Study On Seismic Response Of Shallow Buried Tunnel In Peat Soil

Rail transit is now being used by more and more cities,and Metro shallow tunnel is an important part of rail transit.Kunming will build a considerable scale of rail transit in the next few years,but thick peat soil layers are widely distributed around Dianchi Lake.The peat soil in Dianchi Lake Basin has very poor engineering properties.In addition,Kunming is in a high intensity earthquake fortification area,and there have been large earthquakes in history.Therefore,for the subway shallow buried tunnel structure in peat soil,It is of great significance to study the ground motion response of Shallow Metro Tunnel in peat soil.Therefore,this paper mainly carries out the following work:(1)The basic physical properties of peat soil were studied by indoor soil tests.The stress history of peat soil is studied through standard consolidation test.The calculation results of over consolidation ratio show that the peat soil in this study is in a weak over consolidation state.(2)The relationship between void ratio and consolidation stress of remolded saturated peat soil is studied by isotropic consolidation test,and the normal consolidation curve and unloading rebound curve of soil are obtained.The stress-strain law of remolded saturated peat soil under different confining pressures is studied through indoor static triaxial tests,and the critical state line and critical stress ratio of the soil are obtained.The hysteretic curves of remolded saturated peat soil under different dynamic stress amplitudes,confining pressures,consolidation ratios and frequency control conditions were comparatively studied by laboratory dynamic triaxial tests.(3)Based on the classical elasto-plastic theory and critical state soil mechanics,a dynamic constitutive model which can describe the hysteretic behavior of remolded saturated peat soil under cyclic loading is established by using the single side interface theory and other research results for reference.(4)Through the ABAQUS user material secondary development subroutine UMAT,the boundary interface model of remolded saturated peat soil is numerically realized.The undrained dynamic triaxial test of remolded saturated peat soil is simulated by ABAQUS,and compared with the hysteresis curve under the same test control conditions to verify the applicability of the established boundary interface model of remolded saturated peat soil.(5)Based on ABAQUS,a two-dimensional plane model of a Shallow Metro Tunnel of Kunming Metro Line 3 is established to analyze the response of the tunnel structure to the axial force,shear force,bending moment and lateral displacement of the tunnel lining under the two conditions of peat soil and non peat soil under the action of different seismic waves.The seismic response calculation results of the boundary surface model and the Mohr Coulomb model are analyzed and compared.