Application of high-pressure water jet technology and the theory of rock burst control in roadway

International Journal of Mining Science and Technology xxx (2016) xxx–xxx

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

Application of high-pressure water jet technology and the theory of rock burst control in roadway Yang Zengqiang a, Dou Linming b,⇑, Liu Chang a, Xu Mengtang c, Lei Zhen c, Yao Yahu d a

College of Resource & Safety Engineering, China University of Mining & Technology, Beijing 100083, China State Key Laboratory of Coal Resources & Mine Safety, China University of Mining & Technology, Xuzhou 221116, China c College of Mining Engineering, Guizhou Institute of Technology, Guiyang 550003, China d China Coal Technology & Engineering Group Chongqing Research Institute, Chongqing 400039, China b

a r t i c l e

i n f o

Article history: Received 1 December 2015 Received in revised form 8 January 2016 Accepted 21 March 2016 Available online xxxx Keywords: High-pressure water jet technology Rock burst Weak structure zone Dynamic and static combined load

a b s t r a c t This paper puts forward using high-pressure water jet technology to control rock burst in roadway, and analyzes the theory of controlling rock burst in roadway by the weak structure zone model. The weak structure zone is formed by using high-pressure water jet to cut the coal wall in a continuous and rotational way. In order to study the influence law of weak structure zone in surrounding rock, this paper numerically analyzed the influence law of weak structure zone, and the disturbance law of coal wall and floor under dynamic and static combined load. The results show that when the distance between high-pressure water jet drillings is 3 m and the diameter of drilling is 300 mm, continuous stress superposition zone can be formed. The weak structure zone can transfer and reduce the concentrated static load in surrounding rock, and then form distressed zone. The longer the high-pressure water jet drilling is, the larger the distressed zone is. The stress change and displacement change of non-distressed zone in coal wall and floor are significantly greater than that of distressed zone under dynamic and static combined load. And it shows that the distressed zone can effectively control rock burst in roadway under dynamic and static combined load. High-pressure water jet technology was applied in the haulage gate of 250203 working face in Yanbei Coal Mine, and had gained good effect. The study conclusions provide theoretical foundation and a new guidance for controlling rock burst in roadway. Ó 2016 Published by Elsevier B.V. on behalf of China University of Mining & Technology.

1. Introduction Rock burst refers to the dynamic process of sudden and intense release of elastic energy accumulated in coal-rock mass during underground mining [1]. Rock burst can cause disasters such as gas explosion, abnormal gas-effusion, water inrush and other major disasters. Statistics show that 75% of rock burst disasters have occurred in the haulage gate and material gate of working face. Therefore it is of great significance to study the prevention of rock burst technology in roadway [2–4]. Domestic and foreign scholars considered controlling rock burst in roadway from the aspects of pressure relief and support, and a lot of theoretical and practical research had been conducted. In the aspect of support, since 1960s, Rabcewicz put forward a new ‘‘NATM”. Since then, Jing et al. put forward the roadway support theory based on broken surrounding rock [5]. He et al. put forward the theory of key parts coupling combined support system, which ⇑ Corresponding author. Tel.: +86 13952261972. E-mail address: [email protected] (L. Dou).

realized the support system and surrounding rock to share the load to improve the stability of surrounding rock [6]. Kang et al. studied the characteristics of two kinds of high-stress roadway under the condition of strong dynamic pressure in deep mining, and put forward the theory of high pre-stress and strong support, and highstress roadway support design criterion [7]. Zhang et al. studied the stability control of surrounding rock in deep mining, and put forward the model of ‘‘three high” anchor control technology [8]. The previous research have formed mature support theories and technologies, however, the rock burst still occurs frequently in roadway. On the basis of support theory, many scholars had proceeded thorough researches in the aspect of pressure relief. Dou et al. put forward intensity weakening theory for rock burst [9]. Lu et al. put forward intensity weakening control theory for rock burst [10]. Gao established the mechanical model of ‘‘strong-softstrong” (3S) structure in rock-burst roadway [11]. Pan et al. studied the results of micro-seismic monitoring, and the theory of rock burst start-up was put forward [12]. The theory claimed that rock burst occurred in roadway had three periods: rock burst start-up, rock burst energy transfer and rock burst occurrence.

http://dx.doi.org/10.1016/j.ijmst.2016.05.037 2095-2686/Ó 2016 Published by Elsevier B.V. on behalf of China University of Mining & Technology.

Please cite this article in press as: Yang Z et al. Application of high-pressure water jet technology and the theory of rock burst control in roadway. Int J Min Sci Technol (2016), http://dx.doi.org/10.1016/j.ijmst.2016.05.037

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Z. Yang et al. / International Journal of Mining Science and Technology xxx (2016) xxx–xxx

The above research have important significance for support and prevention of rock burst. The studies pointed out the disadvantages of traditional ways of pressure relief on the basis of support methods in Yanbei Coal Mine. For instance, pressure release blasting in deep holes technology can produce a certain range of distressed zone by instantaneous blasting [13,14]. However, if the quantity of explosive is not reasonable, it may lead to insufficient pressure relief or release a lot of blasting energy and induce rock burst. High-pressure water injection technology has advantages of easy operation and low standard rate, but its mechanism is still a difficult problem and some of the construction process is determined by experience [15]. Large diameter drilling technology is easy to operate and its pressure-relief efficiency mainly depends on the diameter of drilling, however, the larger the drilling, the more energy and mechanical wear [16]. Lin et al. had successfully applied high-pressure water jet technology in the field of prevention of coal and gas outburst [17,18]. This paper creatively put forward using high-pressure water jet technology to control rock burst in roadway. This paper analyzed the influence law of weak-structure zone in roadway by mechanics model and FLAC3D numerical simulation, and the field test and field monitoring were applied in the haulage gate of 250203 working face in Yanbei Coal Mine. It shows that the distressed zone can effectively control rock burst under dynamic and static combined load. The authors attempt to propose a new approach for controlling rock burst based on the high-pressure water jet technology. 2. Prevention of rock burst mechanism in weak structure zone 2.1. Weak structure zone There are two ways for high-pressure water jet to cut the coal. Fig. 1a demonstrates that high-pressure water jet can cut the coal in a discontinuous and rotational way. Fig. 1b demonstrates that it can cut the coal in a continuous and rotational way. The way of Fig. 1a can achieve pressure relief and strong permeability in the coal, and this way can provide advantageous condition for gas release and stress relieving. The way of Fig. 1b can form large range of distressed zone, and the distressed zone can transfer and reduce the concentrated static load. The way of Fig. 1b can form weak structure zone in the coal and effectively control rock burst. 2.2. Mechanism of weak structure zone When the roadway is excavated, the in-situ stress field is destroyed in strata, and the stress in roadway surface is relieved, so that the surrounding rock changes from triaxial stress state to plane stress state. It means that the in-situ stress field will form a new state of plane stress, and there will form concentrated static load in roadway. According to the energy criterion, when the releasable energy stored in coal-rock mass is greater than the energy itself consumed, the system of coal-rock mass breaks its

own equilibrium state and rock burst occurs. The energy judgment criterion of rock burst is expressed as Eq. (1).

dEs dEr dEb þ > dt dt dt

ð1Þ

where Es is the energy stored in coal; Er the energy stored in rock; and Eb the energy consumed when rock burst occurred. According to the energy criterion, when the roadway is excavated, the concentrated static load rs and the concentrated dynamic load rd can induce rock burst, as shown in Fig. 2. The energy judgment criterion of rock burst is expressed as Eq. (2).

dEs dEr dEd dEb þ þ > dt dt dt dt

ð2Þ

where Ed is the energy of the concentrated dynamic load. Eqs. (1) and (2) demonstrate the mechanism of two kinds of typical rock burst in roadway from the perspective of energy criterion. When a new roadway is excavated, using high-pressure water jet to cut the coal wall can transfer the concentrated static load rs to the deep coal wall and reduce the its maximum peak. New concentrated static load r0s and new energy E0s will be stored in the deep coal wall. In this process, the variation of energy stored in the coal wall is expressed as Eq. (3).

E ¼ Es  E0s

ð3Þ

where E is the variation of energy stored in the coal wall. Using high-pressure water jet to cut the coal wall, a certain range of weak structure zone can be formed in the coal wall. The weak structure zone makes coal wall produce a certain extent of plastic deformation. Its strength becomes low and its porosity becomes large. With the change of physical properties of coalrock mass in the weak structure zone, the travel time of elastic stress wave will add Dt. When the energy of concentrated dynamic load goes through the weak structure zone in the form of elastic stress wave, the weak structure zone can scatter and absorb the elastic stress wave and the elastic stress wave will decay. The weak structure zone can effectively weaken the influence of dynamic and static combined load in roadway. As there is a weak structure zone, the energy judgment criterion of rock burst is expressed as Eq. (4). 0

dEs dEr dEd dEb þ þ < dðt þ DtÞ dðt þ DtÞ dðt þ DtÞ dt

ð4Þ

where Ed is the energy of concentrated dynamic load; and Dt the addition of travel time. Weak structure zone is formed by using high-pressure water jet technology. This technology can make the maximum peak of original concentrated static load rmax reduce to r0max , and it also lets the maximum peak area move to the deep coal wall, and in the width range of B, the average value of concentrated static load Pn decreases to a low level. Based on Terzaghi theory, the mechanical model of Fig. 3 shows that when the floor of OCDF area is in a

Drilling

䫫ᆄ Drilling

㕍‭ Distressed ন঻オ䰤 zone オ䰤

Distressed zone (a) Intermittent rotary cutting

(b) Continuous rotary cutting

Fig. 1. High-pressure water jet cutting the coal schematic diagram.

Please cite this article in press as: Yang Z et al. Application of high-pressure water jet technology and the theory of rock burst control in roadway. Int J Min Sci Technol (2016), http://dx.doi.org/10.1016/j.ijmst.2016.05.037

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working face by FLAC3D numerical simulation software. The location of model is shown in the red dashed box of Fig. 4. The model size is 100 m  85 m  60 m (length  width  height), and the roadway size is 5 m  3.8 m (width  height). In order to study the stress distribution of different lengths of high-pressure water jet drilling in coal wall, such as 0, 10, 15, 20 m, the FLAC3D model sets a width of 40 m in both sides of the roadway. Based on the surface-underground contrast plan of Yanbei Coal Mine, the dead weight uniform load of 9.0 MPa is applied to the upper boundary of model. When static load is calculated, the normal direction of the model boundary is fixed at X = 57.5 m, X = 42.5 m, Y = 45 m, Y = 40 m and Z = 25.5 m. When dynamic load is calculated, surrounding boundaries of the model are set to static state, lower boundary of the model is set to be as free state, and the acceleration of gravity is 9.8 m/s2. The mechanical parameters of the coal-rock mass are summarized in Table 1. In the process of excavating roadway, the surrounding rock is damaged under elastic stress and tensile stress combined. The model is founded by Mohr-Coulomb strain softening elements, and the mechanical parameters of the coal-rock mass are presented in Table 1. Based on the results of Dou et al, the optimal distance between high-pressure water jet drillings is 3 m and its diameter is 300 mm [20]. According to the actual size of the drilling bit, the diameter of drilling segment is 100 mm. The FLAC3D numerical simulation model is shown in Fig. 5.

Ed Stress curve of pressure relief

σmax

σ ′max

Original stress curve

Es'

Es Roadway Weak structure zone

Fig. 2. Weak structure zone model of controlling rock burst in roadway.

σ max

σ ′max

B

B

Roadway

Pu

Pu q A'

O' N' C'

F'

F D'

A

O N

D

C

Fig. 3. Mechanical model of limit equilibrium in roadway [19].

plastic limit-equilibrium state, the average value of concentrated static load in the width range of B is shown as Eq. (5).

Pu ¼

1 rBNr þ qNq þ CNc 2

ð5Þ

where Nr, Nq, and Nc are the load capacity coefficient; r the density of coal; q the floor support reaction force; and C the average bond strength of floor. Eq. (5) demonstrates that Pu is related to the mechanical parameter of floor. When Pn P Pu, the average value of concentrated static load in the width range of B exceeds the limit load capacity of floor, and the floor is transformed into a plastic stress state; when using high-pressure water jet to cut the coal wall, P0n is much less than Pn, which means that a stable elastic state forms easily in the floor, and the floor has a weak influence on dynamic and static combined load. It can be concluded that the weak structure zone has a certain influence on controlling rock burst in floor, as shown in Fig. 3.

3.2. Numerical simulation results of static load As shown in Fig. 6, the vertical stress distribution in distressed zone is obviously lower than that in non-distressed zone. The numerical simulation results demonstrate that using highpressure water jet to cut the coal wall can transfer and reduce the concentrated static load, and there will form a certain range of weak structure zone in the coal wall. As shown in Fig. 7a and b, the 2D model of stress nephogram is constructed in a vertical cross-section in the X–Z plane in the 3D model where the field of high-pressure water jet drillings exists. The results show that the stress distribution of drilling segments is independent of each other, and the stress distribution of highpressure water jet drilling segments can form continuous stress superposition zone. The coal-rock mass in continuous stress superposition zone is fractured and weathered, and then a ‘‘weak structure” zone can be formed. It is concluded that the large diameter

Table 1 Mechanical parameters of the coal-rock mass.

3. Numerical simulation of weak structure zone under concentrated dynamic and static combined load 3.1. Model foundation Based on the geological conditions of 2502 mining area in Yanbei Coal Mine, the coal seam dip angle is 5–15°, and it is relatively slow. This paper investigates the simplified haulage gate of 250203

Rock type

T (m)

K (GPa)

G (GPa)

c (kg/m3)

u (°)

c (MPa)

Siltstone Mudstone Coal

19 5 36

6.8 4.4 2.7

4.80 2.60 0.85

2550 2100 1350

30 26 22

2.00 1.20 0.87

Note: c is the unit weight; K the bulk modulus; G the shear modulus; c the cohesion; u the internal friction; and T the thickness.

Tunneling place 250203 haulage gateway Crossheading

250203 working face

250203 materials gateway 250204 haulage gateway 250204 working face 250204 materials gateway 250205 working face

Fig. 4. No. 2502 mining area working face layout (2012.11.15).

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in Fig. 8, the longer the length of high-pressure water jet drilling segment, the greater the distressed zone. In the Z direction, with the increase of distance, different lengths of high-pressure water jet drilling segment have the similar change law, and the highpressure water jet drilling segments have a weak influence over its 1.5 m (Z > 1.5 m).

m

85 m

10 0

Siltstone Mudstone

Tunneling place Weak structure zone

Coal

60

3.3. Numerical simulation results of dynamic and static combined load

m

High-pressure water jet drilling segment

250203 haulage gateway

Z

X

Y

Drilling segment

Fig. 5. FlAC3D numerical simulation model.

Weak structure zone (Pa) SZZ 07 0 1.4E++007 1.2E +007 E 1.0

40 0 3 0 2 0 1 W or 0 kin g f -10 0 ac e ( -2 0 m) -3

0

-4

0 04 03 ) 0 2 n (m 1 0 io 0 rect -1 i 20 ing d 0 v -3 dri 0 -4 way d 0 a -5 Ro

1.33E+007 1.32E+007 1.31E+007 1.30E+007 1.29E+007 1.28E+007 1.27E+007 1.26E+007 1.25E+007 1.24E+007

Fig. 6. Vertical stress distribution in coal wall.

(300 mm) of high-pressure water jet drilling segments can easily form weak structure zone than drilling segments (100 mm). As shown in Fig. 7c and d, the 2D model of stress nephogram is constructed in a vertical cross-section in the Y–Z plane in the 3D model where the field of high-pressure water jet drillings exists and doesn’t exist. It is concluded that the weak structure zone can effectively transfer and reduce the concentrated static load in coal wall. The high-pressure water jet drilling segments can form a weak structure zone, and the drilling segments can make the strong structure of coal wall have better yielding function. The vertical stress distribution of different lengths of highpressure water jet drilling segment is shown in Fig. 8. As shown

3m

Drilling (100 mm)

-6.9106E+06 -7.0000E+06 -7.5000E+06 -8.0000E+06 -8.5000E+06 -9.0000E+06 -9.5000E+06 -1.0000E+07 -1.0500E+07 -1.1000E+07 -1.1500E+07 -1.2000E+07 -1.2500E+07 -1.3000E+07 -1.3500E+07 -1.4000E+07 -1.4500E+07 -1.5000E+07 -1.5125E+07

(c) Stress distribution of non-distressed zone

AðtÞ ¼

1 A0 ½1  cosð2pftÞ 2

ð6Þ

where A0 is the maximum stress value of pulse; and f the frequency of pulse. FLAC3D numerical simulation software can analyze nonlinear dynamic response. The maximum stress value of pulse is 15 MPa and the frequency of pulse is 100 Hz. The dynamic calculation lower boundary of 3D model is static and around the 3D model is free field boundary. The 3D model uses Rayleigh damping and the minimum center frequency value of Rayleigh damping xmin is the natural frequency value of 3D model, and the minimum critical damping ratio of Rayleigh damping nmin refers to the properties of geotechnical materials, and the values are 50 Hz and 0.5. Setting the dynamic monitoring time is 0.1 s [21]. Setting monitoring points in the coal wall and floor of distressed zone and non-distressed zone, and the change law of monitoring points under dynamic and static combined load is shown in Fig. 9. As shown in Fig. 9, the dynamic response time of distressed zone’s surrounding rock is later than that of non-distressed zone’s surrounding rock, and the result demonstrates that the weak structure zone can add the travel time of elastic stress wave. As shown in Fig. 9a, the initial stress monitoring point value of non-distressed zone’s coal wall is larger than that of distressed

Continuous stress superposition zone

3m High-pressure water jet drilling (300 mm)

-7.4992E+06 -7.5000E+06 -8.0000E+06 -8.5000E+06 -9.0000E+06 -9.5000E+06 -1.0000E+07 -1.0500E+07 -1.1000E+07 -1.1500E+07 -1.2000E+07 -1.2500E+07 -1.3000E+07 -1.3500E+07 -1.4000E+07 -1.4500E+07 -1.5000E+07 -1.5500E+07 -1.6000E+07 -1.6360E+07

(b) Stress distribution of high-press water jet drilling segments

(a) Stress distribution of drilling segments

Concentrated static load

The haulage gate of 250203 working face is near 250204 working face, and the mine-induced and roof-weighting events have a strong influence in the haulage gate. This may lead to rock burst disasters in the haulage gate. The dynamic load can be expressed in the form of elastic stress wave, and the elastic stress wave is applied to the upper boundary of 3D model. The range of elastic stress wave is concentratedly applied to the upper boundary of X 2 [0, 100], Y 2 [0, 5]. The time function of wave is expressed as Eq. (6).

-1.2926E+05 -1.0000E+06 -2.0000E+06 -3.0000E+06 -4.0000E+06 -5.0000E+06 -6.0000E+06 -7.0000E+06 -8.0000E+06 -9.0000E+06 -1.0000E+07 -1.1000E+07 -1.2000E+07 -1.3000E+07 -1.4000E+07 -1.4961E+07

High-pressure water jet drilling

Weak structure zone

-1.4947E+05 -1.0000E+06 -2.0000E+06 -3.0000E+06 -4.0000E+06 -5.0000E+06 -6.0000E+06 -7.0000E+06 -8.0000E+06 -9.0000E+06 -1.0000E+07 -1.1000E+07 -1.2000E+07 -1.3000E+07 -1.4000E+07 -1.5000E+07 -1.5418E+07

(d) Stress distribution of distressed zone

Fig. 7. Different stress nephogram of coal wall in non-distressed and distressed zone.

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Z. Yang et al. / International Journal of Mining Science and Technology xxx (2016) xxx–xxx 1.3E+7 Pa 1.1E+7 Pa 9.3E+6 Pa 7.3E+6 Pa

0m 10 m 15 m 20 m

5.3E+6 Pa 3.3E+6 Pa 1.3E+6 Pa -50 m

-30 m

-10 m

10 m

30 m

50 m

30 m

50 m

30 m

50 m

(a) Z=0.5 m

1.3E+7 Pa 1.1E+7 Pa 9.1E+6 Pa 7.1E+6 Pa 5.1E+6 Pa 3.1E+6 Pa 1.1E+6 Pa -50 m

-30 m

-10 m

10 m

(b) Z=1.0 m 1.3E+7 Pa 1.1E+7 Pa 8.9E+6 Pa 6.9E+6 Pa

can effectively diminish the influence of dynamic disturbance, which is caused by dynamic and static combined load. As shown in Fig. 9c, the stress monitoring point value of floor has the similar change law. The stress monitoring point value decreases 0.59 MPa in non-distressed zone’s floor, and the stress monitoring point value decreases 0.43 MPa in distressed zone’s floor. It can be concluded that the weak structure zone in coal wall also has indirect function in floor. As shown in Fig. 9b and d, when the dynamic monitoring time is over, the displacement monitoring point value increases 9.24 cm in non-distressed zone’s coal wall, and the displacement monitoring point value increases 3.96 cm in distressed zone’s coal wall. The displacement monitoring point value increases 2.07 cm in nondistressed zone’s floor, and the displacement monitoring point value increases 1.04 cm in distressed zone’s floor. It can be concluded that the weak structure zone in coal wall can diminish the instantaneous deformation in coal wall and floor, and it can effectively prevent the distressed zone’s roadway from breaking down. In a short period of dynamic monitoring time, the surrounding rock of non-distressed zone can reduce more stress value and increase more displacement. It means that the surrounding rock of non-distressed zone can release more elastic energy than surrounding rock of distressed zone; therefore, the roadway of nondistressed zone is more likely to have rock burst.

4.9E+6 Pa 2.9E+6 Pa

4. Engineering example

9.0E+5 Pa -50 m

-30 m

-10 m

10 m

(c) Z=1.5 m

Fig. 8. Vertical stress distribution above the high-pressure water jet drilling segments.

zone’s coal. Under the dynamic and static combined load, the stress monitoring point value has a strong volatility change. When the dynamic monitoring time is over, the stress monitoring point value decreases 4.37 MPa in non-distressed zone’s coal wall, and the stress monitoring point value decreases 2.25 MPa in distressed zone’s coal wall. It can be concluded that the weak structure zone 1.4E+7

Non-distressed curve

1.2E+7

0.40

Distressed curve

0.35

Displacement (m)

1.0E+7

Stress (Pa)

250203 working face is the fourth working face of 2502 mining area in Yanbei Coal Mine, and at the same time, it is the next main working face. Since the haulage gate of 250203 working face was excavated, the strong mine pressure frequently occurred, and it was easy to cause the occurrence of rock burst in roadway. In late November 2012, the workers began to use high-pressure water jet equipment to cut the coal wall in a continuous and rotational way. By the end of December 2012, a total of 16 group highpressure water jet drillings finished, and each group contained two high-pressure water jet drillings. Using the SOS micro-seismic monitoring system of Yanbei Coal Mine analyzed the energy events greater than or equal 103 J in the haulage gate of 250203 working

8.0E+6 6.0E+6 4.0E+6 2.0E+6 0

0.30 0.25 0.20 0.15 0.10 0.05

0.02

0.04

0.06

0.08

0

0.10

Time (s) (a) Stress of coal wall

0.02

0.04

0.06 0.08 Time (s) (b) Displacement of coal wall

0.10

2.1E+6 1.8E+6

0.12

Displacement (m)

Stress (Pa)

1.5E+6 1.2E+6 9.0E+5 6.0E+5

0.10

0.08

3.0E+5 0

0.02

0.04

0.06

Time (s) (c) Stress of floor

0.08

0.10

0

0.02

0.04 0.06 0.08 Time (s) (d) Displacement of floor

0.10

Fig. 9. Stress and displacement curve under dynamic and static combined load.

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Z. Yang et al. / International Journal of Mining Science and Technology xxx (2016) xxx–xxx 10 3 -10 4 J 10 4 -10 5 J 10 5 -10 6 J

Tunneling place 250203 haulage gateway 250203 materials gateway

Cro sshe adin g

6

250203 working face

(2)

250204 haulage gateway 250204 working face 250204 materials gateway 250205 working face (a) 2012.10.1 - 2012.11.15

250203 haulage gateway 250203 materials gateway

Cro sshe adin g

Distressed zone Tunneling place

250203 working face

250204 haulage gateway 250204 working face 250204 materials gateway

(3)

250205 working face (b) 2013.1.1- 2013.2.1 Distressed zone

250203 materials gateway

sshe Cro

250203 haulage gateway

adin

g

Tunneling place

250203 working face

250204 haulage gateway 250204 working face 250204 materials gateway

(4)

250205 working face

(c) 2013.2.1-2013.3.1

Fig. 10. Locations of energy events in haulage gate of 250203 working face.

face, and filtered out the energy events of the roof and above in the haulage gate. The locations of energy events in haulage gate of 250203 working face are shown in Fig. 10. Before using the high-pressure water jet technology to cut the coal wall of 250203 haulage gate of 250203 working face, the locations of energy events in haulage gate is shown in Fig. 10a. It is known from Fig. 10a that the 250204 working face closes to the haulage gate of 250203 working face in early November 2012, and there are many large energy events in the haulage gate of 250203 working face. As shown in Fig. 10b and c, after using the high-pressure water jet technology to cut the coal wall, there can form a distressed zone in coal wall, and there is not energy events greater than or equal 103 J in the distressed zone in January and February 2013. It concluded that a weak structure zone can be formed by using high-pressure water jet technology to cut the coal wall of 250203 haulage gate, and then strong-soft-strong structure is formed. The strong-soft-strong structure can effectively reduce the dynamic and static combined load in 250203 haulage gate, and it can also make the surrounding rock not form concentrated load zone. The higher the concentrated load is accumulated in the surrounding rock, the more possibly and easily a large amount of energy can be released. Energy events indicate that there is not concentrated load zone in the surrounding rock of 250203 haulage gate after pressure relief. Engineering example result is consistent with theoretical analysis and numerical simulation results. 5. Conclusions (1) Using high-pressure water jet to cut the coal wall in a continuous and rotational way can form large range of distressed zone, and the distressed zone can transfer and

(5)

reduce the concentrated static load, and it also lets the maximum peak area move to the deep coal wall. It is an effectively way to control rock burst. Analyzing the theory of controlling rock burst in roadway by the weak structure zone model, the weak structure zone can weaken the influence of dynamic and static combined load in coal wall and floor in terms of the energy criterion. The weak structure zone can also transfer and reduce the concentrated static load, and this can release the energy stored in the surrounding rock. When the energy of concentrated dynamic load goes through the weak structure zone in the form of elastic stress wave, the weak structure can scatter and absorb the elastic stress wave, and the travel time of elastic stress wave will add. The weak structure can effectively reduce the influence of dynamic and static combined load in roadway. Under static load condition, when the distance between high-pressure water jet drillings is 3 m and its diameter is 300 mm, the stress distribution of high-pressure water jet drilling segments can form continuous stress superposition zone and the surrounding rock of continuous stress superposition zone is fractured and weathered, and then a weak structure zone can be formed. As the diameter of drilling is 100 mm, the stress distribution of drilling segments is independent of each other, but they can make the strong structure near roadway surface have better yielding function. Under dynamic and static combined load condition, the dynamic response time of distressed zone’s surrounding rock is later than non-distressed zone’s surrounding rock, and the stress monitoring point value decreases more in the roadway of non-distressed zone than that in the roadway of distressed zone, and the displacement monitoring point value increases more in the roadway of nondistressed zone than that in the roadway of distressed zone. It concludes that the surrounding rock of non-distressed zone can reduce more stress value and increase more displacement, and it means that the surrounding rock of nondistressed zone can release more elastic energy and it is more likely to occur rock burst. The engineering example result is consistent with theoretical analysis and numerical simulation results. The study conclusions provide theoretical foundation and a new way for controlling rock burst in roadways by high-pressure water jet technology.

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Please cite this article in press as: Yang Z et al. Application of high-pressure water jet technology and the theory of rock burst control in roadway. Int J Min Sci Technol (2016), http://dx.doi.org/10.1016/j.ijmst.2016.05.037

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Please cite this article in press as: Yang Z et al. Application of high-pressure water jet technology and the theory of rock burst control in roadway. Int J Min Sci Technol (2016), http://dx.doi.org/10.1016/j.ijmst.2016.05.037