Settlement Calculation And Control Scheme Optimization Of Lakeside Soft Soil Subgrade Based On Physical And Mechanical Index Statistics

Soft soil is a special type of soil formed by beach deposition and swamp deposition.It has low bearing capacity,high natural moisture content,large compressibility,small permeability coefficient,low shear strength,prone disturbance,significant rheological properties,and strong regionality.In addition to being mainly distributed in coastal areas,soft soil is also commonly found in inland lake banks,river banks,and low-lying areas.During road construction,it is inevitable to encounter soft soil areas,which can easily lead to subgrade settlement,resulting in settlement diseases such as pavement cracks and bridgehead jumping.Therefore,it has become an indispensable part of geotechnical engineering research to carry out research on the characteristics of soft soil,master the settlement law of soft soil subgrade,and carry out reasonable treatment of soft soil.Jinan Weishan Expressway Project is adjacent to Weishan Lake.The lakeside soft soil subgrade sections of the project has the characteristics of high groundwater level,high natural water content,high compressibility,low bearing capacity and poor permeability.These characteristics make it easy to produce large settlement deformation and it will continue for a long time under long-term load.Therefore,the calculation of subgrade settlement in soft soil area is particularly important.In this way,a safe and economical foundation treatment method can be selected to ensure the safety of road engineering.Based on the statistics of the physical and mechanical indexes of the lakeside soft soil layer of a highway project from Jinan to Weishan,this paper studies the settlement calculation and control scheme optimization of lakeside soft soil subgrade.And the paper adopts some research methods of theoretical analysis,laboratory test,numerical simulation and combination of engineering applications to improve the calculation method of subgrade settlement,optimize the subgrade settlement control plan,and guide on-site construction.The main research contents and conclusions are as follows.(1)Based on the statistical results of physical and mechanical properties of lakeside soft soil foundation,the paper analyzes correlations between natural void ratio and natural water content,natural void ratio and wet density,natural void ratio and liquid index,compression modulus and natural water content,compression modulus and wet density,compression modulus and liquid index were analyzed.An empirical formula for the correlation of physical and mechanical properties is established.(2)Through the geotechnical test of subgrade filling,the calculation formula of subgrade settlement with time under traffic load is established.The e-p curve derivation formula is improved,and the Es-p empirical relationship is derived by using the correlation empirical formula of physical and mechanical indexes.Combined with the layered summation method,the calculation formula of foundation settlement is established.Finally,the formula for calculating the total settlement of subgrade under traffic load is established.(3)The indoor test of subgrade settlement is carried out.Through the monitoring results of displacement meter and earth pressure meter buried in different soil layers,the variation law of subgrade settlement and additional stress with time is obtained.The subgrade settlement rate decreases with time.The settlement decreases with the increase of depth and distance from the middle line of subgrade,and the settlement at the top of the middle line of subgrade is the largest.The additional stress gradually decreases with the increase of depth and distance from the middle line of subgrade,and the additional stress at the top of the middle line of subgrade is the largest.(4)Using FLAC3 D finite difference software,considering fluid-solid coupling,the relationship between subgrade settlement and time under traffic load is obtained.Then,comparing it with theoretical calculation results,two findings are drawn.One is that the displacement curve change rule of the top settlement of the center line of both subgrades within2 years is basically the same,and the other is that the displacement deviation of different soil layers of the subgrades after 2 years of settlement is within 10%.These two indicate that the numerical calculation results are basically consistent with the theoretical calculation results.The variation law of subgrade settlement of three foundation treatment schemes of dynamic compaction,CFG pile composite foundation and cement mixing pile composite foundation is analyzed.By using hierarchy process and considering the influence of reinforcement effect,construction rate,construction cost and other factors,the dynamic compaction method is selected as the optimal scheme for foundation treatment and applied to field construction.