盐分对含二氧化碳水合物泥质粉细砂力学特性的影响规律

Influence of salinity on the mechanical behaviors of CO2 hydrate-bearing silty sand

影响含水合物沉积物力学性质的因素较多,深海海床地层处于含盐环境,而目前盐分变化对含水合物沉积物力学性质的影响报道较少,其规律尚未厘清。为此,通过含不同浓度氯化钠盐溶液试样制备含二氧化碳水合物泥质粉细砂土,并在不同围压条件下进行三轴剪切试验,揭示了盐分对应力—应变关系、强度、刚度、剪胀性的影响规律。研究结果表明:(1)盐分使含水合物土的相平衡线发生偏移,在相同初始含水率下,盐分导致土中水合物饱和度降低,未合水含量增加;(2)合成相同水合物饱和度,含盐分水合物土的初始含水率要高于不含盐分水合物土,导致含盐分水合物土的抗剪强度低于不含盐分水合物土;(3)盐分对含水合物土的黏聚力有较大影响,随着水合物饱和度的增加,含盐水合物土的黏聚力略有增加,而不含盐水合物土的黏聚力明显增加。结论认为:(1)盐分对含水合物泥质粉细砂抗剪强度特性的影响是通过改变未合水含量产生的,未合水越多,土的强度越低,割线模量越小,剪胀性越不明显;(2)含水合物土的强度特性不仅与水合物的饱和度有关,还与未合水含量密切相关,传统上仅考虑水合物饱和度对含水合物土抗剪强度的影响,不能准确描述物理—化学作用下含水合物土强度特性的演化。

The mechanical behaviors of hydrate-bearing sediments are influenced by multiple factors,and the strata of deep sea bed are in a salty environment.So far,however,the influence of salinity on the mechanical behaviors of hydrate-bearing sediments has been less reported and its influence laws have not been well addressed.In this paper,COhydrate-bearing silty sand is prepared by using sodium chloride solution with different concentrations,and triaxial shearing tests are performed under different confining pressures,so as to reveal the influence laws of salinity on stress-strain relationship,strength,rigidity and dilatancy.And the following research results are obtained.First,salinity leads to the migration of the phase equilibrium line of hydrate-bearing soil.Under the same initial water content,salinity results in the decrease of hydrate saturation in the soil and the increase of unhydrated water content.Second,to form the same hydrate saturation,the initial water content of hydrate-bearing soil with salt shall be higher than that without salt,so the shearing strength of hydrate-bearing soil with salt is weaker than that without salt.Third,salinity has a greater influence on the cohesion of hydratebearing soil.With the increase of hydrate saturation,the cohesion of hydrate-bearing soil with salt increases slightly,while that without salt increases significantly.In conclusion,the influence of salinity on the shearing strength behaviors of hydrate-bearing silty sand is generated as the unhydrated water content changes.The more the unhydrated water,the lower the soil strength,the smaller the secant modulus and the less obvious the dilatancy.What’s more,the strength behavior of hydrate-bearing soil is not only related to hydrate saturation,but also in a close relationship with unhydrated water content.Traditionally,only the influence of hydrate saturation on the shearing strength of hydrate-bearing soil is taken into consideration,which makes it impossible to accurately describe the evolution of the strength behavior of hydrate-bearing soil under physical-chemical action.