海底斜坡稳定性研究进展及分析

海底斜坡稳定性受风暴潮、海底地震等有许多不确定因素影响,易发生失稳破坏,产生较大的海洋地质灾害问题.简要介绍了国内外海底斜坡稳定性研究进展;利用GEO-SLOPE滑坡分析软件进行海底边坡稳定性计算,建立研究区斜坡有限元模型、滑移模式,确定模型计算的基础资料如海底地形参数、地层结构参数、土体强度参数等指标,模拟大风浪和地震力作用等极端条件下斜坡稳定性可靠度计算和数值分析,确定海底斜坡失稳空间特征和斜坡失稳概率,对促进今后的海底斜坡稳定性分析方法研究将会起到一定的指导作用.     

曹妃甸海底深槽斜坡稳定性分析与评价

海底斜坡稳定性受风暴潮、海底地震等诸多不确定因素影响,易发生失稳破坏,产生较大的海洋地质灾害。简要介绍海底斜坡稳定性分析方法,建立曹妃甸深槽典型斜坡计算模型,确定了模型计算的海底地形参数、地层结构参数、土体物理力学参数等指标,利用GEO-SLOPE斜坡分析软件进行海底斜坡稳定性定量计算,分析了工程建设前自然状态下以及在大规模工程建设后海底斜坡稳定性,并模拟分析了在大风浪和地震等极端条件下斜坡的稳定性,确定了海底斜坡失稳空间特征。首次采用数值计算对曹妃甸海底斜坡稳定性进行定量分析评价,可以为类似近海建设工程提供重要的参考作用。     

国内外海底斜坡稳定性研究概况

海底斜坡物质受地震、风暴潮等动力因素的影响,其强度变弱,发生失稳破坏,对海底工程设施具有较大的破坏性,引起人们的广泛关注。根据近几年来国外海底斜坡稳定性研究领域的最新成果,简要介绍分析与海底斜坡失稳有关的调查方法、分类、失稳机制、失稳空间和稳定性评价等研究情况。这些方面的成果代表了当前国际海底斜坡稳定性研究的进展和动态,对促进我国今后的海底斜坡稳定性研究将会起到一定的帮助作用。     

天然气水合物分解对海底斜坡稳定性影响研究进展

天然气水合物作为一种新型能源,已经逐渐引起人们的重视。赋存于海底沉积物中的天然气水合物虽然本身作为亚稳定胶结物对海底有建造作用,但是由于其对特定温度和压力条件的严格依赖,海底温压条件的改变会引起其分解,从而使海底沉积物失稳甚至导致海底滑坡。本研究系统介绍了近年来国内外针对天然气水合物合成、物理性质及对海底稳定性影响进行...     

基于极限分析上限方法的海底斜坡稳定性评价

极限平衡法仍是当前海底斜坡稳定性的主要工程评价方法,但该法只能给出稳定性分析的近似解答。基于极限分析运动学定理,假定海底斜坡发生对数螺线型滑移破坏模式,将滑体有效自重和简化波浪力等以外荷载形式叠加引入到虚功率方程中,与潜在滑动面上由黏聚力产生的内能耗散率相平衡,建立考虑一阶简化波浪效应的海底斜坡上限解法;利用多变量无导数求极值的逐级迭代方法与最优化技术,结合抗剪强度折减思想,求解波浪加载下不同时刻的海底斜坡稳定性与相应的临界破坏机构,并针对典型算例开展有限元数值解的验证。进而联合采用数值法与上限解,探讨波高、波长、水深等波浪参数对海底斜坡稳定性与滑动机制的影响。结果表明,本文提出的上限解与数值解吻合较好,获得的安全系数与破坏模式等符合一般规律,为波浪作用下海底斜坡的稳定性评价提供了新的途径。     

Newmark位移分析方法在海底斜坡地震稳定性评价中的应用

Newmark地震动力时程分析方法能够考虑自然地震波峰值地面加速度(PGA)、持续时间、地震频率的影响,可以输入不同地震波进行模拟计算,计算了曹妃甸典型海底边坡在发生类似唐山地震的烈度情况下动力响应,得出的位移值大小可以定量的反映地震对场地边坡的影响,根据海底斜坡或坡顶建筑物的允许位移值,可以将其作为安全稳定分析的判断指标,可以为类似边坡稳定性评价、近海工程建设等提供重要的参考作用。     

黄河水下三角洲海底斜坡波致稳定性分析

以 Iversion的海底稳定渗流理论为基础 ,运用静力极限平衡方法和库仑破坏准则 ,提出了以海底水下斜坡坡度、沉积物有效内摩擦角和内聚力为自变量 ,波浪在海底产生的孔压梯度为参变量的海底稳定性分析方法。并给出了黄河水下三角洲不同土质所需的临界孔压梯度判断曲线 ,预测了黄河水下三角洲的海底稳定性 ,其分析结果与实测资料吻合良好     

珠江口盆地海底稳定性分析

本文根据大量野外调查资料,系统地整理了珠江口盆地各种海底不稳定的地质现象,通过分析和讨论,划分出海底比较不稳定区、稳定区、比较稳定区、不稳定区,并进行了工程地质评价,给海洋开发提供了依据。     

海底管线稳定性影响因素分析

实现管线的稳定性是埋设海底管线并使其正常运营的前提。分析了波浪、海流、管线周围土体性质及液化发生等方面对海底管线稳定性的影响，并提出了相应的对策建议．     

Effect of River Discharge on Bay of Bengal Circulation

The seasonal circulation and mixed layer depths in Bay of Bengal is modeled using the three-dimensional Princeton Ocean Model (POM). Along the coastal boundaries a higher resolution is accomplished using the curvilinear orthogonal grid. Model uses a free-surface and terrain following sigma coordinates. The initial climatological salinity and temperature fields for the model are derived from the World Ocean Atlas-2001(WOA01). The Model is forced with wind stress derived from COADS wind climatology. Bilinear interpolation is used to obtain the initial fields and wind stress to the required model specification. Using the seasonal fields and wind stress the model is integrated for simulating Bay of Bengal circulation. The numerical simulations on climatological scale for monsoon months were conducted to study the evolution of dynamics. The simulations bring out not only the typical characteristic features of fresh water plume along the coast but also intensification of the flow over the monsoon period. The increase in the fresh water flow found to affect only the western parts of the BoB. The opposing currents due to monsoon winds and southward flowing fresh water discharge (FWD) were also delineated. The model results show that the wind stress induced turbulence process is subdued in the presence of strong vertical salinity stratification due to the influence of FWD. The simulated mixed layer depths are in agreement with the reported analytical energy required for mixing values.     

孟加拉湾上层环流研究综述

综述了孟加拉湾上层环流研究的主要成果并指出,研究海区环流与季风转换不完全同步。在西南季风期间,南、北海区各有一气旋式环流;在秋季季风过渡期间,出现海湾尺度的气旋式环流;在东北季风期间,气旋式环流减弱北移,南部则为一反气旋式环流控制;春季与秋季的情形相反,整个湾出现一海湾尺度的反气旋式环流。研究海区环流的变异主要受季风、赤道远地作用和浮力通量等复杂外源作用的影响。东印度沿岸流的季节变化与季风转换也不同步,局地风、内部Ekman抽吸、远地沿岸风及赤道远地作用的影响对沿岸流周年变化有重要作用。孟加拉湾上层环流年际变化显著,此年际变化主要受赤道风场的影响。     

基于Aquarius 卫星数据的孟加拉湾海表盐度分析

海洋表面盐度(Sea Surface Salinity,SSS)是海洋的重要物理和化学参量,SSS的时空分布与全球大洋环流和水汽循环密切相关。本文基于美国国家航空航天局(NASA)发射的Aquarius卫星3 a的SSS遥感数据,给出了孟加拉湾及其附近海域海表盐度的空间分布特征,并重点分析了影响孟加拉湾海表盐度变化的可能因素。研究结果从一个侧面说明了利用Aquarius卫星遥感观测海洋大尺度盐度变化的可行性。     

Analysis of multi-channel seismic reflection and magnetic data along 13° N latitude across the Bay of Bengal

Analysis of the multi-channel seismic reflection, magnetic and bathymetric data collected along a transect, 1110 km long parallel to 13° N latitude across the Bay of Bengal was made. The transect is from the continental shelf off Madras to the continental slope off Andaman Island in water depths of 525 m to 3350 m and across the Western Basin (bounded by foot of the continental slope of Madras and 85° E Ridge), the 85° E Ridge, the Central Basin (between the 85° E Ridge and the Ninetyeast Ridge), the Ninetyeast Ridge and the Sunda Arc. The study revealed eight seismic sequences, H1 to H8 of parallel continuous to discontinuous reflectors. Considering especially depth to the horizons, nature of reflection and on comparison with the published seismic reflection results of Currayet al. (1982), the early Eocene (P) and Miocene (M) unconformities and the base of the Quaternary sediments (Q) are identified on the seismic section. Marked changes in velocities also occur at their boundaries.In the Western Basin the acoustic basement deepening landward is inferred as a crystalline basement overlain by about 6.7 km of sediment. In the Central Basin possibly thicker sediments than in the Western Basin are estimated. The sediments in the Sunda Arc area are relatively thick and appears to have no distinct horizons. But the entire sedimentary section appears to be consisting of folded and possibly faulted layers.The comparatively broader wavelength magnetic anomalies of the Central Basin also indicate deeper depth of their origin. Very prominent double humped feature of the 85° E Ridge and broad basement swell of the Ninetyeast Ridge are buried under about 2.8 km thick sediments except over the prominent basement high near 92° E longitude. The positive structural relief of the buried 85° E Ridge in the area is reflected in magnetic signature of about 450 nT amplitude. Flexural bulge of the 85° E Ridge and subsidence of the Ninetyeast Ridge about 24 cm my^–1 rate since early Eocene period have been inferred from the seismic sequence analysis.     

孟加拉湾夏季季节内振荡的湿静力能分析

夏季期间大气季节内振荡(ISO)活跃于孟加拉湾区域,并存在显著的向北传播。采用1979-2016年ERA-Interim大气再分析资料,通过对典型ISO事件进行位相合成,揭示了夏季期间孟加拉湾湿静力能季节内变化的演变特征和控制机理。结果表明,ISO大气对流在向北传播期间伴随着显著的湿静力能累积(充电)和释放(放电)过程。其中,水汽主导的湿静力能水平平流是充电和放电的关键控制因素。水汽水平平流在对流层中高层和对流层低层的变异机理存在一定差异,在中高层主要取决于ISO扰动纬向风对低频水汽的纬向输送,在低层则主要取决于低频经向风对ISO扰动水汽的经向输送。     

孟加拉湾北部逆温现象的观测特征及机制分析

在冬季,孟加拉湾北部存在显著的季节性逆温现象。利用Argo浮标和锚碇浮标资料,分析了冬季孟加拉湾逆温现象的观测特征和维持机制。结果表明,系统性的逆温现象主要局限于15°N以北的区域,它最早于11月份出现在恒河、伊洛瓦底江和戈达瓦里河的河口区域。逆温的强度及分布区域在1月份达到最大,随后从西南部逐步退化,3月逆温现象基本消失。冬季的逆温层位于障碍层之中,厚度在35 m左右,最大海温位于40~60 m深度,整层满足静力稳定条件。对混合层温度和盐度的诊断表明,逆温的出现主要与冬季风导致的强烈海表热量损失有关,低盐水的平流过程也对逆温现象有一定的维持作用。     

Characteristics of Tides in the Bay of Bengal

A vertically integrated 2D numerical model was developed for the simulation of major tidal constituents (M₂, S₂, N₂, K₁ and O₁) in the Bay of Bengal. The bathymetry for the model domain was derived from an improved ETOPO5 dataset prepared in our earlier work. The simulated tidal elevations showed good agreement with the hourly tide gauge observations at Paradip, Visakhapatnam, and Chennai. The amplitudes and phases of M₂, S₂, K₁, and O₁ at the coastal stations, obtained from harmonic analysis of simulated tides, were found to agree well with those obtained from Admiralty Tide Tables with the RMS misfit 9.2, 5.6, 2.9 and 3.1 cm, respectively. In the Bay of Bengal, semi-diurnal tides (M₂, S₂, and N₂) attain highest amplitudes (180, 80, 30 cm, respectively) in the Gulf of Martaban while amplitudes of diurnal tides (K₁, O₁) reaches maximum (20, 12 cm, respectively) in the Malacca Strait. The continental shelf in the head bay and along the southern coast of Myanmar is about 200 km wide and the amplitudes of semi-diurnal tides are doubled in these regions while the diurnal tides amplify only marginally, which is consistent with Clarke and Battisti theory. In the north eastern end of the head bay and the Gulf of Martaban, the geometrical configuration of the coastline, in addition to the wide continental shelf, could contribute to the amplification of both semi-diurnal and diurnal constituents. In the Malacca Strait, the amplitudes of both semi-diurnal and diurnal tides are found to increase gradually from the northern end to the 2.5°N and decreases towards southern boundary. The co-tidal and co-range charts of M₂ and S₂ tidal constituents also show the presence of two degenerate amphidromic points in the head bay. A virtual amphidromic point for M₂ is identified in the Malacca Strait.     

孟加拉湾一次热带气旋过程的海浪场模拟分析

基于第3代海浪模式WW3(WAVEWATCH-III),以具有高精度和较高分辨率的CCMP(Cross-Calibrated, Multi-Platform)风场为驱动场,对2011年12月发生在孟加拉湾的热带气旋“Thane”所致的大浪进行数值模拟。结果表明:(1)以CCMP风场驱动WW3海浪模式,可以较好地模拟热带气旋“Thane”在孟加拉湾造成的大浪,模拟的海浪数据具有较高精度。当有效波高(SWH)在2 m以内和大于5 m时,模拟值略小于观测值;当SWH在2~5 m之间时,模拟值略大于观测值。(2)热带气旋“Thane”所形成的大风和大浪的分布特征具有一定差异:大风区在气旋四周分布较为均匀;在大洋中部时,大浪区主要分布于右半圆,在近海时,大浪区主要分布于气旋行进方向的前方。(3)热带气旋“Thane”的风向和波向整体上保持了较好的一致性,仅在第2象限有一定的差异,该区域的风向主要为西北向,而波向则主要为偏北向。     

孟加拉湾及其毗邻海域中尺度涡旋活动的冬、夏季差异

基于1993—2017年从卫星高度计资料中识别出来的中尺度涡轨迹数据集,对冬、夏季孟加拉湾涡旋的源地和性质进行了研究。研究表明孟加拉湾西部、安达曼海和孟加拉湾通往赤道的出口处的中尺度涡旋活动呈现显著的季节性差异。安达曼海在冬、夏季从北往南中尺度涡旋分别以"反气旋涡-气旋涡-反气旋涡"和"气旋涡-反气旋涡-气旋涡"的格局分布。不同源区涡旋的季节性生长过程有明显差异。孟加拉湾西部的涡旋在夏季生长迅速但消散缓慢,斯里兰卡冷涡生长缓慢但消散迅速。不同源区涡旋半径和振幅大小有不同的特征。孟加拉湾西部,无论冬、夏季,反气旋涡的振幅、半径都比气旋涡大;夏季季风漂流区,气旋涡半径比反气旋涡小但是振幅比反气旋涡大;安达曼海内无论冬、夏季都是最北侧聚集区涡旋的半径和振幅最大。孟加拉湾内生命史为30～40 d的涡旋数量最多,生命史在100 d以上的涡旋主要分布在孟加拉湾西部。