LABORATORY AND INSITU MEASUREMENT OF SHEAR STRENGTH OF RESIDUAL SOIL

The objective of this abstract is to present an ongoing investigation into the behavior of residual soils. Residual soils are found throughout the Southeastern United States and behave somewhat differently than transported soils upon which traditional soil mechanics and geotechnical engineering are based. The test program included both insitu and laboratory tests. A single residual soil research site has been investigated and correlations between field and laboratory parameters are being developed.

The research site was located in Charlotte, North Carolina, near the geographic center of a large residual soil region known as the Southern Piedmont. The specific tests performed were the Standard Penetration Test with Torque (SPT-T), the Shelby Tube Test with Torque (STT-T), and the Consolidated Drained (CD) Triaxial Test. The field tests were performed in two bore holes at ten foot increments to a depth of 55 feet and soil samples were collected for laboratory tests. Using Shelby tube soil samples, three undisturbed CD tests were performed at each depth. The specific parameters being measured and correlated are the field torque (T) and laboratory shear strength (c' and Ö'). The average c' was found to be 4.8 psi and the average Ö' was found to be 25.6 degrees.

The proposed application of this analysis is to develop a reliable residual soil field test that provides a direct correlation to the laboratory shear strength. Due to an increasing amount of geotechnical activities with residual soil, there is an unavoidable need to extend the understanding of residual soils in soil mechanics.