Optimization Analysis Of Envelop Enclosure Based On Monitoring Data Of Xin Fadi Station

Taking foundation pit engineering of Xinfadi Station of Line 19 of Beijing Subway as the background,and using Midas GTS NX simulation test,this paper analyzes the impact on envelop enclosure in detail that every step of foundation pit excavation and support.In this paper,it also concludes the deformation and stress characteristics of envelop enclosure through analyzing the monitoring data which are obtained by monitoring envelop enclosure horizontal displacement.And through comparing the experimental analysis with simulation data,validates the feasibility of the model.Meanwhile,this paper proposes an optimized scheme according to the existing supporting scheme.The specific conclusions are as follows:1)With the increasing of excavation depth,the maximum envelop enclosure horizontal displacement will increase,and the location of the maximum horizontal displacement gradually decline.It shows that the envelop enclosure horizontal displacement has good directivity and sensitivity to the security situation for foundation pit engineering.2)According to the survey,monitoring and simulation data,there is a silty clay layer that it's thick 6 meters below the ground at 24 meter.And the upper and lower layer is the pebbles.The elastic modulus is less than the pebble bed,this will cause that the lower part of the envelop enclosure will appear to the smaller pit migration.3)Through summarizing the monitoring data,it found that the curves of cumulative envelop enclosure horizontal displacement are that at the start of the project and the final the displacement increment is small,large displacement increment between intermediate stage.4)As the foundation pit excavation,the trend of the cumulative envelop enclosure horizontal displacement is that from funnel type(upper large,lower small)gradually to the parabolic type(central part large,upper and lower small),and will eventually stability in parabolic type.5)In this paper,the design scheme of foundation pit support is optimized by changing the embedded depth of the envelop enclosure.Original supporting design scheme for envelop enclosure built in depth and pile length ratio of 1:4,so optimization of build-in ratio of 1:4.2,1:5,1:6,1:7.And combined with the soil information and simulation test data of foundation pit,it proves that selection optimization the second optimized plan(build-in ratio of 1:5)is the most reasonable.