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Gold Science and Technology ›› 2022, Vol. 30 ›› Issue (6): 923-934.doi: 10.11872/j.issn.1005-2518.2022.06.126

• Mining Technology and Mine Management • Previous Articles    

Study on Failure Characteristics of Inclined Soft and Hard Interbedded Rocks Based on Acoustic Emission

Kefan ZHOU(),Kewei LIU(),Tengfei GUO   

  1. School of Resources and Safety Engineering,Central South University,Changsha 410083,Hunan,China
  • Received:2022-09-21 Revised:2022-10-30 Online:2022-12-31 Published:2023-01-06
  • Contact: Kewei LIU E-mail:Zkf52598@163.com;Kewei_liu@126.com

Abstract:

With the economic development,people’s demand for deep resource mining is increasing day by day.Underground projects are more and more frequently carried out in deep,and deep mining of metal mines has gradually become the norm.Soft and hard interbedded rocks generally exist in deep mines.Compared with ordinary rocks,they are more prone to destabilization and failure under disturbance and stress.Therefore,it is of great significance to study the failure characteristics of soft and hard interbedded rocks.In this paper,combined with acoustic emission technology,uniaxial compression tests were carried out on the soft and hard interbedded rock samples with dip angle composed of red sandstone and concrete,and the collected acoustic emission data,such as acoustic emission number,acoustic emission rate,b value,AF-RA value,were processed and analyzed.The conclusions are as follows:(1)According to the influence of dip angle on the failure mode of soft and hard interbedded rock,it can be divided into four categories,namely axial failure,soft layer failure,interface slip and Splitting failure.(2)When the dip angle of soft and hard interbedded rocks changes from 0 ° to 90 °,the peak compressive strength curve presents a N-shaped change.(3)Based on the classification method of rock failure process proposed by Boyce and the cumulative acoustic emission number,the failure process of soft and hard interbedded rocks with different dip angles is classified.(4)The dip angle of the soft layer has a significant influence on the stability of the rock.(5)When the dip angle of the soft layer increases,the area with high acoustic emission rate will move backward and narrow,and the cracks are more likely to occur intensively,leading to instability and failure.(6)In the process of uniaxial compression,the state of instability propagation is affected by the inclination angle,which increases first,then decreases,and then increases with the increase of the inclination angle.(7) With the increase of the dip angle,the proportion of shear cracks in the failure process of soft and hard interbedded rocks increases first,then decreases,and then increases again.The research results can provide reference for solving the engineering problems of soft and hard interbedded rocks.

Key words: layered rock, soft and hard interbedding, acoustic emission, b value, crack propagation, AF-RA value

CLC Number: 

  • TU457

Fig.1

Soft and hard interbedded specimen with inclination from 0 ° to 90 °"

Tabel 1

Mechanical properties of concrete and rock"

材料样品编号抗压强度/MPa密度/(g·cm-3)泊松比弹性模量/GPa
混凝土concrete-1392.020.2532.70
concrete-2432.130.2832.02
concrete-3422.070.2732.55
红砂岩red sandstone-1552.420.2036.20
red sandstone-2552.440.2037.00
red sandstone-3572.450.2137.20

Table 2

Parameter settings of the acoustic emission device"

参数数值
门槛值/dB40
前置增益/dB40
采样长度/kB5
采样频率/MHz10
PDT/μs50
HLT/μs300
HDT/μs200

Fig.2

Schematic diagram of the experimental device"

Fig.3

Failure results and failure mode classification of samples with different inclination angles in the experiment"

Table 3

Basic information of the sample"

试样编号θ/(°)软层厚度/mm抗压强度/MPa破坏模式
A-1019.7042.19轴向破坏
A-2020.0743.80轴向破坏
A-3019.9737.01轴向破坏
B-122.520.0752.29软层破坏
B-222.520.1746.96软层破坏
B-322.519.8549.80软层破坏
C-14519.782.85界面滑移
C-24519.921.39界面滑移
C-34520.232.90界面滑移
D-167.519.922.60界面滑移
D-267.519.892.12界面滑移
D-367.519.352.55界面滑移
E-19019.8854.12劈裂破坏
E-29020.0349.28劈裂破坏
E-39019.7457.49劈裂破坏

Fig.4

Variation of uniaxial compressive strength of sample with the inclination angles of the soft layer"

Fig.5

Schematic diagram of Mohr-Coulomb failure criterion"

Fig.6

Cumulative acoustic emission number curve during rock loading"

Fig.7

Stress,cumulative acoustic emission number and acoustic emission rate curves and loading process segmentation diagram with different inclination angles"

Table 4

Failure stages of specimens with different inclination angles during loading"

θ/(°)破坏阶段
0裂纹闭合,线弹性变形,裂纹非稳定扩展
22.5裂纹闭合,裂纹稳定扩展,裂纹非稳定扩展
45裂纹闭合,裂纹稳定扩展,裂纹非稳定扩展
67.5裂纹闭合,裂纹稳定扩展,裂纹非稳定扩展
90裂纹闭合,线弹性变形,裂纹稳定扩展,裂纹非稳定扩展

Fig.8

b value and stress curve under different inclination angles of the soft layer"

Fig.9

Acoustic emission parameters"

Fig.10

AF-RA crack classification diagram"

Fig.11

Distribution of AF-RA value at different angles"

Fig.12

Variation trend of shear crack propagetion with inclination angles corresponding to different C0 values"

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