Strength and energy exchange of deep sandstone under high hydraulic conditions

To investigate the influence of confining pressure and pore water pressure on strength characteristics,energy storage state and energy release intensity at peak failure of deep sandstone,a series of triaxial compression tests under hydraulic coupling conditions are carried out.By analyzing the process of rock deformation and failure,the stress thresholds of the rock are obtained.The change trend of total energy density,elastic energy density and dissipated energy density of deep sandstone in the pre-peak stage is obtained by the graphical integration method.By comparing the dynamic energy storage level of rocks under different confining pressures,the influence of pore water pressure on the energy dissipation at stress thresholds of crack closure stress,crack initiation stress,crack damage stress and peak stress is analyzed.Based on the ratio of pre-peak total energy density to post-peak total energy density,the interaction mechanism of confining pressure and pore water pressure for the rock burst proneness of deep sandstone is studied.The experimental results show that the peak stress of sandstone increases with the increase of confining pressure,while the existence of pore water pressure can weaken the peak stress of sandstone.In the stress stage from crack closure stress to peak stress,the dynamic energy storage level of rock presents a trend of the inverse“check mark”.Meanwhile,the larger the confining pressure,the higher the energy storage level of rock.However,the pore water pressure increases the degree of energy dissipation of rock and reduces the energy storage capacity of rock,and the degree of dissipation is linear with pore water pressure.The increase of confining pressure aggravates the instability and failure of deep sandstone,while pore water pressure has the opposite effect.The research results will provide necessary data support for the stability analysis of rock mass excavation in sandstone stratum under high stress and high pore water pressure.

Long-term mechanical behavior and characteristics of cemented tailings backfill through impact loading

Cemented tailings backfill(CTB)structures are important components of underground mine stopes.It is important to investigate the characteristics and dynamic behavior of CTB materials because they are susceptible to disturbance by dynamic loading,such as excavation and blasting.In this study,the authors present the results of a series of Split-Hopkinson pressure bar(SHPB)single and cyclic impact loading tests on CTB specimens to investigate the long-term dynamic mechanical properties of CTB.The stress-strain relationship,dynamic strength,and dynamic failure characteristics of CTB specimens are analyzed and discussed to provide valuable conclusions that will improve our knowledge of CTB long-term mechanical behavior and characteristics.For instance,the dynamic peak stress under cyclic impact loading is approximately twice that under single impact loading,and the CTB specimens are less prone to fracture when cyclically loaded.These findings and conclusions can provide a new set of references for the stability analysis of CTB materials and help guide mine designers in reducing the amount of binding agents and the associated mining cost.

夯实矸石压缩-固结蠕变成岩过程及等价采高模型分析

目的为了研究被夯实矸石压缩-固结蠕变成岩过程及其等价采高模型,方法以亭南煤业公司1102矸石充填工作面为工程背景,采用理论分析、数值模拟、室内试验、现场实测等方法进行研究。结果结果表明:矸石充填工作面最大控顶距=端面距+截割深度+顶梁长度+架后触矸距离;顶板回转下沉量等于最大控顶距乘以支架后倾角度正弦值;架后可充填空间高度等于采高减去顶板回转下沉量、欠接顶量、架后底鼓量。被夯实矸石在可充填空间内压缩-固结蠕变成岩的4个阶段及可充压缩率分别为骨架调整段(7.42%),缓慢压缩段(5.39%),固结沉降段(0.34%),蠕变成岩段(12.38%)。由该等价采高模型可知,1102工作面4阶段等价采高为骨架调整段0.94 m,缓慢压缩段1.10 m,固结沉降段1.11 m,蠕变成岩段1.48 m。结论通过概率积分法预测、数值模拟和沉陷观测对比可知,1102工作面走向和倾向主断面地表下沉曲线均为碗形。前两阶段地表下沉曲线平缓,后两阶段地表下沉曲线陡峭。