Study On Ground Settlement Law Of Qingdao Upper Sdft And Hard Composite Ground Tunnel Construction With Conventional Method

With the continuous development of China’s economic level and the increasing traffic pressure,more and more cities have been involved in the construction of urban subways.During the construction of the subway,disturbances of the underground rock and soil layers will inevitably occur,and causing deformation of the layer and surface subsidence,which will adversely affect the urban environment and bring hidden dangers to construction.Therefore,it is of great significance to study the law of surface subsidence during the construction of subway tunnels to ensure the safety of tunnel construction.During the construction of Qingdao Metro,soft and hard composite stratums often appear.When tunnels are in the composite stratum,the mechanical properties of the stratum are different from those in the uniform stratum.The change of the stress state and the deformation characteristics of the subterranean rock and soil are also complicated,and the prediction of the surface subsidence law is more difficult.Based on the construction of the Wunan section tunnel of Qingdao Metro Line 2,this paper studies the ground settlement law and characteristic parameters of single-line and double-line tunnel construction in the upper soft and hard composite stratum.The main research contents and research results are as follows:1.Based on the research results of domestic and foreign scholars on the deformation mechanism of tunnel construction,the mechanics of surface settlement of tunnel construction can be summarized into 3 aspects: the change of geostress field,the consolidation settlement of soil and the rheological characteristics of soil.After the mechanism is analyzed,the spatial and temporal effects of surface subsidence and the main factors affecting the development of surface subsidence are summarized,which lays a foundation for the later research.2.Based on the monitoring data of surface settlement of single-line tunnel in Wunan area,the Gaussian peak function is used to fit the field data.The characteristic parameters of settlement curve such as formation loss,formation loss rate and settlement groove width coefficient are obtained.Then Flac3 D numerical calculation software is used to build model of single-line tunnel.The tunnel model is used to study the formation conditions of the tunnel,the conditions of the overburden layer on the tunnel and the influence of the excavation footage on the settlement parameters.Itwas found that the characteristics of the settlement curve were significantly affected by the formation conditions and the excavation footage of the tunnel,which was less affected by the overlying soil layer.3.For the case where the superimposed Peck formula on the upper soft and hard composite stratum has a large deviation of the surface settlement prediction of the double-line tunnel,the linear regression analysis of the measured data of the surface settlement of the Wunan section double-line tunnel is carried out.The maximum settlement value and the settlement tank width coefficient in the formula are corrected.The modified Peck formula and the measured data have higher conformity,which can provide reference for the prediction of tunnel settlement law under the same geological conditions.4.According to the stratum conditions of the tunnel hole,the conditions of the overburden layer on the tunnel,the buried depth of the tunnel and the excavation footage,the Flac3 D is used to model the double-line tunnel and analyze the changes of different influencing factors to the double-line tunnel.The development law of surface settlement and the influence degree of characteristic parameters show that the main influencing factors of the subsidence parameters of double-line tunnel construction are the tunnel depth,the soft-hard ratio of the stratum and the excavation footage.The influence of the thickness of sand and clay layer on the overburden layer on the tunnel is relatively small.The research results can provide a reference for the prediction of the surface settlement law of double-line tunnels when different influencing factors change.