Research On Soil-water Characteristic Curve Of Unsaturated Laterite In Jiangxi

Most of geotechnical engineering problems are fully or partly belong to thecategory of unsaturated soil in engineering. Therefore, there will be an importanttheoretical and utility value in the study of unsaturated properties of laterite. Theprimary problem of studying the characteristics of unsaturated soil is to know thesoil-water characteristic curve (SWCC) and master the soil water movement whichis under different influencing factors. Soil-water characteristic curve measurementnot only requires specialized instruments, and also needs to spend a lot of time,especially the moisture absorption curve. Therefore, it is not convenient to put soil-water characteristic curve into engineering application, so many scholars putforward the SWCC model, but these models all have their own scope of application.It needs to do some further tests in order to find the right SWCC model. Somescholars also propose the use of dehumidifying curve forecasting moistureabsorption curve of constitutive model, although this can greatly shorten the testtime, but because of the characteristics of regional soil sample, it still needs sometests to verify its applicability. Residual water content in soil-water characteristiccurve is an important parameter. It marks the soil sample into the residual stage anddehydration is getting slower and slower. Residual water content also has somerelationships with the Bishop single strain strength criterion of parameters.In this thesis, the typical laterite in Jiangxi is used to be the research object;using GEO-Experts pressure plate apparatus to do the research about stress is relatedto soil-water characteristic curve and hysteresis. The research content includessoil-water characteristic curve is influenced by different particle sizes and drydensities and water contents and pre-consolidation pressures. It uses three kinds ofcommonly used SWCC model to fit and analysis the test data, in order to find outthe suitable soil-water characteristic curve equation for Jiangxi typic laterite. Then itputs forward the scope of parameters in the model, and results could be a referencefor engineering practice. This paper also does curve fitting and forecasting on themoisture absorption. Finally, this paper puts forwardit hyperbolic curve model of SWCC and this modle is very convenient to calculate the residual moisture content. Main contents of the paper are following:(1) Select soil samples of a secondary road in Nanchang to perform the basic physical mechanics test, then it can obtain the basic physical mechanics indexes of the Nanchang laterite.(2) Give an introduction about the device and test principle of GEO-Experts pressure plate apparatus. And GDS pressure plate apparatus is used to study the soil-water characteristic curve of unsaturated laterite which is affected by different factors, like dry density, water content, grain composition and pre-consolidation pressure.(3) Porous stone is a must in the pre-consolidation process when it uses GEO-Experts pressure plate apparatus to test soil-water characteristic curve. Through the dehydration test of saturated soil sample, it found that the water of porous stone and soil sample would also be into the burette. So the amount of water in the burette is not the same as the sample water content and the result of water content which is obtained the experiment will be not true. In order to reduce the test error, there are six different treatment methods through porous stone.(4) Use GDS pressure plate apparatus to perform the soil-water test on moisture and moisture absorption cycle in order to further understand the hysteresis feature of soil-water characteristic carve.(5) To better understand soil-water transport rules of the non-saturated clay, the test data were fitted and analyzed with three different SWCC models under different factors, which can obtain scope of their respective parameters for three kinds of model.(6) It is found that three SWCC models are all suitable for fitting Curve of moisture, and variation of these parameters is analyzed. Finally, Forecast is more accurate for absorption curves with a simplified model of Feng&Fredlund (1999).(7) This paper puts forward hyperbolic model (w=ua-uw/a(ua-ub)+b) which describes the soil water characteristic curve. By using coordinate transformation can be more convenient and accurate to obtain residual volumetric water content. Under the influence of different factors, hyperbolic model parameter a value is in the rangeof0.06~0.08and the parameter b value is in the range of0.6~0.2. Hyperbolicmodel also has high applicability for other soil samples; the residual water contentcan also be convenient to calculate the effective stress parameters.(8) In the saturated clay samples, the residual volumetric water content which isobtained by hyperbolic curve model is basically the same with BC model, VG modelsand FX models’, indicating that using the hyperbolic curve model can be moreconvenient to get the residual volumetric water content.