficients is shown in Fig. 9. The maximum stress and the stress concentration factor of the roadway surrounding rock under different lateral pressure coefficients can be found in Table 5. Fig. 9 and Table 5 show that, with increasing lateral pressure coefficient, the value of the maximum stress in the surrounding rock reduces, whilst the surrounding rock stress concentration

coefficient decreases and then increases gradually. The distribution area of maximum stress gradually transfers from the two sides to the roof and floor. With increasing lateral pressure coefficient, its value increases gradually in the roof and floor of the surrounding rock. The failure range of the surrounding rock also increases, but the two sides are opposite. When the lateral pressure coefficient, k 6 1.4, high stress zones in the surrounding rock are mainly distributed on two sides, which makes the scope of the plastic zone in the two sides extensive. When the lateral pressure coefficient k > 1.4 the high stress zones in the surrounding rock are mainly distributed in the roof and floor, which makes the scope of the plastic zone in the roof and floor large. With increasing lateral pressure coefficient, the distribution shape of the plastic zone varies from ‘flat’ to ‘tall’ [16].

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(a) λ =0.6

(c) λ =1.0

(b) λ =0.8

(d) λ =1.2

-3.3944e+007 -3.0000e+007 -2.5000e+007 -2.0000e+007 -1.5000e+007 -1.0000e+007 -5.0000e+006 0 (e) λ =1.4

(g) λ =1.8

(f) λ =1.6

(h) λ =2.0

Fig. 9. Roadway surrounding rock stress distribution under different lateral pressure coefficients.

Table 5 Roadway surrounding rock maximum stress and stress concentration coefficients under different lateral pressure coefficients. Coefficient of lateral pressure

0.6

0.8

1.0

1.2

1.4

1.6

1.8

2.0

Maximum stress (MPa) Stress concentration coefficients

36.22 1.45

35.37 1.42

34.02 1.36

32.33 1.29

30.04 1.20

31.65 1.27

33.04 1.32

33.94 1.36

500

300 200 100 0

4

8 12 16 20 Distance to the roof (m) (a) Roof convergence

24

28

500

400

Displacement (mm)

Rectangular Trapezoidal Circular Semicircle arch

400

Displacement (mm)

Displacement (mm)

500

300 200 100 0

4

8 12 16 20 Distance to the sides (m)

24

400 300 200 100

28

0

4

8

12

16

20

24

28

Distance to the floor (m) (c) Floor heave

(b) Side extrusion

Fig. 10. Roadway surrounding rock displacement curves under different section shapes.

Table 6 Roadway surrounding rock displacement, maximum stress and concentration coefficients under different section shapes. Section shape

Circular Semicircle arch straight wall Trapezoidal Rectangular

Deformation (mm)

Maximum stress and concentration factor (MPa)

Roof

Floor

Sides

Maximum stress

Concentration factor

340.1 347.0 365.7 446.3

345.4 423.3 416.2 447.7

371.0 361.5 430.0 465.0

34.54 35.37 35.73 35.78

1.38 1.42 1.43 1.43

2.3. Results of numerical simulation in different cross section shape (1) Analysis of displacement of surrounding rock evolution Four shapes of cross section were considered, including: circle, semicircular arch with straight wall, trapezoidal and rectangular. The roadway burial depth, h = 1000 m, and the lateral pressure coefficient k = 0.8. The arranged survey line is the same as above. Roadway surrounding rock displacement curves in different cross sectional shapes are shown in Fig. 10; the deformation displacement of the surrounding rock at different cross sectional shapes is shown in Table 6.

Fig. 10 and Table 6 show that deformation of the roof, floor and two sides in a rectangular roadway is the largest of the cross sections considered, while the surrounding rock deformation in a circular roadway is minimal. This shows that displacement of the surrounding rock gradually reduces as the cross sectional shape is smoother. Under the same conditions, the stability of a circular roadway is good. Fig. 11 shows that the plastic zone of a rectangular roadway is comparatively large, and the plastic zone of a circular roadway is relatively small. This indicates that the plastic zone of a curved roadway is smaller and the distribution is more uniform than that

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None Shear- n shear- p Shear- n shear- p tension -p Shear- p Shear- p tension -p Tension -p (b) Circular

(a) Semicircle arch straight wall

(c) T rapezoidal

(d) Rectangular

10

Fig. 11. Roadway surrounding rock plastic zone distribution under different section shapes.

3

(a) Step 5

(b) Step 25

4

5

5 2. 2

5 2

2.

75

3

3

10

5

1.5

75

1.5

1.

5

1.

2.5 2

1.7

2.52

2

1.5

2.5 2

34 5

(d) Step 200

2 2.5

10

(c) Step 50

20

4

3

5 (e) Step 800

3

1. 2

2.5

1.7

3

5 2.5

(f) Step 4000

1.5

2

3

4

1.5

1

1

75

10

3

3

2

(g) Step 80000

1.75

2

1.5 2.5

(h) Step 14000

Fig. 12. Failure process of surrounding rock in circular roadway.

of the straight roadway, which is beneficial to the stability of the surrounding rock. Fig. 12 shows that the collapse of the surrounding rock in a circular roadway is distributed evenly around the roadway, develops upward and downward from both sides, and is finally connected in the two groups. After the collapse zone of the surrounding rock around the roadway is connected, the failure mode begins to develop in a diamond pattern, and the rate is basically the same. Fig. 13 shows that the collapse of the surrounding rock in a trapezoidal roadway first occurs in the upper sides, then at the top and bottom plates, and is finally connected in the two groups. After the collapse zone of the surrounding rock around the roadway is connected, the failure mode begins to develop in a diamond pattern, and the development rate of the collapse zone at both sides and the bottom plates is greater than that at the top plates. Fig. 14 shows that the surrounding rock in a rectangular roadway has basically collapsed at the same time as the top and bottom plates, and then collapsed on both sides. After the collapse zone of the surrounding rock around the roadway is connected, the failure mode begins to develop in a diamond pattern, and the development rate of the collapse zone at the top and bottom plates is greater than that at both sides. Overall, the failure mode of the surrounding rock in a circular roadway is also circular, and the failure mode of the surrounding rock in the straight wall, semicircular arched roadway is approxi-

mately circular. The trapezoidal and rectangular cross-sections form the straight roadways. The stress concentration is large at the corner, so the collapse depth of the surrounding rock at the corner is relatively large. But, according to the collapse evolution of the surrounding rock, the failure mode gradually extends in a diamond pattern and is diamond-shaped on the whole. Therefore, as the cross-sectional shape changes, the failure modes are either circular- or diamond-shaped as the failure modes of the surrounding rock in the roadway. (2) Evolution analysis of surrounding rock stress Under different cross-sectional shapes, the stress distribution of the surrounding rock is as shown in Fig. 15; under the same conditions, the maximum stress and stress concentration factor of the surrounding rock are shown in Table 6. As shown in Fig. 15, the rectangular roadways and circular roadways respectively have maximal and minimal maximum stress values and stress concentration coefficients of the surrounding rock, which means that the linear-shaped roadway has a more reasonable stress distribution than a curve-shaped one does; failure at some part of the linear-shaped roadway surrounding rock can be avoided due to the absence of stress concentration in the roadway floor and the apex angle, making it conducive to stability and safety.

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(a) Step 5

10

4

1.75

1.75

1

1

1

1

3

10

1.75

5 2. 2

1

1.5

2 5 2. 2

4 5

2.5

1.5

1 1

(d) Step 200

75 1.

2

5

2.5 2

1.5 5 2. 2

3

2.5

4

75 1.

2

(c) Step 50

(b) Step 25

75

4

1.5 5 1.72

5 (e) Step 800

1.5 .75 12

2

1.5

2.5 (h) Step 14000

(g) Step 80000

(f) Step 4000

1.

1

1

1

1

10

1

1

2 3

Fig. 13. Failure process of surrounding rock in trapezoid roadway.

1.

5

1

2.5

1

1

1

1

10

1

1

1.5

1.75

1

1

75

75 1. 1

2.5

1.5

2

2.5 2 1.5

10

1

3

75

(f) Step 4000

1.75

1.5 2

5

(e) Step 800

2

2.

2

1.

1.5

5

75

1.5

75

1.

2 3 4 5

2.

5

1.5 1.

75

1.

5

2

3 5

3

(d) Step 200

2

2

1

4

(c) Step 50

1.

2 3

4

1.5

(b) Step 25

1.5 1.7

(a) Step 5

(g) Step 80000

(h) Step 14000

Fig. 14. Failure process of surrounding rock in rectangular roadway.

-3.5778e+007 -3.5000e+007 -3.0000e+007 -2.5000e+007 -2.0000e+007 -1.5000e+007 -1.0000e+007 -5.0000e+006 0 (a) Semicircle arch straight wall

(b) Circular

(c) Trapezoidal

(d) Rectangular

Fig. 15. Roadway surrounding rock stress distribution under different section shape.

3. Fracture evolution process in deep soft roadways and numerical simulation research on the failure mode under the effect of multiple factors Based on the project example of the deep soft rock roadway coal mine of Zhujixi in Huainan, the mixed orthogonal

experiment design, including four factors (four levels) and single factor (two levels), is selected and thus 16 experimental models are established, the specific scheme of which is shown in Table 7. Distribution of the failure area under the effect of multiple factors is shown in Fig. 16.

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Table 7 Orthogonal test design. Test 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16

Buried depth of roadway (m) 700 700 700 700 860 860 860 860 960 960 960 960 1200 1200 1200 1200

Orientation between roadway and maximum principal stress

Coefficient of lateral pressure

Roadway shape

Distribution of rock mass

Parallel Parallel Perpendicular Perpendicular Perpendicular Perpendicular Parallel Parallel Parallel Parallel Perpendicular Perpendicular Perpendicular Perpendicular Parallel Parallel

1.0 1.2 1.5 1.8 1.0 1.2 1.5 1.8 1.0 1.2 1.5 1.8 1.0 1.2 1.5 1.8

Circular Semicircular Trapezoid Rectangular Semicircular Circular Rectangular Trapezoid Trapezoid Rectangular Circular Semicircular Rectangular Trapezoid Semicircular Circular

① ② ③ ④ ③ ⑤ ① ② ③ ④ ② ① ② ① ③ ④

arch

arch

arch

arch

Note: ① No soft stratum; ② Soft rock stratum in the roof slab; ③ Soft rock stratum in the middle of the roadway; ④ Soft rock strata in the bottom slab.

2 1.5

3 2

2 1.5 2

1.75 2.5 1.5 1.75 5 2

1.5 1 .75 2.5 3

1.

5

(m) Test 13

(n) Test 14

1.5

(o) Test 15

Fig. 16. Distribution of failure area under the effect of multiple factors.

1.5

(p) Test 16

1. 75

1 1.5 1.75

2.5

1 1.1 .5 .7 1 1

75

1.2

1.

5

2

1

1.

5

2.5

1.

1.7

5 1.

2 2

1.5 2 1.5

1

1.75

1.5

2 2

2

1.5 2

2.5 1.75

2 1.75

1

1.75 1.5

1.5

5

1

3 2 2.5

3 4 3 2.5 1.75 2 1.5

1.75

2

1.5 1.75 1.75

1.

1.

1.75

1.5

(l) Test 12

1.75

1.7 1.75

1.5

1.75 1.5

1

2

2.5

1.5 1.75

(k) Test 11

2.5

5

2.5

2

1.75

1.75 2.5

2.5

1.75

2 2 .5 1.75 1.5

5 2

5 2. 75

1.

1.5

1

1.75 1.5 2 1.75 2.5 2.5

1.75

2 1.5 1.75

3

1.5

2

1.5 2

1.5

2

1.5 2.5

1 75 .5

1. 5

2.5

3

2

2.5

5 1.7

1 1.5

1

1.5

1

2

1.1 1.2 1 1.2

(h) Test 8

1.75

2 (j) Test 10

1.5 1.1

5

2.5

1.5

(i) Test 9

1.5

1. 75

1

2

1.7

1

1.

1.5

2

1.5

1

(g) Test 7

1

5

1

1.5

1.5 1.75

1

1.5

1

1.75

1

2 1.5

1.75

1. 2 75

1.

1.

2.5

5

2

1.7 1.5

1.

1.5

2

1.5 1.75 2

1.7

1

2 1

1.5

1.75

1

(f) Test 6

1

(d) Test 4

2

2 2

(e) Test 5

1

3

1.75

1

2

2 1.75

2.5

1.5

1

75 2

1

1.75

2

1. 1.5 75

1.

1.5

1

(c) Test 3

2.5

2 1.75

1.5

2.5 1.75

1.5

2

2

1.5

1.75

2

2.5

2

1

2

2 2.5

1

1.5

1

(b) Test 2

1.5

3

2

(a) Test 1

2

3

1.5 1.75

5

2.5

3

1.7

2

1.52

2

1.75

1.75

2.5 3

1

3

2.5

1.75 1.5

1

1.5

1.75 2

1.5

2

1

1.5

2.5

2

2 1.75

2

1.75

1

2 1.75

1.75 1

2 2

1.5

2 5

3

1.5

1.75

2 1.5

1.7

2.5

1.75

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Q. Meng et al. / International Journal of Mining Science and Technology 26 (2016) 209–221 Table 8 Failure mode recognition samples of surrounding rock in deep roadway. Specimen 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22

Buried depth (m) 700 860 960 1200 960 960 960 960 960 960 960 700 700 700 860 860 960 960 960 1200 1200 1200

Trend of the roadway

Coefficient of lateral pressure

Cross-section shape

Position of the interlayer

Failure mode

Parallel Parallel Parallel Parallel Parallel Parallel Parallel Parallel Perpendicular Perpendicular Perpendicular Parallel Parallel Perpendicular Parallel Parallel Parallel Parallel Perpendicular Perpendicular Parallel Parallel

1.2 1.0 1.0 1.0 1.0 1.2 1.5 1.8 1.0 1.5 1.8 1.0 1.2 1.8 1.5 1.8 1.0 1.2 1.8 1.2 1.5 1.8

Semicircular arch Semicircular arch Semicircular arch Semicircular arch Semicircular arch Semicircular arch Semicircular arch Semicircular arch Semicircular arch Semicircular arch Semicircular arch Circular Semicircular arch Rectangular Rectangular Trapezoidal Trapezoidal Rectangular Semicircular arch Trapezoidal Semicircular arch Circular

Nothing Nothing Nothing Nothing Nothing Nothing Nothing Nothing Nothing Nothing Nothing Nothing Roof Floor Nothing Roof Floor Below roof Nothing Nothing Floor Below roof

Circular Circular Circular Circular Circular Circular Circular Circular Circular Elliptic Elliptic Circular Inverse triangle Triangle Diamond Inverse triangle Triangle Diamond Elliptic Circular Triangle Diamond

Table 9 Assignment of different factors levels. Specimen

Buried depth per 100 m

Angle per 10°

Lateral pressure coefficient

Section shape

Sandwich position

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22

7.0 8.6 9.6 12.0 9.6 9.6 9.6 9.6 9.6 9.6 9.6 7.0 7.0 7.0 8.6 8.6 9.6 9.6 9.6 12.0 12.0 12.0

0 9 0 0 0 0 0 0 9 9 9 0 0 9 0 0 90 0 9 9 0 0

1.2 1.0 1.0 1.0 1.0 1.2 1.5 1.8 1.0 1.5 1.8 1.0 1.2 1.8 1.5 1.8 1.0 1.2 1.8 1.2 1.5 1.8

1.1 1.1 1.1 1.1 1.1 1.1 1.1 1.1 1.1 1.1 1.1 1.0 1.1 1.3 1.3 1.2 1.2 1.3 1.1 1.2 1.1 1.0

0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 1.0 300.0 0.1 1.0 300.0 10.0 0.1 0.1 300.0 10.0

The test results shown in Fig. 16 are classified as follows: the surrounding rock failure mode of tests 1 and 14 is circular; the surrounding rock failure mode of tests 3, 11 and 12 is an ellipse; the surrounding rock failure mode of tests 2 and 8 is an inverted

triangle; the surrounding rock failure mode of tests 4, 9 and 15 is a regular triangle; the surrounding rock failure mode of tests 7, 10 and 16 is rhombohedral while the failure mode of tests 5, 6 and 13 is a transitional stage. Test results indicate that the coefficient of lateral pressure, the trend of the roadway as well as the position of the soft stratum of the surrounding rock have a significant impact on the failure mode, while the burial depth and the cross-sectional shape have less impact.

4. Study on the failure mode of deep roadway surrounding rock in Zhujixi coal mine The failure mode of the underground roadway surrounding rock in Zhujixi coal mine is identified by use of the fuzzy mathematics method. 22 specimens were selected. The failure mode and the corresponding function factor conditions of these specimens are listed in Table 8 [5]. Numbers are needed when calibrating the variation of each factor. According to the degree of variation of each factor, the shape of the roadway and the change of the soft interlayer are given different values to show the extent of their influence on the test results. Details are seen in Table 9. Before calibration of the specimens, different weights are assigned to influence factors, whose distribution is decided by their degree of influence in the test results. The specific distribution scheme can be seen in Table 10. The iterative method in Matlab is adopted to calculate the Clustering Center Matrix [5]. The 12 roadways were divided into 4 groups based on the different burial depths, orientations and maximum horizontal

Table 10 Weights assigned plan. Factors

Plan 1

Plan 2

Plan 3

Plan 4

Plan 5

Plan 6

Buried depth level Direction of roadway Lateral pressure coefficient Shape of roadway sandwich position

0.01 0.20 0.50 0.05 0.24

0.05 0.30 0.40 0.05 0.20

0.10 0.25 0.40 0.01 0.24

0.05 0.30 0.30 0.05 0.30

0.05 0.40 0.30 0.10 0.15

0.01 0.40 0.20 0.20 0.19

Vertical Parallel Parallel Parallel Parallel

Parallel

860 860 860 962 962 962

principal stress (see Table 11). A total of 6 typical failure modes of roadway were identified by clustering method. The test results shows that failure modes of the 952 m-length level-west main return way, 2#–12# intersection interval of roadway and bunker back cut crossheading connection are elliptic. Whereas the failure mode of the 962 m-depth No. 1 windstone gate is triangular. Circular style failure modes can be seen from the 860 m-depth level the total return airway and the combined return airway. The damage depth of the roadway surrounding rock loose circle test shows that the strike of 2#–12# intersection interval of the roadway, 962 m bunker back cut crossheading connection, is perpendicular to the direction of maximum horizontal principal stress. The side of the laneway is destroyed at a depth of 3.0 m all round, and close to 5.0–6.0 m at the baseboard, meanwhile the roof breakage phenomenon is serious. In both sides of the laneway of the 952 m-depth level-west main return way, the damage depth is 2.5–3.0 m. The floor rock mass is loose and broken and poor in integrity. The maximum damage depth is approximately 6.0 m, therefor it can be seen that the style of damage is oval. The strike of 962 m No. 1 windstone gate is parallel to the direction of maximum horizontal principal stress, and weak layers have been found in the floor. The maximum damage depth is 5.0 m or so. Both sides of the laneway of the 952 m-depth No. 1 windstone gate indicate that damage depth is 2.5 m on average and the surrounding rock failure pattern is in accordance with the regular triangular failure mode. The results of identified failure mode of the surrounding rock of roadways and the surrounding rock loose circle test are in good agreement.

Parallel Parallel Vertical Vertical Vertical Vertical

952 962 962

962

962

962

5. Conclusions

Buried depth (m) Orientation

Levels of total return air lane Western region of return airway on horizontal 2#–12# alternating point interval Roadway

Deputy united lane wind A Group

Table 11 Twelve samples of the Zhujixi mine.

Western region of orbital alleys

B

North of main shaft clean entry

No.1 the total return air Shekmun

No.2 the total return air Shekmun

Auxiliary orbit Shekmun

Level of orbit Shimen

C

Level of total return air roadway

Crossheading of main shaft coal bunker

Q. Meng et al. / International Journal of Mining Science and Technology 26 (2016) 209–221

D

220

(1) This paper describes studies of the displacement and evolutional law of the plastic zone and the stress distribution in the surrounding rock of a roadway with different burial depths, coefficient of lateral pressure and cross sectional shapes based on simulation by FLAC 3D. (2) The orthogonal test method with single and multiple factors was used to examine the relationship between the burial depth of a roadway, lateral pressure coefficient, trend of the roadway, direction of maximum horizontal principal stress, section shape and weak rock formations. Five failure modes were identified which include: circular, oval, del operator, regular triangle and rhombus. (3) Classification and pattern recognition of Zhujixi mine was completed with the clustering method in fuzzing mathematics, the results of which identified the failure mode of the surrounding rock of a roadway. Using this method and the results from surrounding rock loose circle tests are in good agreement, verifying the reliability of pattern recognition.

Acknowledgments Financial support towards this work was provided by the National Natural Science Foundation of China (Nos. 51322401, 51309222, 51323004, 51579239 and 51574223), the Opening Project Fund of Shandong Provincial Key Laboratory of Civil Engineering Disaster Prevention and Mitigation (No. CDPM2014KF03), the State Key Laboratory for GeoMechanics Opening Project Fund of Shandong Provincial Key Laboratory of Civil Engineering Disaster Prevention and Mitigation and Deep Underground Engineering, China University of Mining & Technology (No. SKLGDUEK1305) and China Postdoctoral Science Foundation (Nos. 2014M551700 and 2013M531424).

Q. Meng et al. / International Journal of Mining Science and Technology 26 (2016) 209–221

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