| Since the reform and opening-up,China's infrastructure construction has developed rapidly,the urbanization process has continued to advance,and the urban population has continued to increase.When improving urban traffic congestion,deterioration of living environment,and achieving sustainable development,academician Qihu Qian once said,the development and utilization of multi-level underground space will be promising,which inevitably involves foundation pit engineering.With the increasing construction scale and building height,the excavation area and excavation depth of foundation pits are also increasing,which puts higher requirements on the design of supporting structure.The topic about how to carry out foundation pit support safely,quickly,economically and reasonably to ensure the stability of the foundation pit during the construction process is a subject that needs to be studied in depth in foundation pit engineering.This paper takes a building deep foundation pit project with a excavation area of 8383m2 in Qi Lihe district of Lanzhou city as the research background.On the basis of summarizing the research status of deep foundation pit at home and abroad,supporting forms of foundation pit and stability analysis methods,according to the concrete engineering examples,the design and stability of the support structure are carried out,and the corresponding construction and monitoring schemes are put forward;The calculation and analysis of different working conditions in the foundation pit excavation process were carried out by using Li Zheng geology and Midas/GTS calculation and analysis software,and compared with the on-site monitoring values.Specifically carried out the following aspects:(1)According to the foundation pit design theory and a typical deep foundation pit project in Lan Zhou,the support scheme is determined according to the foundation pit engineering,hydrogeological conditions,support principles and design principles,and the construction technology,earthwork excavation and foundation pit monitoring are analyzed.The results show that the pile-anchor composite support system has strong applicability in deep foundation pit engineering in Lan Zhou area.(2)For the deep foundation pit pile-anchor composite retaining structure system,select the typical section,determine the design parameters,and use the Li Zheng pit support design software to calculate the shearing force and bending moment and displacement of the supporting structure in different excavation depths and use the strip method to check the overall stability of the foundation pit,anti-overturning stability,anti-lifting of the pit bottom and so on.The foundation pit supporting structure and surrounding displacement during the construction process were monitored,and the horizontal displacement of the supporting structure and the surrounding land surface settlement during the excavation of the foundation pit were analyzed.The results show that during the excavation process,the stress and deformation of the pileanchor composite support structure system meet the requirements of the specification,which can ensure the safety and stability of the deep foundation pit.(3)Using the Midas/GTS software,the three-dimensional structural model of foundation pit excavation construction is established,and two typical sections are selected.The pile-anchor composite retaining structure and surrounding soil deformation characteristics of foundation pit excavation under different working conditions are analyzed.And the numerical calculation results and the field measured data are compared and analyzed,and the deformation influence range of the foundation pit under different excavation conditions is determined.The numerical calculation results are close to the actual monitoring data,indicating that the numerical calculation results can provide reference for the analysis of foundation pit supporting structure under the condition that the parameters are consistent with the model. |
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