Effect of gas on the mechanical behavior of medium-dense sands

This paper presents the results of monotonic and cyclic triaxial tests performed on gassy, medium-dense sand specimens. These sands are representative of conditions in a loose-sand deposit that was densified using multiple blasting passes at a site in South Carolina. The equipment and laboratory testing procedures used to reproduce the postblast densification conditions observed at a field test are described in detail. Results of undrained and drained compression tests showed that the gassy-specimen responses were bounded by the fully saturated drained and undrained responses. The undrained test results showed that the presence of gas, even in small amounts, made the soil more compressible and restricted the buildup of excess pore-water pressures as compared with those pressures observed in fully saturated specimens. Additionally, the shear strengths of gassy, medium-dense sand specimens were similar to those observed in saturated, loose sands sheared under drained conditions. For a given cyclic stress ratio and number of cycles, the axial strains and excess pore-water pressures were significantly smaller than those for a saturated specimen with the same void ratio. Implications of the behavior of such blast-densified sands are discussed.