Research On Engineering Geological Characteristics Of Multi-sedimentary Facies And Multi-modal Soft Soil In Shaoxing Area

Soft soil is a kind of special soil with high moisture content,strong compressibility and low strength,which is widely distributed in China.Engineering construction in areas with soft soil usually faces engineering problems such as low bearing capacity of foundation,large deformation of foundation and differential settlement of ground,which seriously endanger the safety of building.Therefore,in order to ensure that the engineering design and construction can be carried out smoothly and orderly,it is very necessary to study the engineering geological characteristics of the target area in advance.Shaoxing is located in the south bank of Qiantang River in Hangzhou,Zhejiang Province and the west of Shaoxing Plain in Ningbo Province.Soft soil in this area is very widely distributed.In recent years,with the revitalization of Shaoxing economy and the pace of capital construction matching with economic construction accelerating,more and more largescale projects have been built in Shaoxing.In the process of project construction,it is inevitable to encounter various engineering geological problems related to soft soil foundation.In this paper,the engineering geological characteristics of soft soil in this region are deeply studied from several aspects,such as the genetic types and distribution characteristics of Shaoxing soft soil,the physical and mechanical characteristics of Shaoxing soft soil,the composite characteristics of Shaoxing soft soil and cement,and the influence of soft soil mode on foundation pit excavation,the following conclusions are drawn:(1)Based on a large amount of drilling data and geotechnical test data,the physical and mechanical properties of the soft soil in Shaoxing area are analyzed by mathematical statistics.The results show that the soft soil in Shaoxing area has the high water content and high void ratio of general soft soil.,High compressibility,low shear strength and low bearing capacity,and its natural moisture content and natural density have a good correlation with physical indicators such as void ratio,liquid-plastic limit,and plasticity index.The empirical formula of the correlation relationship.(2)The content of mica in soft soil is related to sedimentary facies,and the influence of mica content and mesh number on the compressive strength and shear strength of cement soft clay is studied through unconfined compressive strength test and shear test.The relationship between mica content,mesh number and the compressive strength and shear strength index value of cement soft clay(In the formula,w and a respectively represent the content of mica and the number of meshes of mica;qu、c、φ are the unconfined compressive strength,cohesion and internal friction angle in sequence):qu=1.198+0.002117a-2.708w(R2=0.938)c=86.72+0.05167a-27.70w(R2=0.911)φ=22.95+0.0155a-3.364w(R2=0.806)(3)The mode of soft soil was defined according to the depth and thickness of the soft soil and the properties of the adjacent soil.Based on the foundation pit excavation case of Shaoxing Metro Line 1 Higher Education Park Station,the numerical simulation was conducted to study the influence of the mode of soft soil on the excavation deformation of the foundation pit.After comparative analysis of the numerical results,it is known that with the increase of the buried depth of the soft soil,the increase of the layer thickness of the soft soil and the weakening of the engineering properties of the adjacent soil layer,the deformation caused by the excavation of the foundation pit generally presents an increasing trend.