| Sichuan is dominated by mountainous and hilly topography,and construction projects often encounter excavation and filling.With the development of the national economy,many major infrastructure projects and high-rise and super-tall buildings are located in prefecture-level cities in the mountainous areas of Sichuan.These projects will inevitably carry out excavation and support of deep foundation pits.In the deep foundation pits in the mountainous areas,there are deep earth filling layers and soft plastic muddy soil layers.When selecting the support structure,the composite support structure is widely used because of its economical safety,space saving,good support effect,and full performance of the performance of each support structure.This paper selects the composite support of a deep foundation pit project in the prefecture-level city of Neijiang City in the Sichuan mountainous area for analysis and research.Firstly,the design and verification of the deep foundation pit composite support structure are carried out by using the Lizheng design software.Then use MIDAS/GTS finite element software to make an overall three-dimensional modeling of the whole foundation pit,simulate the construction process,and study the variation law of horizontal displacement,surface settlement displacement and soil nail axial force of deep foundation pit under various working conditions.Finally,the numerical simulation value,the calculated value of the rational design software and the actual monitoring value are compared and analyzed.The results of this study show that:(1)The diameter of piles and the depth of piles have an important influence on the deformation of foundation pits.Under the premise of other conditions,this paper uses Lizheng software to solve the problem of row piles only when changing the diameter of piles and the depth of piles.The maximum horizontal displacement can be found to ensure the safety and economy of the foundation pit support structure when the pile diameter is between 1.3m and 1.5m and the depth of the embedding is between 1.0H and 1.2H(H is the pit depth).(2)Simulation of the composite support structure of the foundation pit by MIDAS/GTS finite element software,it is found that the maximum horizontal displacement and vertical displacement occur in the middle of the foundation pit;the maximum displacement of the pile occurs at the top of the pile;With the increase of the depth of the foundation pit,the sprayed concrete surface layer and the soil body are tightly combined,and the displacement is consistent with the displacement of the soil body;the connection effect of the crown beam on the row pile is obvious,and the deformation of the two is consistent.(3)The MIDAS/GTS simulation value is basically consistent with the deformation law of the monitoring value.The displacement deformation curve of the MIDAS/GTS simulation is similar to the shape of the Lizheng calculation curve.The maximum displacement of the row pile is 1.92 mm larger than the MIDAS/GTS simulation value,and the calculated value is safe.For the project,the numerical simulation value and the positive calculation value are higher than the actual monitoring value,and the higher simulated value and calculated value can ensure the safety of the foundation pit construction.In order to accumulate experience in practical engineering modeling in the future,based on the research and analysis of this paper,the next step should be to analyze multiple examples to obtain the Lizheng and economical rationality and MIDAS/GTS recommendations. |
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