Determination of silica sand stiffness

Site investigation and evaluation of properties of soil or rock are important aspects of geotechnical design. Determination of the ground stiffness is one of the important parameters in geotechnical engineering. Since the measurement of shear modulus is very sensitive to soil disturbance, especially for sand, determination of the stiffness of soil in the field is more reliable than in laboratory tests on sampled specimens. Measurement of shear modulus is one of the most common applications of self-boring pressuremeter testing. As an in situ device, the pressuremeter provides a unique method for assessing directly the in situ shear modulus of a soil. This paper describes a laboratory study of silica sand stiffness, which varies with stress level and strain amplitude. The results show that the elastic shear modulus value is mainly dependent on the value of the mean effective stress and relative density.     

An experimental investigation of LNAPL migration in an unsaturated/saturated sand

Accidental spills of hydrocarbons, such as Light Non-Aqueous Phase Liquids (LNAPLs), are one of the most common sources of subsurface contamination. Migration of LNAPL in a porous medium is influenced by various factors such as the number of fluids present in the unsaturated/saturated zones and the proportion of pores occupied by each fluid. The results for relationship between matric suction and degree of saturation are presented in this paper for water–air, water–LNAPL and LNAPL–air systems in a sand. A simple and reliable setup using Buchner funnel was designed to obtain these relations. It was found that the relationship between matric suction head and degree of saturation is hysteretic for all the fluid systems (water–air, water–LNAPL and LNAPL–air). Furthermore, the amount of hysteresis depended upon the fluid system, with the maximum hysteresis occurring for water–air system. The results suggest that the amount of trapped air depends upon the reversal degree of saturation from drying to wetting.     

Wave-influenced deltas: geomorphological implications for facies reconstruction

ABSTRACT A process‐based facies model for asymmetric wave‐influenced deltas predicts significant river‐borne muds with potentially lower quality reservoir facies in prodelta and downdrift areas, and better quality sand in updrift areas. Many ancient barrier‐lagoon systems and ‘offshore bars’ may be better reinterpreted as components of large‐scale asymmetric wave‐influenced deltaic systems. The proposed model is based on a re‐evaluation of several modern examples. An asymmetry index A is defined as the ratio between the net longshore transport rate at the mouth (in m³ year^?1) and river discharge (in 10⁶ m³ month^?1). Symmetry is favoured in deltas with an index below ≈ 200 (e.g. Tiber, lobes of the Godavari delta, Rosetta lobe of the Nile, Ebro), whereas deltas with a higher index are asymmetric (e.g. Danube – Sf. Gheorghe lobe, Brazos, Damietta lobe of the Nile). Periodic deflection of the river mouth for significant distances in the downdrift direction occurs in extreme cases of littoral drift dominance (e.g. Mahanadi), resulting in a series of randomly distributed, quasi‐parallel series of sand spits and channel fills. Asymmetric deltas show variable proportions of river‐, wave‐ and tide‐dominated facies both among and within their lobes. Bayhead deltas, lagoons and barrier islands form naturally in prograding asymmetric deltas and are not necessarily associated with transgressive systems. This complexity underlines the necessity of interpreting ancient depositional systems in a larger palaeogeographic context.     

Laser Ablation ICP-MS Analysis of Geological Materials Prepared as Lithium Borate Glasses

A simple, rapid and precise method is described for determining trace elements by laser ablation (LA)-ICP-MS analysis in bulk geological materials that have been prepared as lithium borate glasses following standard procedures for XRF analysis. This approach reliably achieves complete sample digestion and provides for complementary XRF and LA-ICP-MS analysis of a full suite of major and trace elements from a single sample preparation. Highly precise analysis is enabled by rastering an ArF excimer laser (λ= 193nm) across fused samples to deliver a constant sample yield to the mass spectrometer without inter-element fractionation effects during each analysis. Capabilities of the method are demonstrated by determination of twenty five trace elements (Sc, Ti, V, Ga, Rb, Sr, Y, Zr, Nb, Cs, Ba, REE, Hf, Ta, Pb, Th and U) in a diverse range of geological reference materials that includes peridotites, basalts, granites, metamorphic rocks and sediments. More than 90% of determinations are indistinguishable from published reference values at the 95% confidence level. Systematic bias greater than 5% is observed for only a handful of elements (Zr, Nb and U) and may be attributed in part to inaccurate calibration values used for the NIST SRM 612 glass in the case of Zr and Nb. Detection limits for several elements, most notably La, are compromised at ultra-trace levels by impurities in the lithium borate flux but can be corrected for by subtracting appropriate procedural blanks. Reliable Pb analysis has proved problematic due to variable degrees of contamination introduced during sample polishing prior to analysis and from Pt-crucibles previously used to fuse Pb-rich samples. Scope exists for extending the method to include internal standard element/isotope spiking, particularly where integrated XRF analysis is not available to characterise major and trace elements in the fused lithium borate glasses prior to LA-ICP-MS analysis.     

A Reappraisal of Rb, Y, Zr, Pb and Th Values in Geochemical Reference Material BHVO-1

The geochemical reference material BHVO-1 was analysed by a variety of techniques over a six year period. These techniques included inductively coupled plasma-mass spectrometry and atomic emission spectroscopy (ICP-MS and ICP-AES, respectively), laser ablation ICP-MS and spark source mass spectroscopy. Inconsistencies between the published consensus values reported by Gladney and Roelandts (1988, Geostandards Newsletter) and the results of our study are noted for Rb, Y, Zr, Pb and Th. The values reported here for Rb, Y, Zr and Pb are generally lower, while Th is higher than the consensus value. This is not an analytical artefact unique to the University of Notre Dame ICP-MS facility, as most of the BHVO-1 analyses reported over the last ten to twenty years are in agreement with our results. We propose new consensus values for each of these elements as follows: Rb = 9.3 ± 0.2 μg g-1 (compared to 11 ± 2 μg g-1), Y = 24.4 ± 1.3 μg g-1 (compared to 27.6 ± 1.7 μg g-1), Zr = 172 ± 10 μg g-1 (compared to 179 ± 21 μg g-1), Pb = 2.2 ± 0.2 μg g-1 (compared to 2.6 ± 0.9 μg g-1) and Th = 1.22 ± 0.02 μg g-1 (compared to 1.08 ± 0.15 μg g-1).     

粘粒含量对南京粉细砂液化影响的试验研究

南京粉细砂是一种以片状颗粒成分为主的粉细砂，与通常的圆形颗粒石英砂有一定区别，片状颗粒成分使得南京粉细砂具有各向异性的性质。通过对不同粘粒含量的南京粉细砂进行液化试验，分析其试验结果发现：对于粘粒含量ρc＝5％、10％和15％三种情况，在均压固结情况下，当南京粉细砂达到初始液化时，采用变形标准和孔压标准是一致的；而偏压固结时，只能采用变形标准作为南京粉细砂达到初始液化的标准，此时振动孔压仅达到围压的50％-70％。粘粒含量对南京粉细砂的抗液化强度影响很大，随粘粒含量增加，在不同固结比时，其抗液化强度并不是单调变化，而是在粘粒含量ρc＝10％左右处于一个低谷，其抗液化强度最低。     

一次沙尘暴中尺度低压和沙尘输送的数值模拟

利用ＰＳＵ／ＮＣＡＲ中尺度数值模式（ＭＭ４），以常规观测资料为初始场，成功地模拟了造成“９４．４．５”沙尘暴天气的主要天气系统张掖热低压。并通过给原有的中尺度模式系统加入沙尘输送方程和驱动地面沙尘抬升参数化方案，用改进后的中尺度数值模式系统，成功地模拟了沙尘抬升和输送，与实况比较一致。     

砂岩岩脉(岩墙、岩床)的一种可能成因——冲蚀沟槽的充填

黄河三角洲的边滩、心滩上发育了大量冲蚀沟槽（冲槽）．这些冲蚀沟槽深数厘米至1m～2m，宽数厘米至数米，长数十厘米至十几、二十余米，但以深数十厘米，宽数厘米至十余厘米，长数米者多见。形态多样，有直立板片状、直立楔状、“⊥”状、梯形状、“U”形状及树枝状等，其内有时被风成砂充填。经成岩作用后，它们便会转变成砂岩岩脉（岩墙、岩床）。因此，冲蚀沟槽的（砂）充填可能是一种砂岩岩脉（岩墙、岩床）的形成方式．     

滇黔桂微细浸染型金矿铅同位素组成及应用

滇黔桂微细浸染型金矿铅同位素组成及应用＊刘显凡刘家军朱赖民（中国科学院地球化学研究所，贵阳５５０００２）卢秋霞（成都理工学院，成都６１００５９）关键词微细浸染型金矿铅同位素组成矿质来源上地幔分异混染滇黔桂１矿床地质背景研究区位于扬子地台西南缘与华南加...     

地气测量在内蒙老羊壕金矿区的某些试验成果

以内蒙老羊壕金矿区为试验基地 ,引进抽气法地气测量 ,探讨了地气测量在内蒙干旱荒漠区寻找浅覆盖区隐伏金矿床的有效性。并以试验资料为依据 ,初步探讨了抽气法地气测量中的若干问题 ,指出了抽气法地气测量中存在微尘颗粒干扰。对寻找隐伏金矿床的多元素地气测量 ,采用经 0 .2 2 μm微孔滤膜过滤泡沫塑料吸附为好。已有资料显示可能有超微粒 (接近纳米级 )物质自深部矿体迁移上来