不排水条件下可燃冰分解对海底边坡稳定性的影响  

Influence of Gas Hydrate Dissociation on Submarine Slope Stability Under the Undrained Condition

作　　者：洪隽天 徐明[1,2] Hong Juntian;Xu Ming(Department of Civil Engineering,Tsinghua University,Beijing 100084,China;National Engineering Laboratory of Urban Railway System and Green Construction Technology,Tsinghua University,Beijing 100084,China)

机构地区：[1]清华大学土木工程系,北京100084 [2]清华大学城市轨道交通绿色与安全建造技术国家工程实验室,北京100084

出　　处：《天津大学学报（自然科学与工程技术版）》2019年第A01期49-55,共7页Journal of Tianjin University：Science and Technology

基　　金：国家自然科学基金资助项目(41272280);国家重点基础研究发展计划(973计划)资助项目(2014CB047003)

摘　　要：近年来,可燃冰受到学界的广泛关注:一方面,可燃冰可以作为潜在的新型能源;另一方面,海底边坡中可燃冰的分解是引发海底地质灾害的重要原因.可燃冰分解将产生大量甲烷气体,当含可燃冰土层位于两个透水性较差的土层中间时,孔隙水和气体将无法与外界发生交换,可燃冰的分解过程可以看作不排水(气)过程.此时,沉积物中孔压升高,有效应力减小,抗剪强度下降,当含可燃冰土层位于边坡坡底附近时,边坡将更易沿可燃冰土层发生滑动破坏.因此,可燃冰分解将对海底边坡的不排水开挖造成不利影响.本文基于理想气体状态方程和摩尔库伦模型,提出了一种在任意应力状态下可燃冰分解的数值模拟方法,并在有限差分软件FLAC3D中实现该方法,进而从土单元层面将数值模拟结果和理论推导结果进行了对比,两者基本吻合.最后,本文利用该方法分析了可燃冰分解对海底边坡稳定性的影响,模拟了可燃冰不分解条件下直接进行不排水开挖、以及可燃冰分解后再进行不排水开挖.模拟结果显示,可燃冰分解会导致海底边坡在不排水开挖时发生失稳.Gas hydrate has gained increasing research attention worldwide in recent years. Although gas hydrate has the potential to be a new energy source,it will affect the submarine slope stability. Gas hydrate can decompose into water and methane. If the gassy soil is located between two impermeable soil layers and there are no pathways through which the water and gas can escape,the process of decomposition will be essentially undrained. Thus,the dissocia- tion of gassy sand will increase the pore pressure and decrease the effective stress and shear strength. If the gas hydrate layer is located near a submarine slope,the slope may experience slip failure along the layer. Thus,the existence of gas hydrate will affect the submarine slope stability undergoing undrained excavation. Based on the ideal gas equation and Mohr Coulomb criterion,this study proposes a numerical simulation method to calculate the excess pore pressure resulting from gas hydrate dissociation under the undrained condition. The proposed method is further implemented in the finite-difference program FLAC3D. The simulated results of odometer tests compared well with the theoretical results. The stability of a submarine slope with a gas hydrate layer is also analyzed using the proposed method. The undrained excavation of the submarine slope with and without the dissociation of gas hydrated are simulated and com- pared. The simulation results show that the dissociation of gas hydrate affects the submarine slope stability under the undrained condition.

关 键 词：可燃冰 不排水 超静孔压 海底边坡稳定性 

分 类 号：P751[交通运输工程—港口、海岸及近海工程]