Effects of chemical contamination on microscale structural characteristics of intact loess and resultant macroscale mechanical properties
TL;DR: In this article, the micro-scale structural characteristics of the loess exposed to acetic acid, phosphoric acid, sodium hydroxide, and sodium sulfate respectively are studied using scanning electron microscopy, X-ray diffraction, and energy dispersive spectroscopy tests.
Abstract: Soil contamination not only can cause environmental problems but also lead to a notable change in the mechanical properties of soil. Loess widely distributed over North-West (NW) China is featured with the metastable structure, and chemical contaminants produced especially during the rapid development of NW China in recent years seriously threaten the fragile loess environments. When exposed to chemical contaminants, the impacts on the microstructural characteristics of the loess and the resultant mechanical properties are deemed critical for land reclamation in NW China. In light of this, the microscale structural characteristics of the loess exposed to acetic acid, phosphoric acid, sodium hydroxide, and sodium sulfate respectively are studied using scanning electron microscopy, X-ray diffraction, and energy dispersive spectroscopy tests. Additionally, their resultant macroscale mechanical properties are determined by direct shear tests. The deterioration mechanism regarding the microscale structural characteristics when exposed to the contaminants is revealed, and the resultant macroscale mechanical properties present a good correspondence with the deteriorated microscale structural characteristics. The findings of this work provide some guideposts for contaminated land reclamation in NW China.
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TL;DR: In this paper , a smoothed particle hydrodynamics (SPH) method was employed to simulate the heat transfer process in porous media at the pore scale, and the effective thermal conductivity of a porous medium can be predicted through a simulation experiment of SPH.
Abstract: The smoothed particle hydrodynamics (SPH) method was employed to simulate the heat transfer process in porous media at the pore scale. The effective thermal conductivity of a porous medium can be predicted through a simulation experiment of SPH. The accuracy of the SPH simulation experiment was verified by comparing the predicted values with reference values for ideal homogeneous media and multiphase layered media. 3D simulation experiments were implemented in granular media generated by the PFC method. Based on the SPH framework, a concise method was proposed to produce unsaturated media by simulating the wetting process in dry media. This approach approximates the formation of liquid bridges and water films on granules. Through simulation experiments, the empirical formula of the variation in thermal conductivity with the degree of saturation was tested. The results showed that the reciprocal of the normalized thermal conductivity and the reciprocal of the saturation are linearly related, which is in line with the empirical formula proposed by Cote and Konrad.
66 citations
49 citations
TL;DR: Wang et al. as discussed by the authors explored the potential use of the EICP technology for the protection of heritage buildings in NW China and found that the modified version performed the best with the highest calcite precipitation.
Abstract: Given that acid-rich rainfall can cause serious damage to heritage buildings in NW China and subsequently accelerate their aging problem, countermeasure to protect their integrity and also to preserve the continuity of Chinese culture is in pressing need. Enzyme-induced calcite precipitation (EICP) that modifies mechanical properties of the soil through enhancing the inter-particle bonds by the precipitated crystals and the formation of other carbonate minerals is under a spotlight in recent years. EICP is considered as an alternative to the microbial-induced calcite precipitation (MICP) because cultivating soil microbes are considered to be challenging in field applications. This study conducts a series of test tube experiments to reproduce the ordinary EICP process, and the produced calcite precipitation is compared to that of the modified EICP process subjected to the effect of higher MgCl2, NH4Cl, and CaCl2 concentrations respectively. The modified EICP subjected to the effect of higher MgCl2 concentrations performs the best, with the highest calcite precipitation. The enhancement mechanism of calcite precipitation is well interpreted through elevating the activity of urease enzyme by introducing the magnesium ions. Further, the degradation of calcite precipitation presents when subjected to the effect of higher NH4Cl concentration. The decreasing activity of urease enzyme and the reverse EICP process play a leading role in degrading the calcite precipitation. Moreover, when subjected to the effect of higher CaCl2 concentrations, the slower rate of ureolytic hydrolysis and the decreasing activity of urease enzyme are primarily responsible for forming the ‘hijacking’ phenomenon of calcite precipitation. The findings of this study explore the potential use of the EICP technology for the protection of heritage buildings in NW China.
48 citations
TL;DR: In this paper , the potential of applying the MICP technology to the lead remediation under the effects of urease activity and calcium source was explored, and the values of OD600 corresponding to the ureolytic bacterial activity, electrical conductivity (EC), ureases activity (UA), and pH were applied to monitor the degree of urea hydrolysis.
45 citations
TL;DR: Based on the collapse of a tunnel in Xi'an Metro Line 3 near a ground fissure, potential causes and corresponding mechanisms were analyzed in this paper , which indicated that hydraulic erosion induced loose pressure and crack-rich soil below the initial support were mainly attributed to be the triggering force of the collapse.
37 citations
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01 Jan 1976
TL;DR: In this paper, the authors developed an understanding of the factors determining and controlling the engineering properties of soil, the factors controlling their magnitude, and the influences of environment and time, and developed a two-part book which contains the following chapters: Part 1 - the nature of soils; bonding, crystal structure and surface characteristics; soil mineralogy; soil formation and soil deposits; determination of soil composition; soil water; clay-water-electrolyte system; soil fabric and its measurement; Part 2 - soil behavior; soil composition and engineering properties; effective, intergranular
Abstract: The book is intended to develop an understanding of the factors determining and controlling the engineering properties of soil, the factors controlling their magnitude, and the influences of environment and time. The two-part book contains the following chapters: Part 1 - the nature of soils; bonding, crystal structure and surface characteristics; soil mineralogy; soil formation and soil deposits; determination of soil composition; soil water; clay-water-electrolyte system; soil fabric and its measurement; Part 2 - soil behavior; soil composition and engineering properties; effective, intergranular and total stress; soil structure and its stability; fabric, structure and property relationships, volume change behavior; strength and deformation behavior; and, conduction phenomena. /TRRL/
3,283 citations
TL;DR: In this article, a comparison between the compression curves as observed and as calculated from theoretical considerations indicates that in the case of suspensions of pure clays the compressibility can be accounted for quantitatively by the consideration of these long-range forces only.
Abstract: Synopsis It has been shown that the presence of exchangeable ions in clay systems leads to the presence of long-range repulsion forces between the particles. A comparison between the compression curves as observed and as calculated from theoretical considerations indicates that in the case of suspensions of pure clays the compressibility can be accounted for quantitatively by the consideration of these long-range forces only. On a montre que la presence d'ions interchangeables dans des constitutions d'argile provoque l'apparition de forces repulsives a grande distance entre les particules. Une comparaison entre les courbes de compression observees et calculees d'apres des considerations theoriques indique que dans le cas de suspensions d'argiles pures on peut evaluer la compressibilite quantitativement par la seule consideration de ces forces a grande distance.
411 citations
TL;DR: It is observed that the lead contamination and cement content levels can have a considerable impact on the leaching behavior of the soils and the leachability of lead and calcium is attributed to the stability of the hydration products and their consequent influence on the soil buffering capacity and structure.
221 citations
TL;DR: In this paper, the influence of structure on shear characteristics of unsaturated loess in Lanzhou city of China was investigated with comparison of variation of shear strength and its parameters between six pairs of the undisturbed and remolded samples.
164 citations
TL;DR: A series of ring-shear tests was conducted on saturated loess to investigate the effects of NaCl concentration in pore water and desalinization on the shear behavior under undrained conditions.
151 citations