Physical And Mechanical Properties Of Loess-Paleosol Considering Sedimentary Age And Its Engineering Application

With the development of society,the engineering in the loess area has increased,and the value of the loess strength parameters has significantly affected the evaluation of the stability of the project.The loess has a large thickness and a large number of layers.It requires a large amount of test and a long test period to determine its strength parameters.In practical engineering,in order to reduce costs and save time,the formation has to be simplified.To solve the problem of loess stratification and parameter value,this paper takes the Jingyang loess-paleosol profile as the research object,which includes L₁,L₂,L₃,L₄,L₅,L₆,L₇,L₉ loess and S₁,S₄,S₅,S₈ paleosol,totally 12-layer soils.The basic physical indexes and the saturated consolidation undrained triaxial（CU）test of 12 soils were carried out to study the relationship between the physical and strength parameters of and the sedimentary age,and a finite element model and the parameter value scheme based on the loess-paleosol sequence were established.Results are as follows.The dry density of loess increased significantly with the increase of sedimentary age,showing a nonlinear relationship.The dry density of paleosol increased slowly with the increase of sedimentary age,showing a linear relationship.The pore ratio decreases with the increase of deposition age,and the change of loess pore ratio is obvious,while the paleosol has a weak change trend.The grain size distribution curve of loess is mostly bimodal,and which of the paleosol is trimodal.The specific surface area of loess and paleosol has a linear relationship with the sedimentary age,which of loess is much smaller than that of paleosol.The variation of stress-strain curve and p’-q’curve of 12-layer soil samples were analyzed,and the effective shear strength parameters c?and??of each layer were determined.It is found that the cohesive force of loess is linearly related to the sedimentary age,which of paleosol is nonlinearly related to the sedimentary age.And the functional expressions between the two were separately established.The internal friction angle of loess varies from 16°to 22°,which of paleosol varies from 18°to 20.5°.Compared with paleosol,the internal friction angle of loess is more discrete.There is no significant relationship between the internal friction angle and the sedimentary age.According to the relationship between cohesion and internal friction angle and sedimentary age,coupling stratigraphic division and finite element mesh,the finite element program was developed to establish geological model based on loess-paleosol sequence.Compared with this model,the commonly used three-layer model in engineering（Q₃,Q₂,Q₁layers）may underestimate the stability of the slope;the loess-paleosol layer has a greater control effect on the potential shear outlet of the slope.Based on the relationship between the strength parameters and the sedimentary age,this paper economically and practically solves the problem of the establishment of the loess layer model and the value of the strength parameters.