查看更多>>摘要：? 2022 Elsevier B.V.Gas-charged sediments of shallow water bodies are significant sources of atmospheric methane (CH4), an important greenhouse gas. They are a source of a permanent concern for their contribution to destabilization of coastal and aquatic infrastructure. Past accounts of gas bubbles developed in shallow muddy aquatic sediments and in their surrogates have reported a controversial occurrence of vertical as well as horizontal bubbles morphologies. Our study suggests an explanation of the apparent conundrum about preferred orientations of bubbles in muddy sediments. It is conducted by employing mechanical reaction–transport numerical model, which couples CH4 diffusion-led expansion of gas bubble and elastic-fracturing mechanical sediment response to its growth. Muddy sediment is assumed to exhibit a transverse anisotropy in fracture toughness (describing an easiness of breaking the inter particle bonds), attributed to partial or full alignment of plate-like clay particles. Bubbles growing in isotropic sediment develop a vertically oriented morphology and start their ascent once reaching their mature sizes. Under an increasing measure of anisotropy, the bubbles grow preferentially horizontally. These bubbles can coalesce with neighboring ones and form interconnected permeable horizontal gas networks, as observed in some lab experiments. For the first time, our results suggest that anisotropy-led lateral bubble growth can also play a crucial role in accumulating gas reserve from long distances around large and small scale outlets in aquatic sediments. Moreover, in contrast to the vertical bubbles, horizontal bubbles tend to be stationary, thus being responsible for high gas storage capacity of anisotropic sediments.
查看更多>>摘要：? 2022 Elsevier B.V.To capture the 3D morphological features of drying soils, we explore the potential of using a structured light scanner. Bentonite clay is used for desiccation tests. Both 2D images and 3D scans are obtained at certain time intervals throughout the test. We develop a post-processing methodology to quantify the 2D and 3D features of soil cracking, including surface crack ratio, total volume, surface area, and fractal dimension. Experimental results validate that the structured light scanner enables 3D high-resolution and accurate scanning of the soil desiccation cracking patterns. The change of 3D soil volume is more influenced by the widening of desiccation cracks, with slower soil volume reduction corresponding to the moment when primary cracks propagate vertically downwards. The spatiotemporal evolution of 3D reconstructed model indicates that the soil surface shrinks first, more in the central region and less along the boundaries due to the boundary constraint, before crack initiates and propagates. Both surface area and fractal dimension increase monotonically before the evaporation stops, with both more susceptible to the change of crack depth rather than crack width. Through presenting a new approach for soil desiccation cracking analysis, this study is expected to provide new insights into the soil desiccation process.
查看更多>>摘要：? 2022 Elsevier B.V.The salinization of agricultural soil is a common issue of concern. However, the coupling relationship between soil chemical properties and mechanical behavior has been largely ignored. A constant water content triaxial test was conducted by controlling suction on unsaturated agricultural soils collected from paddy fields. The soil samples were diluted with different salt solutions (a distilled water, a sodium chloride (NaCl) solution and a calcium chloride (CaCl2) solution) to investigate the influence of salinity on the mechanical behavior of soils. The pore water pressure of silt loam was significantly influenced by the pore water salinity, while the pore water pressure of silty clay was significantly influenced by the net normal stress. The results showed that the salt type and concentration significantly affected the cohesion value of silt loam. An empirical constitutive model that incorporated osmotic suction was presented in this paper to explain and quantify the effect of pore water salinity on the shear strength of silt loam. Osmotic suction was considered an independent stress variable in the constitutive model, unlike the salt type and concentration. The Barcelona unsaturated constitutive model explained how the pore water salinity affected the mechanical behavior of agricultural silt loam. With an increase in the osmotic suction in silt loam, the yield surface expanded to both sides of the original ellipses, resulting in an increase in cohesion. The constitutive framework considering osmotic suction provides an improved prediction of the mechanical behavior of agricultural soil under natural conditions subjected to salinization/desalinization. This framework can be implemented in a stabilization plan when the soil and salt are involved in agricultural activities.
查看更多>>摘要：? 2022 Elsevier B.V.The problem of fluid flow in a single fracture with variable aperture is analyzed from a stochastic point of view. The spatially distributed fracture aperture is treated as a random variable and the random aperture process can be characterized as a zero-order intrinsic random process (nonstationary random process with homogeneous increments), resulting in nonstationary flow fields. To characterize the stochastic behavior of the flow process, the general solutions for the mean values of and variances of the pressure head and the integrated flux in the mean flow direction are derived. These derivations are performed using the Fourier-Stieltjes representation approach. The mean is an unbiased estimator and the variance can be used to characterize the uncertainty of the mean model. The theory is applied to the case where the process of random aperture can be described as fractal Brownian motion. The analysis shows that the larger the parameter H, the greater the variance of pressure head and integrated flux. The transfer function helps smooth out much of the small-scale variation caused by the random aperture field. The variance (uncertainty) of the integrated flux in x-direction around the mean flux (or the classical deterministic model solution) increases with distance. Estimation of total flux through a natural fractured system is often evaluated for the purpose of rational management of groundwater resources. The proposed stochastic theory for flow prediction under uncertainty under the natural field conditions as input to the flow model for a fractured system should provide useful information for regional groundwater resource management. To our knowledge, the subject of fluid flow in nonstationary random flow fields has not yet been addressed in fracture. Our findings will be useful for the interpretation of real field data and as a stimulus for further research in this area.
查看更多>>摘要：? 2022 Elsevier B.V.The impact behavior of superspeed granular flows is not sufficiently understood, although it is the basis for establishing an impact model, which is important in barrier design. Centrifuge-based modeling is a promising tool for reproducing the superspeed nature of a granular flow under a prototype stress condition. Therefore, this study established a novel centrifuge model to investigate the effect of flow speed and volume on the impact behavior of superspeed granular flows. To further verify our centrifuge modeling results and reveal more details of granular impact dynamics, a DEM-based numerical model operated under an actual centrifugal field and Coriolis field was used. The results reveal that the interparticle interaction consumed most of the granular flow energy in three ways: dead zone deformation, particle collision within the subsequent flow, and flow–dead-zone interaction, accounting for 8%, 82%, and 10%, respectively. The failure mode of the formed dead zone varied during the debris–barrier interaction, and a static failure mode is proposed to conservatively estimate the action force exerted by the dead zone. The total force on the barrier should include three main parts: the force caused by the self-weight of the dead zone, the force caused by the direct impact of granular flow after climbing on the ramp formed by the dead zone, and the force transmitted by the dead zone and generated by the interaction between the dead zone and the subsequent flow. The third part is also important because it may account for a considerable portion of the total force (the percentage may depend on the dynamic characteristics of granular flow), but is not sufficiently addressed in existing impact models. Additionally, we found that a scale model under the reduced stress condition may underestimate the impact force; therefore, centrifuge-based modeling with a passive Coriolis condition is encouraged for investigating the impact behavior of superspeed granular flows.
查看更多>>摘要：? 2022 Elsevier B.V.It is widely recognised that the engineering behaviour of soils is a function of its structure. In residual soils, which are those derived from the in situ weathering of the mother rock and have not been transported from its formation site, the structure varies with the weathering degree of the material. It is also known that residual soils are usually unsaturated in nature. This study presents and discusses results of mercury intrusion porosimetry tests and soil-water retention tests performed in three sets of samples of a phacoidal gneiss residual soil, each one weathered to a different degree as preliminary defined through field observations and confirmed through extensive laboratory characterization tests and microtomography images. Based on a simplified definition of porosity ranges and through the introduction of a new porosity index, it is shown that the weathering degree affects, in differing ways, pores distribution and soil-water retention characteristics of the double-structure type of tested soils.
查看更多>>摘要：? 2022 Elsevier B.V.Social and economic losses induced by landslides can be reduced by means of effective planning and management. A series of landslide management projects have been implemented for landslide risk reduction since 1977 in Hong Kong. The effectiveness of the landslide management projects needs to be quantified to promote the experience for decision-making. In this study, a database of landslide-induced consequences in Hong Kong from 1984 to 2015 is first compiled. Then the effectiveness of landslide management projects in Hong Kong is evaluated from the implications of the relationship between rainfall and landslide consequences. A new method is proposed to detect the turning years for the management projects by evaluating the coefficient of variation (COV) of dissimilarity. The results are compared to the implementations of landslide management projects in Hong Kong and further verified by the consequences caused by 6 types of slopes. The landslide posed high risks before 2009 and exhibited a decreasing trend. After 2009, the landslide-induced consequences became very small. The years 1992, 2000, and 2008 are identified as the key turning years for landslide management using the proposed method. The landslide management projects work effectively when launched about every eight years. The turning years detected based on proximity of rainfall and landslide-induced consequences agree well with the timings of management projects. The initial Landslip Prevention Measures Programme (LPMP) launched in 1977 might have already reached its limit in 1992. More effort should be put into preventing landslide-caused road failures.
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