Study On The Integral Design Method Of Deep Excavation And Small Strain Parameters Of Typical Strata In Jinan

Excavation is a three-dimensional system,whose deformation is closely related to the shape,size,depth of the pit and the dynamic interaction between soil and retaining structure.The existing theory and design method are difficult to meet the increasing depth of excavation decision-making needs,and numerical analysis has become an important way to solve this problem.The 3-D finite element model of excavation,soil constitutive and its parameters are the key to the numerical calculation.This paper defines the integral design method and suitable constitutive model for the stress history and state of deep excavation,and establishes the standard strata of deep excavation in typical geomorphic unit in Jinan City.Meanwhile this paper defines and obtains the soil parameters and Selection methods,and reveals the deformation law of deep excavation in typical strata of Jinan by using PLAXIS 3D.The findings are summarized as follows:(1)For the whole life decision-making of design,construction,monitoring and optimization of deep or ultra-deep excavation,the integral design method for deep excavation is defined.It takes the deformation of the surrounding environment as guide,and takes the dynamic and active adjustment of the supporting structure as the means to ensure the safety of excavation and its surrounding environment.(2)According to the sequence of age,genesis and lithology,the standard strata and its sequence in Jinan are divided.According to the existing experience and future plans,it is determined that the piedmont alluvial-proluvial,intermountain alluvial-proluvial and Yellow River alluvial geomorphic units in Jinan are three typical strata of deep excavation.(3)The HSSM(Hardening soil model with small strain stiffness)is suitable for the numerical analysis of excavation.The 13 parameters of HSSM in three typical deep excavation strata are determined:9 parameters can be obtained by survey test or general experience;the other 4 stiffness parameters need to be obtained by displacement back analysis.(4)Based on the excavation depth,the deformation laws obtained by numerical calculation with HSSM and M-CM(Mohr-Coulomb model)are compared.The "depth effect" of excavation is proposed,that is,with the increase of the depth,the results calculated by conventional constitutive model such as M-CM are gradually distorted.It is determined that the excavation with a depth of more than 15m is a deep pit.(5)The different deformation laws of soil and soil-rock excavation in Jinan City are obtained:for the former,the maximum lateral displacement of the retaining structure is near the excavation surface,and the surface settlement range behind the wall is 2.5-3.0 times of the excavation depth;for the latter,the maximum lateral displacement of the retaining structure is generally 3-5m above the rock stratum,and the surface settlement range behind the wall is 1.5-2.0 times of the excavation depth.