Study And Application Of Fatigue Mechanical Properties Of Grouted Broken Mudstone At The Bottom Of Railway Tunnel

The mudstone at the bottom of the traffic tunnel is easy to deteriorate under the action of long-term locomotive dynamic load and groundwater,resulting in broken or non dense surrounding rock at the bottom of the tunnel,deteriorating the stress state of the tunnel bottom structure,and then affecting the driving safety.Therefore,grouting is often used to reinforce the stratum.The grouted broken mudstone substitutes the original rock mass to bear the fatigue damage of dynamic load and groundwater erosion.Accordingly,the long-term mechanical properties of grouted broken mudstone also affect the service state of the structure.Based on the material composition and structural type characteristics of grouted broken mudstone,this paper analyzes the fatigue mechanical characteristics and damage evolution characteristics of grouted broken mudstone from the perspectives of "local" and "overall".In order to clarify the bearing mechanism of rock and grout,the concept of "grout-rock binary unit" which can represent the composition and structural characteristics of local materials is abstracted.Through laboratory test theoretical analysis and numerical calculation,the cementation behavior of grout-rock binary unit under uniaxial compression load and uniaxial compression cyclic load is studied.On this basis,the fatigue mechanical response characteristics and damage evolution characteristics of grouted broken mudstone as the whole object are further studied.And the fatigue damage characteristics of grouted broken mudstone under water immersion are also study.The research results are applied to the effectiveness analysis of post reinforcement effect of grouting reinforcement of grouted broken mudstone at the base of a tunnel in Daqin heavy haul railway.The main research contents of this paper are as follows:(1)In order to clarify the common bearing mechanism of rock and grout,according to the material composition and structural type characteristics of grouted broken mudstone,the "grout-rock binary unit" is proposed as the unit representative of the local form of grouted broken mudstone,and the stiffness,strength and failure mode of different cementation units are analyzed through uniaxial compression test.The distribution of strain field and crack propagation process of grout-rock binary unit under load are analyzed by discrete element simulation method,and the cementation mechanism of grout-rock binary unit is discussed.(2)Taking the grout-rock binary unit as the object,the fatigue deformation characteristics of grout-rock binary unit under different cementation types are analyzed through uniaxial compression fatigue test.According to the composition characteristics of cementation unit and from the perspective of macro phenomenology,a new fatigue components describing the fatigue deformation of grout-rock binary interface is proposed.Combining with the fatigue cementation of rock and grout,the fatigue deformation constitutive model of grout-rock binary unit is obtained.(3)Taking the grouted broken mudstone as the object,firstly,the damage evolution characteristics of argillaceous rock,grout-rock interface and grout under cyclic load are obtained through laboratory test.On this basis,the concept of equivalent vibration times is introduced.Based on the process characteristics of cumulative damage growth and the idea of modular method,a calculation method of damage increment under variable amplitude load is proposed,and the corresponding ABAQUS software subroutine is compiled.The Voronoi joint network model is used to establish the numerical model of grouted broken mudstone the condition of multiple fractures.The above subroutine is used to analyze the fatigue damage evolution characteristics,failure mechanism and fatigue life of grouted broken mudstone under uniaxial compression cyclic load.At the same time,combined with PSO-BP neural network prediction model,the application of the above research results is expanded to realize the fatigue life prediction of more types of grouted broken mudstone.(4)The damage characteristics of argillaceous rock and grout-rock interface caused by water immersion are obtained through the Laboratory test,and the damage calculation method considering the coupling effect of cyclic load and water immersion is obtained through the strain equivalence principle.A calculation method of damage increment under multi-source damage factors and multi-order coupling is proposed,and the corresponding ABAQUS software subroutine is compiled.Through the finite element numerical simulation method,the fatigue damage evolution characteristics,failure mechanism and fatigue life of grouted broken mudstone under uniaxial compression cyclic load considering water immersion are analyzed.(5)Based on the above research results,the finite element dynamic model after grouting reinforcement of broken surrounding rock at the tunnel bottom of heavy haul railway tunnel is established,the complex stress change of surrounding rock at the tunnel bottom caused by considering the previous damage factors and its influence on the subsequent damage increment are analyzed,and the deformation characteristics and damage evolution process of grouted broken mudstone and bedding structure under the action of long-term train load and groundwater after grouting are analyzed more accurately,The damage status and development trend of the bedding structure are quantified,which provides a reference for tunnel operation and maintenance.170 Figures,48 Tables and 211 References...