Estimating hysteresis in the soil water retention function from cone permeameter experiments

Abstract

Abstract. Data obtained from modified cone penetrometer experiments were used to estimate the hysteretic soil hydraulic properties with a parameter estimation technique which combined a numerical solution of the Richards equation with Marquardt-Levenberg optimization. The modified cone penetrometer was_designed to inject water into a soil through a cylindrical screen, measure the infiltration rate with time, and track the movement of the wetting front using two tensiometer rings positioned above the screen. After reaching relatively stable tensiometer readings during the experiments, the source of water was cut off and pressure head readings measured while water in the soil profile redistributed. Cumulative inflow and pressure head readings for two experiments with different supply pressures were analyzed to obtain estimates of the soil water retention and hydraulic conductivity functions. Analysis of flow responses obtained during the infiltration period, and of those obtained during the combined infiltration and redistribution phases, demonstrated the importance of hysteresis of the soil hydraulic functions. We found that the redistribution phase could not be described accurately when hysteresis was neglected. Hysteresis in the soil hydraulic functions was modeled using a relatively simple empirical model in which wetting scanning curves are scaled from the main wetting curve and drying scanning curves are scaled from the main dvfing curve. This model was deemed adequate for our examples. Optimization results for various combinations of unknown soil hydraulic parameters were compared to results of standard laboratory and in situ methods. Estimates of the saturated hydraulic conductivity were well within the range of in situ measurements. The estimated main hysteretic loops of the soil water retention curve were for the most part situated between the wetting and drying curves obtained with standard methods.

Simultaneous Inverse Estimation of Soil Hydraulic and Solute Transport Parameters From Transient Field Experiments: Homogeneous Soil

“…Including q s and other soil hydraulic parameters in the optimization could well have improved the model predictions. However, as indicated earlier, we felt it is important to limit as much as possible the number of unknown parameters in view of the limited amount of measured data and the relatively high sensitivity of the parameter estimation technique to the number of unknowns (Simunek et al, 1999b). Only K s was included in the optimization procedure since we did not have direct field measurements of this parameter.…”

“…6 and 7) using the Levenberg-Marquardt optimization procedure (Marquardt, 1963). In the inverse procedure, the unknown parameters are optimized by minimizing the objective function F(q,b) defined as (Simunek et al, 1999b): …”

“…For example, Simunek and van Genuchten (1996) showed that measured infiltration data using a tension disc infiltrometer at constant tension did not provide enough information to inversely estimate soil hydraulic properties, whereas using infiltration data at multiple tensions yielded good estimates of the soil hydraulic properties . The model was also successfully used to inversely estimate soil hydraulic properties from cone permeameter experiments (Gribb, 1996;Kodesova et al, 1998Kodesova et al, , 1999Simunek et al, 1999b). In other studies, Wang et al (1997) used the CHAIN-2D model (Simunek and van Genuchten, 1994), an early version of the HYDRUS-2D, to investigate the effects of different irrigation methods and spatial variability in the saturated hydraulic conductivity on subsurface solute transport.…”

Seasonal effects on geophysical–geotechnical relationships and their implications for electrical resistivity tomography monitoring of slopes

“…However, there is little research into the effects of repeated seasonal cycles on the resistivity response of volume-sensitive clay soils. Hysteresis in near-surface soils is well established in the soil water retention curve [20,22,49] whereby at a given water content a decrease in soil suction is observed between the drying and the wetting paths, due to entrapped air. Associated decreases in soil strength may then be a function of both this suction loss and soil fabric changes incurred by desiccation cracking.…”

Challenges in monitoring and managing engineered slopes in a changing climate

“…However, there is little research into the effects of repeated seasonal cycles on the resistivity response of volume-sensitive clay soils. Hysteresis in near-surface soils is well-established in the soil water retention curve [35,36,37] whereby at a given water content a decrease in soil suction is observed between the drying and the wetting paths, due to entrapped air. If ERT is to fulfil its potential in geotechnical monitoring then it is necessary to understand how soil suction and resistivity interact when subjected to seasonally varying water content, in order to be able to interpret geophysical information gathered from electrical resistivity tomography arrays.…”