Calculation Methods Of Soil-water Characteristics Curve

The soil-water characteristics curve is served as one of the basic parameters of soil, which is used to describe the soil matric potential or the relationship between suction and soil moisture content. Meanwhile, the soil-water characteristics curve is of great importance to further study of soil-water retention and transportation, the permeability of unsaturated soil, soil pollution, land subsidence, and slope instability. However, as the curve is highly nonlinearity, it is hard to deduce its exact mathematical expressions theoretically, and it may be time-consuming and costly. Therefore, it is of great significance to analyze and forecast the soil-water characteristics curve.Aimed at studying the calculation methods of soil-water characteristics curve, the Arya-Paris(A-P) model, Brooks-Corey(B-C) model and soil sectional water content method were employed in this paper to analyze and predict the soil-water characteristics curves of medium sand, fines sand and other four kinds of sands. The conclusions are as follows:1. Different soil particle accumulation curves were used to fitting the six kinds of soil, the results indicated that the Gompertz model and the Mlog model were the best fitted ones, the Weibull model, Morgan model, HP model, S2 P model and the LS model came second, the Fredlund Model took the third place, and the Jaky Model was fitted worst. That is to say the Gompertz model and the Mlog model were more suitable to describe the soil particle accumulation curves, as well as both were the necessary preparations for the calculation by A-P method and B-C method.2. On the basis of soil particle-size distribution, the A-P method and B-C method were employed to indirectly predict the soil-water characteristics curves of the six kinds of sands which were mentioned above. The results showed that the A-P method was suitable for deriving the soil-water characteristics curves of medium size sands, the B-C method was suitable for deriving soil-water characteristics curves of larger grains or smaller grains.3. The Gardner model, Van Genuchten model and Darcy’s law of vertical one-dimensional unsaturated flow were employed to derive the theoretical relationship between the flux q, and the effective water content Se, as well as the parameter estimation formula of Van Genuchten model and Gardner model were obtained. Based on this, the parameters computations of Van Genuchten model and Gardner model were achieved by the sectional water content at different moments. The verification results showed that the method has higher accuracy for deriving the soil-water characteristics curve.