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1.
Abstract The advanced piston cover (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. 相似文献
2.
Liang Yuanbo Lu Bo Huang Shaojian Li Tinghuan Yang Weiguang Wen Yaolin 《Marine Georesources & Geotechnology》2013,31(3-4):189-201
Abstract The possibility of seafloor failure under external loadings on a gently sloping continental shelf is controlled, to a large extent, by the geotechnical characters of subbottom sediments (e.g., shear strength, compressibility, and liquefaction potential) and structural factors (e.g., sedimentary stratification). By means of undis‐turbing coring, in‐situ acoustic measurement, and subbottom profiling, the authors conducted an investigation into the seafloor instabilities and possibilities of sediment slope failure within the continental shelf off the Pearl River mouth, which is one of the most important areas for offshore development in the northern South China Sea. Based on in‐situ and laboratory measurements and tests for sediment physical properties, static and dynamic behavior, and acoustic characteristics, the analyses indicate: (1) subbottom sediments that originated from terrigenous clay during the Pleistocene are compact and overconsolidated, and the mean sound velocity in such sediments is relatively high; (2) the maximum vertical bearing capacity of subbottom sediments is efficiently conservative on the safe side for dead loads of light structures, and the trench walls are stable enough while trenching to a depth of about 2 m below the seafloor under still water; and (3) it is quite improbable that the subbottom sediments liquefy under earthquake (M ≤ 6) or storm wave loading. 相似文献
3.
Tae Sup Yun Guillermo A. Narsilio J. Carlos Santamarina 《Marine and Petroleum Geology》2006,23(9-10):893-900
Seventy whole rounds from conventional cores obtained during drilling to 300 mbsf at Atwater Valley and Keathley Canyon in the Gulf of Mexico in April and May 2005 were tested to determine geophysical and geomechanical parameters (liquid and plastic limit, porosity, specific surface, pH, sediment electrical conductivity, P- and S-wave velocities and undrained shear strength). Available data from a pressure core are included as well. Results show that the sediments are high specific surface plastic clays, and exhibit pronounced time-dependent stiffness recovery. Strains during coring disturb specimens, yet, the water content retains the effective stress history and permits gaining stiffness and strength information from conventional cores. Remolding is exacerbated when gas expands upon decompression; the limited pressure core data available show the advantages of preserving the pore fluid pressure during core recovery and testing. Valuable parameters for sediment characterization and engineering analysis are extracted from the data using pre-existing soil models. 相似文献
4.
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. 相似文献
5.
Michael J. Cruickshank 《Marine Georesources & Geotechnology》2013,31(1):85-86
Abstract The engineering properties of deep continental margin sediments were determined on a worldwide basis. Deep Sea Drilling Project (DSDP) core data and material were utilized from over 900 cores obtained from 89 sites, primarily on the continental margins. Cores were recovered from penetrations to 200 m in water depths averaging 3000 m. Supplementary laboratory testing on selected cores was directed toward determining index properties and shear strength properties of the sediments. The study included a literature review of deep‐sea soil properties, the results of which are to be used by DSDP to evaluate foundation conditions for reentry cones with long casing strings. The results will also be used for a feasibility study of an ultradeepwater marine riser and well‐control system. The marine sediments examined can be divided into three main types: clay, calcareous ooze, and siliceous ooze. Sediment distribution consisted of 48% calcareous ooze, 43% clay, 6% siliceous ooze, and 3% volcanic ash. Because of the sample disturbance inherent in the deepwater coring operation, emphasis was placed on analyzing sediment properties not significantly affected by changes in in situ stresses and structure caused by sampling. Averages and ranges in values of water content and unit weight are presented for the three main sediment types. Plasticity and strength characteristics are discussed in detail and the elastic and compression properties are outlined. The geotechnical properties of deep continental margin soils are summarized. 相似文献
6.
为了研究黄河口海床沉积物固结过程中电阻率同工程力学性质指标的对应关系,探索海床土体固结过程的新型原位监测技术,本文在黄河刁口流路三角洲叶瓣潮坪上,现场取土配置黄河口快速沉积形成的流体状沉积物和观测研究粉质土海床的固结过程。利用静力触探、十字板剪切试验、孔隙水压力监测等原位土工测试手段,实时测定固结过程中海床土强度变化和孔隙水压力消散过程;同时通过埋置自行研制的环形电极探杆,实时测定海床土固结过程中的电阻率变化。通过对比分析海床土电阻率与工程力学性质指标的同步测定数据发现:黄河口饱和粉土的电阻率与微型贯入试验测得的土体贯入强度,静力触探试验测得的比贯入阻力,十字板剪切试验测得的不排水抗剪强度(峰值强度、残余强度)均呈乘幂关系,且相关性良好;海床沉积物在固结过程中的电阻率与孔隙水压力呈负线性相关性。 相似文献
7.
Hiroshi Adachi Hiroya Yamano Toshihiro Miyajima Masahiro Nakaoka 《Journal of Oceanography》2010,66(6):865-872
This article describes a simple, quick, and inexpensive procedure for coring unconsolidated sediment in shallow water (<30
m from water surface). A ∼1 m core is retrieved by a PVC pipe that penetrates sediment in response to the percussive force
of a hand-operated hammering tool or air hammer. After retrieving the first core segment, a casing is inserted to allow access
to deeper sediment layers. Pulverized sediment produced during coring is removed by a water-lubrication system that is powered
by an electric pump attached to a generator. Using this system and procedure, five 2-m-long cores with excellent quality were
retrieved. 相似文献
8.
N. H. Khadge 《Marine Georesources & Geotechnology》2013,31(4):401-417
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. 相似文献
9.
We present in situ strength and pore-pressure measurements from 57 dynamic cone penetration tests in sediments of Mecklenburg (n?=?51), Eckernförde (n?=?2) and Gelting (n?=?4) bays, western Baltic Sea, characterised by thick mud layers and partially free microbial gas resulting from the degradation of organic material. In Mecklenburg and Eckernförde bays, sediment sampling by nine gravity cores served sedimentological characterisation, analyses of geotechnical properties, and laboratory shear tests. At selected localities, high-resolution echo-sounder profiles were acquired. Our aim was to deploy a dynamic cone penetrometer (CPT) to infer sediment shear strength and cohesion of the sea bottom as a function of fluid saturation. The results show very variable changes in pore pressure and sediment strength during the CPT deployments. The majority of the CPT measurements (n?=?54) show initially negative pore-pressure values during penetration, and a delayed response towards positive pressures thereafter. This so-called type B pore-pressure signal was recorded in all three bays, and is typically found in soft muds with high water contents and undrained shear strengths of 1.6–6.4 kPa. The type B signal is further affected by displacement of sediment and fluid upon penetration of the lance, skin effects during dynamic profiling, enhanced consolidation and strength of individual horizons, the presence of free gas, and a dilatory response of the sediment. In Mecklenburg Bay, the remaining small number of CPT measurements (n?=?3) show a well-defined peak in both pore pressure and cone resistance during penetration, i.e. an initial marked increase which is followed by exponential pore-pressure decay during dissipation. This so-called type A pore-pressure signal is associated with normally consolidated mud, with indurated clay layers showing significantly higher undrained shear strength (up to 19 kPa). In Eckernförde and Gelting bays pore-pressure response type B is exclusively found, while in Mecklenburg Bay types A and B were detected. Despite the striking similarities in incremental density increase and shear strength behaviour with depth, gas occurrence and subtle variations in the coarse-grained fraction cause distinct pore-pressure curves. Gaseous muds interbedded with silty and sandy layers are most common in the three bays, and the potential effect of free gas (i.e. undersaturated pore space) on in situ strength has to be explored further. 相似文献
10.
Torque measurements are made by divers with a vane apparatus to a sediment depth of 136 cm in the high-porosity, gassy sediments of Eckernförde Bay. Corrected shear strength values calculated from torque measurements are quite variable in the Eckernförde Bay sediments, varying from less than 0.5 kPa in the top 10 cm of sediment to 4–5 kPa at 136 cm sediment depth. Variability increases markedly below 60 cm sediment depth, probably because of the presence of methane gas bubbles within the sediment fabric. 相似文献
11.
Sediment disturbance associated with the Deep Sea Drilling Project coring and core‐handling program are discussed along with the effects of sample disturbance on some measurements of physical properties. Information was obtained from shopboard observations and testing on Leg 43 and shore‐based testing of several sediment samples. Disturbance results from (1) remolding of the particle structure during coring, and (2) swelling induced by stress release and thermal expansion in the presence of excess water. Remolding is most significant to depth of 50–100 m, whereas swelling effects increase with coring depth. As a result, the shipboard data are not rep‐sentative of in situ sediment properties. The tendency is for porosity to increase and for bulk density to decrease with increased swelling. Strength is significantly reduced for swelled samples with further reductions from remolding. All observations and data suggest a need for improved coring capabilities and an in situ testing program. 相似文献
12.
Quality control in mud coring 总被引：1，自引：0，他引：1
W. R. Parker 《Geo-Marine Letters》1991,11(3-4):132-137
Consideration of factors influencing the interaction between a corer and sediment suggest the likelihood of significant and
anisotropic straining of the particle framework during coring. Direct observations allow the coring process to be discretised,
the relative motion of corer, core and sediment to be visualized and confirm that the development of differences between corer
penetration and core length is not a continuous process. Records suggest the possibility of dislocation of the relative positions
of porewater and particle framework, which may lead to the disequilibration of sorbed species. 相似文献
13.
A seabed 2-m-long cone penetrometer and coring system (Geotechnical Module) has been used at 17 stations in four transects on the Scotian Slope to characterise in situ shear strength and induced pore pressure on several different types of late Pleistocene and early Holocene failure. Study sites were selected using the SAR high-resolution deep-towed acoustic system equipped with a digital 160–190 kHz sidescan sonar and a 3.5 kHz subbottom profiler.
Several distinctive types of “geotechnical signature” were recognised from plots of cone resistance and induced pore pressure with depth in the sediment. Normally consolidated sediments show a progressive increase in cone resistance with depth (to about 75 kPa at 2 m subbottom). Holocene surficial muds show spectacular apparent overconsolidation, reaching a peak of 250 kPa at about 50 cm subbottom and then decreasing down to 1.5 m. This overconsolidation is associated with Zoophycos burrows. Late Pleistocene sediments exhumed by bedding plane slides show strong true overconsolidation consistent with the original depth of burial inferred from high-resolution seismic stratigraphy. Debris flows show only a slight shear stress gradient with depth (40–45 kPa over 0.5–1 m subbottom) with under-consolidation due to remoulding of sediment. 相似文献
14.
S. J. Wheeler 《Marine Georesources & Geotechnology》2013,31(2):113-129
Abstract Where undissolved gas occurs within fine‐grained marine sediments it usually takes the form of discrete bubbles that are much larger than the normal void spaces. The possibility of buoyancy‐induced movement of these relatively large bubbles must be included when considering the transport of gas through marine sediments. A theoretical analysis shows that, under static loading conditions, bubbles larger than a critical size should have sufficient buoyancy to move upward through a fine‐grained sediment stratum, whereas bubbles smaller than the critical size should remain fixed in position. The critical radius is directly proportional to sediment shear strength, and bubbles of a realistic size should move upward only in extremely weak sediments. Further theoretical analysis shows that the critical bubble size is reduced under cyclic loading conditions, but movement of typical‐sized bubbles should still be restricted to sediments of low shear strength. A simple laboratory experiment provides support for the conclusions of the theoretical analysis. The results indicate that buoyancy‐induced movement of relatively large gas bubbles in fine‐grained sediments is most likely to occur under storm loading conditions and is unlikely to occur at depths greater than a few meters below the seabed. 相似文献
15.
N. H. Khadge 《Marine Georesources & Geotechnology》2000,18(3):251-258
As a part of the environmental impact assessment studies, geotechnical properties of sediments were determined in the Central Indian Basin. The undrained shear strength and index properties of the siliceous sediments were determined on 20 box cores of uniform dimension collected from various locations in five preselected sites. The maximum core length encountered was 41 cm and most of the sediments were siliceous oozes consisting of radiolarian or diatomaceous tests. The shear strength measurements revealed that surface sediments deposited in recent times (0-10 cm) have a shear strength of 0-1 kPa; this value increases with depth, reaching 10 kPa at 40 cm deep. Older sediments have greater strength because of compaction. Water content varies in the wide range of 312-577% and decreases with depth. The clay minerals such as smectite and illite are dominant and show some control over water content. Wet density, specific gravity, and porosity do not indicate any notable variation with depth, thereby indicating a uniform, slow rate of sedimentation. The average porosity of sediments is 90.2%, specific gravity 2.18, and wet bulk density 1.12 g/cm 3 . Sediments exhibit medium to high plasticity characteristics, with the average plasticity index varying between 105% and 136%. Preliminary studies on postdisturbance samples showed an increase in natural water content and a decrease in undrained shear strength of sediments in the top 10- to 15-cm layer. 相似文献
16.
Gil Y. Kim Hong J. Yoon Jin W. Kim Dae C. Kim Boo K. Khim Seok Y. Kim 《Marine Georesources & Geotechnology》2007,25(1):37-51
This study was undertaken to investigate the implication of geoacoustic behaviors in the shallow marine sediments associated with the changes in geotechnical index properties. Two piston cores (270 cm and 400 cm in core length) used in this study were recovered from stations 1 and 2, the western continental margin, the East Sea. Scanning electron microscopy (SEM) was employed to illustrate the effects of microstructure on shear properties. The direct SEM observation of sediment fabrics is inevitable to understand the correlation of the changes in geoacoustic properties to the sediment structure. The consolidation of sediments by overburden stress resulting in the clay fabric alteration appears to play an important role in changing shear properties. Water contents and porosity of sediments gradually decreases with increasing depth, whereas wet bulk density shows a reverse trend. It is interesting to note that shear wave velocities increase rapidly from 8 to 20 m/s while compressional wave velocities significantly fluctuate, ranging from 1450 to 1550 m/s with depth. The fabric changes in sediment with increasing depth for example, uniform grain size and well oriented clay fabrics may cause the shear strength increase from 1 to 12 kPa. Shear wave velocity is, therefore, shown to be very sensitive to the changes in undrained strength for unconsolidated marine sediments. This correlation allows an in-situ estimation of shear stress in the subsurface from shear wave velocity data. 相似文献
17.
海底沉积物实验室剪切波速度及其与沉积物的物理性质之间的关系 总被引：1，自引：3，他引：1
采用压电陶瓷弯曲元法和共振柱试验的方法对采自我国海域的一些典型海底浅表层沉积物样品进行了剪切波速测试,获得首批可信数据.两种方法所测得的剪切波速数据具有很好的一致性,且在数赫兹至数十千赫兹频段范围内剪切波速不具明显弥散性.剪切波速与沉积物类型关系密切,不同海区和不同类型海底沉积物的剪切波速有明显差异.近海较细颗粒沉积物粉砂的剪切波速在100m/s左右,细颗粒沉积物的剪切波速在100m/s以下;陆架较粗颗粒沉积物的剪切波速最大,超过100m/s;深海、半深海细颗粒沉积物的剪切波速最低,小于50m/s.剪切波速与含水量、密度、孔隙度、塑限和液限等沉积物物理参数之间具很好的相关性,反映了剪切波速和物理性质之间的密切关系.剪切波速与压缩波速呈正相关性,但在不同的波速范围剪切波速随压缩波速的变化有很大不同. 相似文献
18.
Richard H. Bennett Douglas N. Lambert Matthew H. Hulbert 《Marine Georesources & Geotechnology》2013,31(1-4):245-261
Abstract A relatively large submarine slide (slump block) and apparent unstable surficial sediments undergoing creep have been delineated in bathymetric and seismic reflection profiles along the U.S. Atlantic continental margin northeast of Wilmington Canyon. A downslope core transect was made over selected areas to assess the geotechnical properties of the sediments associated with the slide. Sediments are predominantly silty clays and clayey silts rich in illite, with lesser quantities of feldspar, kaolinite, chlorite, quartz, and smectite minerals. Surficial sediments (cored up to 12 m) upslope from the slump block reveal typical variations in the mass physical properties with core depth. Shear strength and wet unit weight show a steady increase with depth below the mudline commensurate with a decrease in water content. In contrast, surficial sediments downslope overlying the slump block generally have low shear strength and relatively high variability in other mass physical properties with core depth. Chemical evidence of slumping (as defined by the sulfate ion content) is not apparent in the pore waters collected from the upper 10 m of sediment. No important relationships are obvious among the physical and chemical properties, specifically the carbonates or complex solids of iron and manganese oxides or hydroxides. Sediment failure in the form of a major submarine slide appears to have been a significant deformational process during the geological past (late Pleistocene). Creep and associated deformational features recorded in the surficial sediments are presumably a result of recent geological processes. 相似文献
19.