海底沉积物取样的扰动机理研究

海底沉积物取样技术对大洋诸多科学研究来说非常重要,各种研究目标的实现与沉积物样品的质量息息相关.在使用常规管状取样器对松软或轻微固结的沉积物取样时,沉积物样品的扰动总是不可避免的.以机械手持式沉积物取样器为原型机,建立了管状取样器的取样过程模型,分析了沉积物样品的扰动机理;采用球形孔扩张理论获得了沉积物土体受到取样管挤压扩张的理论解;结合太平洋具体沉积物土体物理力学参数,对管状取样器取样造成沉积物扰动的状况给出了一个定量描述,并且提出取样管壁的厚度是减小沉积物扰动的关键参数.     

应力-应变过程中海底沉积物微结构变化对其声速的影响

阐述了对海底沉积物样品在应力-应变过程中进行同步声学测量的实验工具及方法,分析了采自南海45个站位的海底沉积物样品的实验数据资料,结果表明,沉积物颗粒越粗、孔隙越小、无侧限抗压强度越大,声速越高.沉积物样品在受力应变过程中,声速具有明显的随应力而变化的特征.进一步探讨了不同应变阶段沉积物的声学特征以及应力所导致沉积物微结构变化对其声速的影响过程,这一研究将在石油地质测井和海底工程基底稳定性评价等方面具有重要应用意义.     

深海沉积物超长取样系统研究进展

深海沉积物作为一种重要的深海环境变化记录载体,是海洋学尤其是深海研究必不可少的基础研究资料.因此如何获得超长、连续、无扰动的沉积物柱状样品是深入开展深海科学研究的关键技术环节,也是我国在深海研究国际竞争中取得优势的主要技术瓶颈之一.通过综述国内外深海超长沉积物取样系统的研究进展,发现当今通用的沉积物取样系统存在诸多技术问题,从而不可避免地对沉积物产生扰动、压缩、断层等破坏.基于深海取样系统研制的国内外发展动态,提出了一种新的结合普通重力取样器对浅表沉积物样品无扰动取样和重力活塞取样器获取超长沉积物的混合型超长沉积物取样系统的设计构想.     

应力-应变过程中海底沉积物微结构变化对其声速的影响

本文阐述了对海底沉积物样品在应力-应变过程中进行同步声学测量的实验工具和方法,分析了采自南海45个站位的海底沉积物样品的实验数据资料,结果表明,沉积物颗粒越粗、孔隙越小、无侧限抗压强度越大,声速越高。沉积物样品在受力应变过程中,声速具有明显的随应力而变化的特征。进一步探讨了不同应变阶段沉积物的声学特征以及应力所导致沉积物微结构变化对其声速的影响过程,这一研究将在石油地质测井和海底工程基底稳定性评价等方面具有重要的应用意义。     

深海超长沉积物柱状取样系统关键技术优化及应用

作为深海科学研究的重要基础装备,深海超长沉积物柱状取样系统在海底地形地貌、海洋地质构造、气候环境变化等研究领域发挥了重要作用,其在海底矿产资源勘探、海洋工程地质勘察等方面展现了巨大应用价值。针对传统超长柱状沉积物取样系统在作业过程中存在的盲目采样、安全隐患大、甲板作业空间受限等问题,自主研制了一套适用于深海的超长可控可视沉积物柱状取样系统,该系统具有液压锤击、立式收放和实时监控功能,能获取连续、超长、具有精准姿态方位信息的柱状沉积物样品。现通过对独立排缆方式、取样管快速拆装、样品封堵、低扰动取样刀头等关键技术细节进行优化,解决了样品扰动大、取样率低的问题,提高了取样作业效率与样品质量,且降低了作业安全风险。2017—2021年,该取样系统搭载不同母船在南海1 700,1 725 和1 778 m水深分别获取了15.25、16.01和15.83 m的长柱状沉积物样品。该设备的成熟应用,可为我国深海探测研究提供技术支持。     

一种新型的6000米深水可视可控轻型沉积物柱状取样系统

为了获得连续、低扰动、超长的深海海底沉积物样品,研制了一套可应用于最大水深6 000 m,最长取样可达25 m的可视可控轻型沉积物柱状取样系统。本套设备主要包括甲板控制单元、取样系统和立式收放机构3部分。在取样过程中,本系统充分利用动能和深海液压锤夯击双动力组合,即取样过程包括前期的重力贯入和后期的夯击取样两个过程。液压锤夯击机构的配置使取样器在不显著增加自身重量的前提下,完成超长、连续、低扰动的深海沉积物柱状样采集工作。取样器的组合与拆卸采用立式吊装的方式,极大地降低了取样过程中的工作量和所需甲板作业空间。水下监测系统的配置解决了以往盲采样的弊端。除此之外,本取样器还设有多个标准通用端口,可以扩展为多种设备的集成平台,完成多种数据的采集。目前本套设备已经成功进行了海试,并作为主要沉积物取样设备成功应用于多个海上调查航次,取得了一系列连续、低扰动的柱状样品,有效地提高了我国深海可视可控柱状取样的技术水平。     

重力活塞取样器贯入深度研究

重力活塞取样器是一种重要的海底连续沉积物采集仪器,贯入深度和样品质量对海洋地质研究有着重要影响。通过对重力活塞取样器贯入过程建立能量守恒方程,得出贯入深度控制方程。已知取样器参数和土质类型条件,可计算取样管贯入深度,深度受取样器重量、体积、形状、取样管直径和沉积物类型等因素共同影响。已知取样器参数和贯入深度,可推测海底沉积物类型。     

重力活塞取样管的结构及其使用

随着海洋地质科学的不断发展,迫切要求改进采集海底沉积物柱状样品的仪器。在广泛的海洋调查工作中,取样管是采集沉积物柱状样品的主要工具。当前，各国使用的取样管类型很多,重力活塞取样管是其中较为优越的一种取样工具。 1947年, Kullenberg首先设计了重力活塞取样管。随后Silverman等以及Emery等人又进行了进一步的改进。1956年，Ericson等人发表了经过改进的重力活塞取样管的结构图。目前,这类取样管在不少国家都在广泛使用于海洋调查。 1965年前后,我们开始使用重力活塞取样管,同时对其中的夹板结枸、联接器和船舷安装等方面进行了某些改进,使整个仪器的操作使用进一步简化，并先后在几个海区进行了调查,效果良好。这种取样管的特点有二： 1.有一个活塞。当取样管钻人沉积层时,活塞能对沉积物起抽吸作用。从而提高了取样率并使样品不从管內脱落； 2.有一个抗衡装置。它能使仪器获得较大的冲击力并保证活塞的抽吸作用,从而提高取样长度。 海上实际工作说明,这种取样管的主要优点有:(1)对那些粒度较粗和结构较坚硬的沉积物,如细砂、硬质粘土等,用重力活塞取样管比一般重力取样管的效果为好;(2)取样率比较高,在正常情况下可达到90%以上;(3)仪器结构简单,操作方便,取样时不用抛锚,加快了海上调查工作的速度。它不但适用于深水区,也能用于浅海区。但是,目前我们使用的重力活塞取样管存在的主要缺点是:当取样管未全部钻入沉积层而从其中拔取时,活塞不能停留在原位而必须行至联接器处,致使把一部分搅动了的样品也抽取上来,这是今后需要加以改进的。     

南海深海海底沉积物力学性质试验研究

采用土力学中的三轴试验方法,对南海深海海底沉积物进行力学性能研究。得到海底沉积物样品的主应力差与轴向应变曲线及抗剪强度数据,并得到海底沉积物样品的破坏点应力值与含水量、湿密度及孔隙度的关系曲线。通过分析,得到海底沉积物样品的破坏点应力值在含水量40%~45%之间以及在孔隙度50%~55%之间分别取得最大值。通过对比表明试验的海底沉积物样品的力学性能与陆地的半脆性黏土相近。     

在轴向应力-应变下海底沉积物声速及其变化

对南海南部海域海底浅表层沉积物短柱状样进行轴向应力-应变/声学测量,结果表明沉积物纵波声速有三种不同的变化结果:(1)声速从应变过程开始随应力-应变曲线变化,在最大应力时声速同时也是最大值,结束时可能高于或低于开始时的声速;(2)声速从应变过程开始逐渐减小,结束时是最小值;(3)声速从应变过程开始逐渐增大,最大值出现在结束时.这些结果与海底浅表层沉积物的物理力学性质、颗粒接触状态、颗粒的微结构等特征有关.研究结果可为深入认识南海南部各种海底沉积物作为承载界面的可靠性、声遥测遥感海底沉积物的工程力学性质等科学目的提供理论依据.     

Numerical Analysis of Gravity Coring Using Coupled Eulerian-Lagrangian Method and a New Corer

The shortcomings of gravity corers in sampling marine sediments have been observed extensively in various field tests. In order to optimize the coring, this article provides an alternative numerical way to model the gravity coring and analyze the sampling effect. Based on this analysis, a new hydraulic hammer corer is devised. A coupled Eulerian-Lagrangian method with capability of simulating the problem involving extreme deformation, penetration is used to simulate the coring process. The results show that the hydrostatic pressure and deviator stress increase and reach their peak when the pile tip is slightly above or at the level of the observation point and then drop rapidly when the pile tip slides below the observation point. In addition, the stress path indicates that the soil element sustains plastic compression before yielding and then expands until recovering to the original state. The obvious “under-sampling” phenomenon is also well-captured by the finite element model.     

A hydraulic hammer corer utilizing hydrostatic energy for hard seafloor sediment coring

The paper presents the design and preliminary test results of a corer used for hard seafloor sediments sampling.Generally the sediment cores are provided by either gravity-type coring or deep-ocean drilling for a range of studies.However,in consideration of the operability and available sample length in collecting hard sediments,these methods exhibit no advantages.In this paper,a new corer which can exploit both hydrostatic energy and gravity energy for hard sediments coring is presented.The hydrostatic energy is provided by pressure differential between ambient seawater pressure and air pressure in an empty cavity.During sampling process,the corer penetrates into the sediment like a gravity corer and then automatically shifts to the percussion mode.The experiments in the laboratory indicate that the corer can complete 40 cycles in the sea with a cycle time of 2.8 seconds in percussion mode and impact the sample tube with the velocity of 0.2 m/s during each cycle.Besides,its adjustable falling velocity can make the corer achieve the maximum efficiency in coring different sediments.     

基于ABAQUS的卷管式铺管法管道变形敏感性分析

卷管式铺管法在海管铺设中的应用愈发广泛,在铺设作业中管道会发生几何非线性变形,导致出现复杂的力学性能变化。针对管道在上卷、退卷过程中的屈服变化过程,通过弹塑性理论进行分析,推导出管道退卷后残余轴向应力的解析解;随后利用有限元软件ABAQUS建立模型实例,对比解析解与有限元模型,两者的计算结果基本吻合。基于上述有限元模型,研究上卷时的张力和退卷时的后张力对椭圆度、截面轴向应力和剪切应力的影响,并进行敏感性分析。模拟结果表明张力和后张力变化会影响管道截面的变形程度,退卷后截面上残余的轴向应力远高于剪切应力,并且通过敏感性分析,得到了残余椭圆度、残余应力随张力和后张力变化的规律。研究可为卷管铺设过程中张力和后张力的选择提供参考和借鉴。     

Sample Disturbance in Soft and Sensitive Clays: Analysis and Assessment

Despite the sophisticated methods employed to obtain high quality samples, they are prone to disturbance, due to stress release, let apart, due to sampling tools and techniques adopted. Critical reappraisal of different methods suggest that any method of sample quality assessment involving strength and deformation parameters would enable easier implementation and correct other engineering parameters for estimated sample disturbance. In this technical paper, sample disturbance index, using merely the slopes of compression paths, (representing mechanical response), in the pre- and post-yield stress regimes under odeometric loading conditions is proposed. This method is based on single oedometer test results on samples of unknown degrees of disturbance during sampling and handling. The unique feature of this approach is that the ideal rigid plastic material behavior is taken as reference. This eliminates the need for any additional experimental data or any calculations from the relationships formulated with any set of assumptions.     

Sample Disturbance in Soft and Sensitive Clays: Analysis and Assessment

Despite the sophisticated methods employed to obtain high quality samples, they are prone to disturbance, due to stress release, let apart, due to sampling tools and techniques adopted. Critical reappraisal of different methods suggest that any method of sample quality assessment involving strength and deformation parameters would enable easier implementation and correct other engineering parameters for estimated sample disturbance. In this technical paper, sample disturbance index, using merely the slopes of compression paths, (representing mechanical response), in the pre- and post-yield stress regimes under odeometric loading conditions is proposed. This method is based on single oedometer test results on samples of unknown degrees of disturbance during sampling and handling. The unique feature of this approach is that the ideal rigid plastic material behavior is taken as reference. This eliminates the need for any additional experimental data or any calculations from the relationships formulated with any set of assumptions.     

深海刚性跨接管弯管强度关键影响因素研究

深海刚性跨接管是水下生产系统的关键设备,其弯管处易因应力集中导致结构失效。依照理论与规范,并结合工程实例,通过数值模拟分析对影响跨接管弯管强度的关键因素进行研究,并对各影响因素展开敏感性分析。结果表明:跨接管结构形式是影响弯管强度的主要设计因素(M型跨接管可有效降低弯管的结构应力),弯管曲率半径影响较小;管道端部位移是影响弯管强度的主要载荷因素(重点分析此因素在不同方向的敏感性,发现轴向端部位移的影响最大);而工作温度对管道强度的影响很小。     

Loading performance of fish and OMNI-Max anchors in crust-over-soft clays

This paper reports the results from three-dimensional dynamic finite element analysis undertaken to provide insight into the behaviour of the fish and OMNI-max dynamically installed anchors during loading in crust-over-soft clay sediments. Particular attention was focused on the situations where the anchor is embedded to a shallow depth during dynamic installation due to the strong crust layer. Large deformation finite element analyses were carried out using the coupled Eulerian-Lagrangian approach, incoporating the anchor chain effect. Parametric analyses were undertaken varying the initial embedment depth, anchor shape, loading angle, strength ratio between the top and bottom layers. The tracked anchor trajectory confirmed that the diving potential of the fish and OMNI-Max anchors were enhanced by the presence of the crust layer as that somewhat restircted the upward movement. This will be beneficial for many hydrocarbon active regions with layered seabed sediments where the anchor embedment depths during dynamic installation are expected to be low.     

Geoacoustic Characterisation of Fine-grained Sediments using Single and Multiple Reflection Data

Fine-grained sediments commonly occur in areas of the continental shelf where wave and current energy are weak. Bulk density, compressional wave speed and attenuation are fundamental physical properties of these sediments required for predicting the response of the seabed for diverse branches of marine science. The traditional coring approach is time and labor-intensive, with large uncertainties associated with sediment disturbance in the sampling phase. Acoustic methods offer the advantages of remote sensing, i.e., sampling the sediment structure without mechanical disturbance and a significantly larger seabed coverage rate per unit time. Two different acoustic methods are described: one using short-range single-bounce interactions with the seabed, and the second using long-range modal propagation to infer the sediment properties. The relative strengths and sensitivities of each approach are explored through simulations guided by experience with measured data.     

可变角度换能器在海底沉积物声学原位测量应用的探讨

海底沉积物的声学测量是海底测深的关键技术之一,应用于海底地形地貌测量、海洋矿产资源开采和海底工程建设等。海底沉积物声学测量方法中的原位测量方法可以避免保真采样法的强扰动性和遥测法的准确度、精度及灵敏度的不确定性等缺点,如何改进原位测量系统渐成为海底探测的研究热点。通过分析现有海底沉积物原位测量设备测试换能器的工作原理,针对垂直压入方式换能器测量深度有限,提出了一种通过改变换能器压入沉积物的角度来增加测量深度的方法。在理论上论证出在不低于换能器接收阈值时,测量深度随着掠射角的增加而增加。在不增加压入深度的前提下提供了一种增加测量深度方法。     

The consolidation of soft marine sediments

This paper outlines the governing relationships of nonlinear finite strain consolidation. A short review of current literature is presented. Nonlinear finite strain consolidation theory is applied to the analysis of the slow deposition of Gulf of Mexico Holocene sediments. It is shown that the conventional means of calculating rates of sediment accumulation are highly inaccurate. It is further shown that the state of effective stress and excess pore-water pressure, as calculated by nonlinear finite strain theory, is substantially different than when calculated by conventional Terzaghi-Frohlich theory.