Seismic Response Analysis Of Urban Cross-shaped Utility Tunnel Near The Subway

With substantial support from our central government,the construction of urban utility tunnels has made a great progress in recent years and graduall become a lifeline system of our cities.The urban utility tunnel integrates many critical piplines,such as cables,water supply and drainage pipelines,gas pipelines and communication pipelines,which enables us to manage and repair the pipe network system simultaneously.As a earthquake-prone country,China has relatively inadequate research on the seismic response of utility tunnel at special locations.Therefore,it’s hard to ensure the safety of urban utility tunnel under extreme environmental conditions.The study on the seismic response of the utility tunnel under different engineering conditions is the premise and foundation of all relevant quakeproof design.Correspondingly,this paper uses the software ABAQUS to analyze the seismic response of a built utility tunnel in Chengdu.With a comprehensive consideration of the target’s soil texture and engineering information,this thesis focuses on the seismic response of a built underground utility tunnel at a special location in Chengdu.First,we use the software ABAQUS to construct a model with underground pipeline,soil and tunnel.Followed by determining the artificial boundary,examining the soil plasticity and concrete damage,adjusting some important parameters of ABAQUS,and contrasting the stress at the actual observation points with the stress simulated by the software to verify the reliability of this experiment.We analyzed the seismic response of a utility pipeline that is close to a tunnel,then built models of different working conditions.With detailed analysis of the tunnel’s impact and multiple alterations of both soil texture and distance between the utility pipeline and the tunnel,we managed to summarized a change pattern of stress and displacement of the utility tunnel under various working conditions.The experiment on seismic response shows that the observation point by the intersection reaches its peak in vibration displacement around 5 seconds,and the vibration displacement at the midpoint of the bottom plate is longer than that of the top plate.The stress on the plates of the utility pipeline are ranked diminishingly as the bottom plate,the side plate and the top plate.When the tunnel does not exist,the peak of vibration displacement of observation points near the intersection of the cross-shaped utility pipeline is reduced by 22.7%horizontally and 16.2% vertically.The peak of stress on bottom plate,top plate and side plate of the utility pipeline decrease by 12.07%,13.10% and 17.44% respectively.When the distance between the utility pipeline and the tunnel changes from 12.35 m to7.35 m,the peak of vibration displacement of same observation points near the intersection increases by 11.38% horizontally and 13.4% vertically.The peak of stress of the bottom plate,top plate and side plate increased by 9.68%,9.16% and 5.17% respectively.Again,when the distance changes from 12.35 m to 17.35 m,the peak of vibration displacement of same observation points decreases by 7.56% horizontally and 7.04% vertically and the peak of stress of the bottom plate,top plate and side plate decreased by 5.77%,9.73% and 5.57%respectively.Likewise,when the distance shifts from 12.35 m to 22.35 m,the peak vibration displacement decreases by 17.29% horizontally and 13.38% vertically and the peak stress decreased by 8.22%,11.19% and 5.57% respectively.Compared with that when the utility pipine is away from the tunnel,the peak of vibration displacement of the two observation points increases by 6.99% and 3.36%;the peak of stress of the bottom plate,top plate and side plate of the utility pipeline increased by 4.38%,2.15% and 6.19% respectively.This thesis also studies influence of soil texture on the seismic response of the utility pipeline.First,we compare the seismic response with soft soil and hard soil.The result shows that the stress has increased when there is soft soil,but not significant.Therefore,as long as the foundation below the utility tunnel is stable,the overall stress won’t shift significantly in the soft soil environment,but sudden and sharp stress changes occur more frequently.The stress of the bottom,top and side plate increased by 5.69%,4.84% and 3.18% respectively.On the other hand,the peak of the vibration displacement is higher in soft soil than in hard soil.The data of the observation points near intersection increases by 6.09% horizontally and15.4% vertically.To sum up,soft soil enhances the seismic response of the utility tunnel structure.Through four groups of orthogonal tests,we found that when the elastic modulus remains unchanged,the seismic response of the utility tunnel decreases with the increase of cohesion and elastic modulus.When the viscosity remains unchanged,the seismic response of the utility tunnel decreases with the increase of elastic modulus.When the cohesion and elastic modulus increase at the same time,the seismic response of the utility tunnel decreases nonlinearly.When the elastic modulus is 80 MPa,the cohesion has little effect on the seismic response of the utility tunnel.