Analysis of the critical pool level of partially submerged slopes     

Wei Wang  D.V. Griffiths 《国际地质力学数值与分析法杂志》2020,44(3):405-417

Partially submerged c^′ − φ^′ slopes with a horizontal water table exhibit a critical pool level at which the factor of safety becomes a minimum. The phenomenon was first identified using finite element methods, but in this paper, a more thorough analytical investigation is presented. The approach described herein assumes a rigid block sliding with a circular failure mechanism, combined with optimization software to identify the critical circle. The method is initially validated against known slope solutions that assume circular and log-spiral mechanisms and shown to give excellent agreement, especially for flatter slopes. The method is then applied to partially submerged slopes with a focus on the critical pool level. Through detailed investigation of the overturning and restoring moments in the stability analyses, the critical pool level phenomenon is shown to lie in the trade-off between the destabilizing effects of internal pore pressures on soil strength and the stabilizing effect of external hydrostatic water pressures on the slope surface.  相似文献   

Dynamic domain kinematic modelling for predicting interflow over leaky impeding layers     

Menberu Meles Bitew  C. Rhett Jackson  David C. Goodrich  Seth E. Younger  Natalie A. Griffiths  Kellie B. Vaché  Benjamin Rau 《水文研究》2020,34(13):2895-2910

Traditional Boussinesq or kinematic simulations of interflow (i.e., lateral subsurface flow) assume no leakage through the impeding layer and require a no-flow boundary condition at the ridge top. However, recent analyses of many interflow-producing landscapes indicate that leaky impeding layers are common, that most interflow percolates well before reaching the toe slope, and therefore, the downslope contributing length is shorter than the hillslope length. In watersheds characterised by perched interflow over a low conductivity layer through permeable topsoil, interflow with percolation may be modelled with a kinematic wave model using a mobile upslope boundary condition defining the hillslope portion contributing interflow to valleys. Here, we developed and applied a dynamic interflow model to simulate interflow using a downslope travel distance concept such that only the active contributing length is modelled at any time. The model defines a variable active area based on the depth of the perched layer, the topographic slope and the ratio of the hydraulic conductivity of topsoil to that of the impeding layer. It incorporates a two-layer soil moisture accounting water balance analysis, a pedo-transfer function, and percolation and evaporation routines to predict interflow rates in continuous and event-based scenarios. We tested the modelling concept on two sets of data (2-year dataset of rainfall observations for the continuous simulation and a multi-day irrigation experiment for the event simulation) from a 121-m-long open interflow collection trench on an experimental hillslope at the Savannah River Site, South Carolina. The continuous model simulation partially represented the observed interflow hydrograph and perched water depth in the experimental hillslope with correlation coefficients of 0.85 and 0.35, respectively. Model performance improved significantly at event-scale analysis. The modelling approach realistically represents interflow dynamics in hillslopes with leaky impeding layers and can be integrated into catchment-scale hydrology models for more detailed hillslope process modelling.  相似文献   

LunarEX—a proposal to cosmic vision     

A. Smith  I. A. Crawford  R. A. Gowen  A. J. Ball  S. J. Barber  P. Church  A. J. Coates  Y. Gao  A. D. Griffiths  A. Hagermann  K. H. Joy  A. Phipps  W. T. Pike  R. Scott  S. Sheridan  M. Sweeting  D. Talboys  V. Tong  N. Wells  J. Biele  J. Chela-Flores  B. Dabrowski  J. Flannagan  M. Grande  J. Grygorczuk  G. Kargl  O. B. Khavroshkin  G. Klingelhoefer  M. Knapmeyer  W. Marczewski  S. McKenna-Lawlor  L. Richter  D. A. Rothery  K. Seweryn  S. Ulamec  R. Wawrzaszek  M. Wieczorek  I. P. Wright  M. Sims 《Experimental Astronomy》2009,23(3):711-740

While the surface missions to the Moon of the 1970s achieved a great deal, scientifically much was also left unresolved. The recent plethora of lunar missions (flown or proposed) reflects a resurgence in interest in the Moon, not only in its own right, but also as a record of the early solar system including the formation of the Earth. Results from recent orbiter missions have shown evidence of ice or at least hydrogen within shadowed craters at the lunar poles.  相似文献   

Clay‐coat diversity in marginal marine sediments     

Luke J. Wooldridge  Richard H. Worden  Joshua Griffiths  James E. P. Utley 《Sedimentology》2019,66(3):1118-1138

The specific mineralogy of clay grain coats controls the ability of the coat to inhibit quartz cementation in sandstones during prolonged burial and heating. How and why clay‐coat mineralogy varies across marginal marine systems is poorly understood, even though these eogenetic phenomena strongly influence subsequent mesodiagenesis and reservoir quality. The novel development of the ability to predict the distribution of clay‐coat mineralogy would represent an important development for sandstone reservoir quality prediction. In marginal marine sediments, clay minerals occur as grain‐coats, floccules, mud intraclasts, clay‐rich rock fragments or as dispersed material. However, the relationships between clay mineralogy, the amount of clay, and its distribution is poorly understood. This study focused on the Ravenglass Estuary, UK. The key aim was to develop and apply a novel methodology utilising scanning electron microscope – energy dispersive spectrometry, for the first time, on grain coats in modern sediments, to differentiate the clay‐coat mineral signature from that of the bulk sediment, and reveal the distribution of clay minerals across marginal marine sediments. The study showed that marginal marine sediments principally have their clay mineral assemblage present as clay‐coats on sand grains. These clay‐coats have a mixed clay mineralogy and are spatially heterogeneous across the range of marginal‐marine depositional environments. The study further showed that clay‐coat mineralogy is governed initially by the hydrologically‐controlled segregation of the clay minerals within inner estuarine depositional environments, and subsequently by the selective abrasive removal of specific clay mineral types during reworking and transport into the outer estuary and the marine environment. The highest relative abundance of grain‐coating chlorite was in sand‐flat and tidal‐bar depositional environments. The availability of an analogue data set, and an understanding of the controlling processes of clay‐coat mineralogy, offer crucial steps in building a predictive capability for clay‐coat derived elevated reservoir quality in deeply buried sandstones.  相似文献   

Workshop on Areal Value Estimation     

H. Missan  B. R. Cooper  S. M. el Raba'a  J. C. Griffiths  C. Sweetwood 《Mathematical Geology》1978,10(5):433-439

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A laboratory analog study of the surface morphology of lava flows extruded from point and line sources     

Jonathan H. Fink  Ross W. Griffiths 《Journal of Volcanology and Geothermal Research》1992,54(1-2)

In laboratory experiments designed to model lava flow processes, liquid polyethylene glycol wax is forced through either a small hole or a long narrow slit onto the base of a tank of cold water, where it spreads laterally while cooling and solidifying at its surface. We observe the surface structure of the flow, and its dependence on the flow rate, thermal conditions and basal roughness. In each case, solidification of a crust during spreading gives rise to a number of different surface morphologies, each of which forms under a restricted range of conditions. The dominant morphologies, referred to as “pillows”, “rifts”, transverse folds, and marginal levees, correspond to features observed on natural lava flows. Results for radial spreading over a rough base and for spreading in two directions from the line source over both smooth and rough bases complement those reported earlier for radial spreading of solidifying wax from a point source on a smooth base. Together they indicate a robust dependence of morphology on the distance from the vent at which solid crust begins to form. This distance is, in turn, determined by the extrusion rate, the rheology of the liquid wax (or magma), the reduced gravity, the magnitude of the surface heat flux, and the amount of cooling required to solidify the flow surface. The results also indicate factors influencing the distribution of crust and its deformation, and may provide a means by which observations of surface morphology can be used to place constraints on the emplacement conditions of lava flows.  相似文献   

Variation in the value of mineral resources. Part I. The USA     

J. C. Griffiths  W. D. Menzie 《Mathematical Geosciences》1975,7(5-6):447-472

The value of mineral resources produced in the USA during the 93 years, 1880–1972, deflated to 1967=100, totals 921 billions of dollars; this yields a value of $303,289 per mi² for the conterminous 48 states. Alaska has aggregated some 4160 millions of dollars during the same period, an average yield of some 7107 deflated dollars per mi². If we assume Alaska will achieve the average level of the “lower 48,”the potential value of its mineral resources is 178 billions of deflated 1967 dollars. Fuels account for about two-thirds of this value followed by about 20 percent for each of the aggregates, nonmetals and metals. The deflated dollar value of these four aggregate figures, fuels, nonmetals, metals, and total, during the period 1880–1972 are four time series and the economic processes which produced these series may be modelled through Box-Jenkins procedures. The value of fuels has steadily increased through the period, except for the depression years of the 1930s; this series may be represented as a multiplicative seasonal ARIMA(1,1,0)(1,0,1) model with periods at 4 and 3 yr for the autoregressive (AR) and moving average (MA) terms. Forecasts for 1973 to 1980, using the model, show the value of fuels produced to be about 20 billions of dollars per annum. The value of nonmetals also increased throughout the period except for a somewhat larger drop during the depression years of the 1930s. A multiplicative seasonal ARMA(1,0,0)(1,0,1) model with period at 7 yr for both the AR (autoregressive) and MA (moving average) terms appears to best reflect this series; the forecasts with this model fluctuate around their present annual value of some 6 billions of dollars. The value of metals behaves less consistently; it was much more strongly affected by the Great Depression and its subsequent growth is slower and less consistent than those of the fuels and nonmetals. It is appropriately represented by a multiplicative seasonal ARMA(1,0,0)(0,0,2) model with moving average (MA) periods at 6 and 11 yr respectively. Forecasts with this model show a decline in value for years beyond 1972; the large residual “error” \((\hat \sigma _e = 0.0925)\) , which is about twice as large as the equivalent errors for the value of fuels and nonmetals ( \(\hat \sigma _e = 0.0408\) and 0.0532, respectively), makes this forecast less firm. The total value of mineral resources is composed of all three series and, because fuels account for two-thirds of the total value, the two series closely resemble each other. The total value is not a simple aggregate of the three series; it is appropriately fitted by a multiplicative seasonal IMA(0,1,0)(0,0,2) model with periods at 7 and 11 yr (and error \(\hat \sigma _e = 0.0423\) ). Forecasts using this model imply that the total value of mineral resources produced will be over 30 billions of dollars per annum through 1980.  相似文献   

Multivariate analyses of crater parameters and the classification of craters     

Barry S. Siegal  John C. Griffiths 《Earth, Moon, and Planets》1974,9(3-4):397-413

Multivariate analyses were performed on certain linear dimensions of six genetic types of craters. A total of 320 craters, consisting of laboratory fluidization craters, craters formed by chemical and nuclear explosives, terrestrial maars and other volcanic craters, and terrestrial meteorite impact craters, authenticated and probable, were analyzed in the first data set in terms of their mean rim crest diameter (D _r), mean interior relief (R _i), rim height (R _e), and mean exterior rim width (W _e ). The second data set contained an additional 91 terrestrial craters of which 19 were of experimental percussive impact and 28 of volcanic collapse origin, and which was analyzed in terms ofD _r,R _i, andR _e. Principal component analyses were performed on the six genetic types of craters; 90% of the variation in the variables can be accounted for by two components. 99% of the variation in the craters formed by chemical and nuclear explosives is explained by the first component alone. Classification using the CLUS procedure (Rubin and Friedman, 1967) indicates an optimum number of two groups; the main difference between the groups was the presence or absence of rims. The rimmed group of craters could, if desired, be subdivided on the basis of the dimension of the rim crest diameter. Several small rimless craters were classified as rimmed craters, this is believed to have resulted from the small difference in the dimension of their rim crest diameter to rim height, as contrasted with the larger rimless craters; thus, this distinction may also be size dependent. No evidence was found to support an exogenic-endogenic classification scheme of craters, with respect to the variables measured.  相似文献   

An Experimental Performance Evaluation of Spatio-Temporal Join Strategies   总被引：1，自引：0，他引：1  

Seung-Hyun Jeong  Norman W. Paton  Alvaro A. A. Fernandes  Tony Griffiths 《Transactions in GIS》2005,9(2):129-156

Many applications capture, or make use of, spatial data that changes over time. This requirement for effective and efficient spatio‐temporal data management has given rise to a range of research activities relating to spatio‐temporal data management. Such work has sought to understand, for example, the requirements of different categories of application, and the modelling facilities that are most effective for these applications. However, at present, there are few systems with fully integrated support for spatio‐temporal data, and thus developers must often construct custom solutions for their applications. Developers of both bespoke solutions and of generic spatio‐temporal platforms will often need to support the fusion of large spatio‐temporal data sets. Supporting such requests in a database setting involves the use of join operations with both spatial and temporal conditions – spatio‐temporal joins. However, there has been little work to date on spatio‐temporal join algorithms or their evaluation. This paper presents an evaluation of several approaches to the implementation of spatio‐temporal joins that build upon widely available indexing techniques. The evaluation explores how several algorithms perform for databases with different spatial and temporal characteristics, with a view to helping developers of generic infrastructures or custom solutions in the selection and development of appropriate spatio‐temporal join strategies.  相似文献   

Quantitative estimates of the geology of large regions and their application to mineral-resource assessment     

John C. Griffiths  A. D. Pilant  Chester M. Smith 《Natural Resources Research》1997,6(3):157-236

The unit regional value of the mineral resources of a large region may be estimated by accumulating past production records and prorating them over the area of the region. The geological characteristics of a large region is a prime conditioning variable for this purpose. To be useful, however, the geology of a large region must be represented in a standardized form. The “geology,” as here measured, refers to a standardized set of rock types common to the legends in geological maps. By using standardized procedures, the legends of 413 geologic maps at 292 different scales that cover the Earth’s land surface were transformed into a set of 65 three-digit numbers. The set of numbers called the time-petrographic index is associated with the contemporaneous tectonic environments that led to the formation of the rocks and their associated mineral deposits. Application of the time-petrographic index to geologic maps leads to more precise estimates of the mineral-resource values of a large region. Deceased, June 2, 1992  相似文献