Abstract
The soil-water retention surface (SWRS), which describes the variation of the degree of saturation (Sr) with suction (s) and void ratio (e), is of crucial importance for understanding and modeling the hydro-mechanical behavior of unsaturated soils. As a 3D surface in the Sr –e–s space, the SWRS can be projected onto the constant Sr, constant s, and constant e planes to form three different 2D projections, which is essential for establishing the SWRS and understanding its various characteristics. This paper presents a series of investigations on the various characteristics of the three SWRS projections. For the Sr –s and Sr –e relationships, (i) a tangential approximation approach is proposed to quantitatively capture their asymptotes, and (ii) a new criterion is presented to distinguish the low and high suction ranges within which these two relationships exhibit different features. On the other hand, a modified expression is introduced to better capture the characteristics of the s–e relationships. The various projection characteristics and the proposed approaches are validated using a wide set of experimental data from the literature. Studies presented in this paper are useful for the rational interpretation of the SWRS and the hydro-mechanical coupling behavior of unsaturated soils.
Highlights
The hydro-mechanical behavior of unsaturated soils has been a significant research topic in geotechnical engineering over the past three decades [1,2,3,4,5,6,7,8,9,10,11]
It is evident that using the reference hydro-mechanical coupling curves (HMCCs) at low suctions to predict HMCCs at high suctions can lead to deviations that are significant from the experimental data
Based on the soil-water retention surface (SWRS) model of Gallipoli et al [26], three independent 2-D equations were presented in this paper and used to investigate the projection characteristics of the SWRS on the constant e, s, Based on the SWRS model of Gallipoli et al [26], three independent 2-D equations were and Sr planes in order to have an insight into the hydromechanical behavior of unsaturated soils
Summary
The hydro-mechanical behavior of unsaturated soils has been a significant research topic in geotechnical engineering over the past three decades [1,2,3,4,5,6,7,8,9,10,11]. Recent advances in the understanding studies on the hydro-mechanical coupling behavior of unsaturated soils typically require one to incorporate the influence of volumetric strain (i.e., void ratio e) into the description of the SWRC, considering that the degree of saturation is modified by two factors: (i) the variation in the soil water (hydraulic path), and (ii) the volume change in the soil pores (mechanical path) [25,26,27,28,29,30,31]. Water 2018, 10, 1717 the e–s–Sr relationship as a 3D surface (i.e., soil-water retention surface, SWRS) This SWRS model can describe the irreversible changes of degree of saturation caused by the hydraulic (i.e., wetting and drying) and mechanical (i.e., confining pressure and shearing stress) behaviors and can be effectively used in the numerical modelling of coupled flow-deformation problems. Modifications and improvements are introduced with respect to (i) capturing the asymptotes and distinguishing the different behaviors in the high and low suction ranges for the s–Sr and e–Sr relationships and (ii) describing the s–e relationships
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