Improved sampling of soft bottom sediments by combined box and piston coring

Field tests demonstrate that sampling of soft bottom sediments can be significantly improved by combined box coring and shipboard sampling using hand-operated piston coring. A convenient piston equipment devised for such subsampling is presented.     

Observation of core discing and in situ stress measurements; Stress criteria causing core discing

Summary Core discing was typically observed in cores recovered from near horizontal holes drilled in Palaeogene sandstones at a depth of 1055 m in the Horonai colliery, Hokkaido, Japan. We have observed disc- and ring-like cores and measured in situ stress where they were recovered. We compared the measured stress state with an empirical criterion of core discing based on Obert and Stephenson (1965) and a theoretical criterion based on Sugawara et al. (1978) and Ishida and Saito (1989). Consequently, we found that disc-like cores were recovered under lower stress state than predicted by both criteria. The stress state where ring-like cores were recovered satisfied the empirical criterion, however, it was below the critical stress state according to the theoretical criterion. These discrepancies indicate that existing stress criteria are not satisfactory and that further experimental, theoretical and field investigations are needed.     

Comparative study of sampling methods and in situ and laboratory analysis for shallow-water submarine hydrothermal systems

A primary aim for sampling of submarine hydrothermal vents is to minimize inclusion of ambient seawater. Here, we compare the results of three different sampling methods (air displacement, two-valve bottle, and syringes) for shallow submarine systems. Mixing of hydrothermal fluid with seawater is unavoidable; however, calculations based on linear mixing models allow estimation of the hydrothermal fluid end-member composition. The results show that sampling with a two-valve bottle and syringes are the best options because they allow collection of samples with a large proportion of hydrothermal fluid. Additionally, we compare the results of in situ and laboratory analyses of the fluid samples, and demonstrate that determination of chemical composition in situ is the best option for some components, as re-equilibration affects some component concentrations (i.e. bicarbonate). Conversely, silica determination in situ usually underestimates the concentration in the fluid, as it does not account for polymeric silica. Other components can be measured either in the field or in the laboratory.     

Bearing capacity of soft soil model treated with end-bearing bottom ash columns

Granular column technique is a soil improvement method used to increase the bearing capacity of a soft soil area by replacing the soil with a group of granular column materials. The by-product utilisation is a worldwide interest for sustainable infrastructure development. Bottom ash, which is a combustion deposit derived from coal burning, is a potential by-product that could be used alternatively to sand or aggregate as a green granular column material. This research is to study the potential use of the bottom ash column-improved soft clay by conducting a series of small-scale physical modelling test. The bearing capacity behaviour and failure mode of soft clay improved with end-bearing group of bottom ash columns with and without geotextile encasement are investigated. The bearing capacity of soft clay is significantly enhanced by the inclusion of bottom ash columns; that is, 239% of bearing capacity improvement is observed with only 13% of improvement area. The bulging of the bottom ash column is transferred to buckling failure with higher bearing capacity when the bottom ash column is encased by geotextile. The outcome of this research leads to the usage of bottom ash by-product as a granular column material in sustainable soil improvement technique.     

Dehydration dynamics of Ba-phillipsite: an in situ synchrotron powder diffraction study

 The stepwise dehydration process of the Ba-exchanged form of the zeolite phillipsite was studied by in situ synchrotron X-ray powder diffraction. A series of structure refinements were performed using the Rietveld method on powder diffraction data measured in the interval between 332 and 712 K. At 482 K, more than half of the water molecules were lost. The continuous water loss causes the Ba cations to migrate inside the zeolite channels in order to achieve a stable coordination with the framework oxygens. The dehydration process was completed at 663 K, where a new, completely dehydrated stable phase was detected. The temperature range of stability of this phase was more than 100 K, thanks to the stable coordination of the Ba cations with the framework oxygens. This phase is the first example of completely dehydrated zeolite containing divalent (barium) cations. Received: 8 January 2001 / Accepted: 1 November 2001     

基于岩饼几何形态测量的原地应力测定方法

岩饼是工程区高地应力的标志之一,其形状与主应力的大小和方向直接相关,岩饼出现时刻通常的应力解除法不能再用 于原地应力测量。根据国内外众多学者多年来对岩饼现象的研究成果,提出一种根据岩饼的几何形态测量初步计算三维地应力的方法。经实践验证,与同一工程区其他地应力测量方法的结果相比,岩饼几何形态测量方法确定出三维地应力的方向相差不大,倾角差值在10°以内,方位角之差小于20°,主应力大小满足岩饼出现的条件,具有简便实用的优点。     

海洋沉积地层多功能取样钻具研制

目前,海洋钻探取心主要采用提钻或绳索打捞的方式获取岩心。随着对取心质量和采取率要求越来越高,再加上海底沉积层变化多样,单一的取样器具已经不能满足当前的取样需要。为此,本文研制了一种海洋沉积地层多功能取样钻具,能够根据海底地层性质,开展低扰动、高品质的取样操作。通过海洋钻进取样试验表明,针对海底的淤泥、粘土及砂质地层,超前取样钻具、液压剪切取样钻具和半合管取样钻具能够有效获取海底的沉积层岩样,平均采取率为73.34%。研制的多功能取样钻具采用超前取样和液压压入取样技术,降低了对沉积物岩心的扰动,提升了岩心品质和采取率,为下一步的工程化应用奠定了基础。     

Modelling potential impacts of bottom trawl fisheries on soft sediment biogeochemistry in the North Sea

Bottom trawling causes physical disturbance to sediments particularly in shelf areas. The disturbance due to trawling is most significant in deeper areas with softer sediments where levels of natural disturbance due to wave and tidal action are low. In heavily fished areas, trawls may impact the same area of seabed more than four times per year. A single pass of a beam trawl, the heaviest gear routinely used in shelf sea fisheries, can kill 5–65% of the resident fauna and mix the top few cm of sediment. We expect that sediment community function, carbon mineralisation and biogeochemical fluxes will be strongly affected by trawling activity because the physical effects of trawling are equivalent to those of an extreme bioturbator, and yet, unlike bioturbating macrofauna, trawling does not directly contribute to community metabolism. We used an existing box-model of a generalised soft sediment system to examine the effects of trawling disturbance on carbon mineralisation and chemical concentrations. We contrasted the effects of a natural scenario, where bioturbation is a function of macrobenthos biomass, with an anthropogenic impact scenario where physical disturbance results from trawling rather than the action of bioturbating macrofauna. Simulation results suggest that the effects of low levels of trawling disturbance will be similar to those of natural bioturbators but that high levels of trawling disturbance prevent the modelled system from reaching equilibrium due to large carbon fluxes between oxic and anoxic carbon compartments. The presence of macrobenthos in the natural disturbance scenario allowed sediment chemical storage and fluxes to reach equilibrium. This is because the macrobenthos are important carbon consumers in the system whose presence reduces the magnitude of available carbon fluxes. In soft sediment systems, where the level physical disturbance due to waves and tides is low, model results suggest that intensive trawling disturbance could cause large fluctuations in benthic chemical fluxes and storage.     

基于拉丁方抽样及K-S检验的边坡可靠性分析

边坡稳定性是受复杂因素影响下的多维非线性问题,大多数边坡工程都存在着不确定性。大量试验和工程实践证明,影响边坡状态的因素中有许多具有显著的随机性,参数具有变异性。从概率的角度出发,结合实际工程,对于原始数据采用K-S检验法进行假设验证,确定参数变量的分布类型,克服了人为假设的误差,并分别采用Latin方抽样(LHS)法和Monte Carlo法对参数进行抽样,得到状态函数值,确定安全系数及可靠指标,对比两种抽样方法,基于LHS法模拟次数要少于Monte Carlo法,而且破坏概率的收敛性也优于Monte Carlo法,明显节省了计算时间     

渗流作用下软基心墙坝稳定性分析

基于心墙坝的渗流特性建立了渗流分析模型和坝坡渗透稳定分析模型,并进一步考虑坝下软土地基的压缩特性提出了与当前应力状态有关的软土层渗流分析模型,将所建模型应用于某水利枢纽主土坝典型软基断面不同运行工况的计算,详细分析了心墙的防渗作用和软土层变形对渗透稳定的不良影响。     

有纺土工织物加固软土地基可靠性分析

通过室内模型试验，研究了有纺土工织物加筋地基土的横向位移随深度的变化规律、加筋砂垫层的剪应力分布、加筋对地基承载力的影响，以及土工织物预应力处理后对控制地基土早期变形的作用等，还讨论了施工加质量对加固效果的影响，应用实例的成功表明，按研究成果要求实施工程处理是可行的。     

基于LSSVM与MCS的路基沉降可靠度分析

提出了一种计算路基沉降可靠度的新方法。基于FLAC中的修正剑桥模型,以最小二乘支持向量机为核心技术,结合蒙特卡罗法构建计算模型。由于修正剑桥模型参数较多,对模型参数进行了敏感性分析,将对沉降影响较大的参数确定为随机变量。选取训练样本对支持向量机进行训练,按照随机变量的概率分布进行抽样,馈送到最小二乘支持向量机得到相应的响应值,用Matlab编制程序完成可靠度计算,并进行了算例分析。计算结果表明,蒙特卡罗法结合支持向量机的沉降可靠度计算方法应用于公路软基沉降可靠度计算是可行的。     

In situ X-ray diffraction study of an aluminous phase in MORB under lower mantle conditions

In situ X-ray diffraction study was conducted to identify the crystal structure of the “Al-phase”, which was previously reported to form in basaltic compositions at pressures and temperatures of the uppermost part of the lower mantle. Le Bail whole-pattern fitting method was adopted to investigate the structure of the Al-phase under high pressure and temperature as well as ambient conditions. Observed patterns were satisfactorily fitted using the “hexagonal phase” with space group P6₃/m (plus minor amount of garnet) under both of these conditions. On the other hand, the calcium ferrite structure model proposed in some earlier studies based on quench experiments yielded profile-fitting results at significantly lower confidence levels, particularly at simultaneous high pressure and high temperature conditions, suggesting that this phase may not form in oceanic crust materials subducted in the uppermost lower mantle. The difference in densities of hexagonal and calcium ferrite phases, however, is only ~1% under pressures and temperatures of the uppermost part of the lower mantle conditions, which yields a negligible effect on the bulk density of the subducted oceanic crust.     

广东田洋古玛珥湖TY2孔基底岩芯的年龄探讨

田洋玛珥湖是雷州半岛东南部的一个洼地状旱玛珥湖,其连续、高分辨率的湖泊沉积物记录对于热带地区的古气候、古环境研究具有重要意义。1980年在湖盆中心钻取了长为224.82m(TY1孔)和22980m(TY2孔)的两个平行长钻,两孔相距约2m。除了最上部38m以内的冲-洪积沉积物及中部湖相沉积物外,222.4m(TY1)和224.4m(TY2)往下完全是湖盆基底玄武岩。因此,基底玄武岩的年龄就代表着火山喷发并随后开始形成田洋湖泊的极限年龄。     

Iron in a post-glacial lake sediment core; a Mössbauer effect study

The distribution of iron in a 6-m core of post-glacial sediment from an oligotrophic lake (Connistonwater, England) was determined, principally by Mossbauer spectroscopy on dried samples. The immediate post-glacial deposits contain 4.8 wt. % of iron, with a Fe²⁺; Fe³⁺ ratio ～- 4. The iron there is predominantly in the form of chlorite, but there are small amounts in hematite and illite. The distribution of iron is different, and very variable in the recent sediments (~ < 13,000 BP), which contain 25–35 per cent organic matter and 5.2 wt. % of iron relative to the inorganic fraction. Typically half the iron is present there as chlorite, and the rest is ferric, mostly in the form of an amorphous gel which is also present in undried samples. To explain the observed ferrous:ferric profile, it is proposed that the latter includes iron which was once mobile, having been leached from the Fe²⁺-bearing clays under reducing conditions in the soils of the drainage basin, or in the sediment itself. It was subsequently precipitated as ferric hydroxide on contact with the oxic lake water. In contrast, the ferrous iron in the sediments is immobile iron, which remained locked in the chlorite phase of the clay particles as they were carried from soil to sediment intact.All the sediments are rather inhomogeneous. Chlorite, and especially hematite, are mechanically concentrated in pink varves in the immediate post-glacial deposits. In the partly inorganic sediments, the concentration of ferrous iron (chlorite) is approximately uniform, but the ferric content may differ by a factor of five between regions only a few millimeters apart.     

不同取样直径下软土物理力学特性室内对比试验分析

以宁波市轨道交通4号线岩土工程勘察项目为依托,采用软土地区目前普遍使用的敞口薄壁取土器,对两种不同直径取样器（75、100 mm）下采取的软土开展了室内对比试验。基于室内对比试验结果,分析了两种取样直径下软土物理力学性质指标取值的差异性及其产生机理;采用附加体积应变法对两种直径下土样的扰动程度进行了分析评价。结果表明：与直径100 mm的取土器相比,直径75 mm取土器获得的土样含水量、孔隙比有一定程度降低,降低幅度均为9%;密度、压缩模量及抗剪强度指标有一定幅度的增加,增加幅度2%～21%;土样的体积应变均值分别为6.4%、6.6%,扰动程度评价均为很大;大直径取土器获得的土样较小直径土样更接近于软土实际性状。     

Simulation of an in situ iron removal test

This article outlines the main mechanisms for in-situ removal of iron from groundwater. The dependence of ferrous iron kinetic oxidation by dissolved oxygen on the temperature and pH in bicarbonate near neutral groundwater was investigated. The dependence of oxygen consumption efficiency on the iron sorption coefficient, pH, and temperature of groundwater was obtained as a result of modeling of the one well in-situ iron removal test in the Amurskiy water intake facilities.     

水源钻机在超深土层绳索取心钻进中的应用

山西省清徐县区域地质调查项目设计800、2000、3000 m科学钻探孔,以调查填补新生界底板埋深控制空白区,各孔钻入基岩30 m完钻。要求全孔取心,岩心采取率≮85%,岩心直径≮60 mm,采用塑料保护管采取原状岩样。针对超深软土层、各组地层特性及厚度未知、钻遇基岩完钻深度未知、大直径高保真全孔取心、项目价格远低于目前市场成本等难题,经过“水源钻机+大提钻取心+长裸眼孔段”实施800 m孔、“岩心钻机+绳索取心+套管固井”实施640 m参数对比孔,创新性使用“水源钻机+绳索取心+长裸眼孔段”工艺完成了2000 m孔的施工。该工艺岩心采取率达到93%,孔径和孔斜符合地质要求,为3000 m孔顺利施工打下了坚实的基础,为同类型项目提供了经验和借鉴。     

A top to bottom lithospheric study of Africa and Arabia

We study the lithospheric structure of Africa, Arabia and adjacent oceanic regions with fundamental-mode surface waves over a broad period range. Including group velocities with periods shorter than 35 s allows us to examine shallower features than previous studies of the whole continent. In the process, we have developed a crustal thickness map of Africa. Main features include crustal thickness increases under the West African, Congo, and Kalahari cratons. We find crustal thinning under Mesozoic and Cenozoic rifts, including the Benue Trough, Red Sea, and East, Central, and West African rift systems, along with less abrupt crustal thickness changes at passive continental margins. We also find crustal thickness differences in North Africa between the West African Craton and East Saharan Shield. Crustal shear wave velocities are generally faster in oceanic regions and cratons, and slower in more recent crust and in active and remnant orogenic regions. Deeper structure, related to the thickness of cratons and modern rifting, is generally consistent with previous work. Under cratons we find thick lithosphere and fast upper mantle velocities, while under rifts we find thinned lithosphere and slower upper mantle velocities. However, we also find the lack of a thick cratonic keel beneath the central portion of the Congo Craton. There are no consistent effects in areas classified as hotspots, indicating that there seem to be numerous origins for these features. Finally, it appears that the African Superswell, which is responsible for high elevation and uplift over large portions of Africa, has had a significantly different impact (as indicated by features such as temperature, time of influence, etc.) in the north and the south. This is consistent with episodic activity at shallow depths, which is well-expressed in northeastern Africa and Arabia today.