| The stability analysis and evaluation plays a critical important role in practical tunnel engineerings.The safe and reliable construction of the end soil is an important problem that restricts the development of tunnel engineering.The problems often encountered in engineering include gushing sand,ground protrusion and surface Subsidence and so on.Especially for the sand-soil tunnel,once the continuous wall is removed,the end soil lacks self-stability and impermeability,which will cause local slippage and water seepage in the cavern.Over time,large areas of soil collapse,water inrush and sand rushing will occur,which will eventually lead to a large subsidence of the surface,resulting in a safety accident.Therefore,an in-depth analysis of the process of soil sliding failure and its influencing factors in the end of tunnels under sand seepage conditions has certain reference value for solving related engineering problems.Based on the PFC3D particle discrete element software,this paper establishes the numerical model of the soil at the end of the tunnel in the sand layer,discusses the characteristics,variation and main influencing factors of the sliding failure of the end soil,and uses the strength reduction method and energy catastrophe theory that are applied to quantitative evaluation of soil stability.The work of this thesis focuses on the following three aspects:1.The PFC3D numerical modeling analysis method was studied to establish a fluid-solid coupling model that can reflect the interaction mechanism between particles and fluid.Firstly,the particle flow contact model is studied,and the linear contact model is selected based on the low-bonding characteristics of sand.Secondly,the numerical simulation method of particle flow and the calibration method of sand micro-parameters are studied.Then,the particle-flow-solid-coupling model is studied and the flow is written.Solid-coupled Python script calculation program;finally,the application of the fluid-structure coupling program for case analysis and verification.2.The soil analysis model of the end of the tunnel in the sand layer is established,and the law of the slippage of the soil at the end of the fluid-solid coupling is studied,and the factors affecting the soil damage at the end are analyzed.Firstly,the rationality of the value of the numerical model parameters is analyzed,and then the particle flow model is generated.Then,from the stratum movement,the particle displacement and the inter-particle force chain,the variation law of the end soil slip under the seepage condition is analyzed.Finally,the soil friction is selected.The factors such as coefficient,tunnel depth and groundwater depth are studied separately to study the stability of the soil at the end of the tunnel.The results show that the larger the friction coefficient,the deeper the buried depth of the tunnel,the deeper the groundwater depth,and the more stable the end soil.3.Based on the strength reduction method and the cusp catastrophe theory,the stability of the end soil was quantitatively evaluated.Firstly,the friction coefficient of the micro-parameter is reduced.Secondly,the energy data of the model is obtained by using the history command.Finally,based on the energy mutation criterion constructed by the cusp catastrophe theory,the stability coefficient of the end soil is calculated.Based on the method,the soil safety factors of different groundwater depth tunnels are calculated respectively.The calculation results show that the safety factor of the groundwater depth is significantly lower when the groundwater depth exceeds the elevation of the tunnel bottom,indicating that the groundwater level has a significant impact on the safety of the soil at the end of the tunnel. |
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