Undrained monotonic and cyclic shear behaviors of gas-bearing sand

A series of undrained monotonic and cyclic triaxial tests are carried out to compare the shear behaviors of the gas-bearing and saturated sand under varying consolidation conditions. The results show that under the normal consolidation conditions, the shear strength of the gas-bearing sand increases with the gas content, exhibiting a more significant dilatancy characteristic and strain-hardening tendency, and its critical state stress ratio is higher than that of the saturated sand. For the over-consolidated sand, its shear strength decreases with the gas content. It indicates that the presence of gas weakens the increasing trend of soil strength with the over-consolidation ratio. In the meanwhile, the cyclic shear resistance of the gas-bearing sand decreases with the increasing over-consolidation ratio.