Abstract
This paper presents a novel approach to soil–water retention modelling that is based on the analysis of the material pore network. The approach postulates the existence of a differential coupling function, which relates the variation of water ratio to the variation of void ratio at constant suction. Distinct differential coupling functions have been considered, and the most general option has been integrated in a closed-form relationship between water ratio and void ratio with a suction-dependent integration constant, whose expression describes the isochoric retention behaviour. Four alternative expressions of the suction-dependent integration constant have been proposed resulting in four different, but equivalent, models linking degree of saturation, void ratio and suction. Each model predicts the variation of degree of saturation by means of four parameters, namely two parameters accounting for the effect of void ratio and two parameters accounting for the effect of suction. The models have been calibrated against laboratory data from soils with distinct particle size distributions and have shown accurate predictions of degree of saturation at different levels of suction and void ratio. Validation against additional data has also indicated that the models can extrapolate the soil behaviour to stress paths and suction levels beyond those considered during calibration.
Highlights
Modelling water retention in soils is important for a variety of applications from the serviceability and safety of earth structures to the study of landslides and the design of automated irrigation systems
The coupling function of Eq (5) predicts that the water ratio of an unsaturated soil does not change during volumetric deformation at constant suction, which means that the degree of saturation Sr 1⁄4 ew=e is inversely proportional to void ratio, so that it will increase during compression and decrease during swelling
The paper has postulated the existence of a differential coupling function that relates the increments of water ratio and void ratio at constant suction through a proportionality factor depending on degree of saturation
Summary
Modelling water retention in soils is important for a variety of applications from the serviceability and safety of earth structures (e.g. embankments, earth dams, cuttings, building foundations and retaining walls) to the study of landslides and the design of automated irrigation systems. Soils compacted dry of optimum exhibit two distinct pore classes, namely a class of smaller intra-aggregate pores and a class of larger inter-aggregate pores, whose size and volume evolve with stress history These discoveries have led to the formulation of a second category of constitutive laws, which introduce a further dependency of degree of saturation on void ratio [18, 24, 29, 31, 43, 47, 50] and/or pore size distribution [7,8,9,10,11, 20, 23, 25, 27, 28, 35, 36, 40, 48]. The methodology can be extended to account for hydraulic hysteresis [16] and to incorporate a mechanical law for predicting void ratio [5]
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