Research On The Stability Of Asymmetric Excavation Pit And The Influence Of Local Component Failur

The calculation of excavation stability is particularly crucial in the design of excavation engineering.The instability and damage of excavation mainly fall into two categories: firstly,the weak soil strength leads to the instability and damage of the excavation,such as overall sliding,overturning or kicking of the support structure,and uplift of the pit bottom;secondly,insufficient strength of the support structure leads to damage,resulting in instability and failure of the excavation.Many scholars have conducted a series of studies on the instability of excavations caused by soil strength,as well as the progressive collapse caused by insufficient strength of support components.At the same time,national standards have also recommended corresponding calculation methods.However,the types of building foundation pits are increasing with development,and there are increasingly asymmetric excavations with small width to depth ratios and different excavation depths on both sides.There is a lack of research on such excavations.This study analyzed and calculated the stability coefficient and support stiffness coefficient of asymmetric excavation with small aspect ratios;Using indoor model tests combined with the three-dimensional finite element software PLAXIS 3D,a study was conducted on the impact of asymmetric excavation of local components after failure due to insufficient strength.The specific work content and conclusions are as follows:(1)When the retaining piles of a foundation pit constrain the sliding failure of soil,the sliding failure surface and force distribution will change.This study proposed a stability coefficient calculation method for asymmetric excavations with small width-to-depth ratios,based on an analysis of asymmetric soil as backfill.This approach complements traditional theory.A correction approach for the support stiffness coefficient of asymmetric excavations was developed based on the theory of common deformation.The proposed method considers the characteristics of mutual interaction and asymmetric excavation,and can save costs to some extent compared to standard methods.It provides a reference value for the design and calculation of such excavation support structures.(2)Through indoor model tests using asymmetric excavations,the variations in the settlement of the surrounding soil,top displacement of the retaining structure,axial force of the support,soil pressure behind the wall,and bending moment of the retaining structure were studied under different excavation and support failure scenarios.Results showed that,during excavation,the shallow-side board displaced towards the outside due to the support force from the deep-side board.Failure of adjacent supports caused an increase in axial force,while failure of distant supports caused an increase in soil pressure.Multiple support failures led to unloading effects and significant movement towards the excavation.(3)Using PLAXIS 3D software and component removal method,a numerical simulation was conducted on an asymmetric excavation pit with different initial failed components,excavation depth differences,and different failure positions of local components.The response of the overall support system was analyzed.After support failure,the piles located in the failure area produced unloading effects,reducing soil pressure,while nearby support piles showed the opposite effect,with significantly increased bending moment.The maximum settlement of the soil was smaller on the shallow side compared to the deep side,and the settlement increased with the number of failed piles while the settlement range remained almost constant.A design method for enhancing the resistance of the support structure to continuous failure was proposed by amplifying the reinforcement bending moment of the support piles.