海底孔压对波浪响应试验研究及数值模拟

孔隙水压力在海底土尤其在砂性海床中扮演着一个非常重要的角色.波浪的周期性加载作用,在砂土及粉土中产生超静孔隙水压力,其幅值大小是海床发生液化破坏的控制因素.在海上工程的历次调查中发现孔压引起许多液化破坏现象,如粉土海床的塌陷、凹坑、坡度较大处的粉砂流及构筑物基础周围的过量冲刷造成石油管架下沉等等,因此研究海床中孔压对波浪的响应具有重要的理论意义和实践意义.     

Wave-induced pore water pressure in marine cohesive soils

1 IntroductionSeafloor stability has engaged more and more at-tention of mankind with the exploration of ocean re-sources. The damages caused by seafloor instability areubiquitous in the world.Many researchers carried out studies on the porewater pressure buildup and liquefaction caused bywave-induced loading. Seed and Rahman (1978) first-ly developed a methodology in which the generationand contemporaneous dissipation of pore water pres-sure can be evaluated. Then Ishihara and Towhata(1983)…     

Model test of stratum failure and pore pressure variation induced by THF hydrate dissociation

ABSTRACT

A model test program for studying soil stratum failure and pore pressure variation during tetrahydrofuran (THF) hydrate dissociation considering the effects of heating and drainage conditions is presented in this paper. The temperature and pore pressures are recorded during heating. Test results show that the THF hydrate would dissociate to be liquid and then gas when heating. Once pore pressure generated by the flow of released gas/water exceeded the strength of over layer, the layered fractures and soil-gas/water mixture outburst would occur. The high heating temperature and low permeability of over layer both cause excess pore pressure generation and more serious stratum failures.     

Experimental investigation on the wave-induced pore pressure around shallowly embedded pipelines

A series of regular wave experiments have been done in a large-scale wave flume to investigate the wave-induced pore pressure around the submarine shallowly embedded pipelines.The model pipelines are buried in three kinds of soils,including gravel,sand and silt with different burial depth.The input waves change with height and period.The results show that the amplitudes of wave-induced pore pressure increase as the wave period increase,and decay from the surface to the bottom of seabed.Higher pore pressures are recorded at the pipeline top and the lower pore pressures at the bottom,especially in the sand seabed.The normalized pressure around pipeline decreases as the relative water depth,burial depth or scattering parameters increase.For the silt seabed,the wavelet transform has been successfully used to analyze the signals of wave-induced pore pressure,and the oscillatory and residual pore pressure can be extracted by wavelet analysis.Higher oscillatory pressures are recorded at the bottom and the lower pressures at the top of the pipeline.However,higher residual pressures are recorded at the top and the lower pressures at the bottom of the pipeline.     

Experiment and analysis of the formation,expansion and dissipation of gasbag in fine sediments based on pore water pressure survey

Deep-seated gas in seabed sediments migrates upwards from effect of external factors, which easily accumulates to form gasbags at interface of shallow coarse-fine sediments. Real-time monitoring of this process is important to predict disaster. However, there is still a lack of effective monitoring methods, so we attempt to apply multi-points pore water pressure monitoring technology when simulating forming and dissipation of gasbags in sediments through laboratory experiment. This study focuses...     

南黄海海底沉积物声学特性及其影响因素试验研究

利用自南黄海中西部海底取回的沉积物样品,对其声学特性及其影响因素进行了试验研究,结果显示,研究区海底沉积物的压缩波速为1.359 ~1.695 km/s,剪切波速为12.5 ~70.9 m/s;颗粒较细的沉积物与较低的压缩波速、剪切波速对应,主要集中在研究区东侧水深较深处;沉积物的物理力学性质对其压缩波速、剪切波速的影响较显著,沉积物的温度和换能器的频率对上述声学两参数也具有一定的影响,而沉积物的包含物及薄夹层等影响声波传播的理论计算结果。给出了研究区海底沉积物物理力学各参数与压缩波速、剪切波速之间的回归方程,以期为国防、工程提供基础资料。     

Effects of a cover layer on wave-induced pore pressure around a buried pipe in an anisotropic seabed

In engineering practice, a cover layer of coarser material has been used to protect a buried marine pipeline from wave-induced seabed instability. However, most previous investigations of the wave–seabed–pipe interaction problem have been concerned only with such a problem either in an isotropic single layer or a rigid pipe. This paper proposes a two-dimensional finite element model by employing the principle of repeatability to investigate the wave-induced soil response around a buried pipeline. The elastic anisotropic soil bahavior and geometry of cover layer are included in the present model, while the pipe is considered to be an elastic medium. This study focuses on the effects of a cover layer (including thickness B and width W of the cover layer) on the wave-induced pore pressure in the vicinity of a buried pipeline.     

Pore pressures in marine sediments: An overview of measurement techniques and some geological and engineering applications

Pore pressures in the seabed are extremely sensitive to any imposed stress because of the low permeabilities commonly exhibited by marine sediments. Consequently, the measurement of sediment pore pressures can be used to infer either the nature of the imposed stress (if the sediment properties are known) or the physical properties of the sediment (if the imposed stresses are known). Stresses of many different types may be exerted on the seabed either through hydrostatic forces (e.g. tidal and wave effects), or directly by lithospheric forces (e.g. tectonic and thermal forces). Several techniques for measuring in situ pore pressures in the upper few metres of sediments have been developed, and one instrument, the PUPPI, will operate autonomously in water depths up to 6000 m. Basic sediment properties and processes can already be inferred from pore pressure responses using this technique. However, further application and development could greatly enhance its capability, especially for long-term monitoring of sediment conditions. In this Chapter, pore pressure measurement techniques are briefly reviewed and problems are highlighted. An outline is given of some of the many ways in which pore pressure measurements could be used to gain further insight into geological processes and to determine some of the pertinent sediment properties more accurately for engineering applications.     

海底管线区浅表层土孔压静力触探参数特征及应用

利用东海陆架海底输油管道路由调查获得的孔压静力触探数据和钻探资料等,采用统计分析的方法,对管道路由区5 m以浅土体的孔压静力触探曲线特征、土的分类方法鉴别作了探讨,结果表明:研究区5 m以浅黏性土的锥尖阻力(qc),侧摩阻力(fs)值较小,且随深度呈线性增加,粉质土的qc,fs值增大,但随深度线性增加规律不明显,砂类土的qc值急剧增大,但fs值变化不大;Robertson法和Eslami-Fellenius法两种土类划分方法均适用于研究区浅表层软土的土类划分,但Robertson法在判别粉质土时受到一定限制,Eslami-Fellenius法判别较为准确,应用简单。本研究可为我国在海底管线工程路由勘察中直接利用孔压静力触探(CPTU)参数划分土层和判别土类作铺垫。     

基于高光谱传感器的长江口表层悬浮泥沙质量浓度光谱曲线特征研究#br#

悬浮泥沙质量浓度（SSC）是我国河口水体研究的重要水质参数之一,遥感测定SSC是一种重要的方法。为了研究遥感光谱数据和表层悬浮泥沙质量浓度（SSSC）之间的定量梯度关系,本文采集了长江口南汇嘴附近的表层沉积物,定量设计了SSSC的梯度变化值,利用ASD高光谱仪对不同质量浓度含沙水体进行了光学特性测量。结果表明,随着SSSC的增加,水体的光谱反射率曲线具有相似的形态,但也存在一定的差异。当SSSC<36.59 mg/L时,光谱曲线仅在560～580 nm之间有1个反射峰;当SSSC>52.69 mg/L时,光谱曲线第一反射峰位于570～710 nm,并在近红外波段780～820 nm处出现第二反射峰。光谱曲线第一峰值区间存在明显的“红移”现象,且波长的“红移”变化与SSSC的线性拟合R²达到0.91,说明两者呈较强的线性相关性。在400～900 nm光谱范围内,600～860 nm波段对0～200 mg/L范围内的SSSC变化较敏感且比较稳定,740～900 nm波段对>200 mg/L的SSSC的变化具有更强的响应能力。     

基于潮沟定点观测的潮间带水、沙、盐交换研究

为研究潮间带和潮下带的水、沙、盐交换,于2006年6月25~28日（夏季大潮）和2006年12月29日~2007年1月4日（冬季中-大潮和小潮）在长江口九段沙一典型潮沟的固定点利用OBS-3A和ADP-XR进行了水深、浊度、盐度、流速流向剖面和回声强度观测。结果和结论为：（1）夏季大潮、冬季中-大潮、冬季小潮的潮周期垂向平均流速分别为26.5、15.9和8.4 cm/s,夏、冬季观测到的最大流速分别为84 cm/s和35 cm/s。（2）夏季盐度变化范围为0.65~4.91,平均盐度2.14;冬季盐度变化范围为3.5~10.3,中-大潮和小潮平均盐度分别为6.26和7.98。（3）高悬沙浓度出现在涨潮初期和部分落潮末期的低水位阶段;涨潮阶段的平均悬沙浓度是落潮阶段的1.11~7.0倍。（4）涨、落潮阶段的水体和盐输运量大体上趋于平衡;（5）无论是冬夏季或大小潮,潮沟在潮周期内的净输沙方向均指向陆,即落潮输沙量小于涨潮输沙量（平均小40%）;平均每个潮周期的净输沙量为6102 kg,结合潮盆面积推算的潮周期沉积速率为0.0112 mm/tide,或8.2 mm/a。     

黄海月平均风、气压、气温场季节与年际变化时空模态

根据1973年至2016年黄海沿岸风、平均海平面气压与气温观测资料,采用旋转经验正交函数(REOF)、调和分析和延迟相关分析等方法,研究了黄海月平均风应力、风速、平均海平面气压、气温场季节与年际变化时空模态.月平均风应力、风速场主要有4种时空模态,风应力模态空间分量分布与风速模态不完全相同,风应力、风速模态季节周期分量多数为不稳定,风应力、风速场强度年际变化显著线性减弱,对黄海环流以及物理、化学要素场季节与年际变化有显著影响.月平均气压、气温场季节循环与年际变化主要有2种时空模态,气压、气温模态季节周期分量的位相均为准稳定季节变化;振幅为不稳定季节变化.气压模态为准平衡态年际变化,大尺度气压系统季节与年际变化是黄海气压场模态的主要影响因素.气温模态为显著线性升温趋势年际变化,海气、陆气热交换作用对黄海气温场模态季节与年际变化有显著影响.