气体导致海床隆起与裂缝形成过程分析

Analysis of seabed dome and fracture formation induced by gas

海底沉积物中来自深源的气体在突破表层细粒沉积物逸出时,由于气源压力不同、地层结构不同可能会导致不同程度的海床面隆起,进而造成不同细粒沉积物变形破坏过程,引发不同规模和类型的地质灾害。为研究这一过程的演化特征,本文开展细粒沉积物的充气室内模型实验与数值模拟分析,观测气体导致土体隆起过程的典型过程与土体中超孔隙水压力变化,以及不同隆起程度下的土体应力应变变化。结合前人的土体拱起变形研究以及气致裂缝理论,分析实验数据发现:(1)薄板弹性变形理论可以很好地描述恒定气压、气体均匀分布情况下海底细粒沉积物的变形过程;(2)细粒沉积物经历隆起变形后的裂缝发生位置与形成裂缝的临界气压与沉积物底部气囊的尺寸相关,气囊越矮胖,气囊的边缘位置更容易产生拉张破坏,反之则气囊的顶部细粒沉积物更容易产生裂缝。

When gas from a deep source in sediments breaks through surface fine-grained sediments,different gas source pressures and stratum structures may lead to different degrees of seabed dome,and then cause different deformation and failure processes of fine-grained sediments,leading to different scale and types of geological disasters.To study the evolution characteristics of this process,the gas injection laboratory experiment and numerical simulation analysis of fine-grained sediments were carried out to observe the typical process of gas-induced soil heave,the change of excess pore water pressure in sediments,and the stress and strain changes under different degrees of sediments dome.Combined with previous studies on sediments deformation and gas-induced fracture theory,the experimental data were analyzed.It was found that(1)The elastic plate bending deformation theory could well describe the deformation process of fine sediment under constant pressure and uniform gas distribution;(2)After gas domed fine-grained sediments,the location of cracks was related to the critical pressure to form cracks and the size of the gas pocket at the bottom of the sediments.The dumper and fatter the gas pocket were,the more prone the edge of the gas pocket were to be failed with tensile;otherwise,the top of the fine sediments of the gas pocket was more likely to produce fracture.