两共面预制裂纹试样应力场特征与破坏模式研究

Failure mode and stress field for sample with two coplane pre-crack

破坏模式决定着裂隙岩体的基本力学性质,通过对比分析典型两条共面裂纹的节理裂隙岩体试样的模型试验、模拟试验结果,系统地研究了预制裂纹倾角、侧压以及裂纹面摩擦系数等因素对试样应力场、破坏模式以及峰值强度的影响;进一步解释了不同裂隙分布条件下张拉次生裂纹、剪切次生裂纹的起裂、发展以及贯通路径与机理,系统地总结了两条共面裂纹试样贯通模式的演化规律。结果表明:随预制裂纹倾角从0°增大到90°,两共面裂纹试样第一主应力最大值呈现先增大而后减小的规律,倾角较小或较大时试样最大拉应力相对较小,而倾角为20°~70°时试样最大拉应力较大且45°~65°间达到最大;剪应力极值线绕预制裂纹尖端旋转,次生剪切裂纹起裂部位、发展方向均发生变化,接近0°和90°时试样内部最大剪应力值最小,倾角为20°~70°时试样最大剪应力相对较大且30°时剪应力达到最大;裂纹倾角较小时试样破坏路径由两预制裂纹中的一条与其次生裂纹贯通形成破坏路径,倾角较大时破坏路径通过两条预制裂纹以及其次生裂纹贯通形成;试样峰值强度变化曲线呈浅底“V”字形,倾角为0°、90°时峰值强度大体相同,倾角为45°时峰值强度达到最小且约为0°时峰值强度的40%~50%。

The study of failure mode of fractured rock mass is a fundamental problem in rock mechanics and the basic mechanical properties are dominated by the failure modes of the fractured rock mass.In this paper,the influence of pre-crack angle to stress field,the failure modes and failure mechanism are studied via systematic numerical experiments and typical model tests on the fractured rock mass samples with two coplanar cracks,by considering the crack angle,confining pressure and friction coefficient.The results show that the first principal stress of the rock sample with two coplanar pre-cracks increases firstly and then decreases,when the pre-crack angle increases from 0°to 90°.While the pre-crack angles in the interval of 20°~70°,the maximum tensile stress of the sample is larger and reaches its maximum between 45°and 65°.The extreme lineof shear stress rotates around the pre-crack tip,and the initiation location and development direction of secondary shear cracks change dramatically;the maximum shear stress of the sample reaches its minimum near the angles of 0°and 90°.When the pre-crack angel is between 20°and 70°,the maximum shear stress of the rock sample is relatively larger and the shear stress reaches its maximum at 30°.When the pre-crack angle is smaller,the failure path is formed by the penetration of one of the two pre-cracks with the secondary cracks.When the inclination angle is larger,the failure path is formed by the penetration of two pre-cracks and the secondary cracks.The peak strength curve of the specimen shows a shallow"V"shape.The peak strength is generally the same for the angles of 0°and 90°,and when the angle is 45°,the peak strength reaches at its minimum,about 40%to 50%of the peak strength at about 0°.