The Analysis On The Stability Of The Foundation Pit Under Open-cut Station

At present,the subway is in full swing to build.It isn’t be ignored that the stability of the pit during the construction process.Thus,it is an important issue that the study of the foundation pit on the envelope structure stress and strain.Based on the Taihu Road Station of Hefei Rail Transit Line 1,the deformation law of the envelope structure and the surface settlement were researched by combining the real-time monitoring date of the foundation and the finite element Midas GTS/NX numerical simulation.The main work and conclusions are as follows:(1)The development of the envelope structure at home and abroad,and the construction technology of Open-cut were described.And the hydrological and geological conditions,the design,and the monitoring plan of the Taihu Road Station were introduced in this article.(2)The third-party monitoring scheme of the Taihu Road Station was referred.Through the finishing of the real-time monitoring data,the influence of foundation pit on the surface settlement and the horizontal shift of pile body and pile top is analyed.The results show that the horizontal shift of pile body shows the "bow" shape of small at both ends and large in the middle with the depth of the excavation,and the maximum displacement occurs at 0.5H(H is the excavation depth of the foundation).The deformation of the envelope structure in vertical direction of the pit is controlled by the supporting structure that can reduce the horizontal displacement of the pile body and affect the distribution along the excavation depth.With the continuous excavation of the foundation pit,the horizontal displacement of the pile top is gradually increasing,and the whole tends to the foundation pit.And the surface settlement at a certain distance from the outer edge of the foundation pit is maximum,the entire sedimentation curve is a "spoon type".(3)The Midas GTS / NX finite element numerical simulation is used to simulate the excavation process of the Taihu Road Station.The results show that the law of the stress and strain of the envelope structure,the maximum pile horizontal displacement position and the variation law of the surrounding surface settlement are consistent with the real-time monitoring.In the corner of the envelope structure is prone to stress concentration,and the stress concentration is also present on both its sides.(4)The calculated values were compared with the monitoring data,the result of the parameters of the model is reliable.In the actual construction process,there is a certaindeviation because of many uncertain factors during the calculated values and the monitoring data,but it can reflect the whole deformation of the foundation pit in the excavation process.It can be used to predict the envelope structure and the surrounding surface settlement in the region with similar to Heifei geology.(5)The surface settlement is closely related to the horizontal displacement of the pile body and the pile top on the envelope structure.The pile top will be offset by the deflection of the pile body to the pit,accordingly,the surface will be settled,and vice versa.Therefore,in the actual construction project,the need for comprehensive analysis of these three monitoring data to ensure the safety and stability of the foundation pit.