Stability Analysis Of Surrounding Rock Of Urban Overpass Tunnel Based On Fluid-solid Coupling

In recent years,the scale of urban underground space development has been increasing.As an extension of urban ground space,urban overpass tunnels play a pivotal role in balancing the traffic flow of the road network and alleviating urban traffic pressure.The scale of overpass tunnel excavation is larger than that of ordinary urban tunnels,which has caused more serious problems such as deformation and instability of surrounding rocks,dynamic geological damage,and floods.Among them,floods and floods are frequent and prominent,which affects construction safety,restricts the progress of new tunnels,and increases economy.The key factor of consumption.Based on theoretical derivation,numerical simulation,and model testing,this paper takes newly-built up-crossing tunnels and newly-built down-crossing tunnels as the research objects,and conducts research on the stability of the surrounding rock of the overpass tunnel under the action of fluid-solid coupling,and draws the following main conclusions:(1)Based on the basic theory of fluid-solid coupling and the theory of elastoplasticity,the overpass tunnel is divided into non-overpass sections and overpass sections,and the changes in surrounding rock mechanics caused by the excavation of new underpass tunnels at different locations are theoretically analyzed.The non-overpass section of the tunnel is discussed as a general deep-buried circular tunnel,and the expressions of stress and displacement in the elastoplastic zone are given,and the changes of the stress in the plastic zone,the radius of the plastic zone and the displacement of the plastic zone with different internal and external head differences are obtained;The section is discussed according to the layered structure of the overlying rock layer-existing tunnel-new tunnel.The stress reduction coefficient between the two tunnels is solved through numerical simulation,the stress and displacement expressions around the tunnel are given,and the vertical displacement of the new tunnel is obtained.And the horizontal displacement changes with different internal and external head differences.(2)Under the conditions of grade IV surrounding rock and a water head of 50 m,regardless of whether fluid-solid coupling is considered,the surrounding rock of the newly built up-crossing tunnel is relatively stable,and there will be no instability of the surrounding rock;the newly-built down-crossing tunnel is not considered The surrounding rock is relatively stable during fluid-solid coupling.When considering the fluid-solid coupling,the surrounding rock is very easy to lose stability,and there is a high probability that the surrounding rock will be unstable or even damaged.(3)When considering the interaction of fluid-solid coupling,the surrounding rock disturbance and range of the overpass tunnel formed by any construction method will increase significantly when it is excavated to the overpass,and the seepage effect will have a stronger impact on the newly-built underpass tunnel.At the same time,by comparing the displacement increments of different sections,when the tunnel passes through the second existing tunnel,the increase in displacement around the tunnel is greater than that of the first tunnel.