石英云母片岩加卸荷力学特性及其卸荷本构研究

Loading and unloading characteristics of mica-quartz schist and constitutive model for its unloading

为揭示丹巴水电站石英云母片岩在不同应力路径下的力学性质,针对平行片理组和垂直片理组试件,利用MTS815岩石试验系统分别进行常规三轴压缩试验和升轴压、降围压卸荷试验,系统研究石英云母片岩在加、卸荷应力路径下的力学特性。试验结果表明,常规三轴试验下,平行组试件变形大于垂直组,变形表现出明显的各向异性特性;常规三轴试验下,垂直组试件破裂面形成时先产生主裂纹,再与次裂纹贯通、连接,平行组试件则直接由次裂纹贯通、连接,两组试件破坏面形成方式不同;加、卸荷条件下,峰值强度和残余强度均随围压的增大而增大,且垂直组高于平行组;与三轴压缩试验应力应变曲线不同,卸荷曲线具有明显的跌落段,试件表现出脆性破坏;卸荷条件下两组试件的M-C强度参数明显低于加载试验。结合石英云母片岩的卸荷特性,采用强度各向异性系数表征试件卸荷过程中的各向异性软化,建立横观各向同性岩体的卸荷本构关系,并对其合理性进行验证。研究表明,所提出的本构关系与试验结果具有很高的吻合度,能很好地表征石英云母片岩的卸荷过程。

In order to illuminate the characteristics of transversely isotropic rock under different stress paths, the triaxial compressive full tests and the triaxial unloading tests, elevating axial compression and reducing confining pressure, are carried out on the mica-quartz schist samples from Danba Hydropower Station, which are divided into parallel group and vertical group. The test results show that, for the loading test, the deformation of parallel group is larger than that of the vertical one, and deformation exhibits anisotropic feature. For the vertical group, when damaging, the samples form main cracks firstly and failure surface is connected with secondary cracks, but for the parallel group, failure surface is connected through secondary cracks directly, illustrating different formation ways of failure surface. With the increasing confining pressure, both the peak strength and the residual strength are enhanced, and those of the vertical group are larger than those of the parallel group. Different from those of the triaxial compressive tests, the stress-strain curves of the triaxial unloading tests have obvious drop sections, and the samples show brittle failure. Moreover, the cohesiveness and friction under loading are prominent over those under unloading. Eventually, based on the unloading characteristics of mica-quartz schist, the anisotropic coefficient is used to represent the anisotropic softening during unloading, and a constitutive model for transversely isotropic rock is established. In addition, the rationality of the constitutive model is verified. The research demonstrates that the results of the proposed constitutive model agree with the test data, and it can satisfactorily reflect the unloading characteristics of mica-quartz schist.