Experimental Study On Soil-water Characteristic Curve And Its Model Prediction Under The Influence Of Water Content And Stress State

The development of infrastructure to meet the needs of society commonly involves soils from above the ground-water table.These soils have negative pore-water pressures and are referred to as ‘‘unsaturated soils.'' One of the primary issues of the unsaturated soil mechanics is the relationship between soil and water,namely the soil-water characteristic curve.Most SWCCs shows the volume water content changing with various matric suctions.Nowadays,advances in the development of laboratory testing equipment for unsaturated soils along with the ability to measure soil suction have prepared the way for the implementation of unsaturated soil mechanics.The SWCCs plays a more and more important role in interpretation the behavior of unsaturated soils,such as stability of a slope,the breakpoint of a clay lining for containment,the permeability and so on.For further application,another problem turns up.A great number of researchers devote on describing the SWCCs by some certain form of equation,and so does the author here.This article has paid a lot of attention on how to get the SWCCs correctly by a pressure plate apparatus with a normal stress controlling system.The author thinks that stress state affects the SWCCs by changing the soil pore size distribution.And the main factor is that the pore size in the clay has been changed by the stress state.This paper research on the relationship between the SWCC and the stress state and also the water content,combine with the change on pore size distribution and mainly done the following works:(1)Do some basic tests on the sample.And the basic physical properties of the soil sample were obtained.Get well prepared for the follow test.(2)Using the clay to do the dehydration in different stress state by using GEO-experts pressure plate apparatus,and get the whole SWCC.For those samples of roughly the identical saturated water content,the air entry values increase with the axial forces while the slopes of the dehydration regions decrease,the samples show a good retain capacity,it is attributed to the compaction of the axial forces.And the current models are of good performance in fit those SWCCs under different axialforces.(3)Get the air-entry value in the same stress state with different water content,infer how water content influence the SWCC.For those samples of different saturated water contents,the air entry values increase with the saturated water contents.For the SWCCs of samples of different saturated water contents,both the van Genuchten model and the Brooks-Corey model fit well,although they give different residual water content plateau,the reason is assumed to be that there is lack of data with higher matric suctions.(4)Using the Van Genuchten formulation,Brook sand Corey formulation and Fredlund-Xing formulation for fitting the experimental result to conclude a formulation that is suitable for this clay.According the Akaike information criterion,the best model for those samples of different saturated water contents is the Brooks-Corey model which is inconsistent with the statistics.(5)Conduct the pressure mercury test on the former experimental samples,attach the soil pore size distribution with the SWCC and find out how the stress state affect the SWCCs by changing its pore size distribution.(6)By using different number of measured points to fit,and then using the fitting formula to get the SWCC,after a comparative analysis,and then getting a more effective method to forecast the SWCC.