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A first pass workflow for placing cover sequence materials into four broad lithological groups using A-CNK-FM (Al2O3-CaOþNa2OþK2O-Fe2O3þMgO) and A-CN-K (Al2O3-CaOþNa2O-K2O) ternary diagrams in conjunction with the SiO2 vs Al2O3, Fe2O3 and CaO plus the Ca versus Sr XY diagrams has been derived from lithological logging and laboratory whole-rock geochemistry of 2346 samples. These lithological groups include siliciclastics (quartz sands and clays), weathered material, carbonate lithologies (marine limestone, pedogenic carbonate and compositions intermediate between the two end members) and ferruginous lithologies (including ferricrete and ferruginous sediments). Depositional, weathering and groundwater processes influence sample geochemistry during or after the formation of the material and will influence where the sample will plot on the geochemical diagrams used in this study. Geochemical data for discrete lithologies targeted during sampling (e.g. carbonate lithologies) clusters on diagrams used in the geochemical workflow, whereas data from targeted stratigraphic horizons (e.g. basement-cover interface) are more variable. The ability to characterise rock types that are texturally defined using the geochemical workflow is limited. For instance, the geochemistry of diamictite/conglomerate samples is dependent on the matrix versus clast content and composition as well as the source rock and catchment area. This workflow has the potential to be applied in a mineral exploration environment for rapid interpretation of real-time geochemical (e.g. portable XRF) data to gain an understanding of background geochemistry and geochemical signatures that may be related to underlying mineralisation. [ABSTRACT FROM AUTHOR]

The surfaces of soil grains are not perfectly smooth, especially examined at small scale. In geotechnical engineering, surface roughness has been found to be able to influence the inter-particle friction angle at micro scale and small-strain stiffness at macro scale. However, the quantity and quality of the studies on surface roughness of natural soils are still limited. In this study, the evolution of surface roughness of natural sand grains with increasing normal load was investigated by a single-particle compression apparatus. Thirty Leighton Buzzard sand (LBS) grains coarser than 2·36 mm were tested, and the surface roughness was measured before and after compression by an optical interferometer. The deformations of the asperities and of the bulk of the sand grains in the vicinity of the contact were mapped. Three stages were identified as the normal load increased: (a) plastic deformation of the asperities; (b) asperities and bulk plastic deformation; and (c) bulk only plastic deformation. At very small normal load, only the asperities were found to deform plastically, and the surface roughness of the sand grains decreases due to the flattening of the asperities. Within this regime, the load–displacement relationship of LBS grains under compression could be simulated by the modified Hertz model, which takes surface roughness into consideration. With increasing normal load, the bulk of the sand grains began to yield near the contact. The geometry of the surfaces of LBS grains in contact with the loading platen is the main factor that influences the plastic deformation of the bulk. Differently from the plastic deformation of the asperities, the plastic deformation of the bulk could both smoothen and roughen the surfaces. When plastic deformation of the bulk occurred, both Hertz and modified Hertz theory could not predict the load and displacement relationship of sand grains. Through analysing the cumulative distributions of surface roughness of 30 LBS grains at different normal loads by the Weibull function, the surface roughness was found to decrease dramatically with increasing normal load at first and then tended to be constant. [ABSTRACT FROM AUTHOR]

The particle morphology of granular materials comprises different characteristic scales, including particle shape and surface texture. Different methods have been proposed to characterise the morphology using three-dimensional parameters, among which is the fractal method. These methods, however, are applied either at the scale of particle shape or surface texture. A framework unifying the multi-scale morphology obtained from different measuring instruments could advance the current understanding to this topic, but is still lacking. This paper proposes a novel methodology to characterise the morphology of sand particles across different scales based on results from two previously adopted instruments with different measuring capabilities – an X-ray micro-computed tomography (μCT) and a high-resolution optical microscope equipped with an interferometer. The methodology is applied to sand-sized particles of a crushed granitic rock and a natural quarzitic sand (Fujian sand). By using spectrum analysis on data from both μCT and interferometer measurements, a single fractal dimension is found linking the spectrum of the two measurements for the crushed granitic rock. For Fujian sand, two self-affine patterns are observed, which serves as a separation between particle shape and surface texture, and also indicates that the fractal dimension obtained at larger scale may not be simply extended to small scales. The translation of surface measurements into numerically reconstructed particle morphology at particle shape and surface texture scale is demonstrated by using spherical harmonic expansion and power spectral density functions. [ABSTRACT FROM AUTHOR]

Sands are naturally hydrophilic granular materials, yet, rendering them hydrophobic could lend them to a wide range of geotechnical applications. This study describes a powder-coating procedure performed after chemically modifying the surfaces of coarse, medium and fine sands and examines its effect on their hydrophobicity. The purpose is to render these granular materials more hydrophobic than what is conventionally achieved by chemical methods using a simple technique. The procedure consists of first silanising both the sands and silica powder at a similar concentration by means of an organosilane to modify their surface chemistry, then the silica powder is adhered to the sands at a mass mixing ratio to alter their hydrophobicity. Irrespective of the concentrations and mixing ratios, the powder-coating procedure enhances the hydrophobicity of sands in comparison to the sole use of the chemical method. Changes in the morphology of the sand grains, such as their particle size, particle shape and surface roughness, resulting from the powder-coating procedure are examined by means of dynamic image analysis, profilometry and scanning electron microscopy. The effects of surface chemistry, surface roughness and air on the hydrophobicity of the sands are discussed based on theoretical wetting models to analyse the experimental results. [ABSTRACT FROM AUTHOR]

The existence and failures of silty sand have been reported worldwide, and the behaviour of sand–silt mixtures at small to large strains has been intensively studied. Owing to the relatively low stress level achieved in laboratory testing, no unifying framework has yet been proposed for sand–silt mixtures. In the presented work, a crushable sand, made of pumice, was used as host sand so as to reach a unique normal compression line under pressures easily attainable in the laboratory. The sand was combined with non-plastic fines in proportions varying between 0 and 100%, and tested in compression and shearing with associated bender element testing for small-strain stiffness measurements. The unique relationship between pressure and volume on the normal compression line allowed for the normalisation of the data in a way that highlights the effects of fines irrespective of the density. It was found that once the effects of the fines on the index properties and compressibility have been cancelled, by normalising for volume, the behaviour of the sand–silt mixtures can be characterised as unique. [ABSTRACT FROM AUTHOR]

It is widely accepted that both particle shape and mineralogy could have a great effect on the particle strength. However, due to the complexity of nature grains, it is difficult to distinguish the influence of particle shape from mineralogy. This paper shows measurements of the particle shape and mineralogy of carbonate sand, completely decomposed granite, Leighton Buzzard sand and pumice sand. The particle shape of carbonate sand and completely decomposed granite is similar, but the mineral of carbonate sand is carbon dioxide while the mineral of completely decomposed granite is mica and feldspar. It is found that the single particle strength of completely decomposed granite is higher than that of carbonate sand, and the particle breakage caused by one-dimensional compressing tests of completely decomposed granite is higher than that of carbonate sand. The mineralogy of both completely decomposed granite and Leighton Buzzard sand are quartz, but completely decomposed granite is more heterogeneous, result in the single particle strength of completely decomposed granite is much lower than that of Leighton Buzzard sand. It is also found the particle breakage from the one-dimensional compression test for completely decomposed is larger than Leighton Buzzard sand. It should be noted that carbonate sand is stronger than completely decomposed granite after quantitatively analysis the particle shape, particle breakage and compressibility behavior although carbonate sand has extremely irregular shape such as a branch shape, and also several pores. On the other hand, although Leighton Buzzard sand, completely decomposed granite and also pumice sand to some extent have composition of silica, the crystal of those three is completely different, result in the strength or compressibility are quite different. It seems that particle shape is not a major factor to affect strength or compressibility, but the mineralogy could be a major factor. [ABSTRACT FROM AUTHOR]

The ultimate particle size distribution of uniform and gap-graded soils is examined on specimens of carbonate sand that were subjected to large strains in a ring shear apparatus. The gap-graded soils were seen to retain a memory of their initial grading even at large strains. The particle size distributions were plotted in double logarithmic graphs either by mass or by number computed assuming different shapes. It was not possible to find linear subsets of the data, and since the samples were found experimentally to have converged to an ultimate grading, this suggests that the initial bimodal distribution prevented reaching an ultimate fractal distribution. Plots of the probability density functions of the particle sizes before and after shearing show the evolution of the gap-graded soils from a bimodal to a multi-modal distribution. This is accompanied by an evolution of the shape of the particles, visible in microphotographs and projections of the grains before and after test. [ABSTRACT FROM AUTHOR]

The surface of soil grains is not smooth especially when examined at growing smaller scales. In geotechnical engineering there is increasing evidence of the significant role of surface roughness on the micro-mechanical behaviour of particulate samples. Characterizing the particles roughness is therefore an essential and pivotal step in the investigation on its role. Previous studies on the surface roughness generally used the optical interferometer and the roughness was calculated from the roughness profile which was separated from the measured surface profile so that the features at larger scale were not taken into account for the roughness. However, the approach used in this separation procedure is not clear, in particular that to what scale should features that contribute to the roughness be considered, and it may influence the roughness measured. Most research has been performed on engineered surfaces, but when applied to natural sand surfaces which are complex and mostly curved in nature, more uncertainties arise. In this paper, an alternative method is proposed which characterizes roughness with the aid of the power spectrum of the whole surface profile of sand particles. Results from natural quartzitic sand (Leighton Buzzard sand) tested using a high-resolution optical interferometer are presented. Fractal analysis was involved in the characterization. It was found that the sand roughness could be adequately characterized by the power spectrum and the fractal dimension calculated from a cut-off length scale that was inferred from surface area estimation [ABSTRACT FROM AUTHOR]

The surface roughness of soil grains affects the mechanical behaviour of soils, but the characterization of real soil grain roughness is still limited in both quantity and quality. A new method is proposed, which applies the power spectral density (PSD), typically used in tribology, to optical interferometry measurements of soil grain surfaces. The method was adapted to characterize the roughness of soil grains separately from their shape, allowing the scale of the roughness to be determined in the form of a wavevector range. The surface roughness can be characterized by a roughness value and a fractal dimension, determined based on the stochastic formation process of the surface. When combined with other parameters, the fractal dimension provides additional information about the surface structure and roughness to the value of roughness alone. Three grain sizes of a quarzitic sand were tested. The parameters determined from the PSD analysis were input directly into a Weierstrass–Mandelbrot function to reconstruct successfully a fractal surface. [ABSTRACT FROM AUTHOR]

Seven reconstituted sands of different mineralogies and different particle size distributions, from uniform to well-graded and coarse to fine, were tested under one-dimensional compression, with and without reinforcement by discrete fibres. The compressibility, the particle breakage and the associated change in particle shape were examined in the sands with and without reinforcement. Each reconstituted sand was found to have a unique normal compression line. The compressibility increased with increasing uniformity and with larger mean diameters, thus coarse uniform sands were found to be the most compressible. They also underwent more breakage of particles, which was more significant in the weaker carbonate sands. At the grain scale, the addition of fibres seemed to reduce the amount of particle breakage in the soil, more significantly in well-graded sands. A unique NCL was found for each fibre-reinforced sand, parallel to that of the corresponding non-reinforced sand. A strong correlation was found between the ability of the fibres to prevent particle breakage and their ability to limit changes in particle shape. [ABSTRACT FROM AUTHOR]

The transitional fines content is the boundary between fines-dominated and sand-dominated behaviour. Experimental and calculation methods for the determination of the transitional fines content of sand-non plastic fines mixtures are summarized based on former studies. Different methods have been applied to data from several published sources in order to make a comparison. The results indicate that the calculation methods, which use the property indices of the sand and fines, may not always predict the value of the transitional fines content observed in laboratory tests. These differences and their possible causes are discussed. The relative size of the fines and sand particles has been considered as a parameter which influences the value of the transitional fines content. The analysis indicates that when the ratio of large to small grain diameter is large enough, the value of the transitional fines content remains within a relatively small range. [ABSTRACT FROM AUTHOR]

The compression behavior of an artificially cemented soil was analyzed by the adjusted porosity/cement index using a correlation established in the recent literature. It was found that for each value of this index, defined as the ratio of porosity to the volumetric cement content, there was a unique normal compression line (NCL). The NCLs of the cemented specimens for each adjusted porosity/cement index did not converge with the NCL of the uncemented silty sand at large stresses, but reached a line parallel to it. The NCL of the cemented sand plotted further from the NCL of the uncemented sand as the porosity/cement index decreased. [ABSTRACT FROM AUTHOR]

A never solved problem in sedimentary petrology is the origin of sandstone consisting exclusively of quartz and most durable heavy minerals. The Congo River offers an excellent test case to investigate under which tectonic, geomorphological, climatic, and geochemical conditions pure quartzose sand is generated today. In both upper and lowermost parts of the catchment, tributaries contain significant amounts of feldspars, rock fragments, or moderately stable heavy minerals pointing at the central basin as the main location of the "quartz factory". In Congo sand, quartz is enriched relatively to all other minerals including zircon, as indicated by Si/Zr ratios much higher than in the upper continental crust. Selective elimination of old zircons that accumulated radiation damage through time is suggested by low percentages of grains yielding Archean U Pb ages despite the basin being surrounded by Archean cratonic blocks. Intense weathering is documented by the lack of carbonate grains in sand and by dominant kaolinite and geochemical signatures in mud. In sand, composed almost entirely of SiO 2 , the weathering effect is masked by massive addition of quartz grains recycled during multiple events of basin inversion since the Proterozoic. Changes in mineralogical, geochemical, and geochronological signatures across Bas-Congo concur to suggest that approximately 10% of the sand supplied to the Atlantic Ocean is generated by rapid fluvial incision into the recently uplifted Atlantic Rise. The Congo River connects with a huge canyon ~30 km upstream of the mouth, and pure quartzose sand is thus funnelled directly toward the deep-sea to feed a huge turbidite fan. Offshore sediments on both sides of the canyon are not derived from the Congo River. They reflect mixed provenance, including illite-rich dust wind-blown from the arid Sahel and augite, hypersthene, and smectite ejected from volcanic centres probably situated along the Cameroon Line in the north. Because mixing of detritus from diverse sources and supply of polycyclic grains almost invariably occurs in the terminal lowland tract of a sediment-routing-system, no ancient sandstone can be safely considered as entirely first-cycle. Moreover, the abundance of pure quartzarenite in the rock record can hardly be explained by chemical weathering or physical recycling alone. The final cleansing of minerals other than quartz, zircon, tourmaline, and rutile requires one or more cycles of chemical dissolution during diagenesis, which operates at higher temperatures and over longer periods than weathering at the Earth's surface. [ABSTRACT FROM AUTHOR]