Effects of grain morphology on critical state: a computational analysis     

Alex X. Jerves  Reid Y. Kawamoto  José E. Andrade 《Acta Geotechnica》2016,11(3):493-503

We introduce a new DEM scheme (LS-DEM) that takes advantage of level sets to enable the inclusion of real grain shapes into a classical discrete element method. Then, LS-DEM is validated and calibrated with respect to real experimental results. Finally, we exploit part of LS-DEM potentiality by using it to study the dependency of critical state (CS) parameters such as critical state line (CSL) slope \(\lambda \), CSL intercept \(\varGamma \), and CS friction angle \(\varPhi _{\mathrm{CS}}\) on the grain’s morphology, i.e., sphericity, roundness, and regularity. This study is carried out in three steps. First, LS-DEM is used to capture and simulate the shape of five different two-dimensional cross sections of real grains, which have been previously classified according to the aforementioned morphological features. Second, the same LS-DEM simulations are carried out for idealized/simplified grains, which are morphologically equivalent to their real counterparts. Third, the results of real and idealized grains are compared, so the effect of “imperfections” on real particles is isolated. Finally, trends for the CS parameters (CSP) dependency on sphericity, roundness, and regularity are obtained as well as analyzed. The main observations and remarks connecting particle’s morphology, particle’s idealization, and CSP are summarized in a table that is attempted to help in keeping a general picture of the analysis, results, and corresponding implications.  相似文献   

Tailings composition effects on shear strength behavior of co-mixed mine waste rock and tailings   总被引：1，自引：0，他引：1  

Megan M. Jehring  Christopher A. Bareither 《Acta Geotechnica》2016,11(5):1147-1166

The objective of this study was to evaluate the effect of mine tailings composition on shear behavior and shear strength of co-mixed mine waste rock and tailings (WR&T). Crushed gravel was used as a synthetic waste rock and mixed with four types of tailings: (1) fine-grained garnet, (2) coarse-grained garnet, (3) copper, and (4) soda ash. Co-mixed WR&T specimens were prepared to target mixture ratios of mass of waste rock to mass of tailings (R) such that tailings “just filled” interparticle void space of the waste rock (i.e., optimum mixture ratio, R _opt). Triaxial compression tests were conducted on waste rock, tailings, and mixed waste at effective confining stresses (\(\sigma_{\text{c}}^{{\prime }}\)) ranging from 5 to 40 kPa to represent stresses anticipated in final earthen covers for waste containment facilities. Waste rock and co-mixed WR&T specimens were 150 mm in diameter by 300 mm tall, whereas tailings specimens were 38 mm in diameter by 76 mm tall. Shear strength was quantified using effective stress friction angles (?′) from undrained tests: ?′ for waste rock was 37°, ?′ for tailings ranged from 34° to 41°, and ?′ for WR&T mixtures ranged from 38° to 40°. Thus, shear strength of co-mixed WR&T was comparable to waste rock regardless of tailings composition. Shear behavior of WR&T mixtures was a function of R and tailings composition. Tailings influenced shear behavior for R < R _opt and when tailings predominantly were silt. Shear behavior was influenced by waste rock for R ≥ R _opt and when tailings predominantly were sand or included clay particles.  相似文献   

Numerical analysis of 1D coupled infiltration and deformation in layered unsaturated porous medium     

L. Z. Wu  G. G. Liu  L. C. Wang  L. M. Zhang  B. E. Li  B. Li 《Environmental Earth Sciences》2016,75(9):761

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Strength criterion for cross-anisotropic sand under general stress conditions     

Xilin Lü  Maosong Huang  José E. Andrade 《Acta Geotechnica》2016,11(6):1339-1350

By incorporating the fabric effect and Lode’s angle dependence into the Mohr–Coulomb failure criterion, a strength criterion for cross-anisotropic sand under general stress conditions was proposed. The obtained criterion has only three material parameters which can be specified by conventional triaxial tests. The formula to calculate the friction angle under any loading direction and intermediate principal stress ratio condition was deduced, and the influence of the degree of the cross-anisotropy was quantified. The friction angles of sand in triaxial, true triaxial, and hollow cylinder torsional shear tests were obtained, and a parametric analysis was used to detect the varying characteristics. The friction angle becomes smaller when the major principal stress changes from perpendicular to parallel to the bedding plane. The loading direction and intermediate principal stress ratio are unrelated in true triaxial tests, and their influences on the friction angle can be well captured by the proposed criterion. In hollow cylinder torsional shear tests with the same internal and external pressures, the loading direction and intermediate principal stress ratio are related. This property results in a lower friction angle in the hollow cylinder torsional shear test than that in the true triaxial test under the same intermediate principal stress ratio condition. By comparing the calculated friction angle with the experimental results under various loading conditions (e.g., triaxial, true triaxial, and hollow cylinder torsional shear test), the proposed criterion was verified to be able to characterize the shear strength of cross-anisotropic sand under general stress conditions.  相似文献   

On the simulation of multidimensional cyclic loading with intergranular strain     

M. Poblete  W. Fuentes  Th. Triantafyllidis 《Acta Geotechnica》2016,11(6):1263-1285

A sample of soil is subjected to multidimensional cyclic loading when two or three principal components of the stress or strain tensor are simultaneously controlled to perform a repetitive path. These paths are very useful to evaluate the performance of models simulating cyclic loading. In this article, an extension of an existing constitutive model is proposed to capture the behavior of the soil under this type of loading. The reference model is based on the intergranular strain anisotropy concept and therefore incorporates an elastic locus in terms of a strain amplitude. In order to evaluate the model performance, a modified triaxial apparatus able to perform multidimensional cyclic loading has been used to conduct some experiments with a fine sand. Simulations of the extended model with multidimensional loading paths are carefully analyzed. Considering that many cycles are simulated (\(N>30\)), some additional simulations have been performed to quantify and analyze the artificial accumulation generated by the (hypo-)elastic component of the model. At the end, a simple boundary value problem with a cyclic loading as boundary condition is simulated to analyze the model response.  相似文献   

3-D paleotemperature modeling of the geothermal regime of sedimentary basins: Example of the Lunskaya depression,Sakhalin Island     

Yu. V. Pyatakov  V. I. Isaev  V. I. Starostenko 《Russian Journal of Pacific Geology》2016,10(6):408-416

The task of 3-D modeling of the thermal field of a sedimentary basin during sedimentation is considered. The aim of the modeling is to determine the temperature at any point of the basin at a given moment of geological time. The mathematical model is based on a system of equations of thermal conductivity for a heterogeneous layered medium with dynamic boundaries. The conditions of the continuous temperature and thermal flow are given at the boundaries of the adjacent layers. The temperature values, which are determined by the values of the secular course of the earth temperature, are given at the upper boundary coinciding with the sedimentation surface. The thermal flow value is considered to be given at the lower boundary. The medium is approximated using a vertical triangle prism, which is accepted in algorithms of interpretation of the gravitation field and characterized by random upper and lower basements and given values of the thermal physical parameters. The equations of thermal conductivity are solved on the basis of potential theory. The precision of this algorithm is demonstrated by calculation of a test example. The thermal evolution of the sedimentary complexes and dynamics of the major zone of oil formation are reconstructed and possible errors of paleotemperature interpretations caused by ignored 3-D modeling medium are determined on the example of the sedimentary basin of the Lunskaya depression of Sakhalin.  相似文献   

Reflectance spectroscopy and remote sensing data for finding sulfide-bearing alteration zones and mapping geology in Gilgit-Baltistan,Pakistan     

Laeiq Ahmad  M. Tahir Shah  Shuhab D. Khan 《Earth Science Informatics》2016,9(1):113-121

Gilgit-Baltistan region is covering the northern most part of Pakistan where the rocks of the Kohistan-Ladakh island arc and Karakoram plate are exposed. The area has greater potential for precious and base metals deposits which are needed to be explored through spectroscopy and remote sensing techniques. Minerals and rocks can nowadays be identified through the measurement of their absorption and reflectance features by spectroscopic analysis. Spectral reflectance analysis is also very important in selecting the appropriate spectral bands for remote-sensing data analysis of unknown or inaccessible areas. In this study, reflectance spectra in the spectral range of 0.35–2.5 μm of different types of unaltered and altered rocks found in the Machulu and Astor areas of northern Pakistan were obtained using an ASD spectroradiometer. The fresh rock samples showed low spectral reflectance as compared to the altered rock samples. The minerals jarosite, goethite, and hematite showed depth of absorption minima in the range of 0.4–1.15 μm due to the presence of iron (Fe), while jarosite and limonite showed absorption depth at 2.2 μm due to the presence of hydroxyl ions (OH^¯). The clay minerals montmorillonite and illite showed absorption depth at 1.93 and 2.1 μm, respectively. Muscovite showed depth of absorption minima at 1.4 and 1.9 μm in some samples. Calcite showed deep absorption minima at 2.32 μm, while anorthite showed absorption features at 1.4, 1.9, 2.24, and 2.33 μm. Olivine showed a slight depressed absorption feature at 1.07 μm. The copper-bearing phases malachite, chrysocolla, and azurite showed, respectively, a broad absorption feature in the range of 0.6–0.9 μm, a small absorption at 1.4 μm, and a deep absorption at 1.93 μm. The unmineralized samples exhibited high reflectance in the wavelength ranges of 0.6–0.8, 1.6–1.9, 2.0–2.3, 2.1–2.25, and 2.4–2.5 μm, respectively, while the mineralized samples showed reflectance bands in the wavelength ranges of 0.4–0.6, 1.3–1.8, and 2.1–2.2 μm. On this basis, the band ratio combinations 7/5–4/3–6/3 and 7/5–6/3–4/3 of Landsat 8 and 4/7–4/3–2/1 for ASTER data were found to be very effective in the lithological differentiation of major rock units.  相似文献   

A topical evaluation and discussion of data movement technologies for data-intensive scientific applications   总被引：1，自引：1，他引：0  

Chris A. Mattmann  Luca Cinquini  Paul Zimdars  Michael Joyce  Shakeh Khudikyan 《Earth Science Informatics》2016,9(2):247-262

Transferring large volumes of information from one location to potentially many others that are geographically distributed and across varying networks is still prevalent in modern scientific data systems. This is despite the movement to push computation to the data and to reduce data movement needed to compute answers to challenging scientific problems, to disseminate information to the scientific community, and to acquire data for curation and enrichment. Because of this, it is imperative that decisions made regarding data movement systems and architectures be backed by both analytical rigor, and also by empirical evidence and measurement. The purpose of this study is to expand on the work performed by our research team over the last decade and to take a fresh look at the evaluation of multiple topical data transfer technologies in use cases derived from data-intensive scientific systems and applications in the areas of Earth science. We report on the evaluation of a set of data movement technologies against a set of empirically derived comparison dimensions. Based on this evaluation, we make recommendations towards the selection of appropriate data movement technologies in scientific applications and scenarios.  相似文献   

Comparative modelling of laboratory experiments for the hydro-mechanical behaviour of a compacted bentonite–sand mixture     

A. Millard  N. Mokni  J. D. Barnichon  K. E. Thatcher  A. E. Bond  A. Fraser-Harris  C. Mc Dermott  R. Blaheta  Z. Michalec  M. Hasal  T. S. Nguyen  O. Nasir  R. Fedors  H. Yi  O. Kolditz 《Environmental Earth Sciences》2016,75(19):1311

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Sorption behaviour of pentachlorophenol in sub-Saharan tropical soils: soil types sorption dynamics     

Bamidele I. Olu-Owolabi  Paul N. Diagboya  Chukwunonso P. Okoli  Kayode O. Adebowale 《Environmental Earth Sciences》2016,75(24):1494

In order to predict exposure risks as well as appropriate remediation strategies for pesticides in soils, knowledge of pesticides sorption processes onto various representative soils is vital. Hence, laboratory batch experiments were carried out to study sorption of a pesticide, pentachlorophenol (PCP), on five soils obtained from different sub-Saharan agro-ecological zones (AEZs) in order to understand sorption equilibrium, kinetics, and thermodynamics. Experimental data showed that sorption equilibrium was attained within 24 h. The fitting of kinetic results and equilibrium data to different models suggested partly surface adsorption and partly partitioning of PCP within voids of the various soil components. Sorption was mainly attributed to sharing or exchange of valence electrons between negatively charged PCP molecules and positively charged soil sorption sites. The sorption process was spontaneous and accompanied by decreased entropy, but was pH and temperature dependent, reducing with increase in pH and temperature. The various soils’ PCP sorption capacities were directly proportional to their cation exchange capacities. The low PCP sorption observed in these soils suggested high risk of PCP being present in soil water solution, especially at higher temperatures, which can lead to contamination of the aquifer. This risk may be higher for soils obtained from AEZs with warmer natural temperatures.  相似文献