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1.
K. Nagendra Prasad S. Triveni T. Schanz Late T. S. Nagaraj 《Marine Georesources & Geotechnology》2013,31(3-4):181-197
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. 相似文献
2.
G. Vasseur I. Djeran-Maigre D. Grunberger G. Rousset D. Tessier B. Velde 《Marine and Petroleum Geology》1995,12(8)
To provide a better understanding of sedimentary basin geological history, it is important to describe correctly the evolution of the various physical, mechanical and hydraulic properties of clayey rocks as a function of burial depth. As a contribution to this field, a programme of experimental studies on reworked clay samples compacted under various load pressures in oedometric conditions has been set up. The evolution of samples under compaction was followed with microscopic and macroscopic measurements. In a specially designed oedometric cell, samples are compacted under different total stresses from 0.1 to 50 MPa. In this cell, cylindrical cores are submitted to progressive loading from both ends under controlled pore pressure conditions. The symmetrical loading allows more even deformation about the midplane of the sample. This device allows the evolution of hydraulic pressure, radial stress, displacement and expelled pore fluid to be followed as a function of time. In a first step, kaolinite was chosen because it retains a high permeability (compared with other clays such as illite or smectite), which allows compaction tests to be performed within a few days. A complete set of measurements was performed after the tests. These measurements are: (1) micro-structures investigated by means of transmission electron microscopy (TEM), mercury porosimetry, water removal under low water vapour pressure, granulometry and specific area measured by ethylene glycol adsorption; and (2) various physical parameters measured including hydraulic conductivity and thermal conductivity. TEM gives an understanding of the arrangement of particles. It was found that each particle is composed of several crystal units, each unit formed by ≈25 individual kaolinite layers. During compaction, these particles remain undeformed, but are rotated. The angular distribution of grain orientation is a function of the applied effective stress. This reorientation is in agreement with the observed decrease in porosity and pore size. It also explains the occurrence of a strong anisotropy in the thermal conductivity and hydraulic permeability. The combination of these experimental results allows a qualitative and quantitative understanding of the behaviour of kaolinite with respect to parameters such as permeability, porosity, mechanical and thermal properties, the knowledge of which are necessary for basin modelling. 相似文献
3.
Despite a number of geotechnical investigations that have been carried out in the Busan new port area of South Korea, the local practicing engineers have been unable to deduce successfully the geotechnical properties of the clays due to their spatial variation. In the area, clay deposits, so-called Pusan clays, are unusually thick, varying from 20 m to 70 m in thickness. For this study, comprehensive geological and geotechnical investigations were carried out with sophisticated sampling techniques, in situ and laboratory tests as well as geological analyses at an additional three locations. As a result of the investigations, it was found that depositional environments are closely related to the relative changes in sea level and have different features depending on location and depth. The clays consist of soft and stiff clays in the upper and the lower layers, respectively, which are classified as normally consolidated and cemented clay. Moreover, most of the geotechnical properties undergo small changes due to their depositional environment. Information about these effects would be quite helpful to understand the spatial variation of geotechnical properties as well as the effect of sample disturbance. Some correlations which reflect the geological history of the deposts were conducted for physical indexes and mechanical properties. 相似文献
4.
ABSTRACT Despite a number of geotechnical investigations that have been carried out in the Busan new port area of South Korea, the local practicing engineers have been unable to deduce successfully the geotechnical properties of the clays due to their spatial variation. In the area, clay deposits, so-called Pusan clays, are unusually thick, varying from 20 m to 70 m in thickness. For this study, comprehensive geological and geotechnical investigations were carried out with sophisticated sampling techniques, in situ and laboratory tests as well as geological analyses at an additional three locations. As a result of the investigations, it was found that depositional environments are closely related to the relative changes in sea level and have different features depending on location and depth. The clays consist of soft and stiff clays in the upper and the lower layers, respectively, which are classified as normally consolidated and cemented clay. Moreover, most of the geotechnical properties undergo small changes due to their depositional environment. Information about these effects would be quite helpful to understand the spatial variation of geotechnical properties as well as the effect of sample disturbance. Some correlations which reflect the geological history of the deposts were conducted for physical indexes and mechanical properties. 相似文献
5.
A seabed instrument called Lancelot has been developed to measure pore pressure characteristics within potentially unstable marine sediment deposits, in any water depth. An estimate of the coefficient of consolidation can be obtained from the sediment pore pressure dissipation response that occurs following penetration into the seabed. This data can be used to calculate the coefficient of hydraulic conductivity, which is useful in analyzing the seepage velocity of pore fluids moving within the sediment mass. Pore-water pressures in excess of the normal hydrostatic profile are detected and used in static and dynamic liquefaction analyses, with a view toward understanding the origin of unusual seabed features such as pockmarks, as well as short-term instability caused by wave loading. An example of static liquefaction due to seepage stress is given for sites in and adjacent to the well-known 1929 Grand Banks debris flow, along with an example of incomplete liquefaction caused by dynamic wave loading within Miramichi Inner Harbor, New Brunswick. The adoption of in situ measurement techniques is shown to produce data of a quality not normally obtainable from recovered core samples, due to pressure relief and sampling disturbance effects. 相似文献
6.
Effect of Sample Disturbance on Unconfined Compression Strength of Natural Marine Clays 总被引：7，自引：0，他引：7
1 .IntroductionCoastalstructuresoftenencountersettlementandstabilityproblemsofsoftmarinefoundation (Liuetal.,1 999;Zhouetal.,2 0 0 0 ;Liuetal.,2 0 0 3) .Manyresearchershaveillustratedthatnaturalmarineclaysaregenerallysubjectedtotheeffectsofsoilstructureduringtheirdepositionalandpost depositionalprocesses (Zhangetal.,1 995;Hongetal.,2 0 0 3a ;2 0 0 3b) .Thesoilstructureofnat uralmarineclaysiseasilydamagedduringsamplingandhandlingbecausenaturalmarineclaysgeneral lyhavehighwatercontentandlowsti… 相似文献
7.
深水土工调查技术和分析方法新进展 总被引：1，自引：0，他引：1
简要介绍了近年来国外在深水土工调查技术和分析方法方面取得的新进展,包括:钻孔取样技术在钻入模式和取样器的多样化和有效组合,从而实现不同水深和不同土类条件下的高质量取样;带孔压测量的圆锥触探试验在测量方法、孔压测量单元设计、探头的小型化和多样化、数据的快速传输以及分析理论方面的进展;减少土样扰动,准确评估粘土不排水抗剪强度的“SHANSEP”室内试验方法及应用。 相似文献
8.
When a piezocone (CPTU) penetrates the ground, pore pressures are set up due to the stress changes. Pore pressure dissipation occurs in the subsequent consolidation process in a manner dependent on the initial stress distribution. The process of analysis can be used to interpret the consolidation parameters from CPTU data based on strain path approach. For the two approaches to the CPTU analysis, the Houlsby and Teh method used an elastic-plastic model, while the Levadoux and Baligh solution used parameters specifically appropriate for Boston Blue Clay. This article discusses a comparison between the two theoretical predictions and field CPTU measurements deployed in Jiangsu (China) Quaternary clays. The values of the coefficient of consolidation calculated from the two methods are then compared with high-quality laboratory tests. Both theoretical predictions provide good agreement for the shape of the dissipation curve, but the predicted c h values are different and thought should indeed be given to the use of an appropriate value of G/s u. 相似文献
9.
Kjell Jonasson 《Marine Georesources & Geotechnology》2013,31(3):233-257
Abstract The Haamer vibrocorer is a cheap and easily handled sampler for containing continuous cohesive or cohesionless sediment cores. This vibrocorer can be handled on board an ordinary trawler or small vessel. The penetration of the sampling barrel is actuated by two synchronized vibrators. Additional penetration force is provided by the buoyancy of a guiding buoy. To extend the maximum sampling length and to decrease the degree of disturbance, the vibrocorer is equipped with a plastic foil, which encases the core as it enters the liner and reduces inside friction. By providing the sampler with jetting water, the necessary penetration force is decreased. Testing a prototype is always difficult, but a working cycle of up to three cores an hour has been reached using a 6 m vibrocorer. A limited investigation has been conducted to determine the quality of the recovered cores; however, because of the poorly defined quality of the reference samples, no definitive answer to the question of sample disturbance can be given. 相似文献
10.
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。 相似文献
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12.
This paper focuses on the rate-dependent yield stress, undrained strength, and long-term undrained strength of clay. Various oedometer and triaxial tests were performed on Wenzhou marine clay. The uniqueness of rate-dependent and long-term yield stress and strength is discussed. A new anisotropic elastic viscoplastic model is proposed by adopting the concept of anisotropy and isotropy processes. The determination of model parameters is discussed, demonstrating how all model parameters can be determined in a straightforward way requiring the same basic tests as for the Modified Cam Clay model. Experimental verifications are carried out using the constant strain-rate and creep tests on the Wenzhou marine clay. 相似文献
13.
风涌浪分离是研究风浪、涌浪各自特性的基础,但受限于海浪谱数据的匮乏,基于海浪谱的风涌浪分离方法难以普及应用,有效的解决办法是采用波浪观测中容易获取的基本波要素进行风涌浪分离。现有方法无法利用基本波要素全面计算出风浪、涌浪的比例及其特征参数,为此本文将机器学习引入到风涌浪分离中,以多层感知器模型为基础,提出了一种利用基本波要素、风要素准确计算出风涌浪参数的方法。该方法需要每个测站提供至少466笔、建议766笔及以上的实测波浪数据作为训练样本,适用于台湾海峡3个测站,在计算精度上显著优于基于海浪频谱的传统风涌浪分离方法,可为本海域缺乏海浪谱的测站提供替代性的风涌浪计算方案,有助于扩大实测风涌浪资料的来源,进而加强风涌浪分布特性以及预警预报研究。 相似文献
14.
S. G. CHUNG K. NAGENDRA PRASAD T. S. NAGARAJ J. G. CHUNG K. Y. JO 《Marine Georesources & Geotechnology》2013,31(1-2):1-20
It Naturally cemented soft clays have components of strength and stiffness, which cannot be accounted for by classical soil mechanics (Leroueil and Vaughan 1990). This stems from the influence of structure caused by cementation due to environmental factors. It is necessary to evaluate the cementation bond strength at preyield and postyield stress levels of loading, to understand comprehensively the observed response from micromechanic considerations. This helps to better understand and evolve approaches to model the constitutive behavior in a consistent manner, according to the physical phenomenon of formation of cementation as an additional component to what is otherwise normally regarded as frictional behavior arising only from particulate nature of clays. Comparing the behavior of deep deposits of Pusan soft clays under stress with corresponding response of the same clay in its remolded state, it has been possible to take into account particulate and nonparticulate responses. The evolution of cementation bonding is modeled for different Pusan clays with the yield stress in oedometer compression as a normalizing parameter for obtaining the generalized relationship of cementation bonding with increase in stress. The already established model for determining the remolded behavior is appropriately modified to assess the behavior influenced by cementation. The model proposed consists of parameters, which are determined in routine investigations. 相似文献
15.
S. G. Chung K. Nagendra Prasad T. S. Nagaraj J. G. Chung K. Y. Jo 《Marine Georesources & Geotechnology》2004,22(1):1-20
It Naturally cemented soft clays have components of strength and stiffness, which cannot be accounted for by classical soil mechanics (Leroueil and Vaughan 1990). This stems from the influence of structure caused by cementation due to environmental factors. It is necessary to evaluate the cementation bond strength at preyield and postyield stress levels of loading, to understand comprehensively the observed response from micromechanic considerations. This helps to better understand and evolve approaches to model the constitutive behavior in a consistent manner, according to the physical phenomenon of formation of cementation as an additional component to what is otherwise normally regarded as frictional behavior arising only from particulate nature of clays. Comparing the behavior of deep deposits of Pusan soft clays under stress with corresponding response of the same clay in its remolded state, it has been possible to take into account particulate and nonparticulate responses. The evolution of cementation bonding is modeled for different Pusan clays with the yield stress in oedometer compression as a normalizing parameter for obtaining the generalized relationship of cementation bonding with increase in stress. The already established model for determining the remolded behavior is appropriately modified to assess the behavior influenced by cementation. The model proposed consists of parameters, which are determined in routine investigations. 相似文献
16.
Long term macrobenthos data together with physical habitat parameters were analysed to investigate spatial and temporal changes at an estuary under different anthropogenic pressures, mainly increasing shellfish farming. The aim was to assess the possible impacts of these pressures on the macrobenthic communities by comparing a period before and after changes in these pressures. Benthic samples were seasonally collected in 1990 (before major anthropogenic changes), 2000 and 2005 at the same sampling stations located on three different habitats in the Eo estuary (Northern Spanish coast). Multivariate and univariate methods were used to assess spatial variability of benthic assemblages and to compare community changes over time. Data from 1990 was assumed as the reference situation to appraise the subsequent impacts. We observed a significant spatial variability of the benthic assemblages in the system as a function of habitat heterogeneity in relation to sediment composition, presence/absence and density of seagrasses, and hydrodynamic regime. Changes were detected in the community composition at all sites during this 15 year period. The extent of changes was related to initial community conditions, rather than the intensity of the pressure. The results suggest that the responses of the benthic communities to human induced perturbations occurring in the system are largely dependent on its intrinsic buffer capacity, and that these communities have been able to cope with an increasing environmental stress (organic enrichment). In conclusion, to keep shellfish farming at a sustainable level without undesirable impacts, the disturbance intensity must be kept below the system carrying capacity. This will allow natural communities to cope with pressures and thus avoid further deterioration in ecological quality. 相似文献
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A gamma-ray transmission method is discussed for measuring the water content of marine sediment samples during consolidation testing. This method permits obtaining consolidation curves for sediment cores while still in the core liner, thereby eliminating several sources of sample disturbance. A narrow beam of gamma-rays is passed through the sample to a detector and counting equipment. The attenuation of this beam is a function of the sample density and hence water content or void-ratio. Equations are developed for calculating water content from gamma-counts. The results of experiments are presented confirming the validity of these equations. 相似文献
19.
C.L. Kirk 《Applied Ocean Research》1985,7(1):2-13
This paper uses the Galerkin method in the solution of the marine riser differential equation and compares the dynamic bending stresses in a tension-leg-platform riser calculated by the linearised single wave and linearised spectral analysis methods.The results show that it is possible to make some rational assessment of approximate peak values of bending stress in the spectral method.The analysis methods are applicable to any riser system subject to horizontal exciting forces due to fluid and vessel motion. 相似文献
20.
Conrad W. Curry Richard H. Bennett Matthew H. Hulbert Kenneth J. Curry Richard W. Faas 《Marine Georesources & Geotechnology》2004,22(4):231-252
Porosity is a fundamental property of marine sediment from which wet bulk density can be easily determined and used in a variety of geoacoustic, geotechnical, and sedimentological studies, analyses, and models. However, methods of sampling marine sands suffer from the common problem of core disturbance making the in situ porosity difficult to obtain. Embedding the sediment within an epoxy resin matrix will minimize the disturbance to the microfabric and preserve the in situ sedimentary structure for subsequent study. Image analysis can then be used on thin sections to study the microfabric and porometry. A comprehensive review and analysis of published data on the porosity of predominantly clean sands has been completed and a simple, accurate, and nondestructive technique is described for preparing and measuring the porosity of marine sediment (siliciclastic sand) that has been infiltrated aboard ship immediately upon sample collection and chemically fixed and infiltrated with epoxy shortly thereafter. The average porosity of 36 samples of marine sand collected offshore Fort Walton Beach, Florida, and embedded with resin was determined to be 41.30%. From the review of published data the average porosity of sand was determined to be 37.7%, 42.3%, and 46.3% for packed, natural (in situ), and loose packing conditions, respectively, for a range of sorting coefficients and grain sizes. 相似文献