三轴压缩荷载下爆破损伤砂岩强度及变形特征试验研究

Experimental study on strength and deformation characteristics of sandstone damaged by blasting under triaxial compressive loading

为探究不同围压状态下爆破荷载损伤顶板砂岩强度、变形及损伤特征,利用三轴加载装置对3种不同损伤度砂岩试件开展常规三轴压缩试验,并结合电子数码显微镜获取不同损伤度试件细观结构,分析爆破荷载损伤、围压对砂岩试件强度、黏聚力、体积应变、破裂破碎形态及细观结构的影响规律。结果表明:(1)相较于未损伤试件,围压0 MPa时振动损伤、爆破损伤试件损伤度分别为5.53%,18.87%,未损伤试件峰值应力、黏聚力及内摩擦角均高于振动损伤试件与爆破损伤试件,爆破荷载作用对砂岩强度产生明显劣化作用,且爆破损伤试件损伤度高于振动损伤试件。(2)不同损伤度试件峰值应力均随围压的增大呈线性增长,同时围压的存在限制了试件的变形,在达到相同应力时承受围压试件所产生的变形程度更小。(3)0 MPa围压时未损伤试件极限体积应变是振动损伤试件、爆破损伤试件的1.65,1.46倍,10 MPa围压时是振动损伤试件、爆破损伤试件的1.85,1.49倍,未损伤试件整体均质性及承载能力较高,其自身能够承受荷载作用下的变形程度更大。(4)围压的增大使得试件破裂破碎程度先降低后增大,试件呈剪切破坏、张拉破坏及压缩破坏多种破坏模式共存。在细观结构层次上爆破荷载损伤砂岩产生大量新生节理、裂纹及断层,且爆破损伤区损伤程度高于振动损伤区。

In order to explore the strength,deformation and damage characteristics of the roof sandstone damaged by blasting load under different confining pressure conditions,triaxial compression tests were carried out on three sandstone specimens with different damage degrees by triaxial loading system,and the microstructure of the specimens with different damage degrees was obtained by electronic digital microscope.The effects of blasting load damage and confining pressure on the strength,cohesion,volume strain,fracture morphology and microstructure of sandstone specimens are analyzed.The results showed as follows:(1)Compared with the undamaged specimens,the damage degree of vibration damage and blast damage specimens at 0 MPa perimeter pressure is 5.53%and 18.87%,respectively.The peak stress,cohesion and internal friction angle of undamaged specimens are higher than those of vibration-damaged specimens and blasting damaged specimens.The blasting load causes obvious deterioration of sandstone strength,and the damage degree of blasting damaged specimens is higher than that of vibrating damaged specimens.(2)The peak stress of specimens with different damage degrees increased linearly with the increase of confining pressure,and the existence of confining pressure limited the deformation of specimens,and the deformation degree of specimens subjected to confining pressure was smaller when they reached the same stress.(3)The ultimate volume strain of the undamaged specimen at 0 MPa confining pressure is 1.65 and 1.46 times that of the vibration-damaged specimen and the blasting damaged specimen,and 1.85 and 1.49 times that of the vibration-damaged specimen and the blasting damaged specimen at 10 MPa confining pressure.The whole homogeneity and bearing capacity of undamaged specimens are higher,and the deformation degree of undamaged specimens under load is greater.(4)With the increase of confining pressure,the fracture degree of the specimen decreases first and then increases,and the specimen shows multiple failure modes of shear failure,tensile failure and compression failure co-existing.A large number of new joints,cracks and faults are generated in sandstone damaged by blasting load at the mesostructural level,and the damage degree in the blasting damage area is higher than that in the vibration damage area.