The mechanical properties and acoustic emission characteristics of thick hard roof sandstone were investigated. Samples were taken from the 30.87-m thick sandstone roof in a mine in the Shengdong coal field, China. Fi...The mechanical properties and acoustic emission characteristics of thick hard roof sandstone were investigated. Samples were taken from the 30.87-m thick sandstone roof in a mine in the Shengdong coal field, China. Firstly, the composition and microscopic characteristics were analyzed by XRD and FE-SEM, respectively. Moreover, the indirect tensile test, uniaxial compression test, three axis compression experiment and AE test are carried out by using RMT-150C mechanics experiment system with DSS-8B AE test system. The experiment results indicate that the main framework particles of sandstone are quartz and feldspar, and mainly quartz. Cements are mainly pyrite, kaolinite, chlorite and zeolite cross needle, clinochlore, and clay minerals. The microstructure of sandstone is very dense, with few pores and high cementation degree. The tensile strength, compressive strength and elastic modulus of sandstone are 4.825, 85.313 MPa, 13.814 GPa, respectively, so the sandstone belongs to hard rock. The AE cumulative counts of sandstone can be divided into three phases： relatively flat growth period, rapid growth period and spurt period. The signal strength of AE waveform can be used as a warning signal. In the tensile fracture zone, the warning value is 0.4 mV, and in the compression shear failure zone, it is 4 mV. The numbers of cumulative counts of AE under different stress conditions have obvious difference. Moreover, the growth of cumulative counts of acoustic emission is more obvious when the stress is more than 60% of the peak stress.展开更多
The paper presents the influence of varying immediate roof thickness on the lower strong roof strata movement and failure pattern in longwall coal mining with large mining height. The investigation is based on 58 geol...The paper presents the influence of varying immediate roof thickness on the lower strong roof strata movement and failure pattern in longwall coal mining with large mining height. The investigation is based on 58 geological drill holes and hydraulic shield pressure measurements around the longwall Panel 42105 of the Buertai Mine in Inner Mongolia Autonomous Region, China. The longwall Panel 42105 is characterized by relatively soft immediate roof strata of varying thickness superposed by strong strata,herein defined as lower strong roof. A voussoir beam model is adopted to interpret the structural movement of the lower strong roof strata and shield pressure measurements. It is shown that when the immediate roof is relatively thick, the broken overlying lower strong roof tends to form a stable voussoir beam with previously broken layer, thus not exerting high pressure on the hydraulic shield and working face. When the immediate roof is relatively thin, the broken overlying lower strong roof tends to behave as a cantilever beam, thus exerting higher pressure on the hydraulic shield and working face. Comparison of model predictions with measured time-weighted average shield pressure(TWAP) shows good agreement.展开更多
文摘The mechanical properties and acoustic emission characteristics of thick hard roof sandstone were investigated. Samples were taken from the 30.87-m thick sandstone roof in a mine in the Shengdong coal field, China. Firstly, the composition and microscopic characteristics were analyzed by XRD and FE-SEM, respectively. Moreover, the indirect tensile test, uniaxial compression test, three axis compression experiment and AE test are carried out by using RMT-150C mechanics experiment system with DSS-8B AE test system. The experiment results indicate that the main framework particles of sandstone are quartz and feldspar, and mainly quartz. Cements are mainly pyrite, kaolinite, chlorite and zeolite cross needle, clinochlore, and clay minerals. The microstructure of sandstone is very dense, with few pores and high cementation degree. The tensile strength, compressive strength and elastic modulus of sandstone are 4.825, 85.313 MPa, 13.814 GPa, respectively, so the sandstone belongs to hard rock. The AE cumulative counts of sandstone can be divided into three phases： relatively flat growth period, rapid growth period and spurt period. The signal strength of AE waveform can be used as a warning signal. In the tensile fracture zone, the warning value is 0.4 mV, and in the compression shear failure zone, it is 4 mV. The numbers of cumulative counts of AE under different stress conditions have obvious difference. Moreover, the growth of cumulative counts of acoustic emission is more obvious when the stress is more than 60% of the peak stress.
基金the fund supported by the National Natural Science Foundation of China(Grant No.U1261207)
文摘The paper presents the influence of varying immediate roof thickness on the lower strong roof strata movement and failure pattern in longwall coal mining with large mining height. The investigation is based on 58 geological drill holes and hydraulic shield pressure measurements around the longwall Panel 42105 of the Buertai Mine in Inner Mongolia Autonomous Region, China. The longwall Panel 42105 is characterized by relatively soft immediate roof strata of varying thickness superposed by strong strata,herein defined as lower strong roof. A voussoir beam model is adopted to interpret the structural movement of the lower strong roof strata and shield pressure measurements. It is shown that when the immediate roof is relatively thick, the broken overlying lower strong roof tends to form a stable voussoir beam with previously broken layer, thus not exerting high pressure on the hydraulic shield and working face. When the immediate roof is relatively thin, the broken overlying lower strong roof tends to behave as a cantilever beam, thus exerting higher pressure on the hydraulic shield and working face. Comparison of model predictions with measured time-weighted average shield pressure(TWAP) shows good agreement.
