| As one of the important engineering characteristics of soft soil,creep is easy to cause continuous deformation of the soil.and retaining structure of the foundation pit during the excavation of the foundation pit,which brings certain challenges to the deformation control of the foundation pit engineering.Based on this problem,this paper relying on a foundation pit project in Wenzhou with deep silt layer,explores the creep characteristics of silt soil samples through indoor triaxial undrained creep test,and then fits the creep test data to establish a silt empirical constitutive models of strain-time and stress-strain relationships.Finally,the actual foundation pit case is introduced,and the deformation influence law of silt creep effect in foundation pit excavation exposure is analyzed by ABAQUS numerical simulation software.The main research methods and conclusions are as follows:(1)Triaxial undrained creep test and cyclic loading and unloading creep test were carried out on silt soil samples,the development trend of silt creep was systematically studied,and the nonlinear and elastoplastic deformation of silt were analyzed in detail.Analyzing the strain-time curve of the silt soil sample shows that the silt creep is attenuated under low stress levels,and under the middle and high deviator stress levels,the attenuation and constant velocity are connected before and after;the stress-strain isochronous curve of the silt soil samples is obtained.The silt creep is a non-linear creep,and the degree of non-linearity is positively correlated with the surrounding pressure of the soil,the deviator stress level,and time;the superposition analysis of the cyclic loading and unloading creep test data of the silt soil sample shows that the silt’s total deformation is dominated by plastic deformation,and the creep part is dominated by visco-plastic deformation.The proportion of elasto-plasticity is affected by the degree of consolidation and the deviator stress level.When the degree of consolidation is higher and the deviator stress level is smaller,the proportion of elasticity is greater,The smaller the plastic deformation(2)Based on the creep test data of silt soil samples,the Singh-Mitchell(power-finger),Mesri(power-hyperbola),and ABAQUS time hardening(power law)creep are respectively determined for different stress-strain and strain-time relationships.Parameter identification of the model is carried out,and the corresponding constitutive model of silt creep is established.The results show that the Mesri and time-hardening creep model describe the creep characteristics of the silt soil samples in this paper better.(3)Numerical simulation of excavation of foundation pits with ABAQUS software.The results show that when only the Drucker-Prager elastoplastic constitutive model is selected for simulation calculation,the simulation can better reflect the deformation laws of foundation pits under different excavation conditions;when the Drucker-Prager elastoplastic constitutive model is selected for coupling time hardening When the creep model is used for simulation calculation,the deformation calculation results are significantly different than when the creep effect of the silt layer is neglected,and it is closer to the actual monitoring data.(4)The finite element software is used to analyze the creep effect of the foundation pit under long-term exposure.The results show that when the foundation pit is exposed for a long time after excavation,the creep effect of the silt layer soil will continuously increase the horizontal displacement of the pile,the lateral displacement of deep soil,surface settlement,and supporting axial force have little effect on the base uplift.When the bottom of the pit is in an elastic uplift,the effect of creep can be ignored.(5)Analyze the deformation rate when the foundation pit is exposed after excavation,and give some engineering suggestions.When the excavation of the foundation pit is shallow and unsupported,the deformation caused by the creep is extremely severe in the early stage,and then quickly stabilizes.At this time,it should be supported in time to minimize the impact of the early high-speed creep;when the foundation pit is in a supported state When the deformation development is slow,the construction can be arranged according to the monitoring situation.If the engineering conditions are similar to the conditions in this article,the exposure period of the foundation pit shall not exceed 1 month after the completion of the excavation. |
PDF Full Text Request