| Shallow gas is widely distributed in the global offshore seabed sediments,causing potential damage to marine engineering.Due to the high pressure gas in the soil,the saturation is usually more than 85%,which greatly changes the mechanical properties of seafloor sediments,and is regarded as a special unsaturated soil.At present,there is a lack of systematic understanding of its mechanical behavior under external loads or internal stresses in soils.In this paper,the tests of mechanical properties of gassy sand under the conventional shear path and the normal shear stress path are carried out to enhance the understanding of the mechanical properties of marine gas-bearing sediments,further reveal the destabilizing failure mechanism and disaster causing mechanism of gas-bearing submarine soil,provide experimental support for the establishment of constitutive model of marine gas-bearing sandy sediments,and provide reference for disaster prevention and mitigation of marine engineering in the future.The specific research contents are as follows:（1）In the process of preparing gassy sand based on CO2-saturated aqueous solution desolventization,the empirical judgment of gas dissolution and desolventization equilibrium was usually used,and there were many subjective factors.A dissolved equilibrium monitoring caldron with high precision p H probe is developed,which can visually and dynamically monitor the dissolution and desolvation equilibrium of CO2 gas.（2）Triaxial shear tests under conventional stress paths can reveal the failure characteristics of gassy sand under external loading.The experimental results show that the effect of relative density on the stress-strain characteristics should be taken into account first,followed by the drainage condition,the stress-strain characteristics are opposite under the drainage/undrainage condition,and the gas content increases with the gas content,while the dense sand has the opposite effect,but the effective confining pressure only restrains the specimen.The slope of instability line of loose sand increases with the increase of gas content,while that of dense sand is opposite,but the slope of instability line tends to be consistent.The elastic modulus of aerated loose sand is larger than that of saturated sand,that is,its ability to bear external load is stronger,but it decreases with the increase of unloading reloading times.Shearing wave velocity can reflect the change of density of gassy sand under controlled stress-strain,while compression wave velocity mainly reflects the change of free gas content.（3）Under the path of normal shear stress,under the drainage condition,the critical stress of loose sand is larger with the increase of gas content and the prolonging of failure time,but the effect on dense sand is not significant;under the undrainage condition,the critical stress of loose sand is smaller with the increase of gas content and the shortening of failure time,and the effect on dense sand is also not significant.Due to the existence of gas,the change of pore water pressure is delayed under the condition of drainage.Without drainage,the effective confining pressure drops more quickly due to the continuous gas desolvation. |
