| Ground fissure is a typical geological hazard,which is widely developed in the world.China is one of the countries with the most serious ground fissure disasters,and Xi'an ground fissure is the most typical in China.Ground fissure poses a serious threat to the development of underground space,the construction of ground engineering and civil engineering,and the construction and normal operation of bridges in Xi'an city.Taking the Cloud Rail Demonstration Line project in Xi'an High-tech Zone crossing many ground fissure zones as research background,and with finite element numerical simulation and theoretical analysis method,the influence of ground fissure on the Cloud Rail Project was studied in this paper,to aim at revealing the influence of intersection angle,span length and dislocation of ground fissures on the deformation and mechanical behavior of cloud track beams,piers and pile foundations,to determine the deformation and stress mode of bridge pile foundations under the dislocation of ground fissure,and to put forward the preventive measures for cloud track engineering across ground fissure zones.The main conclusions and research results are as follows:(1)Based on field investigation,the distribution and activity characteristics of ground fissures along the Cloud Rail Project in the high-tech zone in Xi'an city were identified.The possible influence and harm degree of ground fissures on cloud rail project were analyzed,and the influence grade of ground fissures was determined.(2)Through the finite element numerical simulation,the deformation and mechanical behaviors of Xi'an Cloud Track engineering crossing the ground fissure zone were studied,the laws of stress redistribution and displacement field variation under the action of ground fissure staggering was revealed,and the quantitative fitting formulas of the relationship betweenverticalstressvariationrangeandburialdepthweregiven:f(h)=Ah~3+Bh~2+Ch+D.Based on the simulation results,displacement and deformation characteristics of cloud track beam,pier and pile foundation were analyzed.(3)Considering the condition of oblique intersection between cloud track engineering and ground fissure zone(?=60 degrees and?=30 degrees),the deformation and mechanical behavior of oblique intersection across ground fissure zone of cloud track engineering were studied.The laws of spatial three-dimensional movement of stratum and track beam under the action of ground fissure staggered movement was obtained.With the decrease of intersection angle,the displacement differences between them in horizontal and vertical direction was the greatest.According to the simulation results,the influence of intersection angle on the inclination of pier,internal force of pile foundation and deformation characteristics was analyzed.(4)Based on the load transfer method,the formulas for calculating the lateral friction resistance,the axial force of any section of the pile body and the settlement of the pile foundation under the action of ground fissure staggered action were derived,and the mechanical model of the pile foundation failure and deformation in the ground fissure site was determined.(5)Based on the two-dimensional finite element numerical simulation,the influence range of ground fissures on cloud track engineering was determined,that was,the width of the influence zone was 14 m in hanging wall and 10 m in foot wall respectively.(6)Based on the numerical simulation of different span lengths of the ground fissure zone of the cloud rail simple supported girder bridge,the inclined deformation characteristics of the track girder and pier of the simple supported girder bridge with different span lengths under the staggered action of ground fissures were analyzed.The optimum span length of the simple supported girder bridge with cloud rail was determined through comparison and selection,that was,In orthogonal design,the span length of simply supported girder bridge was 35m,and the span length is 35 m and 40 m at an oblique Angle of 60 and 30 degrees,respectively. |
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