The Study Of Soil-water Characteristic Curve About Silt Loam In Unsaturated Zone Under Little Infiltration Condition

It is one of common typical studies in unsaturated soil that small-scale rainfallintensity which is not sufficient to supply is used for one-dimensional infiltration.Under the influence of the rainfall infiltration, groundwater level is changed and thischange induces the variation of hydraulic parameters, among which the change of soilsuction and water content is remarkable. Meanwhile, the relation of soil suction andwater content can be explained well by typical retention curves or soil-watercharacteristic curves. At present, silt loam is extensively concerned and researched inengineering and academic domain for its unique characters, such as a wide ofdistribution, strong structure, poor mechanical properties, a lack of stability and weakload-carrying properties etc. All in all, what this paper researches contributes to thesolutions to the problems of soil mechanics and hydraulics in the engineeringconstruction when faced with silt loam.With the support of the key projects in State Key Laboratory of GeohazardPrevention and Geoenvironment Protection (SKLGP2011Z001), we use silt loam asour object of this study, combine the indoor soil-column experiment with theoreticalresearch as well as the coalition of numerical simulation and theoretical analysis,compare the closed underlying surface with open ones to research rainfall infiltrationcharacteristics as well as the difference of typical retention curves under small-sizedrainfall intensity, and make the most of available soil data to forecast soil-watercharacteristic curves with the help of HYDROUS-1D. In consideration of the currentresearches which are mostly based on the experience of scholars, structurecharacteristics of the soil, and curve shapes, this paper is trying to fit the experimental data and get the optimum nonlinear parameters equations. Finally, taking advantage ofparameter equations of both domestic and overseas, and the water contentcharacteristic curve equations by quadratic polynomial, we have fitted the test dataand predicted data via software simulation, then compare the accuracy of respectiveequation.The main results and conclusions are as follows:(1) Under small-scale rainfall infiltration, we analysised the variationcharacteristics of silt loam along with the infiltration time, compared the closedunderlying surface with open ones, including the wetting front, soil moisture contentand soil matrix suction. Among above, it is the quadratic polynomial functionrelationship between soil moisture content, soil matrix suction as well and infiltrationtime; the relationship between the wetting front and infiltration time is linearly related;on account of infiltration and evaporation, the research curves is saltatory sharply; andwhen the underlying surface is open, all characteristics above change faster.(2) Fitting the parameter equations of the measured parameter values by meansof Williams’, Chenggang Baos’ and the quadratic polynomial, we found that thequadratic polynomial parameter equation was preferable to satisfy modern measuretechnology and got the more rational curves of soil-water characteristic.(3) Compared the fitting curves by measured parameter values, we foundWilliams’and quadratic polynomial parameter equations was better fitting for steppedor waving curves, while the equation by Professor Chenggang Bao preferably fittedthe period from air entry value to residual water rate of soil-water characteristiccurves.(4) After the numerical transformation of the numerical simulation results viasoftware HYDROUS-1D, we also used the three equations to fit and we drew theconclusion that the quadratic polynomial parameter equation was still qualified.(5) By comparison with the modern measuring technology, software simulationand obtained parameter values by inversion, we found it clear that the fitting by thequadratic polynomial parameter equation was better than Williams’ and ChenggangBaos’. In brief, the fitting by the quadratic polynomial parameter equation is availableto the research to soil-water characteristic curves of silt loam under small-sizedrainfall infiltration, and there is a proposal that the quadratic polynomial parameterequation should be adopted in future test study.