Shear Strength Development with Burial in Eel River Margin Slope Sediments

As part of the STRATAFORM project, a series of cores were obtained from the Eel River Margin area of Eureka, California. The geotechnical analysis of intact specimens and of reconstituted samples provides some insight on the development of shear strength with burial. The results show the effect of bioturbation in the early part of the lifetime of a sediment. SEDCON tests were used to proposed various relationships which help predict the changes in density, liquidity index, and strength as a function of depth. These relationships are found useful from near the water sediment-interface down to a depth of at least 400 m in the sediment column.     

Investigation of the relationship between seafloor echo strength and sediment type—a case study in Jiaozgou Bay,China

In recent years, increasing attention is being given to investigating the relationships between seafloor echo strength and sediment type. This aspect was assessed in a course of a marine survey conducted in Jiaozhou Bay near the city of Qingdao, China, where various sediment types are known to exist. Multi-beam echo data and sediment samples were acquired, processed and analyzed. The findings demonstrate that multi-beam echo strengths are strongly related to seabed types such as rock, sand and clay. Thus, echo strength increases progressively with the increase in sand content in gravely, sandy, and clayey sediments. However, echo strength is more sensitive to changes in sand content in fine-grained sediment and less sensitive in coarse-grained sediment. Also, high shell content of sediments greatly enhances the acoustic reflection. These findings help to predict seafloor sediment types by analyzing echo strength.     

悬沙的ADCP估测方法

ADCP估测悬沙含量是基于声波的背散射强度正比于悬沙浓度的理论。在实际测验中，由于多种因素干扰，ADCP所得到的背散射强度与悬沙浓度之间存在着不定的非线性关系。同传统的回归方法比较，BP网络模型方法可以使含沙估测精度有较大的提高。     

现代黄河三角洲沉积物临界剪切应力研究

为研究现代黄河三角洲沉积物临界剪切应力空间分布特征及其影响要素,本文在现代黄河三角洲不同沉积区域,垂直海岸线布设测线,采用黏结力仪进行沉积物临界剪切应力测试,并在相应测点开展沉积物物理力学性质与粒度成分测量工作。研究结果表明高潮滩沉积物临界剪切应力最高,在1.1~4.02Pa之间,沉积物不易发生侵蚀,含水量低、干容重大、黏粒与粉粒含量高、平均粒径小、不排水剪切强度大是高潮滩沉积物临界剪切应力偏高的重要因素;中潮滩沉积物受生物活动影响显著,临界剪切应力在0.10~1.90Pa之间,生物活动扰动、生物排泄及遗体遗迹的程度与数量是造成不同区域测试差异的重要原因;低潮滩沉积物临界剪切应力很低,在0.08~0.80Pa之间,沉积物极易发生侵蚀,含水量高、干容重偏低、砂砾含量高、平均粒径大、不排水剪切强度小是其典型的沉积物物理力学性质,也是造成低潮滩沉积物临界剪切应力普遍低于高潮滩的重要原因;现代黄河三角洲沉积物临界剪切应力区域特征表现为北部沉积物临界剪切应力水平最低,在0.11~0.4Pa之间,东部最高,在2.8~4.55Pa之间,南部与东北部居中,分别在0.63~0.84Pa与0.83~2.99Pa之间,东北部空间非均匀性分布显著,粒度组分的分异是导致沉积物临界剪切应力区域差异显著的重要因素,黏粒含量高的沉积区域沉积物临界剪切应力普遍高于砂砾含量高的沉积区;与世界其他大型河口三角洲相比,现代黄河三角洲沉积物临界剪切应力水平偏低但非均匀程度较高。     

枯季长江口南槽悬沙输运过程和机制研究

开展枯季河口悬沙输运机理研究对于揭示弱径流条件下的陆海相互作用、河口季节性冲淤和水沙关系等具有重要的科学意义.本文根据2018年12月18-25日长江口南槽3个站位连续13个潮周期的同步流速、流向和悬沙浓度等观测资料,运用通量机制分解法研究了各输沙项的特征、贡献和输运机理.结果 表明,从小潮至大潮流速和悬沙浓度不断增加,由南槽上部至下部流速和悬沙浓度逐渐降低.观测期间平均流速与平均悬沙浓度存在明显的正线性关系,但受底质空间差异影响,悬沙浓度对流速的响应强度存在显著的空间变化.枯季期间南槽存在着中上部向陆净输沙、下部向海净输沙的空间输运格局.平流输沙和潮泵输沙是影响和控制净输沙的关键因素,二者的强度和贡献存在明显的潮周期变化和空间变化,垂向环流输沙的强度很弱,对净输沙贡献很小.南槽涨落潮输沙不对称现象明显,流速、悬沙浓度和历时都具有一定的涨落潮不对称性,这些不对称现象共同调节和控制着潮周期净输沙强度和方向的时空变化.     

Changes in Geotechnical Properties of Sediments from the Central Indian Basin Induced by Disturbance Experiment

During the Indian Deep-sea Environment Experiment (INDEX) conducted in the Central Indian Basin to simulate nodule mining activity, the sediments were physically disturbed, lifted from the seafloor, and then redeposited to study the effects of sediment redistribution on geological, chemical and biological characteristics of benthic environment. The first monitoring cruise, 44 months after the experiment, was part of long-term observations for restoration of conditions. This study describes the effects of the experiment on geotechnical properties of sediments measured in predisturbance, postdisturbance and monitoring phases. To compare the effects, sediment cores were collected from the same locations during the three phases. Siliceous, fine-grained sediments from the study area showed change in geotechnical properties induced due to the disturbance. Marginal increase in natural water content and significant reduction in undrained shear strength at the 0–5 cm sediment layer of cores from the tow zone during postdisturbance was observed. However, during the monitoring phase, an increase in shear strength and reduction in water content was noticed, which might indicate that the sediments are gradually acquiring predisturbance characteristics. The study also revealed that the meiofaunal density has a positive correlation with the water content, but a negative relationship with the shear strength of these siliceous sediments. Specific gravity of solids and porosity showed marginal change, whereas wet density remained unchanged.     

南海北部陆坡峡谷区海底沉积物工程地质特征及区域稳定性评价

The upper part of the continental slope in the northern South China Sea is prone to submarine landslide disasters,especially in submarine canyons. This work studies borehole sediments, discusses geotechnical properties of sediments, and evaluates sediment stability in the study area. The results show that sediment shear strength increases with increasing depth, with good linear correlation. Variations in shear strength of sediments with burial depth have a significantly greater rate of change in the canyon head and middle part than those in the canyon bottom. For sediments at the same burial depth, shear strength gradually increased and then decreased from the head to the bottom of the canyon, and has no obvious correlation with the slope angle of the sampling site. Under static conditions, the critical equilibrium slope angle of the sediments in the middle part of the canyon is 10° to 12°, and the critical slope angle in the head and the bottom of the canyon is 7°. The results indicate that potential landslide hazard areas are mainly distributed in distinct spots or narrow strips on the canyon walls where there are high slope angles.     

基于电导率测定海水悬沙含量试验研究

为了寻求一种简单、快速、连续确定悬浮泥沙含量的方法,以高含沙量海区黄河口泥沙为研究对象,利用电导率仪测定了不同悬浮泥沙含量水体的电导率,建立起了悬浮泥沙含量与电导率之间的关系,并对影响上述关系的因素进行了分析,结果表明,悬浮泥沙含量与电导率之间有很好的线性关系;盐度、颗粒粒径对电导率具有一定的影响,其中盐度的影响最大,颗粒粒径的影响较小。在盐度变化范围有限的高悬沙含量海区,用电导率的方法来实现现场监测悬浮泥沙含量是可行的。     

悬浮泥沙含量与电导率关系及其影响因素的实验研究

为了寻求一种简单、快速、连续测定悬浮泥沙含量的方法,以高含沙量海区黄河口泥沙为研究对象,利用电导率仪测定了不同悬浮泥沙含量水体的电导率。前期实验结果已经证明悬浮泥沙含量与电导率之间有很好的线性关系。在此基础上扩大研究范围,并对影响悬浮泥沙含量与电导率关系的因素进行定量分析,结果表明,盐度、温度、颗粒粒径对电导率具有一定的影响,其中盐度的影响最大,颗粒粒径的影响最小,几乎可以忽略。在此基础上通过大量的实验数据初步建立起在盐度、温度较大变化范围内电导率与泥沙含量的一般函数关系,为实现海水悬浮泥沙含量的现场电导率原位监测系统提供可靠的数据支持。     

Estimation of bottom scattering strength from measured and modeledmid-frequency sonar reverberation levels

Hamilton-type geoacoustic models were developed for Area Foxtrot, a shallow water test bed south of Long Island, for emerging active sonar systems where the surface sediment type is highly spatially variable. Reverberation levels (RL) were modeled using the finite-element parabolic equation (FEPE) propagation model to augment the generic sonar model (GSM) propagation model because the bottom loss model in GSM did not estimate transmission loss (TL) accurately in shallow water. FEPE estimates reveal that there is a greater than 15 dB difference between TL for sand and that for silt-day sediments in Area Foxtrot. The comparison between modeled RL and measured RL (from a 1991 active sonar exercise) enabled bottom scattering strength kernels to be developed for Area Foxtrot. Bottom scattering strength was found to be a function of sediment type. Hard sand sediment has a bottom scattering strength which obeys Lambert's law (sin² &thetas;) while that of silt-clay sediment is consistent with sub-bottom volume scattering (sine). The RLs in Area Foxtrot are azimuth-dependent and are a function of TL and bottom scattering strength (and hence bottom sediment type). Sonar beams steered towards the hard sand show higher RLs than for silt-clay, and knowledge of the sediment type and its spatial variation must be known to model RL accurately. A method to determine sediment type using measured RLs and RL slopes is given     

悬浮泥沙含量与电导率关系及其影响因素的实验研究

为了寻求一种简单、快速、连续测定悬浮泥沙含量的方法,以高含沙量海区黄河口泥沙为研究对象,利用电导率仪测定了不同悬浮泥沙含量水体的电导率.前期实验结果已经证明悬浮泥沙含量与电导率之间有很好的线性关系.在此基础上扩大研究范围,并对影响悬浮泥沙含量与电导率关系的因素进行定量分析,结果表明,盐度、温度、颗粒粒径对电导率具有一定...     

水动力对越南巴达棱湾表层沉积物和岸滩的影响

基于越南巴达棱湾2007年4月采集的42个表层沉积物样品及实测水文资料,分析越南巴达棱湾表层沉积物特征,并结合GSTA模型分析表层沉积物的运移趋势。结果表明:越南巴达棱湾表层沉积物以粗颗粒为主,在潮流和波浪的作用下呈中西部粗、东部细的分布特征;其西侧表层沉积物沿岸线自西南向湾内运移,中西近岸区沉积物垂直于岸线做离岸输移,在湾的东侧存在自东北向西南的运移趋势,并与从湾西运移过来的底沙相遇,形成运移辐聚区,并在余流的作用下,向西运移;"波浪掀沙,潮流输沙"是该地区表层沉积物输运的主要作用机制;在波浪的作用下,研究海域的海岸线处于侵蚀状态,有后退的趋势。     

Joint perturbation scattering characterization of a littoral oceanbottom reverberation: theory, scattering strength predictions, and datacomparisons

A joint surface roughness/volumetric perturbation scattering theory is utilized to characterize the reverberation from a littoral ocean bottom. The result is a reflected field spectrum that consists of specular and off-specular components. The predicted scattering strength from the off-specular component is shown to be comprised of interface roughness scattering, sediment inhomogeneity volumetric scattering, and interface roughness/sediment inhomogeneity correlation scattering. The sediment inhomogeneity volumetric scattering is shown to contain two contributions that are due to fractional variations in sediment densities and sound velocities. Both contributions are shown to be affected by the interface effect by a round-trip transmission coefficient factor. These two fractional variations are shown to contribute differently to scattering strength but similarly to backscattering strength. Inversely predicted roughness spectra from various sets of backscattering strength data are shown to be consistent with a generally known roughness spectrum. Both inversely predicted roughness and volumetric scattering physical property spectra are found to be self-consistent. However, the use of only ocean bottom backscattering strength data is found to be insufficient to judge whether the roughness or the volumetric scattering dominates. Reverberation characterizations using bistatic scattering strength data and signal spread data are planned for future studies     

Properties of sediments deposited in a fluid with different pH

Abstract

The effect of pH on the physical and mechanical properties of a sediment was investigated through a set of experimental tests. The sediment was formed from deposition of suspended particles in a fluid. Two different types of clay soil were suspended in fluids with different pH (2, 4, 7, 9 and 11) in cylindrical tubes with volume of 1?liter and also in special cylindrical reservoirs. The height of the sediment was measured in the cylindrical tube until equilibrium was achieved. The sediment deposited in the reservoirs was dried in air and then Atterberg limit, compaction and unconfined compressive strength (UCS) tests were conducted on samples prepared from each sediment. The results showed that the final height of the settled sediment is a function of pH; the height of sediment is increased with increasing the pH. Also, the Atterberg limits increased with increasing the pH. The maximum dry unit weight and optimum water content decreased and increased with increasing the pH. The final strength of the sediment decreased with increasing pH. Based on the SEM analysis, it was found that the values of pH influence the properties of the formed sediments.     

莱州湾口弱层结水体中沉积物再悬浮特征及其水平、沉降通量研究

近海悬浮物在海水中的运移受诸多因素影响,其中由于径流输入导致的水体层化是不可忽视的因素之一,研究层结水体中沉积物受潮流、波浪影响的再悬浮特征有重要意义.2005年5月15日在黄河口西侧18海里处的莱州湾口设立了一个周日连续观测站,试图揭示弱层结水体中悬浮物的再悬浮特征及其水平、沉降通量.利用ADCP回声强度反演得到了高...     

Holocene shelf-coastal sedimentary systems associated with the Changjiang River：An overview

The fate of the terrestrial sediment supplied by rivers is a critical issue for understanding the patterns of Holocene environmental change on continental shelves. The East China Sea is a typical broad continental shelf with abundant sediment supply from large rivers. Here, a variety of sedimentary records were formed during the Holocene period. The sedimentary systems associated with these records have unique charac- teristics in terms of spatial distribution, material composition, deposition rate and the timing of deposition, which are related to active sediment transport processes induced by tides and waves, shelf circulations and sediment gravity flows. The sedimentary records thus formed are high resolution slices, i.e., each record has a temporal resolution of up to 10~-10-1 a, but only covers a limited part of the Holocene time. In terms of the spatial distribution, these records are scattered over a large area on the shelf. Further studies of these systems are required to understand the underlying process-product relationships. In particular, the mid- Holocene coastal deposits on the Jiangsu coast, the early to middle Holocene sequences of the Hangzhou Bay, as well as the Holocene mud deposits off the Zhejiang-Fujian coasts, should be investigated in terms of the material supply （from both seabed reworking during the sea level rise event and river discharges）, transport-accumulation processes, the sediment sequences and the future evolution of the sedimentary systems. Advanced numerical modeling techniques should be developed to meet the needs of these studies.     

Determination of In Situ Sediment Shear Strength from Advanced Piston Corer Pullout Forces

The advanced piston corer (APC) has been used by the Ocean Drilling Program since 1985 for recovering soft sediments from the ocean floor. The pullout force measured on extracting the core barrel from the sediment is shown to correlate with the average shear strength of the sediment core measured in the ship's laboratory. A simple rule of thumb is derived relating the shear strength of the sediment to the pullout force. Multiple APC holes at individual sites allow the consistency of the pullout measurements to be assessed. The effects of different operational procedures during APC coring are also explored. Although generally applicable, the correlation between pullout force and laboratory measurements of shear strength breaks down for some APC holes, possibly because of the disturbance of some sediment types during the APC coring process. A better understanding of the physical process of APC coring, and its effect on the properties of the sediment both inside and immediately outside the core barrel, would indicate what confidence can be put on the measurement of pullout force as a way of evaluating the in situ shear strength of deep sea sediments.     

Sediment characteristics and water circulation of Big Jemsa Bay,Red Sea,Egypt

Big Jemsa Bay is one of the indentations dissecting the continuity of the Red Sea north-western shoreline. The data was collected from bathymetric survey, current meters and sediment samples. Analyses have been undertaken of coastal processes, seabed morphology, grain size characteristics and the effect of current circulation on the distribution of sediment characteristics. The sediment pattern varies from coarse sand in the southern part to silt and fine sand in the northern part. The central part of the study area is mainly composed of terrigenous isometric-medium sand facies. The sorting distribution of sediments varies from moderately well sorted to poorly sort. The significant factors that control the sediment transport process are downslope gravity and wave-induced currents that are affected by the seafloor configuration and the shoreline orientation. According to the circulation effect on the sediment transport of the study area where deposition of fine sand and silt was observed in the northern part. Because sediment transport mitigates the occurrence of pollutant deposition in this part of the bay, we recommend that future constructions along the bay should be in the southern part.     

Coupled penetrometer, MBES and ADCP assessments of tidal variations in surface sediment layer characteristics along active subaqueous dunes, Danish Wadden Sea

In-situ geotechnical measurements of surface sediments were carried out along large subaqueous dunes in the Knudedyb tidal inlet channel in the Danish Wadden Sea using a small free-falling penetrometer. Vertical profiles showed a typical stratification pattern with a resolution of ∼1 cm depicting a thin surface layer of low sediment strength and a stiffer substratum below (quasi-static bearing capacity equivalent: 1–3 kPa in the top layer, 20–140 kPa in the underlying sediment; thickness of the top layer ca. 5–8 cm). Observed variations in the thickness and strength of the surface layer during a tidal cycle were compared to mean current velocities (measured using an acoustic Doppler current profiler, ADCP), high-resolution bathymetry (based on multibeam echo sounding, MBES) and qualitative estimates of suspended sediment distributions in the water column (estimated from ADCP backscatter intensity). The results revealed an ebb dominance in sediment remobilization, and a general accretion of the bed towards low water. A loose top layer occurred throughout the tidal cycle, likely influenced by bedload transport and small events of suspended sediment resettlement (thickness: 6 ± 2 cm). Furthermore, this layer showed a significant increase in thickness (e.g. from 8 cm to 16 cm) related to periods of overall deposition. These findings imply that dynamic penetrometers can conveniently serve to (1) quantify potentially mobile sediments by determining the thickness of a loose sediment surface layer, (2) unravel sediment strength development in potentially mobile sediments and (3) identify sediment accumulation. Such data are an important complement and add a new geotechnical perspective during investigations of sediment remobilization processes in highly dynamic coastal environments.     

热释光在南黄海、东海表层沉积物研究中的应用

提出了海洋沉积物热释光的测量方法。对南黄海和东海350个表层沉积物样品进行了热释光测量,研究了它们的热释光强度和发光曲线特征,探讨了沉积物热释光强度与其他指标之间的关系,讨论了热释光作为海洋沉积物的一个研究参数的原理和可行性。研究发现,沉积物热释光强度与砂、粘土和平均粒径有很好的相关关系;根据发光曲线的特征对研究海区进行了分区,发光曲线有明显的区域特征,这与各区的沉积环境有关。因此,热释光特征有可能成为研究海洋沉积物和沉积环境的一个替代指标。