Experimental Study On Reconstituted Soft Clay In Dongting Lake

In the engineering practice,the mechanical property of the soil is related to its stress state.The stress state of the soil is complicated by the stress history and the influence of the later loading path.Therefore,considering the influence of the stress path and the stress history and studying the physical and mechanical properties of the soil have a deeper theoretical and engineering application value.In this paper,the reconstituted soft soil of Dongting Lake as the research object,a series of undrained shear tests under different consolidation conditions and different stress paths are carried out in order to simulate the actual working conditions.The mechanical properties of soft soil in Dongting Lake region are studied.The main contents of this paper are as follows:(1)The physical and mechanical indexes of the soft soil in the Dongting Lake are analyzed and studied,its results show that the water content of the soft soil in the Dongting Lake area is high and is close to the saturation,the soil samples are mostly in the soft plastic or plastic state and it belong to the high-plasticity cohesive soil;the porosity is relatively large,the soil mass is relatively loose,the compressibility is large,and the shear strength of the soil is low.There is a good linear correlation between the physical and mechanical indexes of the soft soil of Dongting Lake,and the linear regression equation between these physical and mechanical indexes is obtained,it have a guiding effect on the engineering practice.(2)Under the condition of isobaric consolidation,the strength of the normally consolidated soil increases with the increase of the mean principal stress p;the larger the over-consolidation ratio OCR,the greater the strength of the overconsolidated soil;the formula for fitting the undrained shear strength under the different overconsolidation ratio OCR and the static soil pressure coefficient K is put forward.The pore water pressure Du of the normally consolidated soil and the overconsolidated soil gradually increase with the increase of the mean principal stress p,and a slight downward trend appears after the peak value is reached.(3)Under the condition of non-isobaric consolidation,the shear stress q of the soil increases with the increase of the over-consolidation ratio OCR and the static soil pressure coefficient K.The pore water pressure Du of the normally consolidated soil and the overconsolidated soil has a relatively small upward trend at the beginning of the test,and the value of the pore water pressure begins to drop and a negative value appears subsequently,and the negative pore water pressure is obviously increased with the increase of the axial strain.Under the condition of the same over-consolidation ratio OCR,when the static soil pressure coefficient K is small,at the beginning of the test the pore water pressure are positive values,it gradually decrease after reaching the peak value and a negative value appears,the negative pore water pressure is increased obviously with the increase of the strain;With the increase of the static soil pressure coefficient K at the start of the test,the pore water pressure no longer appears positive,and the negative pore water pressure increases with the increase of K value.(4)Under the condition of isobaric condition,the effective stress path of the conventional consolidated soft soil under the constant pressure consolidation is similar,and the slope of the failure line is 1.3.The failure line of the overconsolidated soft soil is not over the origin,the slope is 1.1,and slightly smaller than the normally consolidation soil,the effective stress path is different in shape,the initial stage of the shearing,the slope of the stress path is changed from negative value to positive value,and it cross the failure line until it fall on the failure line.The failure line of the overconsolidated soil is not pass through origin,and the slope decreases with the increase of the over-consolidation ratio OCR.In the axial and radial loading shear condition,the shear stress q increases with the increase of the average effective principal stress p′,the slope of the stress path is positive before destruction,and the direction of the partial stress path changes due to the difference of the axial and radial loading increment ratio and the over-consolidation ratio OCR after over the breakdown point.(5)Under the condition of lateral unloading,the undrained shear test is carried out,and the axial loading test as the comparative test,it is found that under the same consolidation condition,the peak value of the shear stress q formed by the lateral unloading is lower than that of the axial load,and the axial strain is larger,the effective stress intensity index is less than the total stress intensity index.(6)The Duncan-Chang model is discussed.Based on the results of the test,it is found that the Duncan-Zhang model can describe the stress-strain relationship of the soft soil in the Dongting Lake region commendably,the Duncan-Chang model parameter of the soft soil in the Dongting Lake is obtained,and the damage ratio is corrected.