Soil-water characteristic curves - Determination, estimation and application

Abstract

The soil-water characteristic curve (SWCC) is a relationship between water content in a soil and suction. The SWCC was first plotted by Edgar Buckingham, a soil physicist, in 1907 for six soils ranging in texture from sand to clay. It was adopted for use in unsaturated soil mechanics by the geotechnical engineering community. The SWCC is now almost treated as the index property of unsaturated soils. It has been used as a proxy for permeability and shear strength of unsaturated soil. Most soils have a sigmoidal SWCC, otherwise known as a unimodal SWCC as opposed to a bimodal SWCC which has been found for some soils. Although determining the SWCC is easier than determining permeability or shear strength for unsaturated soil, the test is still time-consuming and it is not easy to determine the entire SWCC. Incomplete or insufficient SWCC data may lead to an incorrect SWCC and hence inaccurate determination of permeability and shear strength. Progress has been made to expedite the experimental determination of SWCC as well as estimating the SWCC from basic soil properties using pedotransfer functions. In addition, SWCC has been represented using volumetric water content, gravimetric water content or degree of saturation. Different representations may have dire consequences on its application. Determining the SWCC using volumetric water content or degree of saturation presents challenges in estimating the instantaneous volume during the experiment. In this paper, the current state-of-the-art in determining, representing and estimating SWCC and its applications are described and critically examined.

A Novel Hybrid Soft Computing Model Using Random Forest and Particle Swarm Optimization for Estimation of Undrained Shear Strength of Soil

“…Many researchers have attempted to estimate the shear strength of soil using different alternative methods [3,[5][6][7][8][9][10]. The shear strength of unsaturated soil can also be predicted using the empirical correlation function [10,11], using soil-water retention curve [10,12,13].…”

A new framework to determine general multimodal soil water characteristic curves

“…Substituting Eqs. (21) in (20), it is not hard to see that the Burger, Shackelford [8] bimodal model (using VGM to describe S r,i ) is equivalent to DMVGM with N = 2, as shown in Fig. 2b.…”

“…A general framework for a continuous bimodal SWCC was proposed by Ross, Smettem [34] using 'volumetric fraction approach' [21,46]. The overall pore space of the soil is regarded as the superposition of two overlapping subporosities, i.e., the micro-and macroporosity, and the bimodal SWCC function in terms of effective degree of saturation S e can be expressed as…”

“…To overcome the difficulties in parameter calibration, another type of continuous bimodal SWCC functions has been developed based on the independent parameters related to the SWCC shape features, referred to as 'unique parameter approach' [21,46]. Gitirana and Fredlund [18] presented a bimodal model with the parameters determined with bending points from the shape of SWCC, which requires only one additional curve fitting parameter.…”

Study on soil-water characteristic curves in the profiles of collapsing walls of typical granite Benggang in southeast China

“… Wen et al (2021) pointed out that the void ratio of soil is affected by its shrinkage behavior, and thus affects the SWCC. The SWCC has also been applied in modeling flow in unsaturated soils and obtaining other unsaturated soil properties, such as shear strength and permeability ( Leong, 2019 ). On the other hand, it can accurately show the relationship between soil water content and matric suction ( Oh et al, 2012 ; Miguel & Bonder, 2012 ), it is helpful for estimating properties such as shear strength ( Neris et al, 2013 ; Hedayati et al, 2020 ).…”