Accession Number:

ADA586283

Title:

Testing Procedure for Estimating Fully Softened Shear Strengths of Soils Using Reconstituted Material

Descriptive Note:

Technical note

Corporate Author:

ENGINEER RESEARCH AND DEVELOPMENT CENTER VICKSBURG MS GEOTECHNICAL AND STRUCTURES LAB

Personal Author(s):

Report Date:

2013-09-01

Pagination or Media Count:

6.0

Abstract:

A consistent method for reconstituting soil samples is needed for the purpose of creating normally consolidated samples to be used to predict fully softened shear strength. The US Army Engineer Research and Development Center ERDC in conjunction with Virginia Tech University and under the direction of the US Army Corps of Engineers, Fort Worth District SWF, developed a procedure to estimate fully softened strengths using reconstituted samples and direct-shear testing equipment. This technical note describes the procedure used to reconstitute soil and the insights gained from using this method. Fully softened shear strength refers to a condition in which the shear strength of stiff clays and shales decreases over time. This phenomenon was first observed by Skempton 1964 in the 1950s and 1960s in slopes cut into stiff London Clay. Later studies revealed cyclic wetting and drying could also cause fully softened strengths to develop Wright et al. 2007. Skempton 1970, 1977 and others found that the fully softened strength was numerically equivalent to the peak strength of a clay in its normally consolidated state. The fully softened strength is characterized by a non-linear strength envelope and a zero-cohesion intercept. Because of the nonlinearity of the strength envelope, it is useful to determine the strength at more confining stresses than a material with a more linear behavior. It has been found that in most cases, five confining stresses adequately define the curved strength envelope. The fully softened strength can thus be expressed as a secant friction angle, which is simply the inclination of a line from the origin to a point on the curve at a specific confining stress. In general, the fully softened secant friction angle decreases with increasing liquid limit, effective confining stress, and clay fraction.

Subject Categories:

  • Soil Mechanics

Distribution Statement:

APPROVED FOR PUBLIC RELEASE