Field Tests And Numerical Analysis Of Tunnel Deformation Induced By Above Excavation In Soil-Rock Composite Stratum

During underground engineering are built in the urban center area,it is probable that the new excavation will overpass the existing tunnels.Above excavation will result in the rebound of the bottom soil and heave of the existing tunnels.This will threaten the safety of the tunnel and even lead to the accidents.Especially excavation is carried out in the soil-rock composite stratum,deformation of the tunnel will more complex,unclear and need to be further examined due to the very different properties between the soil and the rock.This study is based on an excavation over the Metro Line 1 in soil-rock composite stratum in Xiamen.Filed monitoring of the tunnel deformation are carried out during the process of the excavation.Through the analysis of the measured data and related numerical simulation,the response of the tunnel deformation induced by the above excavation in the soil-rock composite stratum are studied.The main conclusions are shown as follows:(1)The actual deformation of the tunnels during above foundation pit was excavated have been monitored through the automated monitoring method and manual monitoring method.The reponses of the tunnel deformations have been analysed combined with related statistical data.Results indicate that deformations induced by above excavation have been influenced significantly by the fluctuation of the stratum.The maximum vertical deformation in moderately weathered rock decrease by 40% compared with the one in the fully weathered rock.The statistical data show that the tunnel vertical deformation in the soil-rock composite stratum is about 1/5 of the one in soft soil.The tunnel vertical deformation uplift within the range of the excavation presents and some settlements are observed out the range of the excavation.Time effect of the soil deformation will increase dramatically the deformation of the tunnel.(2)The numerical analysis based on the actual engineering is analysed to manifest the appropriate constitutive model and tunnel deformation mechanism in the soil-rock composite stratum.The results the tunnel uplift in the unloading area due to excavation,and subside out of the excavation area because of the effect of surface loads.During the construction,materials,equipment stowage and heavy load vehicles should be avoided to be set directly above the tunnel near the unloading area of the foundation pit.The fluctuation of bedrock surface has a significant influence on the vertical deformation of existing tunnel,the maximum tunnel vertical deformation in soil layer is about four times of the that in rock layers.(3)The related construction impact factors on the response of the tunnel deformation caused by above excavation are studied.The results show that when the unloading depth is constant,the vertical uplift of the existing tunnel increases with the increase of the unloading area,and its increase rate decreases gradually.The unloading span has more influence on the tunnel deformation than the unloading length.Employing the method of stratified excavation can restrained effectively the vertical deformation of the tunnel,but the effect is far less than that in soft soil.Increasing the stiffness of the support system has little effect on the tunnel vertical deformation.