Study On The Constitutive Model Of Unsaturated Silt In The Flooded Area Of Yellow River

At present,the theory of saturated soil mechanics has been very perfect.Many scholars try to apply the theory of saturated soil mechanics to unsaturated soil mechanics.However,because most of soil layers of the earth's surface are unsaturated,and some mechanical properties of unsaturated soil do not conform to the conditions in the theory of saturated soil mechanics.Therefore,there will be many questions in applying the saturated soil mechanics theory to the mechanics of unsaturated soil.In addition,the theoretical study of unsaturated soil mechanics has not yet formed a complete theoretical system,and the research on the mechanical properties of unsaturated soil is not mature enough.Therefore,it is of great value and significance to study the mechanical characteristics and deformation properties of unsaturated soil.At present,the mature models are mainly divided into three categories: nonlinear elastic model,elastoplastic model and structural model.The elastoplastic model is the most widely studied,and the elastoplastic model based on the widely used elastoplastic theory is an important feature in the study of unsaturated soil constitutive theory.For the establishment of elastoplastic model of unsaturated soil,firstly the stress state variable and strain state variable of unsaturated soil should be determined,and then the corresponding strain(including elastic strain and plastic strain)is determined according to changing stress.To determine the elastic deformation is quite easy,and the plastic deformation needs to be determined by the basic plastic theory,such as the yield criterion,the hardening rule and the flow rule.Based on the idea of effective deformation work of multiphase porous media,the effective stress formula of unsaturated soil is derived,and the stress state variable and strain state variable of unsaturated soil are determined.The equation of yield surface of the unsaturated soil is determined by introducing the incremental equation of storage energy and the increment equation of dissipative energy proposed by Collins.The formula of the yield surface equation is further modified by the relation fitted through MATLAB between the matrix suction and the cohesion,and the yield surface equation suitable for the unsaturated silt in the flooded area of Yellow River is obtained,and the Alonso model is combined with the equation.The constitutive model of unsaturated silt in the flooded area of Yellow River is derived from the non-associated flow rule and hardening equation.Compared with the Alonso model,the model has a more solid theoretical foundation and can accurately reflect the soil characteristics of unsaturated silt in the flooded area of Yellow River.According to the soil-water characteristic curve,the consolidation test and triaxial shear test are carried out on the unsaturated silt of the flooded area of Yellow River by controlling the soil moisture content and the suction.Comparing the experimental results and the calculation results of the theoretical model under the constant suction found that the model can better simulate the stress-strain trend of the unsaturated silt in the flooded area of Yellow River.The main research contents are as follows:(1)Experimental study.Firstly,the soil-water characteristic curve of the unsaturated silt in the flooded area of Yellow River is determined by the filter paper method,and the consolidation test and shear test are carried out on the samples with different water content in the GDS triaxial test instrument.By using the measured soil-water characteristic curve,the corresponding suction value can be determined under different water content,and then be measured.The results of consolidation test and shear test of unsaturated silt under different suction are presented.(2)The determination of the constitutive model.Based on the theory of multiphase porous medium,the effective stress expression of unsaturated soil is derived,and the stress state variable of unsaturated soil is determined.The incremental equation of storage energy and the dissipative energy increment equation proposed by Collins are introduced,and the equation of yield surface in dissipative stress space is derived by using the dissipative energy increment equation,and the conversion is used.The stress converts the yield surface equation of dissipative stress space to the yield surface equation of real stress space.The equation of yield surface for the unsaturated silt is obtained by using the relation between the matrix suction and the cohesion fitted by the experimental results to further modify the equation of yield surface.Combined with the non-associated flow rule and hardening equation of Alonso model,the constitutive model of unsaturated silt in the flooded area of Yellow River is derived.(3)Validation of the constitutive model.The stress-strain curves obtained from the shear test and the stress-strain curves calculated by the model are compared and analyzed.By comparison and analysis,it is found that the calculation results of the model are in great agreement with the experimental results,indicating that the model has certain applicability.