Study On Deformation And Safety Control Of TRD Composite Support Structure In Wuhan Soft Soil Area

As high-rise buildings are becoming higher and higher,foundation pit projects are developing further and further and the complexity is also increasing.With the accumulation of more and more foundation pit supporting practices,the methods,forms and construction technologies of foundation pit supporting structures have developed and improved rapidly.Based on the super large deep foundation pit project of Hanzheng Street in Wuhan,the deformation and safety control of the new composite supporting structure in soft soil is studied.In order to effectively control the deformation of the supporting structure of deep foundation pit in soft soil layer,the law of deformation of composite supporting structure is analyzed by numerical model at first.Secondly,the monitoring data is analyzed through the description of the deformation monitoring scheme,especially the comparison of the measured data and the numerical simulation results,in order to find out the rules of the deformation of the foundation pit,and the rules are applied to engineering practice to form the safety control technology of foundation pit engineering of Hanzheng Street in Wuhan.The concrete contents and outcome are as follows:(1)The numerical model is established with software MIDAS to analyze the deformation of the supporting structure under the different working conditions of the composite supporting structure.The rules of horizontal and vertical displacement of the supporting structure of the foundation pit in Hanzheng Street project of Wuhan are analyzed,and the influence of the different supporting structure on the deformation of the foundation pit is figured out.The comparison between the actual monitoring results and numerical models of the simulated results validates the effectiveness of the MIDAS/GTS software in the simulation of foundation pit supporting engineering,and all the analysis results are within the permitted scope of the specification.(2)The detailed monitoring plan for actual projects has been worked out.The surrounding environment and the whole foundation pit are monitored,and the horizontal displacement of pile top,the deep horizontal displacement of TRD walls,settlement of pillars,and changes of underground water are monitored dynamically.Then the data obtained from the monitoring is analyzed,and they are reflected back to the construction.The deformation of the foundation pit in the following part of the same working condition and the next working condition are predicted,so as to determine whether the design and construction methods need to be changed,and give a direction to the construction.(3)The deep foundation pit excavation plan and the diaphragm wall as well as the inner support as the deep foundation pit retaining system are the key techniques to reduce the deformation of deep foundation pit.In the design,the middle braces,double row piles(middle TRD wall),and passive zone reinforcement(three axis mixing piles)increase the resistance of the passive areas to reduce the deformation of the supporting structure.In the construction,the island-type excavation and full usage of the time-space effect theory is applied,which refers to doing the jobs of excavating,cleaning and supporting at the same time.The scheme of "stratification,segmentation,symmetry,balance" is done.The whole process of monitoring is carried out on the foundation pit construction,and the deformation and safety-control measures of deep foundation pit are adjusted and optimized in time according to the monitoring results.The dynamic feedback guidance is carried out to realize the dynamic control of the deep foundation pit excavation,which can ensure the safety and reliability of foundation pit in the process of excavation..This new composite support method has wide application value in soft soil areas in Wuhan.