Measurements of the yield surfaces and critical state of some unsaturated agricultural soils

Abstract

Yield surfaces and the critical-state condition have been measured on unsaturated agricultural soils using a standard uniaxial compression test and a constant-volume direct shear test. The yield surfaces and critical-state line are all readily described in terms of applied or total stresses, and such an approach offers practical advantages over approaches based on effective stresses. Four soils were tested, these being a silt, a tilth with aggregates mostly from 5-15 mm, a cracking clay and a red-brown earth.Each soil was tested at a single constant moisture content in all tests, although the moisture content differed from soil to soil. The range of saturation covered by the four soils was approximately 2&98%. All the soils displayed yield and deformation behaviour qualitatively consistent with the critical-state concept. All approach a condition of shear with no volume change (the critical state) under continuing shear. All show collapse with shear in states looser than critical, and expansion with shear in states denser than critical. The silt, being a non-cohesive soil, cannot support shear stresses much above the criticalstate line, whereas the other three soils can support much higher shear stresses in the overconsolidated condition. The yield surfaces of the silt and the tilth, which were tested at low saturation, are similar in shape with increasing stress level. However, the other two soils, tested when near saturation, display yield surfaces that are not constant in shape with increasing stress level. While the critical-state concept is applicable both qualitatively and quantitatively, unsaturated soils may be considered to have properties that differ in detail from those of saturated soils.

Use of triaxial stress state framework to evaluate the mechanical behaviour of an agricultural clay soil

“…11). The distance between the Critical state line and the normally consolidated line in this case is different from that observed from the data in Kirby (1989), Adams and Wulfsohn (1996) or O ' Sullivan et al (1996). This fact shows that the distance between the NCL and the CSL may depend on the soil type.…”

“…Examples are works by Kurtay and Reece (1970). Hettiarachi andO'Callaghan (1980, 1985), Leeson and Campbell (1983), Hettiarachi (1987), Kirby (1986Kirby ( , 1989Kirby ( , 1991, and Wulfsohn (1994) to list a few. These investigations were conducted using the critical state theory developed in geotechnical engineering.…”

Modelling soil distortion during compaction for cylindrical stress load paths

“…Qualitative agreement with the critical-state concept has been demonstrated also in a number of studies based on uniaxial compression tests and translational direct-shear tests (e.g. Kirby, 1989Kirby, , 1991 and torsional-shear tests (e.g. Greacen, 1960).…”

Numerical Simulation of an Agricultural Soil Shear Stress Test

“…These parameters were the input data for the Abaqus program code [1], and they were determined by well-known and standardized procedures performed by triaxial test apparatus as already used by numerous authors including [5], [17], [18], [20], [23], and precisely:…”