Soil-Water Characteristics Of Loess Over The Full Suction Range Based On TRIM And VSA

Loess is a kind of special soil with high water sensitivity,its mechanical properties are totally different under dry and wet status,which constitutes the essence of water-induced loess landslide,soil water characteristic curve(SWCC)is an important constitutive relation of water sensitivity.In order to reveal the soil water characteristics over the high suction range and construct the complete SWCC in the full suction range,this study relied on the key fund project(41530640)and the key research development program(2018 YFC15047000),the TRIM and VSA testers were introduced to test the SWCC of the typical loess profile in Xifeng,Qingyang.The SWCC of the loess and paleosol over the full suction range and their influencing factors were studied.The main results are as follows:(1)The variation of SWCC for loess in high suction range is summarized.The SWCC in the range of high suction for the Xifeng loess section(L2,L5,S5,L6,L7,L8,S8,L9,S10,L15)soil are obtained by VSA.The results show that there are inflection points in the SWCC in the suction range of 7.1 MPa?482.9 MPa,The moisture content at the inflection point of drying and wetting path is similar but not the same,and the drying or wetting rate of soil changes after the inflection point;the hysteresis of SWCC for unsaturated loess decreases with the increase of suction,and disappears when the suction is about 200MPa;the water-holding capacity for paleosol over high suction range is all stronger than that of loess,and there is a linear positive correlation between it and clay content.(2)A new method of testing SWCC over the full suction range based on VSA to modify TRIM is proposed.Based on the results of VSA,it is found that the moisture content measured in residual zone of TRIM is higher than the actual value,the reason is that TRIM cannot accurately predict the SWCC when adsorbed water is dominant because it controls of suction based on axis-translation technique.Therefore,VSA test was introduced to modify the TRIM method,and a new model is used to fit the data.The results show that the scheme can accurately measure the SWCC for the full suction range in a short time.(3)The hysteresis of SWCC for loess over the full suction range is explained.The new method proposed in this paper is applied to test the SWCC in the range of full suction for the Xifeng loess section.The results show that there is obvious hysteresis in the SWCC of each soil.Under the same suction,the water content of the drying path is higher than that of the wetting path,and the difference between them decreases with the increase of suction the SWCC obtained under the two hydraulic paths coincide when the suction is larger(about 200MPa).Meanwhile,by comparing the characteristic parameters of fitting curve under different hydraulic paths,it is found that the saturated volume water content and air entry value under drying path are larger than those under wetting path,the parameters n and m have little change.Moreover,the hysteretic circle area of each soil is calculated.The results show that the hysteretic tends to weaken with depth,increases with the increasing of C_u,decreases with the increasing of d₁₀,and the hysteresis of paleosol is obviously stronger than that of loess.(4)The variation of soil water characteristics and its influencing factors on the loess section are revealed.The characteristic parameters of different soils were compared and established the relationship between them and the physical indexes of each soil was established.The following conclusions are obtained:the saturated volumetric water content under the drying path,?_s^d,fluctuates along the loess section,the parameters?_s^d of the paleosol is smaller than that of the adjacent loess,the?_s^d tends to decrease with the depth,and?_s^d has a negative linear correlation with?_d;the air entry value parameter,?,of the paleosol are all larger than those of the adjacent loess,and?decrease with the increasing of?and d₁₀;the parameters of n tends to decrease with the increase of depth,which reflects that the range of pore density becomes wider and the peak value decreases with the increase of burial depth;the slope of transition zone is defined as the maximum drying rate of SWCC.The results show that the maximum drying rate of paleosol is less than that of adjacent loess,and tends to decrease with depth,and it decreases with the increase of?_d,increases with the increase of e;The parameter m of loess is higher than that of adjacent paleosol,and there is a negative correlation between m and soil clay content.