Experiments On Time-dependent Characteristics And Its Constitutive Modeling Of Unsaturated Soil Under Controllable Matrix Suction

With the rapid improvement of China’s national economy and large-scale infrastructure construction,unsaturated soil problems are particularly obvious in engineering construction,especially unsaturated soil moisture content,embankment wetting deformation and landslide caused by rainfall.Unsaturated soil is different from general due to the existence of gas phase saturated soil,soil moisture operation rules should be considered as well as the field coupling relationship,in which stress variable matrix suction of unsaturated soil(moisture content)can be used to describe the relationship between the strength and deformation analysis compared with saturated soil,unsaturated soil test difficulty and limitations,the current study of unsaturated soil are fewer.Therefore,by effectively analyzing the strength and deformation law of unsaturated soil under controllable matric suction and considering the creep deformation characteristics under time effect,the model parameters are determined based on the elasticplastic constitutive model,and then the elastic-viscoplastic constitutive model of unsaturated soil considering matric suction is constructed.For this reason,the test instrument adopts the standard dynamic and static three-axis system of the British GDS company with double pressure chamber,and realizes the matrix suction control based on the shaft translation technology.The following research work is carried out in this paper:(1)The basic physical properties test of unsaturated compacted soil was carried out,and the matric suction range in the time-dependent characteristic test was determined through soilwater characteristic curve test.The results showed that the soil-water characteristic curve had obvious stage division,and the intake value of the test was 100 k Pa.When the matric suction was greater than this value,the soil-water characteristic curve showed a sharp decline.At the same time,it can be known that at 20% natural moisture content,the corresponding matric suction of the soil sample in this paper is 262 k Pa.(2)The time-dependent characteristic test of unsaturated compacted soil under controlled matric suction was carried out,and the effects of matric suction(0k Pa,100 k Pa,200 k Pa,300 k Pa),overconsolidation ratio(1,4,8)and different loading rates(0.4mm/min,0.02mm/min)were considered.The time-dependent characteristics of unsaturated compacted soil were studied by inducting and analyzing the deformation law and strength law of stress-strain curve,volumetric deformation-strain curve.In the creep test,the Chen loading method is used to carry out the graded loading and process the data,and the long-term strength deformation and creep rate law are analyzed.The relationship between rate sensitivity and creep is established by strain rate,which provides a new idea for rate sensitivity prediction of creep.(3)BBM for reference model for the compressive yield curve correction,normal consolidation of saturated soil and unsaturated soil curve(NCL)conversions,and through the elastic-plastic unit unsaturated soil model parameters of λ(s)and a(s)are determined as a function of the matrix suction s,introducing surface constitutive model under the load,to improve the yield function,Considering the influence of matric suction and overconsolidation ratio,an elasto-viscoplastic constitutive model of unsaturated soil considering matric suction is established according to the overstress theory.(4)Using UMAT subroutine interface of finite element software ABAQUS,the aging characteristic test was verified and analyzed.The results show that the model can fit the aging characteristic test curve correctly and reasonably,the simulation results are basically consistent with the trend of the test curve,and the coupling effect of matrix suction and loading rate is good.Based on the unsaturated soil slope model,the proposed constitutive model can accurately characterize the strength deformation of unsaturated soil slope,effectively analyze the displacement deformation and stress distribution under different matric suction,and provide a basis for engineering examples.