Research On Mechanism And Numerical Simulation Method Of Mudstone Expansion And Deterioration In Tunnel Engineering

With the growing of our country’s comprehensive national strength,especially the Belt and Road Initiative,the strategic conception of " a country with strong transportation network" and the implementation of the South-to-North water diversion project,the construction of tunnels involving transportation,water conservancy and hydropower projects in our country has ushered in a great opportunity for rapid development.In recent ten years,the construction of tunnel projects in our country has been extending to northwest,west and southwest regions,with the increase of project scale and construction difficulty,it is a great challenge to construct these tunnels safely and efficiently,especially water conservancy tunnels because of its functional needs,the length is often far beyond the traffic tunnels.Due to the long distance and large burial depth of the water transmission tunnel,it may pass through various complex geological environments along the route,and the problem of large deformation of soft rock caused by unknown water bodies often occurs.The large deformation of soft rock may cause engineering disasters such as tunnel floor heeling,uplift,diameter shrinkage,support failure,surrounding rock collapse,lining cracking and even damage,which brings great challenges to the construction and operation of water transmission tunnel.This thesis takes swelling mudstone as the main research object and relies on a deepburied tunnel project in Xinjiang Uygur Autonomous Region of China.By means of experimental research,theoretical analysis,formula derivation,numerical simulation and combination with practical engineering,the deterioration law of mechanical properties,expansion law and water absorption law of swelling mudstone after water treatment are deeply studied,and deduces the elastic constitutive model and elastic-plastic constitutive model considering the expansion and deterioration of swelling rock encountering water,proposed the diffusion equation of humidity in swelling rock,proposed a humidity mechanics chemistry coupling model,built a finite element-discrete element coupling platform based on the generalized bridge domain method,and successfully wrote the humidity mechanics chemistry coupling model into it to complete the HMC-FEM-DEM coupling analysis platform,and some research results are obtained,which mainly include the following:(1)The expansion law and water absorption law of swelling mudstone are obtained through water absorption test and lateral constrained expansion test;the variation of various mechanical properties of mudstone with water content was obtained through uniaxial compression test,Brazilian splitting test and triaxial compression test for swelling mudstone with different water content;finally,the reason of water deterioration and disintegration of swelling mudstone are qualitatively derived by X-ray diffraction test and scanning electron microscope test.(2)Based on the elastic constitutive model theory,combined with the humidity stress field theory,the elastic constitutive model considering the change of water content and the effect of water content on the mechanical properties of swelling rocks is derived;based on the elastic-plastic constitutive model theory,combined with the humidity stress field theory,the swelling-softening composite elastic-plastic constitutive model considering the swelling characteristics and water deterioration characteristics of swelling rocks is derived.The model not only considers the expansion characteristics of swelling rock,but also considers the softening characteristics of swelling rock,which provides ideas and methods for the subsequent study of constitutive models of swelling rock.(3)The moisture diffusion equation in rocks is derived,and the moisture-mechanicschemistry coupling model is proposed according to the law of water degradation and swelling of swelling mudstone,and the code of humidity-mechanics-mechanics coupling model is compiled and developed in open-source discrete element software.The correctness of the humidity diffusion model is verified by several examples,and then the humidity-mechanical-chemical coupling model is used to simulate the swelling water absorption test and the uniaxial compression test with different moisture content.The simulation results matched well with the test results.(4)The finite-element-discrete-element coupling platform based on the generalized bridge domain method theory was built in the open-source discrete element software Yade,and validated for common slope problems and static touch problems in actual engineering,which proved the correctness of this finite-element-discrete-element coupling platform.The humidity mechanics chemistry model was also added into the FEM-DEM coupling platform,and the HMC-FEM-DEM coupling analysis platform was successfully built.The platform lays the foundation for the subsequent study of large deformation of tunnel surrounding rock.(5)Based on the coupled HMC-FEM-DEM analysis platform,the engineering problem of large deformation of soft rock tunnel(channel)triggered by moisture diffusion and the effects of expansion coefficient,initial moisture of bottom slab and moisture diffusion coefficient on the deformation of tunnel surrounding rock are quantitatively studied.The results show that the deformation of tunnel bottom is the largest and should be focused on in the actual project,and both the physical and mechanical properties of surrounding rock and environmental moisture have a great influence on the structural performance and stability of soft rock tunnel.