Design Of Support Parameters For Deep Foundation Pit In Sand And Cobblestone Stratum

With the rapid and steady development of China’s economy,the scale of urban construction continues to expand,such as public transport,underground commercial streets,high-rise housing and other projects.Subsequently,urban land resources became increasingly scarce,and the attention of urban space development gradually shifted to the development of underground space,forming a three-dimensional city.At present,there are more and more large excavation areas and deep foundation pits,but there are also some tragic cases in the excavation of foundation pits.It is particularly important to ensure that the foundation pit excavation process is stable and will not affect the surrounding buildings and land surface settlement.Deep foundation pit support is a very complex engineering,involving soil mechanics,structural mechanics and material mechanics and other complex disciplines,some experts and scholars at home and abroad have also made a lot of achievements in the research of foundation pit support.But in sandy pebble formation in the construction of foundation pit how to select the type of foundation pit supporting is correct and reasonable doubt,therefore,based on kang la river south of Yunnan Province to regulate pool the engineering background of foundation pit supporting project,through field survey,geological exploration data analysis,theoretical analysis and numerical simulation methods of retaining structure,the sandy pebble stratum of the foundation pit supporting design theory and method of foundation pit supporting,south la river regulation pool type identification and type stress distribution under different working conditions were analyzed,and obtain the following results:(1)The main formation at the site of foundation pit of tiaoyu reservoir in nanla river is composed of gravel sand,pebbles and residual slope stratification.The main factors affecting the deformation of the foundation pit are as follows: the first is the deformation of the retaining structure;the second is the deformation of the surrounding surface caused by the excavation of the foundation pit,which is caused by the insufficient supporting force of the retaining structure.At the same time,the geological conditions where the foundation pit is located should be taken into account to design and optimize the design parameters.(2)Sorting out and analyzing the comparison and selection methods of foundation pit support schemes,and analyzing the applicability of each method.This paper introduces the general situation of the foundation pit supporting project and the relevant contents of the hydrogeological conditions of the regulating and storing pond in Nanla river,Mengla county,Yunnan Province,and points out that the foundation pit is located in the sand and gravel stratum and the depth of the foundation pit is up to 10 m.It is concluded that the supporting scheme for the foundation pit of Nanla regulating and storing pond in Mengla county of Yunnan Province is the supporting scheme of anchor and pull piles.(3)In the excavation process of the foundation pit,the lateral wall is displaced to the side of the foundation pit excavation.The lateral displacement of the top of the foundation pit is small,and the lateral displacement increases with the increase of the burial depth.The settlement of the soil outside the pit is of the "inverted triangle" type,and the maximum settlement occurs at the side of the foundation pit.The influence range is mainly at the place 10 meters away from the foundation pit.In the process of foundation pit excavation,the deformation law of support structure is as follows: with the advance of foundation pit excavation,the maximum stress position of pile body gradually decreases while the stress of pile body gradually increases.Therefore,in actual construction,support and detection frequency of bottom pile foundation should be strengthened.In the process of foundation pit excavation,applying bolt can reduce the lateral displacement value of the side wall of the foundation pit.The stress of the upper row bolt is obviously greater than that of the lower row bolt,and the supporting effect of the prestressed bolt is not obvious.The control effect of changing the depth of the pile is the best,followed by increasing the strength of the pile.