Research On The Wetting Soil-Water Characteristic Curves Of Intact Loess In South Jingyang Plateau

As an important constitutive relation in unsaturated soil mechanics,soil-water characteristic curve（SWCC）is the key to study the engineer properties of unsaturated soil.To study SWCC of loess,on the basis of testing the basic physical index of L₁、S₁、L₅ and L₉loess of South Jingyang plateau,this paper is mainly focused on the following aspects:（1）Testing the Wetting SWCC of L₁、S₁、L₅ and L₉ loess by filter-paper method;（2）Testing the pore distribution curves of L₁、S₁、L₅ and L₉ loess by mercury intrusion method;（3）The tested result on the relationship between the matric suction and water content is fitted using the single and double drop mode of SWCC equation;（4）Collecting the basic physical indexes and the SWCC of L₉ of intact Ma Lan loess in Gansu、Shaanxi and Shanxi etc.,and the empirical formula for predicting the intact Ma Lan loess SWCC by using the basic physical indexes is established.According to the characteristics of pore distribution,the soil is divided into four types:pore structure soil,uniform pore structure soil,single pore structure soil and double pore structure soil,The pore between the skeleton particles and the aggregate is defined as macroscopic pore,and the pore in the granule is defined as Micropores.L1,L5,L9 between macro and micro pore diameter value of around 0.1μm,there are a set of dominant pores in the macro and micro pores,they have bimodal characteristics;the threshold of S1 macro and micro pore pore size is about 5μm,there is no obvious advantage of pore.L1 is a typical double-pore structure soil,SWCC has two significant steep descending segments,and corresponds to the dominant pore range in macro and micro porosity respectively;although the pore distribution curves of L5 and L9 have bimodal characteristics,the advantage of micro pore volume is not significant,SWCC has only a significant steep descent,which corresponds to the dominant pore range in the macroscopic pore,it can be regarded as a single pore structure;the pore distribution of S1 is relatively uniform,the macro and micro pore distribution is not significant,corresponding to SWCC is a oblique line,the pore distribution is closer to the uniform pore structure soil.The results of SWCC measurements of L1,S1,L5 and L9 were fitted by Gardner,van Genuchten and Fredlund&Xing single drop SWCC equations,and the results shows that the van Genuchten equation and Fredlund&Xing fit better.The datas of SWCC fitted by the double descending equation of Li and the superimposed double descending equation of Fredlund&xing,the fitting results are closer to the test value than the single drop equation.Proposing‘One-point method’to predict SWCC of intact Ma Lan loess,that is,predicting the three parameters of Fredlund&Xing equation through the physical parameters of soil and an actually measured point of moisture content and corresponding matrix suction,which will be convenient for practical application.