| The turfy soil is a special soil with a lot of undecomposed fiber residue and humus under the oxidative decomposition of plant residues in the marsh environment.The turfy soils are widely distributed in the piedmont basins in the seasonal frozen areas,such as the hinterland of Changbai mountains in northeast China,Siberia region of Russia and Alberta in central Canada.In recent years,the subgrade constructed in the turfy soil area has been damaged by uplift or shearing extrusion caused by the foundation being squeezed,which seriously affects the safe use of highway.This paper selects the typical turfy soil area in Jiangyuan town,Dunhua city as the research object.According to the turfy soil layer of different depths,fiber content and organic matter content were obtained by washing method and loss method,and effected on natural density,specific gravity,water content and pore ratio.The turfy soil was classified according to fiber content,and then undisturbed and remolded samples were prepared according to different fiber content.According to direct shear tests,the shear failure mechanism and deformation characteristics of turfy soil were analyzed by means of fiber content,consolidation characteristics and microstructure.The stress-strain characteristics and shear strength indexes of undisturbed and remolded turfy soils with different fiber contents were obtained by consolidation and undrained triaxial test.The volume modulus and the shear modulus(K-G)model was used to analyze the shear stress-shear strain of the remolded turfy soil under different fiber contents by isotropic pressure loading tests and consolidated drained tests,and then the parameters of corresponding volume modulus and shear modulus and their variation were obtained,which provided theory and parameter basis for stability evaluation of the turfy soil subgrade.The main conclusions are as follows:(1)The average thickness of turfy soil in Jiangyuan town is 1.2m~3.5m.The site sampling and basic physical properties test were experimented.The fiber content and organic matter content of turfy soil ranged from 21.95% to 73.73% and 42.30% to 78.56% respectively.Referring to the standard ASTM D4497-13 commonly used in the world,the turfy soil was divided into three types according to the fiber content,the original samples were prepared and the fiber content was 24%、48% and 71% respectively.After that,according to the fiber content range of Jiangyuan town,seven kinds of remolded samples with different contents were prepared and the fiber content was 0%、20%、30%、40%、50%、60% and 70% respectively.(2)In the fast shear test of the turfy soil,the curve between the normal stress and the peak shear stress increases linearly.In the consolidation fast shear test,the curve between the normal stress and the peak shear stress is shown as a piecewise turning point,and the turning point is 200 kPa,showing obvious piecewise performance.In the early period of fast shear and consolidation fast shear,soil particles,fiber residues and organic matter aggregates provide shear strength.In the later period of consolidation fast shear,the shear strength is mainly provided by the tightly occluded soil particles.(3)The turfy soil samples have the phenomenon of anisotropy crossing.The samples in the shear front section show vertical anisotropy,while the soil in the shear back section shows obvious transverse anisotropy.With the increase of fiber content,the transverse anisotropy of remolded samples became more obvious.For undisturbed samples,the cohesion and internal friction angle increased with the fiber content.For remolded samples,the cohesion increased with the increase of fiber content,but the internal friction angle didn’t change more.The shear strength of undisturbed turfy soil was lower than that of remolded soil.(4)The volume modulus and the shear modulus formula is deduced,through to reshape the turfy soil on the isotropic pressure loading test and the consolidated drained test data,were indicated that the turfy soil shear stress-shear strain curve also conforms to the hyperbolic.On this basis,the parameters and expressions of K-G model to reshape the turfy soil are derived by mathematical statistics. |
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