Contamination assessment of heavy metals in the soils of an abandoned copper mine in Lasail,Northern Oman

ABSTRACT

Abandoned mine areas exhibit heavy metal contamination. This severely reduces the soil quality. This paper concerns the assessment of soils near an abandoned copper mine in Lasail, northern Oman. Seventy-two soil samples were collected and analysed for heavy metals using inductively coupled plasma optical emission spectrometry (ICP-OES). The extent of heavy metal pollution was evaluated based on the geo-accumulation index (Igeo), enrichment factor (EF), and pollution index (PI). According to these indices, Copper (Cu), Mercury (Hg), Zinc (Zn), Arsenic (As) and Iron (Fe) are impacting the soils. Of these, Cu and Hg concentrations are 50 and 300 times more than the permissible limits set by the World Health Organization (WHO). There is an urgent need for the remediation and restoration of the soils in this area and a proposal is presented here.     

高层建筑上部结构与基础和地基共同作用研究

介绍了上部结构与基础和地基共同作用的整体分析概念，逐一阐述了上部结构与基础和地基共同作用的研究历程、研究方法和研究成果，最后对上部结构与基础和地基共同作用的研究前景进行了展望。     

Assessment of chromium biostabilization in contaminated soils using standard leaching and sequential extraction techniques

The iron reducing microorganism Desulfuromonas palmitatis was evaluated as potential biostabilization agent for the remediation of chromate contaminated soils. D. palmitatis were used for the treatment of soil samples artificially contaminated with Cr(VI) at two levels, i.e. 200 and 500 mg kg^− 1. The efficiency of the treatment was evaluated by applying several standard extraction techniques on the soil samples before and after treatment, such as the EN12457 standard leaching test, the US EPA 3060A alkaline digestion method and the BCR sequential extraction procedure. The water soluble chromium as evaluated with the EN leaching test, was found to decrease after the biostabilization treatment from 13 to less than 0.5 mg kg^− 1 and from 120 to 5.6 mg kg^− 1 for the soil samples contaminated with 200 and 500 mg Cr(VI) per kg soil respectively. The BCR sequential extraction scheme, although not providing accurate estimates about the initial chromium speciation in contaminated soils, proved to be a useful tool for monitoring the relative changes in element partitioning, as a consequence of the stabilization treatment. After bioreduction, the percentage of chromium retained in the two least soluble BCR fractions, i.e. the “oxidizable” and “residual” fractions, increased from 54 and 73% to more than 96% in both soils.     

地铁盾构隧道周边建筑物地基基础变形控制研究

城市地铁隧道穿越建筑物地基基础施工前一般要进行评价,并且要求提出相邻建筑物地基基础在施工期间的变形控制标准,这是地下空间开发利用的一大技术难题。本文结合北京地铁十号线一工程实例,详细阐述了对相邻建筑物的一系列工程评价方法,提出了该段地铁隧道周边建筑物地基基础变形控制标准。为地铁隧道成功穿越该建筑物地基邻域提供了科学有效的技术支持。     

大连港大窑湾吹填区软基的堆载预压处理研究

结合大连港大窑湾吹填区软土地基处理具体工程,通过现场试验与监测比较详细地介绍了堆载预压方法中关于分级堆载设计、施工及监测等各方面的技术问题。通过对监测结果的综合分析,探讨了堆载预压处理过程中地表沉降、深层沉降等关键参数的变化规律及堆载级数、堆载高度与固结时间等参数之间的依赖关系,为吹填造陆地区软基处理提供了经验和依据。     

Unsaturated elasto-plastic constitutive equations for compacted kaolin under consolidated drained and shearing-infiltration conditions

Transient process of water flow changes the equilibrium conditions of an unsaturated soil, resulting in volume change of a soil. The volume change alters the hydraulic properties of the soil and thus influences the transient process of water flow through the soil. Therefore, the interactive processes between stress-strain behavior and pore-water pressure are the primary processes affecting the mechanical behavior of unsaturated soils. This paper presents coupled elasto-plastic constitutive equations for unsaturated compacted kaolin under consolidated drained and shearing-infiltration conditions. The study focused on the development of the suction increase (SI) yield curve that incorporates changes in matric suction during transient processes. In addition, the relationship of change in specific water volume with respect to net mean stress and matric suction was also proposed by incorporating the hysteresis of soil-water characteristic curve. The simulated results by the proposed constitutive model were compared with those obtained from isotropically consolidated drained tests and shearing infiltration tests of compacted kaolin to verify the proposed model. The simulated results are in close agreement with the experimental results.     

A new design equation for drained stability of conical slopes in cohesive-frictional soils

New plasticity solutions to the drained stability of conical slopes in homogeneous cohesive-frictional soils were investigated by axisymmetric finite element limit analysis. Three parameters were studied, i.e. excavated height ratios, slope inclination angles, and soil friction angles. The influences of these parameters on the stability factor and predicted failure mechanism of conical slopes were discussed. A new design equation developed from a nonlinear regression of the lower bound solution was proposed for drained stability analyses of a conical slope in practice. Numerical examples were given to demonstrate a practical application of the proposed equation to stability evaluations of conical slopes with both associated and non-associated flow rules.     

Compaction-induced stress in geosynthetic-reinforced granular base course——A discrete element model

A discrete element method (DEM) model was used to simulate the development of compaction-induced stress in a granular base course, with and without geogrid reinforcement. The granular base course was modeled as a mixture of uniformly sized triangular particles. The geogrid was modeled as a series of equally spaced balls that interact with each other through long-range interaction contacts. The long-range interaction contact was also used to simulate a deformable subgrade. The compactor was modeled as a solid cylinder rolling at a constant speed. The DEM model shows that the geogrid-reinforced granular base course gains additional compaction-induced stress due to the residual tensile stress developed in the geogrid. The residual tensile stress in the geogrid increases with the number of compaction passes. Parametric analyses were also conducted to assess the effects of geogrid stiffness and subgrade modulus on the compaction-induced stress.