Study On Construction Optimization And Time-space Effect Of Ultra-wide Deep Excavation In Soft Ground

Due to the characteristics of high water-containing nature,creeping and being disturbed of soft soil layer easily,deep foundation pit engineering in soft soil area has been the focus and difficulty in the research of deep excavation engineering.This article relies on the super-wide and deep foundation pit project of Minglou Station of Ningbo Rail Transit Line 3.It uses numerical analysis,fuzzy analytic hierarchy process and value engineering theory,combined with the on-site monitoring data,to study the construction optimization of super-wide and deep foundation pits in soft soil and the space-time effects of super wide and deep foundation pits in soft soil.The findings and conclusions are as follows:(1)The article uses the PLAXIS finite element software based on the HS constitutive model in to numerically analyze the overall excavation conditions.The results show that the deformation of the foundation pit under this condition is large,and the construction safety of the foundation pit is difficult to guarantee.Therefore,a method for zoning excavation of the ultra-wide deep excavation project is proposed: a middle partition wall is added in the middle of the deep excavation to transform the super-wide deep foundation pit project into two deep excavation projects of equal width.(2)The numerical analysis of each working condition of the district excavation shows that the deformation of the foundation pit excavated by the district excavation is obviously smaller than that of the overall excavation,which verifies the feasibility of the district excavation scheme.Combining FAHP method and value engineering theory,to the article chooses the beat choice between the four working conditions of district excavation.The optimal working condition is: constructing all the ground connection walls firstly,and then separately constructing the two foundation pits.The optimal ground connection wall thickness and the number of steel support channels are 800 mm and 4 respectively.(3)The optimal plan is used to guide on-site construction.Analysis of the spatiotemporal effect of the foundation pit deformation through on-site monitoring data.The analysis shows that the numerical analysis of the deformation trend of the foundation pit is consistent with the monitoring data;the deformation of the long side of the foundation pit is greater than the short;When one foundation pit is excavated,the other foundation pit has a better restraining effect on the deformation of the foundation pit on this side;The change of the supporting axial force is affected by the location of the excavated soil.(4)During the construction on site,there are three suspended excavation time periods.The analysis of the monitoring data revealed that: The deeper the excavation depth of the foundation pit,the smaller the creep deformation of the foundation pit.The SCC constitutive model is used for numerical analysis to the suspended excavation conditions.The analysis shows that the deeper the excavation depth,the greater the structural rigidity of the foundation pit,so the creep deformation is smaller;The deformation of the foundation pit is affected by the soil pressure and the creep deformation of the soil together.