Contaminant extractability by electrokinetics

Electrokinetic extraction is an emerging technology that has shown considerable potential for efficient and effective removal of both inorganic and organic contaminants from fine-grained soils of low hydraulic conductivity and large specific area when conditions are favorable. The cleanup technology is basically the application of a direct-current electric field across contaminated soils through electrodes installed in the subsurface. The contaminant is removed by (1) electro-osmotic advection of pore fluid flushing the contaminants; (2) ionic migration or electromigration of contaminants carrying charges; and (3) electrophoresis of charged colloidal-sized particles carrying contaminants. However, many complicated electrochemical phenomena that can change the electrokinetic properties of soil particles and the chemistry of pore fluid occur simultaneously. The resulting soil-chemical interactions may enhance or inhibit the extractability of contaminants by electrokinetics, as various electrochemical processes are dynamic, reversible, and interdependent. The impacts of these phenomena on contaminant extractability by electrokinetics are discussed in this paper. A comprehensive list of useful references on electrokinetic extraction is also included for use by readers interested in the subject. © Mary Ann Liebert, Inc.published_or_final_versio

Innovative installation techniques for PHC piles

The high population density in Hong Kong necessitates the adoption of heavy infrastructures and high-rise buildings for public and private uses. These heavy infrastructures and high-rise buildings require the support of pile foundations. Among different pile types, the prestressed spun high strength concrete (PHC) pile is probably the most economical. Moreover, it has a smaller carbon footprint than the steel H-pile of comparable design load-carrying capacity. Installation of PHC piles by percussion is probably the most economical. However, noise, vibration and air pollution problems are often inseparable from percussion of piles. Innovative installation techniques for PHC piles to achieve environmental friendliness, quality and rapid construction, and economy are always in demand. Depending on geologic conditions, different innovative installation techniques for PHC piles have been developed and these techniques are presented in this paper.published_or_final_versio

Installation of prestressed spun high strength concrete piles by hydraulic jacking

Theme: Challenges and Recent Advance in Geotechnics for Foundation EngineeringThe technique of hydraulic jacking has been applied to install prestressed spun high strength concrete PHC) piles in Macau. It should be noted that PHC piles are significantly cheaper than steel H-piles of comparable load-carrying capacities. PHC piles also have a lower carbon footprint than steel H-piles. The Macau experience will be presented in detail in this paper to introduce this pile installation technique, and to demonstrate how this technique can reduce material and construction costs, reduce construction time, increase environmental friendliness, improve site quality control and reduce construction risk. The limitations of the technique will also be presented. Moreover, the engineering performance of PHC piles installed by this technique deduced from full-scale maintained pile load tests will be presented. Lastly, the obstacles to the introduction of this cost-effective, efficient and environmentally friendly pile installation technique to Hong Kong will be discussed.published_or_final_versio

Construction and demolition materials management in Hong Kong

The management of construction and demolition materials is a problem being tackled by many government agencies worldwide. The problem is particularly acute in Hong Kong due to rapid economic development and urban renewal over recent decades, and the situation is aggravated by the dense population on a small plot of usable land. The Hong Kong Special Administrative Region (HKSAR) government is implementing many initiatives in both public and private sectors to handle the ever-increasing municipal problem. Some of these strategies and practice are reviewed in this paper. The effectiveness of these initiatives is being closely monitored by the HKSAR government and adjustments are being made from time to time as required.published_or_final_versio

Discussion of "Forms and sand transport in shallow hydraulic fractures in residual soil"

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Desorption of cadmium from a natural Shanghai clay using citric acid industrial wastewater

The sorption/desorption characteristics of heavy metals onto/from soil particle surfaces are the primary factors controlling the success of the remediation of heavy-metal contaminated soils. These characteristics are pH-dependent, chemical-specific, and reversible; and can be modified by enhancement agents such as chelates and surfactants. In this study, batch experiments were conducted to evaluate the feasibility of using citric acid industrial wastewater (CAIW) to desorb cadmium from a natural clay from Shanghai, China at different soil mixture pHs. It can be observed from the results that the proportion of cadmium desorbed from the soil using synthesized CAIW is generally satisfactory, i.e., >60%, when the soil mixture pH is lower than 6. However, the proportion of desorbed cadmium decreases significantly with increase in soil mixture pH. The dominant cadmium desorption mechanism using CAIW is the complexion of cadmium with citric acid and acetic acid in CAIW. It is concluded that CAIW can be a promising enhancement agent for the remediation of cadmium-contaminated natural soils when the environmental conditions are favorable. As a result, CAIW, a waste product itself, can be put into productive use in soil remediation. © 2011 Elsevier B.V.postprin

Discussion of "Forms and sand transport in shallow hydraulic fractures in residual soil"

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Effects of test conditions on shear behaviour of composite soil

Test conditions, such as shearing rate and normal stress, have been long recognised as influencing the measured shear strength of clays and sands. However, their influence on composite soils, which have a wide range of particle sizes, has attracted much less attention from researchers. In this study, a total of 35 direct shear tests at different shearing rates under different normal stresses were conducted on specimens prepared by mixing different proportions of kaolin and glass beads. The changes in volume and water content of sheared specimens and the mesostructure of shear surfaces were studied. The results reveal a positive correlation between volume change and deviation of water content between the shear zone and outer zones, suggesting that the shear-induced volume change occurred primarily in the shear zones. Moreover, high normal stress and low shearing rate produced a relatively small void ratio in the shear zones, facilitating volumetric contraction of the specimen and the development of polished and evenly slickensided shear surfaces. In addition, the residual friction angle of the specimens tested was found to decrease with the increase in normal stress. The high shearing rate caused an increase in residual strength in specimens with low fines fraction, and reduced it in specimens with high fines fraction.published_or_final_versio

Effects of subsurface cavity expansion in clays

Subsurface cavity expansion in clay induced by compaction grouting can generate upward displacement of clay and/or increase in effective stress leading to consolidation, resulting in settlement compensation and/or shear strength enhancement respectively. However, the two potential benefits of subsurface cavity expansion may offset each other. Experiments and numerical simulations on the engineering behaviour of E-grade kaolin induced by subsurface pressure-controlled cavity expansion were conducted to investigate the interrelationship between compensation effectiveness and shear strength enhancement. The results of numerical simulations are in reasonably good agreement with the experimental data, indicating that the numerical simulation procedure adopted is a plausible and reliable technique to describe the engineering behaviour of clays induced by pressure-controlled cavity expansion. Effects of cavity expansion rate, cavity expansion volume, injection point spacing, and stress history on compensation effectiveness and shear strength enhancement were studied. Practical applications of the results are also proposed.published_or_final_versio

HKU's double professional civil engineering and law programme

The scale and complexity of civil engineering projects are increasing exponentially. Coupled with the growing trend of globalisation, the demand for high-calibre civil engineers who are also knowledgeable in legal matters is increasing. Driven by an aspiration to prepare civil engineering graduates with a solid foundation in both civil engineering and law, The University of Hong Kong has developed the first 5-year credit-based double professional degree programme in Hong Kong, which leads to the award of the degrees of Bachelor of Engineering in Civil Engineering (Law) and Bachelor of Laws. The considerations, development process and launching details of the programme are presented in this paper. The students admitted to date perform better academically than other civil engineering students on civil engineering courses. However, they do not perform as well as law students and other law-related double-degree students.published_or_final_versio