The effects of atmospheric stability intensity on the movement of windblown sand

Using a model that couples wind flow with the motion of sand particles under different atmospheric stability intensities, this paper studied the effects of atmospheric stability on the trajectory and velocity of sand particles in the saltation layer, and the duration before a steady state was achieved. The vertical velocity, horizontal distance, and the maximum height of saltating sand particles increased with increasingly negative stability intensity under unstable conditions. The wind–sand flow reached equilibrium more quickly with increasingly negative stability intensity under unstable conditions, but reached equilibrium more slowly with increasing stability intensity under stable conditions.     

Effects of windblown sand damage on desert highway guardrails

Natural Hazards - Barriers, which are normally used as highway safety instruments, cause adverse sand deposition damage to pavements along desert highways. To select a suitable barrier type for...     

流滑型崩岸河岸侧蚀模式初探

流滑型崩岸是冲积河流河岸常见的一种崩塌形式,其发展速度快、破坏力强;该类崩岸主要取决于水流的直接冲刷,河岸崩退过程中水面与岸顶高差较小.依据此类崩岸的特征,基于水流冲刷分析,在基础层面上初步探讨并建立了流滑型崩岸的河岸侧蚀模式.结合水槽试验与土工离心模拟试验,对该模式进行了分析研究,初步率定了模式中的河岸侧蚀系数,计算...     

Capacity of quartz fibers with high filtration efficiency for capturing soot aerosol particles

Two proposed quartz fibrous filters with dissimilar solid volume fractions and thicknesses are investigated for their efficiency in removing soot aerosol particles from air. Soot particles are sourced from a candle burning in a chamber, and the tests involve 1.5 h of continuous loading of particles at three different flow rates: 4.5, 8.15 and 9.55 l/min. The fractional efficiency, morphology and pressure drop of both clean and loaded filters are studied using a scanning mobility particle sizer, scanning electron microscope and differential pressure gauge. Both filters have relatively similar levels of efficiency 93% for particle size (100–400 nm) at the lowest flow rate. At higher flow rates, the re-entrainment process effects the filtration efficiency of both filters. At the higher flow rate of 8.15 l/min, the filter with a higher solid volume fraction and thickness shows a higher pressure drop and an efficiency level of 95%. Increasing the flow rate to 9.55 l/min helps to pass the particles with diameters larger than 100 nm through two filters. This phenomenon decreases the fractional efficiency of both filters during the loading time.     

Determination of efficiency of Vaseline slide and Wilson and Cooke sediment traps by wind tunnel experiments

The trap efficiency of a catcher in wind erosion measurements plays a significant role, and in many cases suspension trap efficiencies at high wind velocities are still unknown. The sediment trap efficiency generally changes with particles size and with wind speed. In this study, the efficiency of Vaseline Slide (VS) and Modified Wilson and Cooke (MWAC) catchers were determined with different sand particle sizes (<50, <75, 50–75, 200–400, and 400–500 μm) at a fixed wind speed (13.3 ms⁻¹) and with different soil textures at different wind velocities (10.3, 12.3, and 14.3 ms⁻¹) in the wind tunnel of the International Center for Eremology (ICE), Ghent University, Belgium. The traps were placed at different heights (4, 6.5, 13, 20, 120, and 192 cm for VS and 1.5, 3, 5, 8, 11, and 30 cm for MWAC) to catch saltating and suspended sediments in a 12-m long, 1.2-m wide and 3.2-m high working section of the wind tunnel. In the sand particle experiments, the efficiency of the VS catcher was 92% for particles smaller than 50 μm and decreased with increasing particles size, falling to 2.2% for 400–500 μm particle size at 13.4 ms⁻¹. However, the MWAC’s efficiency was 0% for particles smaller than 50 μm and increased with increasing particle size to 69.5% at 400–500 μm. In the experiments with different soil textures, the efficiency of each catcher significantly changed with soil and with wind speed. It also considerably varied with the catchers: for instance, for sand (S), the MWAC efficiency was very high (67.4, 113.4, and 90.5% at 10.3, 12.3, and 14.4 ms⁻¹, respectively) while the efficiency of VS was relatively very low (5.2, 4.4, and 1.9% at 10.3, 12.3, and 14.4 ms⁻¹, respectively). Results indicated that the efficiency depends critically on the particle size, type of catcher, and wind speed, and these could be helpful to increase the robustness of wind erosion measurements.     

条带煤柱的抗滑稳定性分析

本文给出了走向条带开采条带煤柱抗滑稳定性分析的力学模型。提出了确定条带煤柱稳定性主要影响因素的敏感性分析法。通过峰峰矿务局九龙口矿的条采实例。介绍了走向条带煤柱抗滑稳定性分析的方法与步骤。     

Mechanical trapping of fine particles in a medium of mono‐sized randomly packed spheres

Mechanical trapping (or straining) of fine particles is a key mechanism in many filtration systems. For example, the performance of rapid sand filters depends in part on mechanical trapping of larger fine particles, while relying on adsorptive processes to trap very small fine particles and microbes. The ability to trap these particles is directly related to the construction of the packed bed used for filtration in this system. Thus, the ability to model the effect of the inner structure of the packed bed can lead to more efficient design for improved filtration. Because of its significant efficiency, gravitational sphere packing is employed in this work to simulate a bed of mono‐sized randomly packed spheres. The simulated bed provides a way to visualize the pore network and estimate the pore size distribution associated with the void space between particles. Furthermore, by subsequently introducing fine particles into the bed, we evaluate the mass‐rate of fine particles passing through and possibly saturating the packed bed. Results show that fine particles between 15% and 25% of the coarse particle size can be physically strained within the randomly packed bed. These results differ significantly from the results obtained assuming a periodically spaced bed. The technique therefore provides an efficient yet accurate alternative for understanding how fine particles pass through a coarse particulate medium. Copyright © 2014 John Wiley & Sons, Ltd.     

Effect of particles on the photodegradation of PAHs in natural waters-A case study for the Yellow River

Photodegradation of chrysene, benzo （a） pyrene and benzo （g, h, i） perylene in natural water of the Yellow River was studied using simulation sunlight. The effects of particulates on the photodegradation were explored. Several results arose from this study. （1） The photodegradation of PAHs can be fitted with first-order kinetics when no particulate exists in water system, and the first-order constant increases with decreasing of initial concentration of PAHs. The photodegradation rates of the three PAHs are related to their molecule absorption spectrum. （2） The existence of loess exerts two kinds of effects on the photodegradation of PAHs, including the inner filter effects and the photosensitizing effects of humic substance in loess. These two contrary effects lead to the difference of net effects among different contents of loess. When the loess contents are 0.1 and 5.0 g/L, the existence of loess stimulates the photodegradation of chrysene, benzo （a） pyrene. When the loess content is 5.0 g/L, the existence of loess stimulates the photodegradation of benzo （g, h, i） perylene. In addition, the photodegradation of PAHs can be fitted with the second-order kinetics when there is loess in the water system. （3） The soluble humic substances in loess can accelerate the photodegradation of PAHs while the in soluble part cannot. （4） Since the soluble humic substances in the suspended solids of the river have been dissolved in water,     

Effect of relative humidity on the scattering properties of urban aerosol particles

The effect of increase in relative humidity on the angular variation of scattered light intensity distribution function and on asymmetry factor has been studied theoretically for three sizes of particles which are representative of urban aerosols. The increase in relative humidity causes change in physical properties of the particles, like radius (r) and complex refractive index (n?ik). The study is based on these changes in physical characteristics. It has been found that there are almost negligible changes in the functioni at low humidities (≤40%) for all the three aerosol sizes studied, which may be due to insignificant changes in the physical properties. At higher values, however, the physical parameters as well as the functioni show significant changes. The changes ini are systematic for the particle very small compared to the wavelength of incident radiation but for the particles comparable or larger it is not so. The asymmetry factor changes with the increase in relative humidity, for smaller particle it increases and for two larger particles changes are of fluctuative nature.     

Effect of concrete waste particles on infiltration characteristics of soil

Demolition of old buildings to create space for new development resulted in the near surface soil (topsoil) to be mixed with particles derived mostly from concrete wastes. This condition could affect the infiltration capacity and surface runoff, therefore, storm-water management of the area. This paper presents results of study on the effect of concrete waste particles on the hydraulic properties and infiltration capacity of the topsoil. Laboratory tests were performed to compare the hydraulic properties of the topsoil and the mixture of topsoil and concrete particles. Laboratory infiltration column test was performed on the mixture to evaluate its infiltration capacity. Results from the laboratory tests indicated that the presence of particles from concrete waste decreased the water-holding capacity and permeability, thereby the infiltration capacity of the ground surface. The results were supported by numerical analysis performed using the same material and boundary conditions as the column test. Parametric study was performed on both the topsoil and the mixture to extend the results of infiltration test to different materials under different ranges of rainfall intensity. The parametric study showed that the presence of concrete particles increased the run-off and the effect increased as the rainfall intensity increased. Therefore, the increase in runoff coefficient should be considered for the storm-water management when the near surface soil is mixed with concrete waste.     

Effect of waste rubber particles on the shear behaviour of bio-cemented calcareous sand

Calcareous sand, a special type of sand commonly used for the construction of coastal engineering in tropical coasts, is usually required to be strengthened due to its poor engineering mechanical properties. Microbially induced carbonate precipitation has been proved to be a promising method for this purpose. A higher cementation level generally leads to a greater strength enhancement, but tends to cause brittle failure of bio-cemented calcareous sand, which in turn brings great potential risks for the coastal engineering. Therefore, the shear behaviour, especially the brittle behaviour, of bio-cemented calcareous sand needs to be understood properly, and taking some measures to improve its brittle behaviour is also necessary. In this regard, a series of triaxial compression tests were conducted to study the shear behaviour of bio-cemented calcareous sand with various cementation levels, and the waste rubber particles are used to improve the brittle behaviour of bio-cemented calcareous sand. The test results show that the shear strength of bio-cemented calcareous sand increases with the increase in cementation level, and the brittle behaviour is significant gradually. The waste rubber particles contribute to improve the brittle behaviour of bio-cemented calcareous sand, reducing the dilation of bio-cemented calcareous sand and slowing the changes in dilatancy with the increment of stress.

     

硬土软岩滑坡近水平滑移的离心机模型试验研究

中国西北地区存在大量的新近纪硬土软岩滑坡灾害,为研究该类滑坡的变形特征,开展两组离心机模型试验模拟滑带劣化引起滑坡变形破坏的全过程,获取模型坡体土压及位移的实时变化曲线。研究表明,当软弱带强度降低时,硬土软岩滑坡的上部滑体呈块体状滑动,在快速运动滑动过程中,滑体呈现块状平移,不会彻底解体、液化;硬土软岩滑坡中前部出现水平应力集中,导致下伏滑带塑性流动变形,诱发其中前部上覆滑体的水平运动,并向滑坡后缘扩展,最终形成多级水平滑动。     

细颗粒组分含量对钙质砂抗剪强度的影响

由于吹填过程的水力分选作用钙质砂土地基颗粒分布不均匀,容易形成分布不均、形态各异的以不同细粒含量的粉细砂层为主的细粒汇集层,引起钙质砂土地基承载力和不均匀沉降问题。开展不同细粒含量的粉细砂三轴固结排水剪切试验,分析细粒含量对钙质砂土力学特性的影响。研究结果表明,（1）当细粒含量增加时相同围压下土样剪胀性逐渐减弱,且峰值偏应力也逐渐减小;（2）各组试样干密度为1.40 g/cm3状态下各含量粉细砂均表现出应变软化特征,当细粒含量为10%时粉细砂土体强度稳定性最差,之后稳定性随细粒含量增加而逐渐增大;（3）钙质细砂由于颗粒咬合作用,具有表观黏聚力,当细粒含量小于40%时,随着细粒含量增加,颗粒之间的咬合作用显著降低,表观黏聚力线性减小。研究成果可为粉细砂层的地基处理及边坡稳定分析提供参考。     

Effect of some operating variables on the efficiency index of a coal flotation operation

Coal cleaning performance can be evaluated by a simple index called the efficiency index. The effect of operating parameters on the efficiency index has been qualitatively discussed. Maximization of the efficiency index implies process optimization and a method is indicated to optimize the process variables for maximization of the efficiency index.     

Simulation-based hazard management of a constructed landfill for flow slide scenario

Natural Hazards - Sanitary landfills have advantages in low investment, large treatment volume, and strong adaptability, which is now the main treatment for municipal solid waste in China. However,...     

Effect of coulomb losses on the spectra of heavy particles accelerated in prolonged solar events

This paper examines the possibility of using the energy spectra of accelerated solar cosmic-ray ions and features formed by Coulomb losses to study the solar plasma (the power-law index S for the scattering turbulence, particle number density N, and temperature T of the background medium). For an individual solar flare, Coulomb losses can be manifest to different degrees in the spectra of different ions, providing a means to determine S. A comparison of theoretical spectra for H, He, C, O, and Fe ions with observed spectra for the prolonged solar flare of October 20, 1995 yields S≈3, N≈5×10⁹ cm^?3, and T≈10⁶ K, assuming that the characteristic time scale over which these particles gain energy is about a second.     

长大顺层边坡渐进滑移失稳演化机理研究

目前对长大顺层边坡在开挖过程中的变形与渐进破坏过程研究较少。因此,深入进行长大顺层边坡变形破坏机理的研究,能为边坡稳定性分析和治理提供重要依据。首先对长大顺层边坡进行定义,随后通过对长大顺层边坡进行数值分析,得到了长大顺层边坡滑面应力的基本特征,在此基础上分析得到了长大顺层边坡的渐进失稳演化机理。鉴于模型实验研究方法具有直观性的优点,研究中引入模型实验,并通过试验现象和675组试验数据分析,发现这类边坡的主要变形方式均为滑动变形,破坏模式为滑移—拉裂破坏,滑动过程为分级滑动。模型试验和数值分析均表明长大顺层边坡的破坏模式为渐进多次滑移拉裂失稳模式。     

Experimental study on the brittle failure of the locking section in a large-scale rock slide

A locking section is a conceptual model employed to analyze large-scale rock slides, of which the role was commonly found governing the mechanism of such mass movements. The physical experimental study presented herein is designed to study the failure mechanism of the locking section by measuring its basic characteristics. Dataset on the magnitude of the energy release, stress state, and displacement near and within the locking section are obtained by acoustic emission sensor, strain gauge, and micrometer gauge. The study captured the continued stress and energy accumulation at the locking section under increasing loads and the final brittle shear failure, which depicts the comprehensive deformation and failure processes occurred at the locking section. The concurrence of the locking section failure is the abrupt intensive energy release that results in the occurrence of the high-speed rock sliding. In conclusion, the experiment aims at investigating the initiation mechanism of large-scale rock slides governed by a locking section.