中文摘要：

软岩三轴加、卸载试验中的抗压强度参数取值是一个非常关键的问题，目前还没有比较确定的方法，通常根据经验或工程要求确定。基于此，结合一组砂质泥岩的三轴加、卸载试验进行了详细研究，试验结果表明：（1）当围压大于10MPa时，不论是三轴加载试验还是卸载试验，砂质泥岩均表现出明显的应变硬化特性；（2）砂质泥岩在三轴压缩和三轴卸荷两种应力路径的力学响应差别明显，在卸荷条件下通常只存在一条完整的剪切破坏面，而压缩条件下岩样没有明显的控制破裂面，并且剪胀效应明显；（3）将半对数法引入到软岩三轴加、卸载试验数据分析中，可以比较方便地确定软岩三轴加、卸载试验的抗压强度；（4）基于三轴加、卸载试验过程中的应力、应变增量分析，将软岩变形破坏过程分为3个阶段：平滑阶段、规则跳跃阶段和急剧跳跃阶段，各阶段划分的意义明确，可以作为抗压强度确定时的重要参考，因此，在软岩三轴试验数据分析时，可以综合采用这两种方法。研究提出的抗压强度确定方法可操作性强，在其他软岩三轴试验数据分析中值得参考借鉴。

英文摘要：

In triaxial loading and unloading tests of soft rock, the determination of compressive strength is a critical problem, which always tends to use empirical method, while less corresponding standards at present. Based on this, a set of triaxial loading and unloading tests of sandy mudstone were carried out and the experiment results show that： （1） Sandy mudstone samples always show obvious strain hardening characteristics in both triaxial loading and unloading tests when the confining pressure is more than 10 MPa. （2） The mechanical response differences of sandy mudstone under triaxial loading and unloading tests are obviously, the samples always have only one macro shear failure surface in triaxial unloading tests; while the samples have no obvious control fracture surface under the condition of triaxial loading, and the dilatancy effect is obvious. （3） The semi-log method was introduced into the data analysis of soft rock triaxial loading and unloading tests, which can determine the compressive strength more conveniently. （4） Based on the analysis of stress and strain increment in the process of triaxial loading and unloading tests, the deformation and failure process of soft rock can be divided into three stages： smooth stage, rule jump stage and sharp jump stage; the division has obvious physical significance, which can be used as an important reference for determining the compressive strength. Therefore, the two methods can be integrated used to determine the compressive strength of soft rock in triaxial loading and unloading tests. The methods for determining the compressive strength is very applicable, and can also provide reference for similar soft rock tests.