Factors affecting the strength of undisturbed cores from soils with low structural stability

Undisturbed core samples of two similar sandy clay loam soils (Big Ground and Plum Orchard) were equilibrated at matric potentials of −0.01, −0.1 and −1 MPa and tested for indirect tensile strength (ITS) and unconfined compressive strength (UCS). Rate of deformation was found to have significant and large effects on the measured ITS and UCS. In general, both ITS and UCS increased with increasing deformation rates although, particularly for UCS tests, the effect was variable. For ITS, the effect of rate of deformation was attributed to water having insufficient time to move towards any incipient failure plane. For UCS, the effect of rate of deformation was partly attributed to loss of moisture during loading, since samples strained at lower deformation rates generally had lower moisture contents; and partly to the different modes of failure seen. ITS and UCS of Big Ground were invariably higher than those of Plum Orchard at all matric potentials. This was attributed to Big Ground having been under an intensive management system for approximately 10 years longer than Plum Orchard. Simple pretreatment effects are also considered. In a comparison of measured and theoretically predicted ITS and UCS, theory provided good estimates of measured strengths of samples equilibrated at −0.1 MPa, although samples were considerably weaker than theoretically predicted at −1 MPa. Copyright © 1991, Wiley Blackwell. All rights reserved