The Effect And Numerical Analysis On Mechanical Parameters Of Surrounding Rock In The Process Of Tunnel Excavation Unloading Damage

With the rapid development of tunnel and underground works,the number of engineering problems in the excavation construction is also increasing.As an important geotechnical engineering research method,numerical simulation is commonly used in the stability analysis of tunnels and various underground caverns.It has been demonstrated that the mechanical parameters of the rock mass deteriorated due to unloading under tunnel excavation in plenty of engineering projects.It is not accord with the reality that the mechanical parameters remain constant during the calculation in a conventional numerical simulation.In this paper,the rock damage characteristics during the compression process were researched by means of rock damage experiment and acoustic emission test in the laboratory.The damage evolution of the mechanical parameters was explored from the perspective continuum damage mechanics.Finally,numerical simulations of dynamic damage based on modifications of the mechanical parameters were carried out for the uniaxial compression tests on rocks and tunnel excavation by secondary development of FLAC^3D software.The main research work is as follows:?1?Discusses the topic basis and the significance of this research.A large number of engineering examples show that the basic mechanical properties of the surrounding rock in the process of excavation of underground caverns or tunnels will gradually deteriorate.In view of this engineering fact,from the perspective of the theory of continuum damage mechanics,a numerical simulations method of dynamic damage based on modifications of the mechanical parameters is proposed.?2?The process of rock damage failure under uniaxial compression were researched through rock uniaxial compression test in laboratory and acoustic emission testing technology.The stress-strain parameters and the acoustic emission parametersare integrated under the same time axis.Moreover,the damage variables of each stage of the rock during the compression process are deduced by the acoustic emission cumulative ringing count,and the mathematical relationship between the cumulative strain and the damage variable is fitted according to the Weibull statistical distribution formula.?3?The failure mechanism of surrounding rock in tunnel is elaborated.Not only the process of gradual deterioration of stress environment in surrounding rock,but also the deformation and failure mechanism of surrounding rock due to stress redistribution and unloading rebound caused by tunnel excavation was analysed.The relationship between deformation modulus,cohesion,internal friction angle of rock and damage variable was deduced by damage mechanics theory,Lemaitre strain equivalence hypothesis and Mohr-Coulomb strength theory.The iterative formulation of stress increment with damage variable and the computation function of yield stress were obtained by introducing the damage variable and deducing elasto-plastic damage constitutive relation.?4?Using the FLAC^3D software as the simulation platform,for secondary development and application,the damage calculation function and the dynamic damage correction program of the mechanical parameters are edited.Uniaxial compression tests were simulated.The feasibility of numerical simulations on dynamic damage based on the modification of damage on mechanical parameters were verified by comparing the results of the conventional numerical simulation,numerical simulations on dynamic damage and experiments in laboratory.?5?Taking the practical tunneling project as an example,three-dimensional numerical simulation was established.The conventional numerical simulation and numerical simulations on dynamic damage were established respectively in the process of tunnel excavation.The reasonability of numerical simulations on dynamic damage was verified by comparing and analyzing these two results of simulation from the aspect of stresses,displacements,distribution characteristics of plastic damage area,damage properties,etc.The reliability of numerical simulation of dynamic damage was further verified by comparing vault settlement and peripheralconvergence displacement values between monitor data and results of numerical simulation.Finally,this paper concludes the research results and some shortcomings and deficiencies.Based on the theory of continuum damage mechanics,this paper takes the dynamic damage evolution of rock mechanics as the starting point,and carries on the dynamic damage numerical simulation of the surrounding rock stability of tunnel excavation.The results of numerical simulation can provide references for design and construction of similar engineering.