Reducing uncertainties and improving sand soil-water retention curve (SWRC) predictions for hazard screening analyses

Abstract

An energy-based laboratory-testing program was undertaken to investigate the effects of different testing methods, numerical model fits, and soil fabrics and densities on the soil-water retention curve (SWRC) using a poorly graded sand. Four different reconstitution energies and three saturation levels were used to generate different soil fabrics and structure within a narrow band of possible densities, as limited by the mechanical properties of the soil particles. Tests were performed using a “transient retention imbibition method” and a Fredlund device to develop a statistically representative laboratory SWRC. Testing results for the poorly graded sand indicate little aleatory variability in SWRC from the soil structure. The dominant source of data variability is a function of the epistemic uncertainty associated with the testing methods and fitting models but can be accounted for by a bounded mean SWRC. This bounding allows for the development of a laboratory “proxy” soil, representative of generalized sand SWRC behavior, for use as a hazard screening tool for modeling unsaturated sand behavior. The proxy soil SWRC is compared with other generalized SWRC models and independent SWRC field and laboratory tests, wherein the proxy soil SWRC yields significant increases in accuracy between the estimated and field SWRC behavior.