Study On Optimization Of Foundation Pit Support Considering The Influence Of Important Adjacent Building

Based on the foundation pit engineering of parking lot entrance and exit line of Nanchang Urban Rail Transit Line 3,the optimization of foundation pit support for important buildings nearby is studied.In the paper,a comprehensive fuzzy evaluation system for building safety is established.In this system,the safety factors such as the building conditions,the current use situations of the building and the deformations of the building before the foundation excavation,which are often neglected by previous researchers in the process of relevant research,are taken into consideration as the evaluation factors of building safety.Based on the numerical simulation and comprehensive fuzzy evaluation system,the optimization method of foundation pit support are put forward,and then the support scheme of foundation pit is optimized by these optimization ideas.After all,the main results of this paper are drawn as follows:(1)According to the depth of foundation pit and the characteristics of surrounding environment,the entrance line is divided into four sections in order to select the most appropriate supporting scheme for the foundation pit.The structure of section 3 and section 4 are designed and calculated by Lizheng deep foundation pit calculation software.Furthermore,a multi-objective decision-making model is used for section 4 to optimize the support schemes(2)By establishing a three-dimensional numerical model,the law of retaining structure's deformation,surface settlement and the influence of foundation pit excavation on building are analyzed.Then,the inclination deformation,horizontal deformation and additional deformation of buildings caused by foundation pit excavation is obtained.(3)By inducing the comprehensive fuzzy evaluation method into the safety evaluation of buildings,a comprehensive fuzzy evaluation system for building safety has been established.This system includes five evaluation factors: excavation depth of foundation pit,structure and connection,service life,inclination and horizontal deformation of buildings.When the evaluation system is used to evaluate the safety of buildings before excavation and under the influence of foundation pit excavation the influence degree of foundation pit excavation on buildings is determined.It is found that after considering the conditions of the building itself and the deformation before excavation,although the deformation of the building during excavation does not exceed the specification,the building still will be in a safety state of grade 3,That to say,the damage of the building will affect the safety and stability of the structure,and the foundation pit excavation has a great impact on buildings,so the support of foundation pit needs to be further optimized.(4)Based on the numerical simulation and the comprehensive fuzzy evaluation of building safety,the optimization method of foundation pit support is put forward.The membership degree of the third-level safety state equal to 0.3 is taken as the building safety threshold.Based on the safety threshold,the residual allowable values of inclination and horizontal deformation of buildings in this project are calculated.Finally,by sensitivity analysis of the key support parameters,the optimization parameters and schemes are determined.(5)Field measured data show that the building eventually undergoes 0.39‰ tilt deformation and 1.6 mm horizontal deformation,which are all within the allowable range of residual deformation.The subordinate degree is not more than 0.3 for the buildings on the safety grade of third level.