Time Dependent Deformation Characteristics Of Unsaturated Compacted Soil And Its Application In Settlement Calculation Of Subgrade

With the advancement of Chinese expressways to the central and western regions,a large number of high-filled unsaturated compacted backfills are inevitably faced,resulting in long-term cycling of the subgrade.This is particularly difficult for subgrade settlement after construction,which has become a problem that plagues the engineering community.In addition,due to the stratified rolling effect of the high-fill embankment,it accumulates a certain stress history and evolves into an over-consolidated soil.The triaxial shear test of the over-consolidated soil under certain confining pressures is characterized by strain.Softened deformation characteristics,and most of these soils are above the groundwater level and are in an unsaturated state.Therefore,the calculation and prediction of high-filled embankment during construction and post-construction settlement,and the elimination of disasters caused by subgrade settlement have become an important issue in the field of engineering construction At the same time,using constitutive model to describe the rheological properties of soil has become an effective method.Based on this,the following research work is mainly carried out:(1)By conducting a series of laboratory tests,we can finally determine the physical and mechanical properties of the test soil.The liquid limit and plasticity were 49.3 and 26.7,the specific gravity was 2.74,the optimum moisture content was 24.6%,and the maximum dry density was 1.61 g/cm~3.Soil-water characteristic curve test was carried out on soil samples,and the soil-water characteristic curves of the soil used in the experiment were drawn to lay the foundation for determining the parameters of the model.(2)The triaxial consolidation drainage shear compression test of the unsaturated subgrade compacted soil under the conditions of different matrix suction(100 kPa,200 kPa and 300 kPa)with a loading rate of 0.02 mm/min was carried out using a GDS unsaturated soil dynamic triaxial apparatus.In order to investigate the influence of matric suction on the strength and deformation characteristics of compacted soil and the effect of volume change,the shear strength parameters of the specimen are obtained,and the formula of consolidation drainage strength of compacted soil compacted soil is derived.(3)For samples with matrix suction(100 kPa,200 kPa),two different loading rates(0.4mm/min,0.02 mm/min)and different overconsolidation ratios under ORC(8,4,1)consolidation undrained three Shaft shear compression test,The effects of overconsolidation ratio,strain rate,etc.on the strength and deformation characteristics,stress ratio and volume change of compacted subgrade compacted soil were investigated.(4)Considering the influence of matrix suction S on the basis of elastic viscoplastic constitutive model,and establishing the functional equation between matrix suction S and model parameters a_s=3.75S+796.67,M_s=0.0009S+1.583,and predicting the rate sensitivity of unsaturated compacted soil with new parameters.It is indicated that the new model can characterize the time-dependent deformation characteristics of the rate sensitiveness of unsaturated compacted soil.This model can be applied to the long-term settlement analysis of unsaturated compacted soil roadbed.(5)Relying on the high-fill embankment of the K50+650~K50+860 dam type embankment and the intelligent driving section K1+430~K1+620 on the Lanhai Expressway,using the roadbed equilibrium humidity theory to the high-fill embankment under long-term meteorological conditions The matric suction function is estimated,and the viscoplastic constitutive model of the soil compacted soil considering the matrix suction is proposed.The ABAQUS numerical calculation is used to calculate the high fill embankment condition under complex boundary conditions,and the bomb without considering the matrix suction.The calculation results of the viscoplastic constitutive model are compared.It is found that the construction settlement of the model is closer to the on-site monitoring results,and the settlement is predicted to be smaller in the 10 years after work,which is closer to the actual engineering situation.