Analysis Of Influence Of Excess Pore Pressurecaused By Hydrate Decomposition On Stability Of Submarine Energy Soil Slope

Submarine energy soil slopes are submarine slopes containing gas hydrates(combustible ice).Natural gas hydrate reserves,large distribution,high energy density,is the most promising new strategic alternative energy source in the 21st century.However,the conditions for the high pressure and low temperature of natural gas hydrates are extremely harsh.The changes in temperature and pressure caused by environmental changes and subsea engineering may cause the hydrate to decompose.After decomposition of 1 m~3 of gas hydrate at normal temperature and pressure,164 m~3of gas and 0.87 m~3 of water can be released.As the hydrate decomposes,the cementation of the soil particles weakens and the porosity increases and energy soil becomes under-consolidated or loose sand.The analysis of the natural gas causes the pore water pressure to rise rapidly,and the effective stress is reduced,causing the static liquefaction of the energy soil,which in turn leads to a submarine landslide.The close relationship between the instability of submarine energy soil slope and the decomposition of hydrate has been proved by many research institutions all over the word.The establishment of relevant mechanical models for analysis is of great significance for assessing the stability of the seabed slope during the process of combustible ice mining.Based on a brief analysis of the submarine landslide induced by hydrates,this paper completed the following work:(1)The finite element strength reduction method and numerical calculation software ABAQUS are briefly introduced.The feasibility of studying the submarine landslide by finite element strength reduction method with ABAQUS as the numerical calculation platform is verified by a typical slope example.(2)Using the basic theory of thermodynamics,and considering the phase evolution of the final decomposition state of hydrate and the dissolution of methane gas by seawater during hydrate decomposition,the Grozic model of non-escape of pore gas is modified.The modified pore pressure model was verified and compared by a typical submarine landslide case.(3)According to the modified Grozic model,the value of the excess pore pressure under different decomposition degrees of hydrate is calculated,and the finite element strength reduction method is used to simulate the slope stability of the submarine energy soil under the large-scale decomposition of hydrate layer.In the process of hydrate dissociation,compared with the unfavorable factors of softening of soil strength parameters,the accumulation of excess pore pressure has a more negative impact on slope stability.Therefore,it is necessary to consider the adverse factor of excess pore pressure in the analysis of slope stability of submarine energy soils.(4)Calculate the range of hydrate decomposition caused by single shaft mining based on gas production,and compare with the monitoring data to ensure the accuracy of subsequent simulation schemes.The conditions of different lengths of horizontal wells and the different number of shafts are respectively formulated into simulation schemes,taking into account factors such as excess pore pressure,softening of soil strength parameters and the initial stress field.Simulate and evaluate the stability of submarine energy soil slope.