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砂土材料常压至高压下的强度、变形特性是构建砂土模型的首要问题。开展3种粒组砂土8 MPa围压范围内的等向压缩试验以及0.2~6.4 MPa围压范围内的三轴剪切试验,将砂土常压至高压范围内的力学特性进行系统分析,以获得能够将常压至高压范围内的强度、变形特性进行统一描述的力学参数。通过研究发现:(1)砂土在高压下出现一定量的颗粒破碎,改变了砂土的剪切耗能机制,使得砂土三轴压缩剪切由剪胀软化特征向剪缩硬化特征转变;(2)砂土材料的三轴压缩剪切峰值应力比受砂土粒径、围压共同影响,M-C强度准则在高压条件下不再适用;而残余应力比则基本不受粒径、围压的影响,是典型的无黏性摩擦型岩土力学参数,应作为砂土基本力学特性指标;(3)砂土材料在常压至高压范围内的剪切过程中存在较明显的临界状态现象,临界状态曲线与等向压缩曲线形态相同均呈指数衰减型并在高压条件下产生交叉,两者共同构成砂土材料的状态区间能够体现常压至高压范围内的剪胀与剪缩特征。
The strength and deformation characteristics of sand material under normal pressure to high pressure are the most important problems in the construction of sand model. The isostatic compression tests of 3 kinds of granule sand in the confining pressure range of 8 MPa and the triaxial shear tests in the confining pressure range of 0.2-6.4 MPa were carried out to systematically analyze the mechanical properties of the sand in the atmospheric pressure to high pressure range, So as to obtain the mechanical parameters that can describe the strength and deformation characteristics in the range of atmospheric pressure to high pressure uniformly. The results show that: (1) a certain amount of particle breakage occurs in sand under high pressure, changing the shear energy dissipation mechanism of sand so that triaxial compression shear of sand changes from dilatational softening to shear shrinkage hardening; (2) The triaxial compression shear peak stress ratio of sand material is affected by the sand particle size and confining pressure, while the MC strength criterion is no longer applicable under high pressure conditions; while the residual stress ratio is basically not affected by the particle size and confining pressure , Which is a typical non-viscous frictional geomechanical parameter, should be used as an indicator of the basic mechanical properties of sand. (3) There is a more obvious critical phenomenon in the shear process of sand material in the range of atmospheric pressure to high pressure , The critical state curve and the isotropic compression curve have the same exponential decay pattern and intersect under the high pressure condition. The combination of the two together can form the dilatancy and shear-shrinkage characteristics in the range of normal pressure to high pressure.