Research On The Application And Settlement Prediction Of Foamed Lightweight Soil In The Expansion Of Existing Soft Soil Subgrade

The existing road expansion has become the main measures to improve road capacity,meet the traffic growth and social demand.However,the settlement deformation will be occurred in the old subgrade under the action of additional loads when the existing road expansion.Different settlements will be occurred between the old and new subgrades,which can cause road damage in severe cases.In order to ensure the quality of road expansion project,the subgrade deformation characteristics of the new and old roads,as well as the differential settlement are issues to be noticed in the expansion of soft foundation roads.The background of the paper is the application of foamed lightweight soil in the expansion proj ect of Limu Road in Jiangmen.Based on the combination of on-site investigation,theoretical analysis,laboratory test,on-site monitoring and numerical simulation,the deformation laws of the existing soft foundation road expansion and the settlement characteristics of soft soil foundation replaced by foamed lightweight soil are studied.The main work and research results completed are as follows:(1)Based on the laboratory soil test of the undisturbed soil,the basic physical and mechanical parameters of soil in the new and old subgrade are obtained.The results show that there are obvious differences in the soil parameters between the new and old roads.The natural density and specific gravity of the soft soil in old road are larger than those in new road.The water content,void ratio,compression coefficient and compression index of the soft soil in old road are smaller than those in new road.Morover,the goodness of fit test of the physical index parameters in the Jiangmen area is carried out based on K-S test.The distribution of the parameters mainly obeys the normal distribution and log-noraml distribution.(2)Based on the correlation characteristics of physical and mechanical parameters of muddy soil in Jiangmen area,the empirical equations of compression index are established by regression analysis method.The evaluation index,ranking distance,is introduced to evaluate the applicability of the new equation and existing empirical equations in Jiangmen area.The results show that the empirical equations’applicability has a regional sensitivity.The new equations for the Jiangmen region can achieve a better performance than the existing empirical equations,and the calculated compression index value is more accurate.(3)Based on the different control standards of compression layer thickness,the compression layer thickness of soft soil foundation replaced by foamed lightweight soil is studied.The results show that the "deformation ratio" method is reasonable for determining the compression layer thickness.Based on the theoretical calculation and numerical calculation,the effects of lightweight soil replacement thickness and soft soil thickness on the settlement of the extended roadbed and their interaction relationship are studied.The equation y=0.7174e0.0435x between the soft soil thickness and the lightweight soil replacement thickness is established based on the regression analysis.The verification analysis based on numerical simulation and engineering examples proves that the equation has good applicability.(4)The deformation and settlement characteristics of the new and old subgrades are studied on the basis of the obserbation data.The monitoring results show that the expansion project has more influence on the shallow soil of the new and old roads than the deep soil,and the settlement of new road is larger than that of the existing road.The maximum settlement is generated at the joint of the new and old subgrades.The settlement of the section shows a "spoon" shape.(5)Based on the numerical model considering the fluid-solid interaction,the dynamic simulation of the whole process for road expansion construction is realized.It reveals that there are some problems such soil rebound,secondary settlement of old subgrade in the construction process of road expansion.Comparing the numerical simulation results with the monitoring results,the trend of profile settlement,stratified settlement and pore water pressure are basically the same.which verifies the rationality of the application for foamed lightweight soil in the expansion proj ect of existing soft foundation road.(6)According to the analysis of the characteristics for Richards model,the characteristic properties of the model can reflect the instantaneous settlement,satisfy the consolidation conditions,and meet the law of the subgrade settlement.Then the Richards growth model is introduced to predict the settlement of the soft soil subgrade.To improve the prediction accuracy of the Richards growth model,the bidirectional difference-weighted least squares method is proposed.The settlement prediction analysis is carried out based on the obserbation data of the engineering examples.The results show that the performance of the Richards model with the bidirectional difference-weighted least squares method is superior to those of other available models.The method can yield high prediction accuracy.