| Metro is an important part of urban rail transit.It not only promotes the rapid development of the city,but also is an important part of lifeline engineering.However,ground fissures are widely distributed in Xi’an area and then it is impossible to avoid going through the ground fissures zone in the process of metro construction.At present,the construction of Xi’an Metro crossing the ground fissure site is basically carried out by shallow buried excavation method.Due to the fractured strata of ground fissure site,shallow buried excavation of metro tunnel going through the ground fissure site may cause engineering disasters,such as uneven settlement,structure seepage and tunnel collapse.Therefore,it is an important engineering problem to ensure the safety construction of metro tunnel in ground fissure site and reduce the impact of construction on surface and adjacent buildings.This paper takes the shallow buried excavation construction section of Xi’an Metro Line 6phase I project between Zhangba 4th road station and Zhangba 1st road station crossing the ground fissure site as background.Based on historical data and field investigation,the characteristics of ground fissure activity along the first phase of Metro Line 6 are clarified,the future activity trend of F8 ground fissure is analyzed,and the possible influence of F8 ground fissure on underground tunnel is clarified.By combining field test and numerical calculation,the direction of tunnel excavation during shallow excavation of metro tunnel in ground fissure site is revealed.According to the influence mechanism of tunnel depth,intersection angle between tunnel and ground fissure,tunnel diameter and other factors on ground settlement,the optimized CRD construction method for metro tunnel shallow excavation in ground fissure site is constructed.The main results are as follows:(1)Through data collection,field investigation and geological survey,the landform features,stratum lithology,geological structure conditions and meteorological and hydrological conditions of tunnel excavation section of metro tunnel are obtained.The general situation and genesis mechanism of ground fissures in Xi’an are clarified,and the ground fissure activity characteristics along the first phase of Metro Line 6 project are identified,and the possible influence of ground fissure of F8 on tunnel in the shallow excavation area is analyzed.(2)Through field monitoring of ground surface,ground fissure,tunnel and surrounding rock in underground excavation construction section of ground fissure site,the ground settlement,ground fissure settlement,tunnel vault settlement,horizontal convergence deformation of tunnel and variation law of contact pressure between with tunnel and surrounding rock in underground excavation construction of metro tunnel in ground fissure site are revealed..(3)Based on numerical simulation calculations,taking Xi’an Metro Line 6 crossing F8 ground fissure as the prototype,the three-dimensional geological model(strata-ground fissure-tunnel)under multiple working conditions is established,and the influence mechanism of tunnel excavation direction(from hanging wall to bottom wall and from bottom wall to hanging wall),buried depth(10m、15m and 20m),section size(8m、10m and12m),angle between tunnel and ground fissure(30°、60°and 90°)on ground settlement during construction process of shallow buried excavation are revealed.(4)Based on the particularity of the ground fissure site and the existing CRD construction method,the construction optimization method is constructed.The whole excavation process of the traditional CRD construction method and the optimized CRD construction method is dynamically simulated by using numerical software.Combined with the field monitoring data,the ground ground settlement deformation law and the stress deformation characteristics of the tunnel structure induced by the metro tunnel construction in the ground fissure site under the two construction methods are compared and analyzed,the reliability of the optimized CRD method is verified. |
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