RAPID SHEAR STRENGTH EVALUATION OF IN SITU GRANULAR MATERIALS

Abstract

Dynamic Cone Penetrometer (DCP) and rapid-loading (1.5 in./sec) triaxial shear strength tests were conducted on six granular materials compacted at three density levels. The granular materials were sand, dense-graded sandy gravel, AREA No. 4 crushed dolomitic ballast, and material No. 3 with 7.5, 15, and 22.5% FA-20 material. (FA-20 is a nonplastic crushed-dolomitic fines material--96% minus No. 4 sieve : 2% minus No. 200 sieve.) DCP and triaxial shear strength data (including stress-strain plots) are presented and analyzed. The major factors affecting DCP and shear strength are considered. DCP-shear strength correlations are established and algorithms for estimating in situ shear strength from DCP data are presented. To the authors' knowledge, this is the first study in which the shear strength of granular materials has been related to DCP test data. Such relations have significant potential applications in evaluating existing transportation support systems (railroad track structures, airfield and highway pavements, and similar types of horizontal construction) in a rapid manner. A DCP test can be conducted to a depth of 2 to 3 ft in a matter of minutes. Several tests can be conducted to establish the variability of the in situ material.