The soil water retention curve (SWRC) describes a soil’s constitutive relation between matric suction and volumetric water content. The suction stress characteristic curve (SSCC) describes a soil’s constitutive relation between suction stress and volumetric water content. Both the SWRC and SSCC are often established assuming a soil is nondeformable. Under a shallow field environment, however, the total stress can change several hundreds of kilopascals due to self-weight variation with depth, surface structural loading, or soil excavation, leading to changes in volumetric strain and consequently the SWRC and SSCC. This work experimentally examined the effect of a confining stress on the SWRC and SSCC under both drying and wetting conditions through a silty sand. The SWRCs were measured under different confining stresses up to 200 kPa, allowing assessment of the uniqueness of the SWRC or SSCC. We found that under wetting conditions, even though the SWRCs and SSCCs were different under different confining stresses, a unique SWRC or SSCC could be defined if the effective degree of saturation was used. Under drying conditions, the uniqueness of the SWRC or SSCC held approximately; the differences mainly reflecting in the air-entry pressure. Furthermore, the failure envelope by the effective stress representation based on the SWRC was unique for either wetting or drying and was well represented by the saturated failure envelope. The SSCC inferred from the shear strength tests was similar to that from the SWRC measurement under the respective wetting or drying states. Therefore, the SWRC and SSCC are practically independent of the confining stress up to 200 kPa for a silty sand.

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