Electrokinetic Treatment Technique for Improving the Engineering Characteristics of Low Permeable Problematic Soils
In recent years, major settling or tilting of buildings and bridges, instability of dams and road embankments have been observed and many attempts have been made in order to mitigate such damages. In this regard, it is necessary to determine the soil improvement alternatives, technically and economically, from the ultimate state design in accordance with geotechnical categories, to stabilize and remediate the existing soft problematic soils prior to the commencement of any construction activities. The aims of improving soils (as foundation and construction materials) are to increase strength, reduce distortion under stress, reduce compressibility, control shrinking and swelling, control permeability and reduce water pressure (redirect seepage), prevent detrimental physical or chemical changes due to environmental conditions, reduce susceptibility to liquefaction, reduce natural variability of borrow materials and etc.
Conventional remediation methods have been known successful in minimizing several damages, however, they are expensive, time-consuming and may be difficult to implement in some existing structures. In this regard, electrochemical or electro kinetic (EK) treatment method can be used as an alternative soil treatment method for remediation of those deficiencies underneath building foundations, roads, railways or pipelines. The use of this technique involves an approach with minimum disturbance to the surface while treating subsurface contaminants and improving the engineering characteristics of subsurface soils.
The use of EK treatment which is a comparatively new methodology is being investigated in some parts of the world for the potential application through several laboratory experiments to verify the versatility and effectiveness of this technique in practice as a viable in-sit soil remediation and treatment method. Therefore, this review represents an overview of the EK phenomena, as well as previously performed research activities on this technique. Besides, advantages and disadvantages (limitations) of this technique are discussed and some recommendations and directions for future needs are described for this newly developed technique.
Low Permeable Problematic Soils
The EK method is applicable to fine grained soils because this process takes place basically due to the presence of clay particles in the low permeable soil (that cannot readily drain), possessing specific mineralogical properties, hence electrically and chemically active. Low permeable problematic soils have been distributed all over the world as expansive soils, dispersive soils, high compressible clays, marine clays, sensitive clays, quick clays, saline/sodic soils, soft peat and etc.
Soft clay soils are commonly found in many parts of the world. In coastal areas of Australia, the soft soils often outlying the estuaries of creeks and rivers and pose serious problems in design and construction of roads and foundations. The soft problematic clays of Southeast Queensland (SEQ) are classed as very soft to soft, moist to wet and with medium to high plasticity. Their general characteristics include low shear strengths in the order of 10kPa to 15kPa, natural moisture contents between 60 and 120% and high compressibility . As the population increases, the demand for new land increases at a similar rate, therefore in order to prevent excessive settlements, increasing their bearing capacities and control seepage, some ground improvement techniques are required.
Research Gaps and Directions for Future Research
A review of the EK technique, as well as the previous research performed on EK has been carried out. This review indicated that some laboratory tests and field applications have proven to have practical application and technical effectiveness of the EK treatment for the industries.
However, there are still a lot of scopes to be covered and research gaps need to be closed in this newly developed technology.
The following highlight some of the reasons:
(1) most of the studies focused on contaminant removal and remediation of the contaminated soils, while very few studies have investigated the role of EK technology on strengthening and improving mechanical and engineering characteristics of the problematic clay soils; (2) the understanding of complex micro-structural behavior of different clay minerals and chemical species under coupled chemical, hydraulic and electrical (CHE) gradients is limited and (3) a solid theoretical understanding based on experimental investigations and evidences does not still exist. Based on the review, a fundamental research question that needs to be posed is: can EK treatment method be technically effective and practically viable as an exist and inset methods, for improving the engineering characteristics of the low permeable problematic soils? In short, can this method be considered as a good ground improvement technique? Therefore, in order to address the question: (1) several field and laboratory studies need to be conducted on different problematic soils in order to investigate several alterations in soil composition, physicochemical and engineering characteristics of the soil under EK treatment; (2) there is even a greater need to build up new models in order to predict the modification of soil chemo-mechanical properties, which would be of great assistance in infrastructure management and development applications; (3) the effects and degree of improvement of the soil with and without permeating different enhancement (stabilizing) agents through the soil should also be discussed; (4) several changes in soil composition and chemistry, soil physical properties (water content, consistency limits, etc.), pH, nature and spacing of the electrodes, processing time, levels of voltage, current and many optimizations need to be further investigated and optimal design concept should be verified through the EK treatment of the problematic soils; (5) additional research is also needed to gain a better understanding of the relative importance of the transport mechanisms involved and to develop methods of identifying, quickly and simply, the most important factors affecting the EK treatment process at each specific site.
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Journal of Chromatography & Separation Techniques