The Experts below are selected from a list of 12960 Experts worldwide ranked by ideXlab platform
Wenxin Zhu - One of the best experts on this subject based on the ideXlab platform.
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Effect of Wetting-Drying Cycle on the Deformation and Seepage Behaviors of Rock Masses around a Tunnel
Geofluids, 2020Co-Authors: Qingzhen Guo, Hongwen Jing, Wenxin ZhuAbstract:Water inrush caused by the Wetting-Drying Cycle is a difficult problem in tunnel excavation. To investigate the effect of the Wetting-Drying Cycle on the stability of the tunnel surrounding rock, physical experiments and numerical simulations regarding the process of tunnel excavation with different Wetting-Drying Cycle numbers were performed in this study. The evolutions of stress, displacement, and pore water pressure were analyzed. With the increase in Cycle number, the pore water pressure, vertical stress, and top-bottom approach of the tunnel surrounding rock increase gradually. And the increasing process could be divided into three stages: slightly increasing stage, slowly increasing stage, and sharply increasing stage, respectively. The failure process of the surrounding rock under the Wetting-Drying Cycle gradually occurs from the roof to side wall, while the baseplate changes slightly. The simulation results showed that the maximum principal stress in the surrounding rock mass of the tunnel increases, while the minimum principal stress decreases. Furthermore, the displacement of the rock mass decreases gradually with the increasing distance from the tunnel surface. By comparing the simulation results with the experimental results, well consistency is shown. The results in this study can provide helpful references for the safe excavation and scientific design of a tunnel under the Wetting-Drying Cycle.
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Influences of Saturation and Wetting-Drying Cycle on Mechanical Performances of Argillaceous Limestones from Liupanshan Tunnel, China
Advances in Materials Science and Engineering, 2019Co-Authors: Bo Meng, Hongwen Jing, Wenxin ZhuAbstract:Water-rock interaction is a vital factor to affect the stabilities of rock projects. This paper conducted a series of experiments on argillaceous limestones to investigate the influences of saturation and Wetting-Drying Cycle on the physical and mechanical performances of rocks. The results show that the increasing saturation increases the dissolution of clay minerals and lubrication among mineral grains, resulting in an obvious reduction effect on the strength and deformation performances of argillaceous limestones. Wetting-Drying Cycle increases the porosity and changes the pore structure of argillaceous limestones, leading to the pore transformation from small pore (0.01∼0.1 μm) to relatively large pore (0.1∼1.0 μm). Both the physical and mechanical performances of argillaceous limestones are weakened by the Wetting-Drying Cycle. Besides, the variation process of the physical and mechanical parameters, including mass loss, density, ultrasonic velocity, compression strength, peak strain, elasticity modulus, and secant modulus, can be divided into two stages: 0∼6th Wetting-Drying Cycle, gently changing, and 6th∼12th Wetting-Drying Cycle, drastically changing. The whole change process of these physical and mechanical parameters with the increase in the Wetting-Drying Cycle number can be expressed with the exponential function in general.
Linchang Miao - One of the best experts on this subject based on the ideXlab platform.
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research of soil water characteristics and shear strength features of nanyang expansive soil
Engineering Geology, 2002Co-Authors: Linchang MiaoAbstract:Abstract Nanyang expansive soil is investigated in its unsaturated state in this paper. The wetting–drying Cycle tests of soil–water characteristics of Nanyang expansive soil have been performed in the laboratory. The test results show that the soil–water characteristic curve of the pre-load specimen can well reflect the soil property function of expansive soil. The strength features of the different suction states of the unsaturated expansive soil are also investigated. The hyperbolic model of the suction strength is presented and the parameters of this model are easily determined by tri-axial tests of unsaturated soils. The hyperbolic model is conveniently applied to predict suction strength of an unsaturated soil.
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Research of soil–water characteristics and shear strength features of Nanyang expansive soil
Engineering Geology, 2002Co-Authors: Linchang Miao, Songyu Liu, Yuanming LaiAbstract:Abstract Nanyang expansive soil is investigated in its unsaturated state in this paper. The wetting–drying Cycle tests of soil–water characteristics of Nanyang expansive soil have been performed in the laboratory. The test results show that the soil–water characteristic curve of the pre-load specimen can well reflect the soil property function of expansive soil. The strength features of the different suction states of the unsaturated expansive soil are also investigated. The hyperbolic model of the suction strength is presented and the parameters of this model are easily determined by tri-axial tests of unsaturated soils. The hyperbolic model is conveniently applied to predict suction strength of an unsaturated soil.
David G Williams - One of the best experts on this subject based on the ideXlab platform.
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precipitation pulse use by an invasive woody legume the role of soil texture and pulse size
Oecologia, 2005Co-Authors: A Fravolini, Kevin R Hultine, Enrico Brugnoli, Rico M Gazal, Nathan B English, David G WilliamsAbstract:Plant metabolic activity in arid and semi-arid environments is largely tied to episodic precipitation events or “pulses”. The ability of plants to take up and utilize rain pulses during the growing season in these water-limited ecosystems is determined in part by pulse timing, intensity and amount, and by hydrological properties of the soil that translate precipitation into plant-available soil moisture. We assessed the sensitivity of an invasive woody plant, velvet mesquite (Prosopis velutina Woot.), to large (35 mm) and small (10 mm) isotopically labeled irrigation pulses on two contrasting soil textures (sandy-loam vs. loamy-clay) in semi-desert grassland in southeastern Arizona, USA. Predawn leaf water potential (Ψpd), the isotopic abundance of deuterium in stem water (δD), the abundance of 13C in soluble leaf sugar (δ13C), and percent volumetric soil water content (θv) were measured prior to irrigation and repeatedly for 2 weeks following irrigation. Plant water potential and the percent of pulse water present in the stem xylem indicated that although mesquite trees on both coarse- and fine-textured soils quickly responded to the large irrigation pulse, the magnitude and duration of this response substantially differed between soil textures. After reaching a maximum 4 days after the irrigation, the fraction of pulse water in stem xylem decreased more rapidly on the loamy-clay soil than the sandy-loam soil. Similarly, on both soil textures mesquite significantly responded to the 10-mm pulse. However, the magnitude of this response was substantially greater for mesquite on the sandy-loam soil compared to loamy-clay soil. The relationship between Ψpd and δ13C of leaf-soluble carbohydrates over the pulse period did not differ between plants at the two sites, indicating that differences in photosynthetic response of mesquite trees to the moisture pulses was a function of soil water availability within the rooting zone rather than differences in plant biochemical or physiological constraints. Patterns of resource acquisition by mesquite during the dynamic wetting–drying Cycle following rainfall pulses is controlled by a complex interaction between pulse size and soil hydraulic properties. A better understanding of how this interaction affects plant water availability and photosynthetic response is needed to predict how grassland structure and function will respond to climate change.
Rongguang Yu - One of the best experts on this subject based on the ideXlab platform.
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experimental investigation of the compactability and cracking behavior of polyacrylamide treated saline soil in gansu province china
Polymers, 2019Co-Authors: Tongwei Zhang, Yongfeng Deng, Fanyu Zhang, Huyuan Zhang, Chong Wang, Rongguang YuAbstract:Polyacrylamide (PAM) is a water-soluble polymer with the ability to enhance a soil’s stability. PAM is currently being used to prevent irrigation-induced erosion and enhance the infiltration in farmland soil. To improve the compaction properties of the saline-soil-based filling material that is used in highway subgrade and the cracking resistance capacity of a saline soil’s crust, the consistency limits, compactability, microstructure, and cracking morphology of untreated and PAM-treated saline soil were investigated. The saline soils were sampled from the soil crust and a depth of 2.0–3.0 m in Gansu Province, China. Two PAM concentrations (0.1% and 0.5% in mass ratio) were selected. The liquid limits and plastic limits of the saline soil samples from the surface (0–0.05 m) and a depth of 2.0–3.0 m noticeably increased as PAM concentration increased. The maximum dry densities decreased as PAM concentration and plasticity increased, and the optimum water contents of the two saline soil types did not significantly change. These results suggest that a higher shearing resistance between particles partially prevented compression from occurring during compaction. Mercury intrusion porosimetry (MIP) and scanning electron microscopy (SEM) test results showed that the PAM agent dispersed the bulky pellets, and the soil’s structure was formed by flaky and acicular platelets that filled the micropores. A quantitative analysis of crack patterns showed that the cross-points of the crack network and the crack length decreased as the PAM concentration increased. These results indicate that an increase in PAM reduces the shrinkage strain and the flaws or pores within saline soils. Therefore, PAM’s stabilizing effect on saline soil under a wetting–drying Cycle was proven.
Merche B Bodi - One of the best experts on this subject based on the ideXlab platform.
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the wettability of ash from burned vegetation and its relationship to mediterranean plant species type burn severity and total organic carbon content
Geoderma, 2011Co-Authors: Merche B Bodi, Jorge Mataixsolera, Stefan H Doerr, Artemi CerdaAbstract:Abstract Immediately following a wildfire, a layer of ash and charred material typically covers the ground. This layer will gradually be reduced, being redistributed by rainfall, wind or animals, by partial dissolution and by incorporation into the soil. Ash can increase or decrease the post-fire runoff and erosion response, depending upon the soil and ash properties and the ash thickness. One aspect of ash that has remained unknown and which may affect the variability in the hydrological response of the burned soil is its wettability. This study examines the wettability of ash using the Water Drop Penetration Time (WDPT) test, its relationship with total organic carbon (TOC) content and colour, and its effects when incorporated into the soil. Ash samples (n = 48) were taken from five wildfires in the Mediterranean basin encompassing a range of burn severities. Additional ash material was generated from exposing plant leaves (Rosmarinus officinalis, Pinus halepensis and Quercus coccifera) to specific temperatures in a muffle furnace (200–700 °C). Selected laboratory ash types were also mixed with wettable and water repellent soil material to assess their effect on soil wettability. Over 30% of ash samples from the wildfire sites exhibited water repellency (WR), with WDPT levels ranging from low to extreme. This variability appears to be related to differences in fire severity, combustion completeness of the biomass, vegetation type and subsequent rainfall events. The laboratory-generated ash exhibited a greater frequency and persistence of water repellency at lower furnace temperatures (200–300 °C), with ash from R. officinalis being generally less water repellent than that derived from the other two species. The water repellency levels of ash correlated well with TOC (r = 0.80), whereas neither of these parameters correlated very well with ash colour (r = 0.57 for TOC and r = 0.59 for WR). This suggests that ash colour, which is widely used as a parameter in classifying burn severity in the field, may not necessarily be a very accurate indicator. Adding water repellent ash to wettable soil induced WR, whereas the addition of wettable ash to water repellent soil had the opposite effect. A wetting–drying Cycle can reduce the water repellency of a soil–ash mixture. There were substantial differences between wildfire- and laboratory-generated ash in terms of organic carbon content and colour, suggesting that the combustion conditions in a furnace may not adequately represent those in wildfires. In contrast to what is generally assumed, our findings demonstrate that ash from vegetation fires can be water repellent. This is likely to have implications for runoff responses and nutrient fluxes not only when ash is present on the ground surface, but also following its redistribution and incorporation into the soil.
