单轴压缩破坏下分层型煤电阻率响应分析

Analysis of resistivity response of stratified briquette during uniaxial compres-sion

地层电阻率是地球物理勘探考察的重要参数,不同结构煤体受载破坏过程中电阻率变化特征存在差异。建立受载煤样电阻实时测试实验系统,对所压制未分层及不同厚度、不同强度的2分层型煤试样进行了单轴压缩实验,得出试样破坏过程的力学强度及电阻率变化规律,研究分层界面影响下不同结构型煤的电阻率响应特征。实验结果表明:型煤单轴压缩破坏下的电阻率呈现阶段性变化,未分层试样在压密后存在“U”型变化过程,最低点接近试样应力应变曲线屈服点;不同强度分层试样破坏过程中电阻率曲线先增加后呈现“U”型,破坏后电阻率为初始状态的2~4倍;不同厚度分层试样破坏过程中电阻率表现为先增后减,两分层厚度差异大的试样厚分层破坏更为剧烈,整体表现出的宏观电阻率值更大。分层试样弹性模量及抗压强度均较未分层试样小,峰值应力处的电阻率变化率为1~2,未分层试样则小于0.5;试样两分层厚度及强度越接近,压缩破坏产生的剥离部分越均匀,更容易产生区域“串-并联”现象,破坏后电阻率变化率越大。煤样本身或分层面空隙骨架的挤压破碎会导致煤层电阻率的增加。分层型煤试样破坏后表现出表面剥离,裂隙均匀连通的破坏形式,根据型煤受载破坏过程得出试样存在“纵向裂隙”和“纵向+横向裂隙”影响下电阻率变化数学模型。两分层及贯通界面的裂隙使试样呈“串-并联”形式连通电路,试样整体电阻率与裂隙电阻率及裂隙体积占比呈正相关。对分层型煤单轴压缩规律的描述反映了部分煤矿区地层物探过程中的电学各向异性特征。

Resistivity is a key physical parameter in geophysical exploration,and the characteristics of resistivity variation with different coal structures are different during its failure.Real-time resistance test system for coal samples under compression was established.Uniaxial compression experiments were carried out on two-layered briquette samples with different thickness and strength.According to the mechanical strength and resistivity variation during the failure process,the resistivity response characteristics of different structural briquette under the influence of layered interface were studied.The results show that the resistivity of briquette under load failure presents a phased change,and the unstratified sample has a u-shaped change after compaction,and the lowest point coincides with the yield point of the stress-strain curve of the sample.In the process of failure,the resistivity of the stratified samples with different thickness first increased and then decreased.Stratified samples with a larger difference in thickness of the two layers were more severely damaged,and the overall macroscopic resistivity value was larger.Also,the resistivity curves of stratified samples with different strength first increased and then presented a“U”shape.After failure,the resistivity was 2-4 times of that at the initial state.The elastic modulus and compressive strength of the stratified sample are lower than those of the non-stratified sample,and the rate of resistivity change at the peak stress is 1-2,while that of the non-stratified sample is less than 0.5.The closer the thickness and strength of the two layers,the more uniform the peeling part generated by compression.The more apt the regional“series-parallel”phenomenon,the greater the resistivity change rate after failure.The squeezing and breaking of the coal sample body or the interlayer void skeleton will lead to an increase in the resistivity of the coal seam.After the failure of the stratified briquette,the surface is exfoliated and the cracks are uniformly connected.According to the failure process of the briquette under load,the mathematical model of resistivity change under the influence of“longitudinal cracks”and“longitudinal+lateral cracks”in the sample was obtained.The cracks in the two layers and through the interface of the two layers make the sample into a“series-parallel”connected circuit,and the overall resistivity of the sample is positively correlated with the crack volume proportion.The description of uniaxial compression law of stratified briquette reflects the electrical anisotropy characteristics in strata geophysical exploration in some coal mines.