Discussion of “Shear Strength of an Accumulation Soil from Direct Shear Test” by J. Wang,H. Zhang,H. Wen,and Y. Liang

According to the article named “Shear Strength of an Accumulation Soil from Direct Shear Test” by J. Wang, H. Zhang, H. Wen, and Y. Liang, this paper proposes a more reasonable expression to characterize shear strength in the original paper. The angle of shearing resistance is expressed by the combination of initial and incremental angles of shearing resistance, the relative compactions and water content were used to analyze the effects. The initial and incremental angles of shearing resistance are generally increasing with the increment of the relative compaction, increasing then decreases with the increment of the water content. The finial expressions which combined by the series of simulation equation was given to precisely predict the accumulation soil's angle of shearing resistance in relation to the relative compactions and water content.     

大洋多金属结核矿区沉积物土工性质

利用1994年大洋多金属结核调查所获得的土工资料,结合以往有关资料进行了综合分析。研究了大洋沉积物类型、沉积物土工性质、土质强度等,为未来海底工程设施和多金属结核开采设备的设计与制造提供依据。     

Geotechnical Investigations at the Dalian Offshore Airport,China

Based on the geotechnical investigation data of artificial island at Dalian Offshore Airport, the spatial distribution of the physical and mechanical properties of deposit soils was statistically analyzed. The field investigation revealed that the deposit soils could be subdivided into three strata, i.e., the top marine deposit stratum, middle marine-continental deposit stratum, and deep continental deposit stratum. Field and laboratory test results demonstrated that the marine deposit soils had high water content (31.2% < w_n < 63.10%), large void ratio (0.88 < e₀ < 1.75), low permeability (k_v < 10^?6 cm/s), flow-plastic state (I_L > 1), under consolidated (OCR < 1), high compressibility (E_s < 4 MPa), low shear strength (11.7 kPa < c_u < 43.7 kPa), and low bearing capacity (0 < f_ak < 120 kPa), they could not be used as natural foundation. The marine-continental and continental deposits were normally consolidated to over-consolidated (OCR ≥ 1), medium compressibility (4 MPa < E_s < 20 MPa), high shear strength (29.7 kPa < c_u < 73.7 kPa), and high bearing capacity (f_ak > 120 kPa). In addition, regression analysis results showed that the compression ratio was positively correlated with the natural water content, the coefficient of vertical consolidation was negatively correlated with the plasticity index, and the coefficient of vertical permeability was positively correlated with the initial void ratio. The results of the field and laboratory tests were synthesized to provide a basis for reclamation design.     

Geotechnical properties of oceanic sediments in polymetallic nodules belts

I~IOWOver years POlylnetallic noduleS are considered one of POtential rererces with the most econOAnc value in ocean rererces. MOSt countries have conducted thorOUgh investigations and researcheS in polyTnetallic nodules belts and a vast amount of data have aam collected. These dataprovide bases for cornmercial exploitation Of the polyrnetallic nodules in the future.~echnical properties are very imPOrtant to the selection of mining methods, and affect thedesign and manufacture of ocean…     

水下土体剪切界面摩擦力试验研究

基于在自行改进设计的水下土体剪切界面摩擦力测定装置进行的室内试验结果,对不同粒组、含水率及剪切速率条件下土体剪切界面抗剪强度和摩擦力进行了研究。试验结果表明,不同土体间剪切界面抗剪强度和摩擦力与土体颗粒粒组、含水率相关性表现不同。随着含水率的增加,粉砂抗剪强度和摩擦力呈增加趋势,细砂、中砂抗剪强度和摩擦力受含水率变化影响较小。土体颗粒粒组不同,抗剪强度和摩擦力有明显差异,表现在粉砂大于细砂和中砂,小于黏粒含量较高的粉土,细砂和中砂的差别较小。试验条件下得到的粉砂、细砂、中砂土体与粉质土底床间的水下剪切界面摩擦力值在0.2~1.0 kPa区间,并结合海洋地质实例说明界面摩擦力的应用。     

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.     

Experimental study on strength characteristics and microscopic mechanism of marine soft clays

Abstract

The effect of microstructure on shear strength of saturated marine clays was investigated by conducting a series of consolidated-drained (CD), consolidated-undrained (CU) triaxial shear tests and mercury intrusion porosimetry (MIP) tests on undisturbed and reconstitute specimens. The valuable findings from the experimental study are follows: (1) The shear strength of undisturbed specimens is lower than that of corresponding reconstituted specimens due to larger void ratio at the same confining pressure. However, undisturbed specimens have higher strength than reconstituted specimens when their void ratios are the same. (2) The main reason for the lower shear strength of reconstituted specimens with the same void ratio as undisturbed specimens is that more volume of inter-aggregate pores exists in the reconstituted specimens according to the MIP test results. And the difference in shear strength between undisturbed and reconstituted specimens is mainly caused by the difference in soil fabric. (3) The shear test results dealt with a reference void ratio, as a fabric index, show that there is a unique linear relation between strength and void ratio at failure to the reference void ratio. Moreover, the linear relation is suitable for other marine clays from the literature. Therefore, the reference void ratio can be used as a soil fabric index to normalize the strength characteristics of marine soft clays.     

Strength Sensitivity of Marine Ariake Clays

ABSTRACT

Natural Ariake clays are characterized by high sensitivity. In this study, the mechanism and the factors controlling undrained shear strengths of both undisturbed and remolded Ariake clays are discussed. A series of unconfined compressive tests were performed on undisturbed samples of natural Ariake clays. The remolded undrained shear strength is predicted using a quantitative expression derived from extensive data of remolded undrained shear strength for a number of soils compiled from resources in the literature. The sensitivity of natural Ariake clays derived from the ratio of half of unconfined compressive strength for undisturbed samples to remolded undrained shear strength is found to be affected by both natural water content and normalized water content that is defined as the ratio of natural water content to liquid limit. The smaller the natural water content, the higher the sensitivity is at the same normalized water content. At the same natural water content, the larger the normalized water content, the higher the sensitivity is.     

Strength Sensitivity of Marine Ariake Clays

Natural Ariake clays are characterized by high sensitivity. In this study, the mechanism and the factors controlling undrained shear strengths of both undisturbed and remolded Ariake clays are discussed. A series of unconfined compressive tests were performed on undisturbed samples of natural Ariake clays. The remolded undrained shear strength is predicted using a quantitative expression derived from extensive data of remolded undrained shear strength for a number of soils compiled from resources in the literature. The sensitivity of natural Ariake clays derived from the ratio of half of unconfined compressive strength for undisturbed samples to remolded undrained shear strength is found to be affected by both natural water content and normalized water content that is defined as the ratio of natural water content to liquid limit. The smaller the natural water content, the higher the sensitivity is at the same normalized water content. At the same natural water content, the larger the normalized water content, the higher the sensitivity is.     

茂名地区海雾的微物理结构特征

2007年3月16日至4月29日期间,在广东茂名海洋气象科学实验基地对海雾进行了连续观测,共取得51个雾滴谱样本,在此基础上分析了茂名地区海雾的微物理结构特征。观测分析表明:茂名地区海雾的雾滴谱分布符合Junge分布,平均数密度为57.1个/cm3,平均含水量为0.018 3 g/m3,算术平均直径为4.7μm,算术峰值直径为2.9μm。文中还比较了雾和轻雾情况下雾滴谱分布的不同特征,分析了能见度与含水量之间的关系。     

On Physical and Mechanical Behavior of Natural Marine Intermediate Deposits

Coastal structures may be built on natural sedimentary intermediate grounds, which mainly consist of silty soils and fine sandy soils. In this study, extensive field and laboratory tests were performed on the nattwal marine intermediate deposits to demonstrate the difference in behavior between natural marine clayey soils and natural marine intermediate deposits. The natural intermediate deposits have almost the same miles of natural water content to liquid limit as those of the soft natural marine clays, but the former have much higher in-situ strength and sensitivity than the latter. The research results indicate that grain size distributions of soils affect significantly tip resistance obtained in field cone penetration tests. The mechanical parameters of natural marine intermediate deposits are also significantly affected by sample disturbance due to their high sensitivity and relatively large permeability. Unconfined compression shear tests largely underestimate the strength of natural marine intermediate soils. The triaxial consohdated compression shear tests with simulated insitu confined pressure give results much better than those of uncomfined compression shear tests.     

Numerical simulation of water content dependent undrained shear strength of clays

Abstract

A nonlinear mathematical model for estimating the water content dependent undrained shear strength of clayey soils was developed. Three types of clay mixtures (kaolinite, bentonite, and kaolinite-bentonite) were considered. The shear strength of the given soil samples was determined via torvane tests. Experimental results were compared with three numerical results: (i) the analytical function fit, (ii) modeling without the water content effect, and (iii) modeling with the water content effect using the Mohr-Coulomb (M-C) model. There was good agreement among the experimental, analytical, and numerical results with and without the water content effect in the fully softening zone. However, there was a large difference between the numerical results obtained from the developed model with and without the water content effect in the flow zone with a high liquidity index, because the shear strength may decrease significantly to low value in the case of an abrupt increase of the water content. The greatest advantage of the developed model is that it can simulate the reduction of the shear strength and shear band development under the high water content condition, which may trigger a large mobile mass movement.     

厦门吴冠海岸潮间带沉积物粒度特征及其沉积动力学涵义

潮滩沉积物的粒度参数可以用来反映沉积物沉积的水动力、沉积物来源和沉积物搬运趋势等环境信息。对厦门吴冠潮间带35个表层样的粒度资料进行分析的结果表明,研究区沉积物类型以黏土质粉砂和粉砂质砂为主;沉积物主要来源于海岸侵蚀物质的输入,随着沉积物向海方向搬运,沉积物粒度参数表现出有规律的变化趋势,即由岸向海粒径具有细化趋势,分选程度变好。与开敞海岸淤泥质潮滩粒度特征相比,研究区的粒度参数组合特征具有明显差异,这可能是由于水动力条件的差异引起的。     

大连复州湾底质沉积物粒度特征与沉积环境分析

对辽东半岛西部复州湾海域底质沉积物样品进行粒度分析结果表明,其粒度特征有较大差异:样品平均粒径值为1.2~6.5Φ;分选系数为1.4~2.6,分选为较差—差;偏度特征表现为极正偏和极负偏并存。粒度的空间分布存在一定分异规律,由湾内至湾外粒径表现出粗—细—粗的变化特征。粒度变化是对该区域物质输运和地形变化的响应,借助Weibull分布,推断河流携带物质可以被推送至5 m等深线外堆积,5~10 m等深线间沉积物表现为细粒的浅海台地沉积,10 m等深线以外沉积物受河流的影响微弱。矿物学证据也表明,河流输运对湾内沉积物贡献有限,仅限于5 m 等深线以内的水下三角洲,湾内沉积物主要来自于辽东湾沿岸冲刷和湾内基岩的剥蚀。     

Mechanical properties of calcareous silts in a hydraulic fill island-reef

Abstract

The mechanical characteristics of calcareous silt interlayers play an important role in the stability of island-reef foundations. Direct shear and consolidation tests were performed to study the relationship between the mechanical properties and the physical parameters of calcareous silt. Based on the consolidation test results and analysis of the settling examples, different calculation methods for soil settling were compared. The results show the following. (1) The relationship between the cohesion and water content of calcareous silt can be represented by an M-shaped curve. The water contents corresponding to the two peaks of the M-type curve increase with increasing dry density. (2) When the dry density is less than 1.33?g/cm³, increasing the density significantly improves the internal friction angle of calcareous silts. When the dry density of the calcareous silt is greater than 1.33?g/cm³, the internal friction angle is affected by both the dry density and the water content. (3) The shear strength decreases when the water content exceeds the optimum level. (4) The compressive modulus of calcareous silt is larger than that of terrigenous silt. Specifically, it decreases with decreasing dry density and increasing water content. (5) The stepwise loading method should be used to estimate the soil settling before fill engineering construction.     

Role of Siliceous Fossil Dissolution in Downcore Variations of Grain Size and Water Content: Western Margin of Clarion-Clipperton Fracture Zone,NE Equatorial Pacific

Abstract

Grain size and water content in box-core sediments from the Clarion-Clipperton fracture zone (C-C zone) in the northeast equatorial Pacific were analyzed in detail to understand the downcore variations across a hiatus between Quaternary and Tertiary layers. Grain-size distributions in the topmost core sediments show two modes: a coarse mode (peaked at 50 μm) and a fine mode (at 2–25 μm). The coarse mode disappears gradually with depth accompanied by the dissolution of siliceous fossil tests, whereas the fine mode coarsens due to the formation of authigenic minerals. Water content increases abruptly across a color boundary between an upper pale brown layer and a lower dark brown layer that is the hiatus between Quaternary and Tertiary layers. Abundant smectites and microvoid molds, which are created by the prolonged fossil dissolution in the underlying sediment, are attributed for the abrupt downcore variation of water content. Overall variations in grain size and water content in the topmost core sediments in the western C-C zone are possibly constrained by the dissolution of biogenic siliceous fossils. Variations in geotechnical properties related to these changes must be considered in the design of nodule collectors.