A pore-scale numerical investigation of the effect of pore characteristics on flow properties in soils

Abstract

Flow properties of soils can impact a wide range of geotechnical, agricultural, and geophysical processes. Few studies focus on the physical understanding of how pore characteristics can affect flow properties in soils. In this paper, pore network modeling is utilized to investigate intrinsic permeability, water pressure distributions, flow patterns, and critical flow paths in soils with pores varying in size, connectivity, and anisotropy. The results show that increased mean diameter, decreased standard deviation, and increased coordination number of the pores can lead to an increase in intrinsic permeability in soils. Non-uniform water pressure and flow rate distribution will more likely occur in soils with a larger pore size variability. A higher coordination number mitigates the pressure localization but slightly exacerbates non-uniform flow. With the increase in the coefficient of variation (COV) of pore diameters, the percolation path becomes more tortuous and carries more flow. When COV increases from 0 (homogeneous) to 1 (large pore size variability), the tortuosity increases from 1.00 to ∼1.71 and the flux carried by the percolation path in soils increases from 2.0% to 7.8%. Pronounced preferential flows may take place in soils with uniformly distributed pore sizes, in which the percolation path can carry as much as 9.2% of the total flux. The anisotropy in pore throat sizes also increases the flow tortuosity and the fraction of flux carried by the percolation path. The permeability anisotropy Kh/Kv increases linearly as the pore throat size anisotropy µdh/µdv increases logarithmically. These results provide insight for designing soil barriers for either uniform flows or exacerbated preferential flow for fast transport.