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Acta Geotechnica - Dynamic loading experiments of single glass bead cement-covered by epoxy resins of different compositions demonstrate the existence of diverse fracture patterns under similar... 相似文献
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Pile foundations are frequently subjected to cyclic lateral loads. Wave and wind loads on offshore structures will be applied in different directions and times during the design life of a structure. Therefore, the magnitude and direction of these loads in conjunction with the dead loads should be considered. This paper investigates a loading scenario where a monotonic lateral load is applied to a pile, followed by two‐way cycling in a direction perpendicular to the initial loading. This configuration is indicative of the complexity of loading that may be considered and is referred to in the paper as ‘T‐shaped’ loading. The energy‐based numerical model employed considers two‐dimensional lateral loading in an elasto‐plastic soil, with coupled behaviour between the two perpendicular directions by local yield surfaces along the length of the pile. The behaviour of the soil–pile system subjected to different loading combinations has been divided into four categories of shakedown previously proposed for cyclic loading of structures and soils. A design chart has been created to illustrate the type of pile behaviour for a given two‐dimensional loading scenario. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
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Radioactive iodine is one of the most problematic radionuclides because of its long half life and high mobility. Mobility of iodine depends on the chemical form to a great extent. This paper reports the results of soil column experiments we conducted to evaluate the mobilities of IO3− and I−. In order to determine the mechanisms of adsorption of IO3− and I− on soil, adsorption isotherms were obtained by batch experiments. Both adsorption isotherms of IO3− and I− are well explained by Langmuir model. The adsorption maximum of IO3− is about five times larger than that of I−. In the column experiments, iodine distributions between soil and pore water in the soil column were determined at various depths. Chemical forms of iodine in soil and pore water were determined by X-ray absorption near-edge structure (XANES), and high performance liquid chromatography connected to inductively coupled plasma mass spectrometry (HPLC–ICP-MS), respectively. Vertical profiles of iodine in pore water were simulated using Visual MODFLOW. Our results showed, upon I− infiltration through the column, that a small amount of I− adsorbed on soil, and its mobility is mainly controlled by advection and dispersion. The profile of iodine concentration in pore water was well simulated by assuming equilibrium-controlled Langmuir type adsorption without considering any chemical transformations. For the IO3− addition system into the column, however, IO3− adsorbed to soil to a larger degree, which causes a much larger retardation effect than I−. In addition, reduction of IO3− to I− was also confirmed in both soil and pore water by XANES and HPLC–ICP-MS, respectively. The fraction of I− increased toward the deeper end in both phases because of its lower affinity for soil than IO3−, where the reduced I− was released to the pore water and transported by the water flow. In this study, such reduction effect was clearly demonstrated by the speciation analyses of iodine in both soil and water phases, which confirmed that the mobility of I− is a dominant factor that controls the fate of iodine in the surface environment. 相似文献
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Evolution and degradation of flat‐top mesas in the hyper‐arid Negev,Israel revealed from 10Be cosmogenic nuclides 
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下载免费PDF全文 Ronen Boroda Ari Matmon Rivka Amit Itai Haviv Maurice Arnold Georges Aumaître Didier L. Bourlès Karim Keddadouche Yehuda Eyal Yehouda Enzel 《地球表面变化过程与地形》2014,39(12):1611-1621
Mesas are ubiquitous landforms in arid and semiarid regions and are often characterized by horizontal stratified erodible rocks capped by more resistant strata. The accepted conceptual model for mesa evolution and degradation considers reduction in the width of the mesa flat‐top plateau due to cliff retreat but ignores possible denudation of the mesa flat‐top and the rates and mechanism of erosion. In this study we examine mesas in the northeastern hyperarid Negev Desert where they appear in various sizes and morphologies and represent different stages of mesa evolution. The variety of mesas within a single climatic zone allows examination of the process of mesa evolution through time. Two of the four sites examined are characterized by a relatively wide (200–230 m) flat‐top and a thick caprock whereas the other two are characterized by a much narrower remnant flat‐top (several meters) and thinner caprock. We use the concentration of the cosmogenic nuclide 10Be for: (a) determining the chronology of the various geomorphic features associated with the mesa; and (b) understanding geomorphic processes forming the mesa. The 10Be data, combined with field observations, suggest a correlation between the width of flat‐top mesa and the denudation and cliff retreat rates. Our results demonstrate that: (a) cliff retreat rates decrease with decreasing width of the flat‐top mesa; (b) vertical denudation rates increase with decreasing width of the flat‐top mesa below a critical value (~60 m, for the Negev Desert); (c) the reduction in the width of the flat‐top mesa is driven mainly by cliff retreat accompanied by extremely slow vertical denudation rate which can persist for a very long time (>106 Ma); and (d) when the width of the mesa decreases below a certain threshold, its rate of denudation increases dramatically and mesa degradation is completed in a short time. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献
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Tengattini Alessandro Nguyen Giang D. Viggiani Gioacchino Einav Itai 《Acta Geotechnica》2023,18(1):57-75
Acta Geotechnica - This paper presents an experimental and analytical/numerical study of the mechanics of cemented granular materials (CGMs). This study incorporates both in situ X-ray tomography... 相似文献
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The Energetics of Cataclasis Based on Breakage Mechanics 总被引：1，自引：0，他引：1
We develop a constitutive model for rocks that are constituted from brittle particles, based on the theory of breakage mechanics. The model connects between the energetics and the micromechanics that drive the process of confined comminution. Given this ability, our model not only describes the entire stress-strain response of the material, but also connects this response to predicting the evolution of the grain size distribution. The latter fact enables us to quantify how the permeability reduces within cataclasite zones, in relation to aspects of grain crushing. Finally, our paper focuses on setting a framework for quantifying how the energy budget of earthquakes is expensed in relation to dissipation events in cataclasis. We specifically distinguish between the dissipation directly from the creation of new surface area, which causes further breakage dissipation from the redistribution of locked-in stored energy from surrounding particles, dissipations from friction and from the configurational reorganisation of particles. 相似文献
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Yuval Shmilovitz Efrat Morin Yair Rinat Itai Haviv Genadi Carmi Amit Mushkin Yehouda Enzel 《地球表面变化过程与地形》2020,45(7):1644-1659
Documenting hillslope response to hydroclimatic forcing is crucial to our understanding of landscape evolution. The evolution of talus-pediment sequences (talus flatirons) in arid areas was often linked to climatic cycles, although the physical processes that may account for such a link remain obscure. Our approach is to integrate field measurements, remote sensing of rainfall and modeling to link between storm frequency, runoff, erosion and sediment transport. We present a quantitative hydrometeorological analysis of rainstorms, their geomorphic impact and their potential role in the evolution of hyperarid talus-pediment slopes in the Negev desert, Israel. Rainstorm properties were defined based on intensity–duration–frequency curves and using a rainfall simulator, artificial rainstorms were executed in the field. Then, the obtained measured experimental results were up-scaled to the entire slope length using a fully distributed hydrological model. In addition, natural storms and their hydro-geomorphic impacts were monitored using X-band radar and time-lapse cameras. These integrated analyses constrain the rainfall threshold for local runoff generation at rain intensity of 14 to 22 mm h-1 for a duration of five minutes and provide a high-resolution characterization of small-scale runoff-generating rain cells. The current frequency of such runoff-producing rainstorms is ~1–3 per year. However, extending this local value into the full extent of hillslope runoff indicates that it occurs only under rainstorms with ≥ 100-years return interval, or 1% annual exceedance probability. Sheetwash efficiency rises with downslope distance; beyond a threshold distance of ~100 m, runoff during rainstorms with such annual exceedance probability are capable of transporting surface clasts. The erosion efficiency of these discrete rare events highlights their potential importance in shaping the landscape of arid regions. Our results support the hypothesis that a shift in the properties and frequency of extreme events can trigger significant geomorphic transitions in areas that remained hyperarid during the entire Quaternary. © 2020 John Wiley & Sons, Ltd. 相似文献