Study On The Safety Of Pile-supported Retaining Structure Based On Soil And Rock Combination

With the rapid development of urbanization and the continuous improvement of infrastructure level,the urban traffic problem is becoming increasingly prominent.As an important project of people’s livelihood,the construction cost of urban subway is huge,and there are many concealed works,and there are many uncertain factors.Therefore,the requirements for the construction of deep foundation pit are very high.Rapid development and urban rail transit in China,the complexity and anisotropy of foundation pit engineering are increasingly prominent.The past general specifications need to be detailed and summarized on the geological conditions,hydrological conditions and other external conditions.Geological differences can lead to biased conclusions.Therefore,it is necessary to carry out regular analysis on the safety of the envelope structure under special geological conditions.For deep foundation pit engineering,the stability of foundation pit is an important aspect to be considered.Due to the special geological conditions in Jinhua area,it is a typical binary stratum,the upper part is soft soil and the lower part is weathered rock.There are few researches on actual engineering and related researches of bored cast-in-place pile with internal support,and there is a lack of engineering experience for reference.Related problems need to be further explored.In this paper,based on the Jinhua Wanda Plaza project,Statistics and Analysis engineering measured data,compared with other soil pile bracing foundation pit.The deformation law and characteristics of foundation pit of soil and rock composite pile bracing retaining structure in Jinhua area are analyzed.Combined with the establishment of the corresponding finite element model,the single factor foundation pit stability analysis was carried out on the insertion ratio,the depth of geotechnical interface and support spacing,and the variation rule of foundation pit stability was summarized.To provide some reference for similar foundation pit engineering in Jinhua area,the research results of this paper are as follows:1.Arrange the Wanda Plaza Station measured soil pressure data,draw the curve of earth pressure with depth,combining the soil distribution and other binary soil foundation pit engineering,summarized in Jinhua region soil rock combination of two kinds of earth pressure distribution form.The earth pressure distribution approximates to triangle distribution when the excavation face is above the geotechnical interface,and the earth pressure distribution is approximately "R" type when the excavation face is below the geotechnical interface.This rule is also found in the soil and rock combination engineering in other areas.2.The measured data of foundation pit deformation of Wanda Plaza Station are analyzed.The curve of surface settlement,horizontal displacement of pile body and pile top displacement are summarized,and find the deformation range.It provides reference for the deformation control standard value of deep foundation pit in Jinhua area.The surface settlement distribution behind the surface settlement pile presents a groove type,and the maximum settlement is located at 0.2-0.4H behind the pile.The horizontal deformation of the pile presents a spindle-shaped distribution with small ends and large middle ends.The maximum value is14.1mm,located at 0.35 H close to the pile top and close to the depth of the geotechnical interface.The horizontal displacement of the pile is between 0.013% H and 0.125%H.The horizontal displacement direction of pile top is mainly in the pit,and the vertical displacement is mainly represented as settlement.The average vertical displacement of pile top is 0.94 times the horizontal displacement of pile top.3.Combined with the finite element model calculation results,it is concluded that the different the depth of geotechnical interface,insertion ratio and support interval stability coefficient variation law.The antioverturning stability increases negatively with the height of the rock face and positively with the insertion ratio.There is a 1.89 times relationship between the growth relaxation point and the anti-overturning critical point in the insertion ratio.Anti-uplift stability coefficient is positively correlated with insertion ratio,but there is no-significantly correlated with support spacing.The overall stability coefficient is positively correlated with the insertion ratio,but there is no obvious correlation with the depth of rock surface.Insertion ratio has great influence on anti-uplift stability and overall stability.