Experimental Investigation For Soil Water Retention Curve And Microstructure Evolution Of Guilin Lateritic Clay In Full Suction Range

SWRC is an important relation curve to describe the hydraulic characteristic of unsaturated soils,and it has an impact on many characteristics of unsaturated soils,such as permeability,volume change and strength.At the same time,as a basic constitutive relation to explain behavior of unsaturated soils,SWRC is one of the important relations of combining theory,experiment and prediction technique and also the basis for constructing various important relationships of unsaturated soils.Therefore,it is of great significance to study the related properties of unsaturated soils through SWRC.SWRC is affected by many factors,including the type of soils,stress state,pore ratio,pore distribution,initial water content,suction range,temperature,chemical composition,and so on.Existing studies have shown that for a given soil sample,the pore ratio is the most direct and important factor affecting the SWRC.However,when the pore ratio is the same,soil samples with different microscopic pore structures show different soil water characteristic curve.For the soils in the actual engineering such as foundation,embankment and slope,its volume will be reduced caused by the loads.On the other hand,when the natural soil is in the process of wet and dry cycle due to the influence of rainfall and evaporation,its pore ratio and micro-pore structure will also change,resulting in differences of engineering response.In order to study the influence of different pore structures on SWRC of unsaturated soils,Guilin lateritic clay was used as the research soil sample.First we develop the slurry clay sample of single pole structure device independently and use consolidation and compaction method to prepare the single and double pore structure of soil samples respectively.Then,based on the different suction control methods such as axis-translation technique,filter paper method and saturated salt solution balance method,the soil-water characteristics of 129 soil samples of Guilin lateritic clay are analyzed for the two different pore structures and different initial porosity ratios.Finally we make use of Mercury intrusion method and scanning electron microscopy(SEM)experiments to observe the microstructure of slurry soil samples and compacted soil samples in different suction during drying,wetting and wet-dry cycle,and it is revealed the evolution of microscopic pore structure in the hydraulic process for the single and double pore structure of soil samples.The main research results are as follows:(1)We develop the slurry clay sample of single pole structure device,and optimize the preparation methods of soil samples in different pore structure.The device is simple in principle and easy to use.It can flexibly control consolidation pressure by weight or jack,and control the density of soil samples by the scale of the sample barrel and the measured displacement of the cylinder.At the same time,based on the developed device of slurry soil sample and traditional device of compaction sample we optimize the preparation methods of single pole structure slurry soil and.double pore structure compacted soil.(2)The SWRC of Guilin lateritic clay with different pore structures in full suction range are studied through different suction control techniques,and it is revealed the influence of initial porosity ratio and microscopic pore structure on SWRC.We make the slurry clay samples of single pole structure with three kinds of the initial void ratio by the slurry clay sample of single pole structure device,and make compacted clay samples of double pole structure with three kinds of initial void ratio by compaction method.The SWRC of Guilin lateritic clay with different pore structure and different initial porosity were obtained by using the axis-translation technique,filter paper method and saturated salt solution balance method to control the different suction levels,and it is revealed the influence of microscopic pore structure and initial pore ratio on SWRC,including the effect on drying curve,wetting curve and hysteresis characteristics.(3)The evolution of microscopic structure in the wet-dry cycle for the single and double pore structure of soil samples is revealed by carrying out Mercury intrusion method and scanning electron microscopy(SEM)experiments at different stages of wet-dry cycle.The microscopic pore structures of slurry soil samples and compacted soil samples with three kinds of the initial void ratio are studied during drying,and wetting processes in different suction are studied through Mercury intrusion method and scanning electron microscopy(SEM)experiments and it is revealed the evolution of microscopic structure of Guilin lateritic clay with different pore structures,and focuses on analysis of the influence of pore structure types on hysteresis behavior of SWRC.