Large Scale Constrained Modulus Test: Constrained Modulus of Crushed Rock Test Results

A series of one-dimensional compressions tests were performed on crushed rock to determine the constrained modulus (M_s). The tests utilized a 17 ½ inch diameter test specimens confined in a steel cylinder utilized as a floating ring. Twenty-seven tests were completed on five clean, crushed rock samples obtained from four sources in the Colorado area. Twenty-one of the tests were performed wet and six were performed dry. For each sample, a series of at least four tests was performed using three different placement compaction efforts in order to obtain a representative range of M_s values. The maximum particle sizes for the samples ranged from ½ inch to 1 ½ inch. It is demonstrated that M_s of hard, uniformly graded and shaped crushed rock: (1) Is not greatly dependent on stress level; (2) Is strongly dependent on placement compaction effort; (3) Is weakly dependent on placement moisture condition; (4) Varies significantly with changes in crushed rock particle characteristics.