【作者】 周丹；

【导师】 孔宪京； 邹德高；

【作者基本信息】 大连理工大学 ， 防灾减灾工程及防护工程， 2012， 硕士

【摘要】 进入21世纪,随着经济全面飞速发展,人们对能源的需求与日俱增,油气资源巨大消耗,经济发展面临巨大考验。天然气水合物被认为是21世纪最具有开发前景的替代能源之一。然而,当环境条件改变时,破坏天然气水合物沉积层稳定性,释放出大量的气体和水,极大地降低海底沉积物工程力学特性,引起海底土体软化、边坡失稳、海底滑坡等地质灾害,进而毁坏海底工程设施,如海底基础、管线、钻井平台等。由于水合物分解过程极其复杂,加之研究深海环境困难重重,目前关于水合物分解对海底结构物影响的研究较少,刚处于起步阶段。因此,现阶段有必要通过数值模拟手段针对水合物分解对水合物沉积层及其上工程设施的影响进行研究,以便为今后大规模海底开发活动提供参考。本文主要通过有限元数值模拟,研究水合物分解对海底结构物的影响规律,主要工作包括以下几个方面：(1)为研究水合物分解过程中水合物沉积物模量软化和强度衰减的过程,采用应力释放法,建立能够考虑水合物分解软化的有限元数值计算方法,开发了相应计算程序,并通过计算算例分析该程序的可靠性。(2)首先,利用该程序计算水合物分解对海底斜坡稳定性影响,设计三种计算工况,分别研究模量软化和强度衰减对斜坡变形的影响。然后,进一步讨论水合物分解过程中斜坡上面不同厚度覆盖土层对斜坡稳定性和变形的影响。(3)然后,分析在水合物沉积层中布设桩基础,当桩基础位于地层不同深度时,考虑桩端部承载力不同,分别比较桩端部在水合物层中和下部沉积层两种不同工况,分析水合物分解对桩基础及附近土层应力和变形影响规律。(4)最后,研究桩基础距离水合物层不同距离时,水合物分解对桩基础的影响。对比设计了间距为10m,50m,70m和80m四种计算工况,以分析桩基础与水合物层间安全距离是多少时,水合物分解对桩基础应力和变形影响最小,可以忽略。以期为天然气水合物开发中海底桩基础的布置和稳定性分析提供参考。更多还原

【Abstract】 With the comprehensive and rapid development of economy, energy demand is growing quickly. The oil and gas resources are hugely consumed. And the development of economy faces enormous challenges. The gas hydrate is considered to be the most development prospects of alternative energy in the21st century. However, when environmental conditions change, the stability of gas hydrate bearing sediments is damaged and large amounts of gas and water are released, which greatly reduces the engineering mechanical properties of seabed sediments. The softening of the seabed soil, slope failure and submarine landslides geological disasters will occur, and thus causing the destruction of the seabed engineering facilities, such as seabed pipelines, communication cables, drilling platforms.Therefore, it is very necessary to research stabilities of the seabed structures due to hydrate dissociation. In this paper, finite element numerical simulation is used to study the influences of seabed structures due to hydrate dissociation. The main works could be summarized as follows:(1) To study the process of hydrate sediments modulus softening and strength reduction, the finite element numerical method is established to consider the hydrate dissociation using stress release method. The corresponding computer program is developed and the reliability of the program is discussed.(2) The program is used to simulate the influences of submarine slope stability due to hydrate dissociation. Three calculation conditions are designed to study the effects of modulus softening and strength reduction on slope deformation respectively. Then, the effects of overlying soil thickness on the slope stability and deformation in the process of hydrate dissociation are discussed.(3)Then, laying the foundation in hydrate sediments is simulated. When pile foundation is located in the strata at different depths, two different conditions of pile end in the hydrate layer and the lower sediment layers are compared. The effects of pile foundation and the surrounding soil stress and deformation due to hydrate dissociation are analyzed.Finally, when pile foundation is at different distances from the hydrate layer, the effect of hydrate dissociation on the pile foundation is researched. Four calculation conditions of10m,50m,70m and80m spacing are designed. When how far the pile foundation and hydrate layer, there is the minimal impact in the stress and deformation of the pile foundation due to the hydrate dissociation, which provides a reference for the development of gas hydrate in the seabed pile foundation stability.更多还原