岩土三轴压缩破坏试验的劈裂破坏、张剪破坏、剪切破坏、鼓胀破坏、剪胀破坏及三轴挤长破坏的张性断裂、剪切断裂和混合断裂等八类破坏模式，可归为剪切破坏、拉张破坏及混合破坏三种。然而，是什么控制其破坏模式是被剪坏或被拉坏或被混合破坏，至今仍困扰着材料力学界而不得其解。本项目拟通过受压岩土内侧向应力及其破坏模式的系列试验和理论研究，阐明岩土受压过程中能量的耗散与转化、泊松比及应力转换系数的变化规律及量化关系，研究受压岩土中内侧向应力的产生过程并建立其与三轴应力、泊松比及应力转换系数的关系，研究受压岩土的抗拉张强度特性，阐明受压岩土中剪切与拉张并存博弈的破坏过程，揭示受压岩土中侧向拉张应力及破坏模式的形成机理，建立受压岩土破坏模式的力学判据，揭示剪切强度包线呈现非线性的本质，建立莫尔强度非线性包线的本构方程。研究有助于岩土力学变形破坏理论的完善，进一步发展莫尔剪切强度理论，有力地指导岩土力学的实践。

It is observed that, in geotechnical laboratory test, soils and rocks manifest very different failure modes when subjected to various types of external compressed load, for example, splitting and dilatancy failures in triaxial compression test, extension and shear fractures in axial tensile test, etc. According to the dominant stress, these failure modes can be classified into three categories: shear, tensile and mix failures. The study of failure modes is of significance for better understanding the failure behavior of porous materials like soils and rocks, however, what is the essential parameter controlling such behavior is yet to be answered.. The project aims to systematically investigate the relationship between the internal lateral stress and failure of compressed soils and rock. Through laboratory test and theoretical analysis, the following aspects will be considered: i) to clarify the rules of energy dissipation and transformation, and quantify the corresponding change of the Poisson's ratio as well as the coefficient of stress conversion; ii) to study the internal tensile stress and its relationship with external stress level, Poisson’s ratio and coefficient of stress conversion; iii) to analyze the failure behavior of compressed soils and rocks with special consideration of the co-effect of shear and tensile stresses; iv) to reveal the intrinsic relationship between tensile stress and the formation of failure, and to establish the mechanical criteria of the failure mode of compressed soils and rocks and v) to provide theoretical evidence of the nonlinearity of the Mohr strength envelope and at the same time to establish the corresponding nonlinear constitutive law to characterize such behavior. The study will not only contribute to improving the current geotechnical mechanics on failure behavior of compressed soils and rocks, developing new Mohr shear strength theory, but also providing pertinent guidance for the engineering practice.