Analysis Of The Influence Of Pit-in-Pit On The Deformation Of Foundation Pit Enclosure Structure In Hengqin Soft Soil Area

With the rapid development of chinese urban modernization construction,to meet people's growing demands for work and life,a large number of super high-rise buildings have emerged and nearly half of the 100 tallest buildings in the world have been built in China.There were oversized and deep foundation pits,even excavated twice or more at the bottom of the foundation pit to form special pit-in-pit.At present,the development of the pit-in-pit projects presents a greater and deeper trend.However,the researches on pit-in-pit foundation pit at home and abroad are still limited,and the number of pit-in-pit has increased year by year.If the design of the pit-in-pit foundation project is too conservative,it will cause waste,on the contrary,it may lead to engineering accidents.Therefore,attention must be paid to the pit-in-pit construction problem.Hengqin New Area is a key demonstration area for exploring the new model of deep cooperation between Guangdong,Hong Kong and Macao under the principle of“one country,two systems”.Currently,as many as 27 buildings with more than 200 meters are planned to be constructed.The project examples which are rare in the country were analyzed as a typical pit-in-pit foundation pit projects in this paper.With the characters of large volume,deep excavation,soft soil thickness and so on.The article combines the main work and results of the project with the following aspects:(1)The theory and application scope of several commonly used rock and soil constitutive models are summarized,and verified through a foundation pit engineering example.Choose from the modified Mohr-Coulomb model for simulating the excavation of foundation pit in soft soil area as the constitutive model for numerical simulation.(2)The yifangda foundation pit was monitoringed,what is more,arrange and analyze the variation law of displacement and retaining structure in the process of ground settlement around foundation pit excavation.The yifangda excavation project of nonlinear finite element analysis is carried out at the some time,and the pit-in-pit excavation and pit retaining pile horizontal displacement curves of the two conditions of the foundation pit excavation is derived.It is consistent with the overall trend of the measured deformation curve.(3)Based on the existing calculation model,simplify it by single factor method of sensitivity analysis of many factors,the influence of pit-in-pit deformation such as,the depth ratio of pit-in-pit,the distance of inner-pit and outer-pit,pit-in-pit retaining pile stiffness,pit-in-pit retaining pile length,the stratum of foundation pit the depth of the soil properties,passive zone reinforcement depth and other parameters were simulated and analyzed.Summarize the influencing factors of pit-in-pit influence of foundation pit supporting structure deformation.(4)Finally,based on the above parameters and the measured data,the main causes of the alarm are analyzed,and the two kinds of bracing schemes are simulated by MIDAS/GTS.So choose the most reasonable supporting scheme.