干湿循环与动态压缩耦合作用下砂岩力学特性的试验研究

Experimental study on mechanical characteristics of sandstone under drying-wetting cycles and dynamic compression

水库的建设与管护过程中,库岸边坡岩石不仅会受到天然降水与水库蓄排水导致的干湿循环作用,还会受到地震、爆破、隧道掘进等动态冲击荷载扰动,二者耦合作用影响着库岸边坡稳定性。为研究干湿循环与动态压缩荷载作用下岩石的力学特性,利用分离式霍普金森压杆对经历不同干湿循环次数的砂岩展开动态冲击压缩试验,分析动力学参数、能量耗散规律、破碎分形维数受干湿循环条件的影响,并借助扫描电子显微镜观测不同干湿循环次数下砂岩的微观结构,揭示砂岩宏观物理力学行为的劣化机制。结果表明:干湿循环作用会削弱砂岩的超声特性和静、动态力学参数。干湿循环次数增加,砂岩单轴抗压强度、弹性模量、P波波速、动抗压强度、动弹性模量与耗散能减小,破碎分形维数增加;干湿循环条件下,应变率增加,砂岩动抗压强度、动弹性模量、动峰值应变、耗散能与破碎分形维数呈增长趋势。微观分析表明:干湿循环条件下砂岩劣化是由于微观结构发生了显著变化,即孔隙增加,颗粒表面受损,胶结弱化,裂纹间距增加。研究结果可为干湿循环条件下水库除险加固设计与施工提供理论基础。

In the process of reservoir construction and management,the rock would be under an alternating state of drying-wetting owing to the seasonal rainfall and storage and drainage of the reservoir.In addition,the rock is commonly subjected to dynamic loadings such as earthquake,blasting,and tunneling,which have significant influences on the stability of the reservoir.To investigate the effect of drying-wetting cycles and dynamic compression on the mechanical behaviors of rocks,the dynamic test of sandstone undergoing different drying-wetting cycles was carried out using the split Hopkinson pressure bar system.The influences of wetting and drying cycle conditions on the rock dynamic characteristics,energy dissipation law,and fractal dimension of fragmentation were systematically analyzed.The microstructure of sandstone was observed using the scanning electron microscope to reveal the physical deterioration mechanism.The results show that drying-wetting cycles would weaken the ultrasonic characteristics,static and dynamic mechanical characteristics of sandstone.With the increase of drying-wetting cycles,the static uniaxial compressive strength,elastic modulus,P-wave velocity,dynamic compressive strength,dynamic elastic modulus,and dissipative energy of sandstone decrease,while the fractal dimension of rock fragmentation increases.In addition,with increasing strain rate,the dynamic compressive strength,elastic modulus,peak strain,dissipative energy,and fragmentation fractal dimension of sandstone show an increasing trend.The macroscopic analysis results illustrate that the deterioration of sandstone under drying-wetting cycles is caused by the significant change in microstructures,i.e.,pores increasing,particle breakage,cementation weakening,and crack spacing expanding.The research findings in this study could provide a theoretical basis for the design and construction of reservoir de-risking and reinforcement under drying-wetting cycles.