The Study On Excavation And Support Technology Of Urban Underwater Underground Excavation Double-Deck Tunnel

With the improvement of urban utilization rate,the tunnel form of integration of underground pipeline and underground highway tunnel has been developed,and such tunnel is often shallow and long-span.Groundwater is usually abundant in southern cities of China,so the influence of groundwater has to be taken into account in tunnel excavation.Based on the engineering background of Guangzhou Kangwang Road underpass Huahu Tunnel,this paper studies the excavation and support technology of the tunnel under the condition of rich groundwater.The main research work is as follows:(1)Based on the fluid-solid coupling theory,the numerical model is established by using finite element analysis software ANSYS and FLAC3 D.The rationality of the step method and CRD method,the reasonable thickness of reinforcement ring and the influence of the face reinforcement on tunnel stability are emphatically analyzed.At the same time,the paper also considers the variation of tunnel deformation,pore water pressure distribution and seepage volume under the condition that the permeability coefficient of plastic zone increases due to tunnel excavation.(2)Without considering the influence of the increase of permeability coefficient in plastic zone,the deformation of tunnel constructed by step method is larger than that of CRD method in surface settlement,vault settlement,horizontal convergence and floor uplift.However,the pore water pressure distribution and seepage volume on both sides of the tunnel are basically the same.Considering the increase of permeability coefficient in plastic zone,the deformation of tunnel has little change,but the pore water pressure will decrease and the seepage volume will increase.(3)According to the different thickness of reinforcement ring,eight thickness models of reinforcement ring from 0.5m to 4 m are established.According to the deformation of tunnel,pore water pressure distribution and seepage volume,the reasonable thickness of reinforcement ring of tunnel is 2.5m,which is the reasonable thickness of reinforcement ring.(4)On the basis of the 2.5m reinforcement circle model,the influence of the reinforcement and non-reinforcement of the face of the model on the deformation of the tunnel,the change of pore water pressure in front of the face and the seepage of the face on the stability of the tunnel is analyzed.(5)According to the amount of seepage,whether the convective Huahu Lake needs drainage is analyzed.