Robustness Study On The Retaining System For Underground Storey Supplement Based On The Component Importance Coefficient

Pile row is one of the commonly used excavation support forms in the construction of underground storey-adding reconstruction and expansion project.In order to control the risk of excavation,it is particularly important to evaluate the robustness of pile row retaining system.Existing support may fail due to accidental events during excavation.In order to further study of foundation pit retaining system robustness,this paper established a pile layer plane truss model,puts forward the importance of a single component evaluation index,and using numerical simulation software to analyze the support failure procession the process of increasing layer excavation combining with the conclusion of the shape of the foundation pit,soil parameters,the supporting stiffness of row spacing on the component importance coefficient etc.The main work and achievements of this paper are as follows:(1)In view of the existing(old)-new row pile support system for underground layer increment,a theoretical calculation model of plane strain was established.Based on the importance coefficient of stiffness of row pile members,corresponding algorithms were developed to search for the key risk factors in the process of underground layer increment.(2)The three-dimensional finite element modeling software was used to simulate the continuous failure of the foundation pit support system structure,and the importance coefficient of the component was further simplified to make it possible to evaluate the importance of the support system component in the three-dimensional space.Then to figure out how the length of the foundation pit in different positions,different soil quality,different diameter of new row pile take influence on the robustness of it.The results show that the soil condition is the main control condition for the soil to be able to bear the damage during the excavation.(3)Based on the analysis of an example of excavation with additional layers,the three-dimensional finite element modeling is carried out by using the soil parameters measured and the actual design structure parameters.,to simulate the effct of component local failure in actual situation.Furthermore,the components of different lengths of the sides of 1-type foundation pit,the stiffness of different row piles,the spacing of different rows,and whether there is support are analyzed.The results show that the importance of existing support is different in different sides.The importance of existing support decreases with the increase of side length.For the foundation pit with the same soil condition,the number of damages can be borne is limited.The degree of continuous foundation pit failure does not change with the change of failure location.The support in the support system can improve the deformation of the support system in the normal excavation stage,and has little effect on the resistance to continuous damage when the local members fail.