Research On Expansion And Fracture Rule Of Rock Mass Fracture Under The Action Of Hydro-mechanical Coupling

In the construction process of underground engineering,under the action of hydraulic gradient and excavation disturbance,the underground water permeates into the rock mass along the expansion direction of discontinuity surface.As a result,joint surface occurrence pore water pressure causes the original mechanical property of rock mass changes,which influences the stability of engineering rock mass and threatens the safety of engineering construction.Therefore,it is particularly important to research the expansion and fracture rule of jointed rock mass fracture under the action of hydraulic coupling.The multi-function rock specimen preparation equipment are developed in combination with the indoor experiment,theoretical analysis and secondary development of numerical simulation,and a kind of discontinuous deformation characterization method is proposed to remedy the deficiency of characterization method of finite element technique.In the meanwhile,such characterization method is utilized to analyze the joint parameters upon rock mass loading and the expansion and fracture rule of joint rock fracture under the action of pore water pressure.As a result,the rule of weakening jointed rock mass by occurrence pore space water pressure is worked out,the rock mass constitutive model in consideration of hydraulic coupling action is established,and the user-defined constitutive model is applied to analyze the stability of surrounding rock of tunnel under the action of hydraulic coupling,mainly including the following contents:Firstly,the independently-developed multi-function joint rock specimen preparation equipment is utilized to prepare various joint rock specimens based on similar principles in order to carry out the indoor uniaxial compression test and establish the stress-strain relationship of rock-like materials.The rule of influence of single-joint distribution form on rock mass destruction is analyzed based on the stress-strain curve.In the meanwhile,a kind of discontinuous deformation characterization method is proposed based on finite difference,and its effectiveness is verified through contrastive analysis with indoor test results to achieve the true characterization of germination,expansion and penetration of jointed rock mass fissure in the finite difference software.Later,such method is utilized for simulation analysis of rock mass with different double jointed distribution forms.The rule of loading damage of double jointed rock mass is summarized,and the rules of expansion and fracture of rock mass in different joint parameter conditions are revealed.Secondly,the simulation of uniaxial compression for the jointed rock mass of occurrence pore water pressure reveals the role of weakening compressive strength and elastic modulus of jointed rock mass by pore water pressure.After fitting of weakening function,relation equation between effective normal and shear stress actually delivered on joint surface is amended,the constitutive equation of jointed rock mass under the action of hydraulic coupling is established,and the judging condition of rock cracking is confirmed on the basis of the maximum circumferential force criteria and in combination with the rule of influence of pore water pressure and joint parameters on expansion and fracture of rock mass fissure.Based on the M-C constitutive model in Flac3 D as blueprint,the incremental form equation,failure criteria and flow rule about principal stress and principal strain of jointed rock mass under the action of hydraulic coupling is worked out.The header file and source file of constitutive program of jointed rock mass under the action of hydraulic coupling are programmed with C++ language to achieve the constitutive model for secondary development of jointed rock mass which can comprehensively consider the stress and pore water pressure interaction.Later,contrastive analysis with M-C constitutive model example results is used to verify that SL constitutive model,under the premise of improving work efficiency,can accurately reflect the crack extension and fracture characteristics of jointed rock mass under the action of hydraulic coupling.Finally,constitutive model with secondary development is utilized for the simulation research on large-scale tunnel project under the action of hydraulic coupling.Taking the Level4 Rock Section of certain project to be established in Shantou as example,different excavation methods(full-face tunneling and double benching tunneling)and different excavation advance(2.5m/day and 5m/day)are adopted to research the surrounding rock's principal stress,pore water pressure and displacement change,respectively.After analysis of surrounding rock's stability,district construction scheme shall adopt the double benching tunneling method with advance of 2.5m to provide technical support for smooth progress of project.