Analysis Of Stability And Ground Surface Subsidence In The Course Of City Tunnel Construction Considering The Effect Of Fluid-Solid Coupling

In underground engineering in city, unfavourable influence on environment ,such as the ground surface subsidence, the building subsidence differences etc. will be produced inevitably in the construction of the tunnel.Generally,there are trict restrictions to the ground surface subsidence of tunnel constrction because of numerous buildings and underground pipes around.Therefore,it seems to be very important to predict ground surface subsidence exactly .Because tunnel engineering of city is shallow and underground water level is very high,there usually exist coupling problems of seepage field and stress field in predict analysis of the ground surface subsidence in the course of tunnel construction after the dewatering or without the dewatering.For these reasons,the following study work has been finished in this paper.(1)Basic equation of saturated-unsaturated seepage is built based on seepage continuity and motion Equations,which take saturation zone and unsaturation zone into account together and avoid difficult problems of traditional numerical solution,such as solution of free surface of seepage etc.Made use of Bishop's effect stress formula and basic equation of saturated-unsaturated seepage,fluid-solid coupling equation in saturated-unsaturated soil is built.(2)The rule of influence of pre-support(including thickness, elastic modulus, position of reinforced field) and method of excavation on construction stability and ground surface subsidence in the course of tunnel construction is studied with FEM based on total stress theory.(3)The rule of influence of elastic modulus of soil skeleton,permeability coefficient of soil,dewatering depth and inserting depth of diaphragm wall on ground surface subsidence , subsidence differences and radius of ground surface subsidence funnels in the course of the dewatering before tunnel construction is studied with FEM based on elasto-plastic fluid-solid coupling theory. The rule of influence of ratio of permeability coefficient of surrounding soil to reinforced field, seepage position of reinforced field and reservoir water level on ground surface subsidence,the vault downward displacement and ground stress in the course of tunnel construction without the dewatering is still studied.(4)The numerical analysis of the practical case is performed using FEM based on total stress theory and elasto-plastic fluid-solid coupling theory,and is compared with actual measurement value.It has been showed that it is adequate to estimate the ground surface subsidence in the course of tunnel construction with FEM based on elasto-plastic fluid-solid coupling theory.