Development of Three-Ring Compaction and Direct Shear Test Mold for Soils with Oversized Particles

Abstract

Abstract

A three-ring compaction and direct shear mold has been developed to determine the optimum water content, maximum dry density and shear strength of compacted soil samples with particle sizes up to 10 mm.  It is designed to be used as a compaction mold and direct shear mold without removing the soil sample, and hence eliminating the sample disturbance.  Commercial grade bentonite is tested to verify that the three-ring mold can provide the results comparable to those obtained from the ASTM standard test methods.  Clayey sand, poorly-graded sand and well-graded sand with oversized particles are tested to assess the performance of the device.  Their results are also compared with those obtained from the ASTM standard methods.  The results indicate that the shear strength, maximum dry density and optimum water content of the bentonite obtained from the three-ring mold and the ASTM standard mold are virtually identical.  For the soils with oversized particles the three-ring mold yields higher maximum dry densities than those obtained from the ASTM mold.  The shear strengths obtained from the three-ring mold are also higher than those from the standard shear test device.  This is primarily because the three-ring mold can accommodate the soil particles up to 10 mm for the shear test, and hence resulting in higher shear strengths that are closer to the actual behavior of the soils under field conditions.