锚固正交各向异性岩体的本构关系和破坏准则

CONSTITUTIVE RELATIONSHIP AND FAILURE CRITERION FOR BOLTED ORTHOTROPIC ROCKMASS

从理论上对由系统锚杆加固的正交各向异性岩体,取出包含锚杆的表征单元.根据“等效材料”的概念,在原岩体的本构关系和破坏准则中计人锚杆刚度和强度的“贡献”,从而建立了相应锚固岩体的木构关系和破坏准则.然后列举算例,考察了表征单元的应力-应变关系和破坏强度随锚杆安置角度变化的各向异性表现.最后将计算与一个简单试验的结果作了对比,看到二者的吻合程度较好,因而初步地验证了所提力学模型的可靠性.

According to the concept of equivalent material-the material that exhibits naturesof uniformity and singleness in macro sense , the constitutive relationship of the material is the same as that of the material that exhibits meso-nonuniformity and contains various compositions. Some researchers have performed many studies on the mechanical properties of the rockmass anchored with systematic bolts such as deformability and strength through model simulation and obtained both theoretical and empirical relation equations between the mechanical indexes and the bolt parameters (diameter, length, spacing for example) of the bolted rockmass. Unfortunately, theirstudies neglect an important nature of the bolting support-quite strong directivity becausethe bolted rockmass under their consideration are almost treated as an isotropic body. In fact, no rockmass, if bolted, will exhibit isotropic changes in its mechanical properties and the most obvious improvement of the properties due to bolting takes place along the bolt axial direction whereas the least takes place in the direction perpendicular to the bolt. Accordingly, the bolted rockmass is a kind of anisotropic body in more strict physical sense, whose characters should be studied thoroughly.Out of this consideration mentioned about, the authors have made attempts to proceed from establishing the theoretical model for the bolted rockmass then to analyze numerically the mechanical behavior of the rockmass. In doing so, firstly consider an orthotropic country rockmass and cut off a representative element containing a bolt in the light of the concept of equivalent material from the mass which has been anchored with systematic bolts, and then deduce and establish the constitutive relationship and the failure criterion of the bolted rockmass by the method in whichthe contributions of the bolt to both stiffness and strength of the country rockmass have been fully taken into account, and afterwards perform numerical computations to analyze the anisotripic behavior of both bolted and non-bolted representative elements in the variations of their stress-strain relation and strength with the installing angle of the bolt. It can been seen from the calculation results for a bolted rockmass, its deformability is constrained due to the increment in its stiffness and strength, i.e., it can bear a higher stress. Finally comparison is made between the theoretical analysis and the result from a simple model simulation in which a tested specimen made from similar materials was compressed uniaxially to failure, showing a good coincidence between them. The mechanical model proposed in the present paper has been proved reliable tentatively. The authors will introduce this model into such numerical analyzing program as FEM code in near future and check it through engineering practice to make it perfect.