Design And Numerical Simulation Of Foundation Pit Support Scheme Of Civil Air Defense Engineering Under Complex Environment

Due to its strong specialty,comprehensiveness and complexity,the foundation pit engineering is a hot and difficult problem in geotechnical engineering research.As China’s economic level continues to advance,urban construction land is more limited.How to ensure the safety of deep foundation pits under the conditions of narrow construction site and complex surrounding environment,and reduce the impact of deep foundation pits on existing building facilities has become a foundation pit project.Unreasonable design schemes not only cause waste of manpower and financial resources,but also may lead to engineering accidents,resulting in casualties.Therefore,this topic has certain practical significance.Foundation pit dewatering,support and monitoring are the three most important steps in the excavation process.Efficient precipitation can create a dry environment for the next step.An economical and reasonable support design is a prerequisite for ensuring the safe excavation of foundation pits.Foundation pit monitoring is a necessary measure to verify the design and guide the construction.This paper takes Yanji City’s anti-foundation pit project as the research background.Firstly,the Beijing Lizheng software was used to design the foundation pit support scheme and check the calculation.Then the numerical simulation software FLAC3 D was used to carry out the numerical simulation to obtain the deformation,settlement and internal force of the deep foundation pit supporting structure and its influence range and law.Considering that there are many buildings around the project and the distance is close,it is necessary to reduce the impact of the project and shorten the construction period.After comparative analysis,the support method of pile anchor support and row pile support and roof support is selected.Among them,the pile anchor support is constructed by the smooth method,and the pile support and the roof support are constructed by the reverse method.The foundation pit was divided into four sections according to the load on the upper part of the foundation pit and the surrounding buildings.The A-A section and the B-B section were supported by pile anchors,and the C-C section and the D-D section were supported by row piles and roof.The design results were verified by the overall stability check,anti-overturn check and anti-lift detection,and the rationality of the design is preliminarily verified.Using FLAC3 D software to numerically simulate the four section excavation process,the simulation data and monitoring data have a high degree of coincidence.The maximum values of the horizontal displacement of the pile top and the monitored values were 18.28 mm and 16.14 mm,respectively;the maximum values of the vertical displacement of the pile top and the monitored values were 20.64 mm and 19.22 mm,respectively.Moreover,the displacement values of the four sections at the loading location were large.In the A-A section and the B-B section,the inner force of the anchor cable was farther away from the pit wall,and the axial force of the anchor was smaller;while the bottom of the foundation pit of the C-C section and the D-D section had obvious bulging phenomenon.The simulation results can guide the construction.The design schemes made in this paper have been successful in practical engineering.