Study On Working Characteristics Of Foundation Pit Retaining Structure Under Vertical Load

The rapid development of China’s economy has accelerated China’s urbanization process.With the development of urban underground space,a large number of deep foundation pit projects for subway stations have emerged.Foundation pit safety is currently the focus of attention in the engineering community.The failure of the foundation pit retaining structure is the direct cause of foundation pit accidents.In the past,scholars have rarely studied the working characteristics of the foundation pit retaining structure under vertical load.Rare,so the research content of this article has strong practical engineering significance,which can reduce safety risks for the design and construction of similar projects.This paper takes the foundation pit of the Jinqiao Passenger Subway Station of Nanning Metro Line 5 as the engineering background.The foundation pit retaining structure scheme adopts the structure system of "enclosing piles + rotary grouting between piles + internal support",which is analyzed through on-site monitoring data and numerical calculation models.The deformation law of the retaining pile of the foundation pit under the vertical load and the change of the axial force of the internal support,and according to the gray correlation theory,the importance of the factors affecting the maximum horizontal displacement of the retaining pile under the vertical load is calculated and sorted,and the results are obtained The main conclusions are as follows:(1)The monitoring results show that with the increase of the excavation depth,the deformation of the retaining pile body with or without vertical load is the same,indicating that the pre-acting vertical load has little effect on the deformation of the retaining pile body;When there is no vertical load,the horizontal displacement of the retaining pile body increases with the increase of the excavation depth.The pre-acted vertical load increases the maximum horizontal displacement of the retaining pile body by 20.2%,and the position of the maximum horizontal displacement of the retaining pile body It also dropped by 3m,which is about 18.8% of the excavation depth.At the same time,the pre-applied vertical load increased the axial force of the support in the first channel by about 14.9%,and the axial force of the support in the second channel by about 11.0%.The supporting shaft force has no obvious influence.(2)The numerical calculation results are in good agreement with the on-site monitoring values,indicating that the numerical calculation model and parameter values are reasonable.The numerical calculation shows that the horizontal displacement of the retaining pile is slightly larger than the measured value,and the established numerical calculation model is safer;the maximum level of the retaining pile The displacement increases in the form of an increasing power function within the range of 0.5 to 3.0 times the original design vertical load.When the vertical load increases to 3.0 times the original design load,the maximum horizontal displacement of the retaining pile is close to the warning value of 30 mm.The designer should be adequate Consider the adverse effects of vertical load;when the embedded depth of the retaining pile increases,the maximum horizontal displacement of the pile is less affected,but when the embedded depth decreases,the maximum horizontal displacement of the retaining pile is greater.The original embedded depth The design is reasonable;when the soil parameter c value and φ value increase in the range of0.8 to 1.3 times,the corresponding maximum horizontal displacement of the retaining pile is reduced by 7.5mm and 7.0mm,respectively,which are 29.5%and 27.6% of the original design maximum horizontal displacement,Which shows that the c value and φ value have a greater impact on the horizontal displacement of the pile.(3)According to the grey relational theory,the order of importance of the six factors is calculated as follows: soil parameter cohesion,soil parameter internal friction angle,second steel support diameter,second steel support wall thickness,and retaining pile Embedded depth,the magnitude of the vertical load have the greatest influence on the maximum horizontal displacement of the retaining pile.The impact of the vertical load on the horizontal displacement of the retaining pile is the only positive correlation among the six factors,so the vertical load is still an important factor to be considered.