水压环境下砂岩蠕变特性试验研究

Experimental Study on the Creep Characteristics of Sandstone Under Water Pressure Environment

水利工程中的坝基和库岸岩体长期在高应力和高水压的共同作用下会产生蠕变现象,对工程稳定性影响很大。针对水利工程中岩石在流固耦合作用下的蠕变问题,选取某水电站引水隧道线路上震旦系砂岩为研究对象,利用MTS试验机和扫描电镜(SEM)分别对干燥和饱和状态下砂岩的常规物理力学参数和微观结构进行测试,分析砂岩在不同状态下的主要物理参数和微观结构变化;基于此,利用专用的微机控制轴压水压联合作用岩石流变试验系统,通过对砂岩试样施加不同的水围压,对其蠕变过程进行试验研究,分析水压对蠕变变形量、蠕变速率和长期强度的影响。结果表明:砂岩内部存在大量的微孔隙,砂岩在饱水状态下,呈现出软化特性,饱水砂岩的抗压强度与弹性模量均小于干燥砂岩;砂岩在稳定蠕变阶段的变形量随水压的增大而增加,水压的增加降低了砂岩的强度和抵抗变形的能力,导致岩石初期和稳定蠕变阶段蠕变量的增大;水压越高岩石蠕变的初始应变率越大,衰减至稳定蠕变阶段所需时间越长;水压能通过岩石表面的孔隙渗入到岩石内部,在裂纹发展的过程中,孔隙水压力能及时到达裂纹尖端,形成"锲入"作用,促使裂隙的扩展和贯通,加速岩石破坏变形,从而降低岩石的承载能力和长期强度。

The creep of dam foundation and reservoir bank in hydraulic engineering,under the action of long-term high stress and high water pressure,will exert a significant impact on the engineering stability.Aiming at the creep of rock under the fluid-solid coupling in hydraulic engineering and choosing the Sinian-sandstone of some hydropower station's draw water tunnel as the research subject,the physical and mechanical parameters and micro-structure of dry or saturated sandstone were tested using MTS testing machine and SEM method,respectively,and the main physical parameters and changes of micro-structure under different conditions were analyzed.On this basis,the creep experiment of sandstone under different water pressure was carried out using the exclusive rock mechanical creep testing system to analyze the impact that water pressure exerted on the creep deformation,the creep rate and long-term strength of the rock specimen.The results indicated that there was numerous micro-pores in the sandstone,which exhibited softening behavior in saturated condition,and both the compressive strength and elastic modulus of saturated sandstone were less than that of the dry sandstone.The acceleration of rock creep,the reduction of sandstone strength and the decrease of sandstone's deformation-resisting ability were caused by the increase of water pressure.The higher water pressure was,the larger the initial strain rate of creep would be,the longer the time needed to reach the stable state of creep would be as well as the larger the creep deformation of stable stage was.The water could penetrate the rock internal through its pores on the surface,and during the development of fissures,the water pressure forced into the crack tip resulting in a kind of wedging action,which prompted the extension and transfixion of fissures and quickened the crack and deformation of rocks,therefore,the bearing capacity and long-term strength of rocks both decreased.