Spatial characterization of salt accumulation in early stage limestone weathering using probe permeametry     

O. Buj  J. Gisbert  J. M. McKinley  B. Smith 《地球表面变化过程与地形》2011,36(3):383-394

This research characterizes the weathering of natural building stone using an unsteady‐state portable probe permeameter. Variations between the permeability properties of fresh rock and the same rocks after the early stages of a salt weathering simulation are used to examine the effects of salt accumulation on spatial variations in surface rock permeability properties in two limestones from Spain. The Fraga and Tudela limestones are from the Ebro basin and are of Miocene age. Both stone types figure largely in the architectural heritage of Spain and, in common with many other building limestones, they are prone to physical damage from salt crystallization in pore spaces. To examine feedbacks associated with salt accumulation during the early stages of this weathering process, samples of the two stone types were subjected to simulated salt weathering under laboratory conditions using magnesium sulphate and sodium chloride at concentrations of 5% and 15%. Permeability mapping and statistical analysis (aspatial statistics and spatial prediction) before and after salt accumulation are used to assess changes in the spatial variability of permeability and to correlate these changes with salt movement, porosity change, potential rock deterioration and textural characteristics. Statistical analyses of small‐scale permeability measurements are used to evaluate the drivers for decay and hence aid the prediction of the weathering behaviour of the two limestones. Copyright © 2010 John Wiley & Sons, Ltd.  相似文献   

Microscale controls on the fate of contaminant uranium in the vadose zone, Hanford Site, Washington     

James P. McKinley  John M. Zachara  Steven C. Heald  Brian W. Kempshall 《Geochimica et cosmochimica acta》2006,70(8):1873-1887

An alkaline brine containing uranyl (UO₂²⁺) leaked to the thick unsaturated zone at the Hanford Site. We examined samples from this zone at microscopic scale to determine the mode of uranium occurrence—microprecipitates of uranyl (UO₂²⁺) silicate within lithic-clast microfractures—and constructed a conceptual model for its emplacement, which we tested using a model of reactive diffusion at that scale. The study was driven by the need to understand the heterogeneous distribution of uranium and the chemical processes that controlled it. X-ray and electron microprobe imaging showed that the uranium was associated with a minority of clasts, specifically granitic clasts occupying less than four percent of the sediment volume. XANES analysis at micron resolution showed the uranium to be hexavalent. The uranium was precipitated in microfractures as radiating clusters of uranyl silicates, and sorbed uranium was not observed on other surfaces. Compositional determinations of the 1-3 μm precipitates were difficult, but indicated a uranyl silicate. These observations suggested that uranyl was removed from pore waters by diffusion and precipitation in microfractures, where dissolved silica within the granite-equilibrated solution would cause supersaturation with respect to sodium boltwoodite. This hypothesis was tested using a reactive diffusion model operating at microscale. Conditions favoring precipitation were simulated to be transient, and driven by the compositional contrast between pore and fracture space. Pore-space conditions, including alkaline pH, were eventually imposed on the microfracture environment. However, conditions favoring precipitation were prolonged within the microfracture by reaction at the silicate mineral surface to buffer pH in a solubility limiting acidic state, and to replenish dissolved silica. During this time, uranyl was additionally removed to the fracture space by diffusion from pore space. Uranyl is effectively immobilized within the microfracture environment within the presently unsaturated Vadose Zone.  相似文献   

Tracer applications of radiocaesium in the sea of the hebrides     

I.G. McKinley  M.S. Baxter  D.J. Ellett  W. Jack 《Estuarine, Coastal and Shelf Science》1981,13(1):69-82

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Use of Variography in Permeability Characterization of Visually Homogeneous Sandstone Reservoirs with Examples from Outcrop Studies     

J. M. McKinley  C. D. Lloyd  A. H. Ruffell 《Mathematical Geology》2004,36(7):761-779

Sandstones of different ages provide economically significant oil, gas, and water reservoirs. In sandstones where heterogeneities are not visually obvious, it is particularly difficult to predict the location of permeability barriers and the scale at which high and low permeability zones occur, yet this is critical in providing information on hydrocarbon reservoir performance. This study uses variogram analysis to investigate spatial variation in permeability in visually homogeneous reservoir sandstone successions. Air permeability measurements were taken using unsteady state probe permeametry following regular grid schemes with centimeter spacing. Spatial variation in permeability was characterized using omnidirectional and directional variograms. This study combines variography with geological interpretation to assess the degree of heterogeneity of permeability in visually homogeneous sandstone successions. Variography indicates spatial dependence and short-range variation at 1 cm grid spacings that is not apparent at a larger 5 cm grid spacing in the visually homogeneous sandstones studied. The range of the models fitted to the variograms provide a potentially important index of spatial variability in permeability for different depositional settings including aeolian, fluvial, shallow marine, and marine/mass- flow turbidite.  相似文献   

Integrating aerial geophysical data in multiple-point statistics simulations to assist groundwater flow models     

Neil E. M. Dickson  Jean-Christophe Comte  Philippe Renard  Julien A. Straubhaar  Jennifer M. McKinley  Ulrich Ofterdinger 《Hydrogeology Journal》2015,23(5):883-900

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Degradation of carbon disulphide (CS2) in soils and groundwater from a CS2-contaminated site     

Siobhan F. Cox  John D. McKinley  Andrew S. Ferguson  Gwen O’Sullivan  Robert M. Kalin 《Environmental Earth Sciences》2013,68(7):1935-1944

This study is the first investigation of biodegradation of carbon disulphide (CS₂) in soil that provides estimates of degradation rates and identifies intermediate degradation products and carbon isotope signatures of degradation. Microcosm studies were undertaken under anaerobic conditions using soil and groundwater recovered from CS₂-contaminated sites. Proposed degradation mechanisms were validated using equilibrium speciation modelling of concentrations and carbon isotope ratios. A first-order degradation rate constant of 1.25 × 10^?2 h^?1 was obtained for biological degradation with soil. Carbonyl sulphide (COS) and hydrogen sulphide (H₂S) were found to be intermediates of degradation, but did not accumulate in vials. A ¹³C/¹²C enrichment factor of ?7.5 ± 0.8 ‰ was obtained for degradation within microcosms with both soil and groundwater whereas a ¹³C/¹²C enrichment factor of ?23.0 ± 2.1 ‰ was obtained for degradation with site groundwater alone. It can be concluded that biological degradation of both CS₂-contaminated soil and groundwater is likely to occur in the field suggesting that natural attenuation may be an appropriate remedial tool at some sites. The presence of biodegradation by-products including COS and H₂S indicates that biodegradation of CS₂ is occurring and stable carbon isotopes are a promising tool to quantify CS₂ degradation.  相似文献   

Variable weathering response in sandstone: factors controlling decay sequences     

P. A. Warke  J. McKinley  B. J. Smith 《地球表面变化过程与地形》2006,31(6):715-735

Differences in weathering response characteristics of fine‐ and coarse‐grained Stanton Moor sandstone samples were assessed in a laboratory weathering simulation experiment using a variable combination of salt weathering and freeze/thaw cycles. Preliminary analysis of permeability characteristics identified similar mean values for each type of Stanton sandstone but significant differences in the range of values between the two sample sets, with coarse‐grained samples of Stanton Moor sandstone displaying a restricted range of values in comparison to fine‐grained samples which showed much greater within‐block variation. Data indicated that the greater the range in initial permeability values, the greater the potential for salt and moisture ingress and retention and hence eventual disruption of the fabric of the stone. Experimental data also identified different stages in decay sequences, with significant structural change occurring during the initial preparatory stage before material breakdown and loss became apparent. Evidence suggests that relatively minor structural and mineralogical differences between samples of the same stone type can have a significant influence on weathering behaviour, resulting in distinct rates and patterns of breakdown. Copyright © 2005 John Wiley & Sons, Ltd.  相似文献   

Geostatistical analysis in weathering studies: case study for Stanton Moor building sandstone     

Jennifer M. McKinley  Patricia Warke  Christopher. D. Lloyd  Alastair H. Ruffell  Bernard J. Smith 《地球表面变化过程与地形》2006,31(8):950-969

Geostatistical techniques for spatial prediction and spatial simulation have been used in an innovative application to the study of weathering of natural building stone. The study investigates the differences in the spatial variation of permeability characteristics between fine‐ and coarse‐grained Stanton Moor building sandstone. Non‐destructive permeability measurements, using an unsteady‐state Portable Probe Permeameter, were made on three adjacent faces of two cubic blocks representative of fine‐ to medium‐grained and medium‐ to coarse‐grained Stanton Moor Sandstone. The findings provide greater understanding in the investigation of the durability characteristics of the Stanton Moor Sandstone and show that the spatial distribution and variability of permeability is more important in predicting the overall strength and weathering properties than mean permeability and absolute minimum and maximum values. The results suggest that both primary textural characteristics (such as grain size) and extent of cementation appear to be important factors in determining the overall durability properties of Stanton Moor Sandstone as a building stone. Geostatistical analysis has been shown to be an important tool in the characterization of spatial variation for the investigation of weathering of building stones. Copyright © 2006 John Wiley & Sons, Ltd.  相似文献   

Discussion of “In absurdum: long-term predictions and nuclear waste handling”: By N.A. Mörner (Vol. 61, pp. 75–82)     

I. G. McKinley  R. Munier   《Engineering Geology》2003,68(3-4):401-403

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Relative timing of tropical storm lifetime maximum intensity and track recurvature     

J. L. Evans  K. McKinley 《Meteorology and Atmospheric Physics》1998,65(3-4):241-245

Summary An intriguing picture is emerging of coupled track and intensity links in tropical cyclones. Since recurvature represents a dramatic track shift, recurving tropical storms are isolated in this study and their time of maximum lifetime intensity is compared to their time of recurvature. Thirty-one percent of all western North Pacific tropical storms and 28% of all such storms in North Atlantic recurve. Seventeen years of track and intensity data for recurving tropical cyclones in these basins are examined here.The overwhelming majority (80%) of western North Pacific tropical storms (including typhoons) reach their lifetime maximum intensity prior to recurvature. More than 45% of all recurving storms have coincident recurvature and lifetime maximum intensity, with weaker tropical storms clearly more likely to reach peak intensity at recurvature than strong systems.Inspection of tropical storm intensity and track data for North Atlantic systems reveals few clear patterns. The most robust observation to be made here is that the majority of these systems reach their peak intensity prior to recurvature. Exclusion of landfalling extratropically transforming tropical cyclones from this sample greatly reduces the number of systems, making the significance of any results questionable.With 2 Figures  相似文献