湿热力作用下粉砂质泥岩开裂特性研究

Study on Fracturing Characteristics of Silty Mudstone under Moisturethermo-mechanical Loading Conditions

为探究湿热力作用下粉砂质泥岩的开裂特性,开展裂隙演化试验,得到湿热力单因素及多因素耦合循环作用下粉砂质泥岩的裂隙演化规律,同时利用X射线衍射、扫描电镜研究其微观结构变化特征,分析宏观和微观试验结果关联性,揭示湿热力作用下粉砂质泥岩裂隙扩展机制.研究结果表明:粉砂质泥岩裂隙发育表现为增长-平缓趋势;在单因素循环作用中,湿度循环(浸水~烘干)最易造成粉砂质泥岩开裂,温度循环(5~60℃)次之,荷载循环(0~50 kPa)最弱;在多因素耦合循环作用中,裂隙发育程度排序为:湿热力>湿热>湿力>热力,验证了湿度循环致裂性最强的结论.湿热力耦合循环作用15次后裂隙率达0.92%,裂隙条数增至30条,平均长度延伸至60.58 mm,而平均宽度稳定在0.47 mm左右.孔隙率与裂隙率的灰关联度最大,为0.813,即微观结构变化中孔隙发育与裂隙扩展的关联程度最大.湿热力耦合循环作用中,湿度循环引起黏土矿物晶层间距变化,导致颗粒破碎、孔隙扩张形成微裂隙,温度循环使试样产生差异性热应力、水分分布,促使微裂隙发育贯通,荷载作用增加尖端应力,最终导致裂隙网络形成.

To investigate the fracture characteristics of silty mudstone under moisture-thermo-mechanicalconditions,fracture evolution tests were carried out,and the fracture development of silty mudstone under single-factor cycles and multi-factor coupling cycles was obtained.Meanwhile,X-ray diffraction and scanning electron microscope were employed to examine the microstructural change of silty mudstone.By combining the correlation of macro and micro test results,the crack propagation mechanism of silty mudstone under moisture-thermo-mechanical conditions was revealed.The results show that the fracture development of silty mudstone under moisture-thermo-mechanical conditions generally exhibits a growth-gentle trend.Under single-factor cycles,humidity cycles(soaking-drying)are most likely to cause fracturing of silty mudstone,followed by temperature cycles(5~60°C)and mechanical cycles(0~50 kPa).Under multi-factor coupling cycles,their order to cause fracturing is moisture-thermo-mechanical cycles,moisture-thermo cycles,moisture-mechanical cycles,and thermo-mechanical cycles,which verifies the finding that humidity cycles are the dominant factor in causing fractures.After 15 moisture-thermo-mechanical cycles,the fracture rate can reach 0.92%,the number of fractures increases up to 30,the average fracture length extends to 60.58 mm,and the average fracture width is stable at about 0.47 mm.The gray correlation between the porosity and fracture rate is the largest,which is 0.813,indicating that the correlation between pore development and fracture expansion is the greatest in microstructure changes.Under moisture-thermo-mechanical conditions,humidity cycles cause the interlayer spacing changes of clay minerals,resulting in particle breakages and pores expansion to form microcracks.The temperature cycle produces differential thermal stress and water distribution in silty mudstone,which promotes the development of microcracks.The mechanical cycle increases the fracture tip stress and finally leads to a fracture network.