Abstract: The hydraulic properties of soil (i.e. soil-water characteristic curve (SWCC) and coefficient of permeability) govern the moisture flow in it. Previous research has indicated that the hydraulic properties of soil are dependent on its pore-size distribution. An improved capillary model is now proposed to explain the concept of the pore-size distribution in soil and its relationship to SWCC. A new model, the “valve model”, is also proposed as the explanation for water flow in unsaturated soil. The pore-size distribution function is incorporated in the “valve model” and is used to calculate the relative coefficient of permeability for unsaturated soil. In this paper, the role of the pore-size distribution function in the estimation of SWCC and the permeability function are explained. Equations are proposed for estimating the pore-size distribution function from the experimental data of relative coefficient of permeability. The results from the proposed equations agree with the experimental data from laboratory measurement and published data.

孔径分布函数对水分在非饱和土体中迁移的作用

[1]Brooks RH, Corey AT, 1964. Hydraulic Properties of Porous Media. Colorado State University, Fort Collins, CO, USA.

[2]Childs EC, Collis-George N, 1950. The permeability of porous materials. Proceedings of the Royal Society A: Mathematical, Physical and Engineering Sciences, 201(1066):392-405.

[3]Fredlund DG, Rahardjo H, 1993. Soil Mechanics for Unsaturated Soils. Wiley, New York, USA.

[4]Fredlund DG, Xing AQ, 1994. Equations for the soil-water characteristic curve. Canadian Geotechnical Journal, 31(3):521-532.

[5]Fredlund DG, Xing AQ, Huang SY, 1994. Predicting the permeability function for unsaturated soils using the soil-water characteristic curve. Canadian Geotechnical Journal, 31(4):533-546.

[6]Fredlund DG, Rahardjo H, Fredlund MD, 2012. Unsaturated Soil Mechanics in Engineering Practice. Wiley, New York, USA.

[7]Gardner WR, 1958. Mathematics of isothermal water conduction in unsaturated soils. Proceedings of the 37th Annual Meeting of the Highway Research Board.

[8]Goh SG, 2012. Hysteresis Effects on Mechanical Behavior of Unsaturated Soil. PhD Thesis, Nanyang Technological University, Singapore.

[9]Goh SG, Rahardjo H, Leong EC, 2015. Modification of triaxial apparatus for permeability measurement of unsaturated soils. Soils and Foundations, 55(1):63-73.

[10]Kosugi K, 1994. Three-parameter lognormal distribution model for soil water retention. Water Resources Research, 30(4):891-901.

[11]Kunze RJ, Uehara G, Graham K, 1968. Factors important in the calculation of hydraulic conductivity. Soil Science Society of America Journal, 32(6):760-765.

[12]Lambe TW, 1955. The permeability of compacted fine-grained soils. Symposium on Permeability of Soils, ASTM.

[13]Leong EC, Rahardjo H, 1997. Review of soil-water characteristic curve equations. Journal of Geotechnical and Geoenvironmental Engineering, 123(12):1106-1117.

[14]Marshall TJ, 1958. A relation between permeability and size distribution of pores. Journal of Soil Science, 9(1):1-8.

[15]Millington RJ, Quirk JP, 1961. Permeability of porous media. Nature, 183(4658):387-388.

[16]Mualem Y, 1976. A new model for predicting the hydraulic conductivity of unsaturated porous media. Water Resources Research, 12(3):513-522.

[17]Pedroso DM, Sheng DC, Zhao JD, 2009. The concept of reference curves for constitutive modelling in soil mechanics. Computers and Geotechnics, 36(1-2):149-165.

[18]Priono, 2016. Anisotropy in Hydraulic Properties of Unsaturated Soils. PhD Thesis, Nanyang Technological University, Singapore.

[19]Rahimi A, Rahardjo H, 2016. New approach to improve soil-water characteristic curve to reduce variation in estimation of unsaturated permeability function. Canadian Geotechnical Journal, 53(4):717-725.

[20]Reinson JR, Fredlund DG, Wilson GW, et al., 2005. Unsaturated flow in coarse porous media. Canadian Geotechnical Journal, 42(1):252-262.

[21]Richards LA, 1952. Water conducting and retaining properties of soils in relation to irrigation. Proceedings of International Symposium on Desert Research, p.523-546.

[22]Tuli A, Hopmans JW, 2004. Effect of degree of fluid saturation on transport coefficients in disturbed soils. European Journal of Soil Science, 55(1):147-164.

[23]Tuli A, Hopmans JW, Rolston DE, et al., 2005. Comparison of air and water permeability between disturbed and undisturbed soils. Soil Science Society of America Journal, 69(5):1361-1371.

[24]van Genuchten MT, 1980. A closed-form equation for predicting the hydraulic conductivity of unsaturated soils. Soil Science Society of America Journal, 44(5):892-898.

[25]Vogel HJ, 1997. Morphological determination of pore connectivity as a function of pore size using serial sections. European Journal of Soil Science, 48(3):365-377.

[26]Wildenschild D, Hopmans JW, Rivers ML, et al., 2005. Quantitative analysis of flow processes in a sand using synchrotron-based X-ray microtomography. Vadose Zone Journal, 4(1):112-126.

[27]Zapata CE, 1999. Uncertainty in Soil-water Characteristic Curve and Impacts on Unsaturated Shear Strength Predictions. PhD Thesis, Arizona State University, Tempe, USA.

[28]Zhai Q, Rahardjo H, 2012a. Determination of soil–water characteristic curve variables. Computers and Geotechnics, 42:37-43.

[29]Zhai Q, Rahardjo H, 2012b. Reply to the discussion by Bellia et al. on “Determination of soil–water characteristic curve variables”. Computers and Geotechnics, 45:151-152.

[30]Zhai Q, Rahardjo H, 2015. Estimation of permeability function from the soil-water characteristic curve. Engineering Geology, 199:148-156.

[31]Zhai Q, Rahardjo H, Satyanaga A, et al., 2017a. Effect of bimodal soil-water characteristic curve on the estimation of permeability function. Engineering Geology, 230:142-151.

[32]Zhai Q, Rahardjo H, Satyanaga A, 2017b. Effects of residual suction and residual water content on the estimation of permeability function. Geoderma, 303:165-177.

[33]Zhai Q, Rahardjo H, Satyanaga A, 2017c. Uncertainty in the estimation of hysteresis of soil-water characteristic curve. Environmental Geotechnics, in press.

[34]Zhai Q, Rahardjo H, Satyanaga A, 2018a. Estimation of the air permeability function from the soil-water characteristic curve. Canadian Geotechnical Journal, in press.

[35]Zhai Q, Rahardjo H, Satyanaga A, 2018b. A pore-size distribution function based method for estimation of hydraulic properties of sandy soils. Engineering Geology, 246: 288-292.