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Goh S.G.,Surbana International Consultants Pte. Ltd. | Rahardjo H.,Nanyang Technological University | Leong E.C.,Nanyang Technological University
Journal of Geotechnical and Geoenvironmental Engineering | Year: 2014

Under the same stress state, a soil behaves differently when it follows drying and wetting processes because of hysteresis. The purpose of this study was to understand the shear strength characteristics of unsaturated soil under multiple cycles of drying and wetting.Aseries of unsaturated consolidated drained (CD) triaxial tests were conducted using three different sand-kaolin mixtures. All sand-kaolin mixtures experienced hysteresis during multiple cycles of drying and wetting processes. TheCDtest results indicated that the specimens on the drying paths have higher shear strengths than those on the wetting paths owing to the hysteresis effects on the soil during drying and wetting processes. The differences between the shear strengths on the drying and wetting paths of the first cycle were found to be more significant than the differences between the shear strengths on the drying and wetting paths of the subsequent cycles. The specimens on the first-cycle wetting path and the subsequent cycles of drying and wetting paths had similar shearing characteristics; generally, they had lower axial strain at failure and exhibited less ductility, more stiffness, and dilative behavior during shearing compared to the specimens on the first-cycle drying path. In addition, the predictions of the drying and wetting shear strengths of different sand-kaolin mixtures as computed from the shear strength equation showed good agreement with the measured data obtained in this study. © 2013 American Society of Civil Engineers. Source


Karthikeyan M.,Surbana International Consultants Pte. Ltd. | Phoon K.K.,National University of Singapore | Toll D.G.,Durham University
14th Asian Regional Conference on Soil Mechanics and Geotechnical Engineering | Year: 2011

This paper presents a simple method for evaluating potentially unstable soil slopes subject to surface infiltration based on convenient closed-form seepage/stability equations containing slope geometry, soil strength, and infiltration parameters. The method is based on a formulation proposed by Lu and Godt (2008), which provides the change in the factor of safety for a slope subject to steady state infiltration. The key advantage is that no numerical modeling is needed and fairly reasonable factors of safety can be determined. Several case studies are presented to illustrate the potential usefulness of the proposed method. Source


Goh S.G.,Surbana International Consultants Pte. Ltd. | Rahardjo H.,Nanyang Technological University | Leong E.C.,Nanyang Technological University
Soils and Foundations | Year: 2015

Both the shear strength and the permeability of unsaturated soils are important engineering properties that are required in numerous geotechnical designs. Many studies on the shear strength of unsaturated soils have been reported; however, only a limited number of studies on the permeability of unsaturated soils have been presented. This might be due to the fact that the time and the costs associated with unsaturated permeability measurements are excessive. The purpose of this paper is to introduce the modification of a triaxial apparatus for the direct measurement of permeability in conjunction with shear strength tests on unsaturated soils under multiple cycles of drying and wetting. Detailed designs and modifications are carried out to allow the unsaturated permeability and the shear strength of a soil to be measured for the same soil specimen. The test results are found to be more consistent as both measurements are conducted on the same specimen. A series of unsaturated permeability tests and then a series of unsaturated consolidated drained (CD) triaxial tests, under multiple cycles of drying and wetting, are conducted on three different soils, and the results are shown to be compatible with the theory reported in literature. © 2015 Japanese Geotechnical Society. Source


Jangam S.V.,National University of Singapore | Karthikeyan M.,Surbana International Consultants Pte. Ltd. | Mujumdar A.S.,National University of Singapore
Drying Technology | Year: 2011

Low-rank coals (LRCs) constitute about 45% of the total coal reserves and hence will soon be the fossil fuel of choice in many countries despite their high moisture content on mining, which varies from 30% to as high as 66%. It is important to reduce their water content to enhance the heating value and reduce transportation costs while enhancing combustion efficiency, safety, and reduction of emissions on combustion. The level of moisture to be achieved upon drying LRCs depends on the end application; it varies from as low as 0% for hydrogenation processes to 15% for briquetting and gasification processes. Numerous drying technologies have been proposed for drying coal; they include pulse combustion, vacuum, fluid bed, rotary, flash, microwave, and superheated steam drying. Each technology has some pros and cons, which are not always clearly spelled out in the literature. In addition, it is necessary to develop sustainable rather than just cost-effective drying systems for LRC. In this article we assess various coal drying techniques critically and identify their strengths and weaknesses. Some theoretical comparisons of different dryer types are carried out based on energy utilization and carbon footprints. The jury is still out on optimal drying technology for LRC and innovative design concepts should be evaluated before finalizing the selection. © 2011 Taylor & Francis Group, LLC. Source


Chua K.E.,Housing and Development Board HDB | Lim S.K.,Housing and Development Board HDB | Lim Jerry K.C.,Housing and Development Board HDB | Chew S.H.,National University of Singapore | And 5 more authors.
14th Asian Regional Conference on Soil Mechanics and Geotechnical Engineering | Year: 2011

As part of preliminary site investigation for the Marina East area, an extensive soil investigation works were planned. The project site is located in waters off Marina East, Singapore. The whole project site covered an area of around 600 Hectare. The water depth at the project area varies from 0 m CD to -23 m CD. The seabed within the project site is mainly covered by Kallang Formation and Old Alluvium. The seabed geology, in particular, the thickness and distribution of the soft sediment and soft clay within this project site, as well as the strength and stiffness characteristic of these soft deposit are the main concerns for any new development over this site. The knowledge of seabed geology and the engineering properties will help in deciding the appropriate facilities to be built or/and the appropriate method of construction. In view of the nature of the design requirements, an integrated soil investigation works has been designed. This includes 4 key components: seismic survey, CPT, borehole, and Large Diameter Borehole. Proper planning and management was significant for such a mega soil investigation project, which covers a huge project area and includes a few different types of work. Source

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