颗粒抗滚动作用对水合物沉积物宏观及微观力学特性的影响

Impact of rolling resistance effect of particles on macro/micro mechanical properties of hydrate-bearing sediments

因其清洁无污染且储量巨大,天然水合物被认为是21世纪重要的战略资源。为有效考虑水合物沉积物中由于不规则的颗粒形状对宏观响应产生的影响,在离散元数值模拟中引入抗滚动线性接触模型,对抗滚动系数为0、0.2、0.4、0.6、0.8以及不同饱和度(10%、20%、30%、40%)的水合物沉积物数值试样进行了20组常规三轴压缩试验,探究了抗滚动作用对水合物沉积物的宏观力学特性的影响及微观作用机理。研究结果表明:抗滚动作用可以有效提高水合物沉积物的宏观强度和剪胀程度,但是抗滚动作用对于强度和剪胀的促进作用并不会无限增大,而是存在一个临界值,大于临界值之后,抗滚动作用对宏观力学特性的影响越来越小。这是由水合物沉积物内部微观结构的演化决定的:抗滚动系数的增大,虽然配位数降低,孔隙率有所增加,但颗粒的平均接触力将会随之增大,内部形成贯穿试样的强力链,从而使沉积物体系更加稳定,而当抗滚动系数增大至特定值时,平均接触力、配位数以及孔隙率受到抗滚动作用的影响逐渐减小,从而使水合物沉积物的宏观力学特性受到抗滚动作用的影响也会越来越小。

Hydrate-bearing sediments are seen as important strategic resource in the 21 st century,characterized with cleaness and huge reserves.In order to effectively analyze the effect of irregular particle shapes on the macro response in hydrate-bearing sediments,a rolling resistance linear contact model is introduced into the discrete element numerical simulation;then 20 sets of conventional triaxial compression tests are performed for the numerical samples of hydrate-bearing sediments with the rolling resistance coefficient of 0,0.2,0.4,0.6 and 0.8 as well as the saturation of 10%,20%,30%and 40%;finally,this paper explores the impact of rolling resistance effect on the macro-mechanical properties of hydrate-bearing sediments and the corresponding microscopic action mechanism.The results show that rolling resistance effect can effectively improve the macro-strength and degree of shear dilatation of hydrate-bearing sediments,but the rolling resistance effect will not enhance the strength and shear dilatation indefinitely.There is a critical value;when it is greater than the critical value,the influence of rolling resistance effect on the macro mechanical properties is getting smaller and smaller.This is determined by the evolution of the internal microstructure of hydrate-bearing sediments.With the increase of the rolling resistance coefficient,although the coordination number decreases and the porosity increases,the average contact force of the particles will increase accordingly and the strong force chain is formed inside through the sample,and therefore the sediment system is more stable.When the rolling resistance coefficient increases to a certain value,the impact of rolling resistance effect on the average contact force,coordination number and porosity gradually decreases,so the influence of rolling resistance effect on the macroscopic mechanical properties of hydrate-bearing sediments will also be less and less.