Research On Deformation Characteristics Of Foundation Pit In Soil-Rock Combination Strata Based On HSS Model

As the city’s infrastructure is becoming more and more perfect,the surrounding environment has become increasingly demanding on the deformation of the underground pits of subway stations.Jinhua City,Zhejiang has a special combination of soil and rock formation conditions,that is,the excavation of the foundation pit is composed of overlying soil layers and underlying rock layers.Because of the large difference in physical and mechanical properties between the soil layer and the rock layer,the foundation pit has its unique characteristics Deformation characteristics.In this paper,based on the foundation pit of Renmin Road Metro Station in Jinhua City,based on the HSS model,the deformation characteristics of the foundation pit in soil-rock composite strata are investigated.First,the BP neural network optimized by genetic algorithm is used to invert the parameters of the HSS model.The three-dimensional numerical simulation software PLAXIS 3D is used to study the deformation characteristics of the foundation pit of the soil-rock composite stratum using the HSS model.The main contents and conclusions are as follows:(1)Through orthogonal analysis and design,determine the sensitivity of the foundation pit deformation to the typical parameters of the HSS model.The study found that the small strain parameters and the reference tangent modulus of the HSS model affect the deformation of the foundation pit Larger.The three sensitive parameters are selected,and the BP neural network model optimized by genetic algorithm is established to reverse the parameters of the HSS model of the soil-rock combination stratum in this study.(2)Based on the study of the HSS model,it was found that during the excavation of the foundation pit,the deformation experienced three stages of gentle-rapid growthstability.In the first stage,the excavation depth is shallow,and the deformation is relatively smooth;in the second stage,when the excavation reaches the soil-rock interface,the deformation of the foundation pit develops rapidly,which is a rapid growth stage;in the third stage,when the excavation enters the lower rock layer,The deformation of the foundation pit slowed down significantly and tended to be stable.Moreover,the deformation of the foundation pit mainly occurred during the excavation of the overlying soil layer.The deformation of the foundation pit slowed down significantly during the excavation of the lower rock layer,indicating that compared with the soil foundation pit,the foundation pit of the soil-rock composite formation due to the presence of the lower rock layer makes the foundation pit stable has seen an increase.(3)Based on the HSS model,the simulation study on the influencing factors of the deformation characteristics of the foundation pit shows that under the premise of reasonable control of the construction influencing factors and design parameter influencing factors,the thickness of the overlying soil layer,the strength of the rock and the depth of the embedded rock are the deformation of the foundation pit of the combination of soil and rock.The main influencing factors.With the increase of the thickness of the overlying soil layer in the foundation pit,the deformation of the foundation pit is significantly increased,indicating that the presence of the lower rock layer in the foundation pit of the combination of soil and rock has a certain limiting effect on the development of the deformation of the foundation pit;There is a certain impact.When the strength of the overlying soil layer decreases,the deformation of the foundation pit gradually increases;the change of the strength of the lower rock layer also affects the deformation of the foundation pit,which can play a role in limiting the deformation of the foundation pit to a certain extent;The influence of the pit deformation characteristics is relatively limited.When the depth of rock-embedded is increased to a certain value,the restraining effect on the foundation pit envelope structure is not very obvious.