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Rahardjo H.,Nanyang Technological University | Nio A.S.,Nanyang Technological University | Leong E.C.,Nanyang Technological University | Song N.Y.,Housing and Development Board
Journal of Geotechnical and Geoenvironmental Engineering | Year: 2010

Rainfall, hydrological condition, and geological formation of slope are important contributing factors to slope failures. Parametric studies were carried out to study the effect of groundwater table position, rainfall intensities, and soil properties in affecting slope stability. Three different groundwater table positions corresponding to the wettest, typical, and driest periods in Singapore and four different rainfall intensities (9, 22, 36, and 80 mm/h) were used in the numerical analyses. Typical soil properties of two main residual soils from the Bukit Timah Granite and the sedimentary Jurong Formation in Singapore were incorporated into the numerical analyses. The changes in factor of safety during rainfall were not affected significantly by the groundwater table near the ground surface due to the relatively small changes in matric suction during rainfall. A delay in response of the minimum factor of safety due to rainfall and a slower recovery rate after rainfall were observed in slopes from the sedimentary Jurong Formation as compared to those slopes from the Bukit Timah Granite. Numerical analyses of an actual residual soil slope from the Bukit Timah Granite at Marsiling Road and a residual soil slope from the sedimentary Jurong Formation at Jalan Kukoh show good agreement with the trends observed in the parametric studies. © 2010 ASCE. Source


Zhao X.,Central Queensland University | Hwang B.-G.,National University of Singapore | Gao Y.,Housing and Development Board
Journal of Cleaner Production | Year: 2016

In recent years, green building has attracted wide attention from both academia and industry. As green building projects are inevitably plagued with risks, this study attempted to assess the risks in green building projects in Singapore. Categorizing a list of 28 risk factors into 11 groups, the study performed a questionnaire survey and received 31 responses from project managers in Singapore. A risk assessment model was developed using the fuzzy synthetic evaluation approach. Using the proposed model, the likelihood of occurrence, magnitude of impact and risk criticality of each risk factor, group and the overall risk were calculated. "Inaccurate cost estimation" was the top risk factor, and "cost overrun risk" was the most critical risk group. The overall risk criticality was high, implying risk management was still necessary for green construction in Singapore. The proposed risk assessment model is reliable and practical for professionals in the green building industry, and can be applied in risk assessment in other countries. As few studies focused on risks in green projects, this study expands the knowledge and literature. © 2015 Elsevier Ltd. Source


Rahardjo H.,Nanyang Technological University | Satyanaga A.,Nanyang Technological University | Leong E.C.,Nanyang Technological University | Santoso V.A.,R.J. Crocker Consultants Pte Ltd. | Ng Y.S.,Housing and Development Board
Soils and Foundations | Year: 2014

Green technology, an integrated design approach that combines vegetation and engineering design methods, can be applied to improve slope stability. Orange Jasmine is a small tropical evergreen shrub which has deep root systems and is considered to be a drought-tolerant plant that adapts well to a wide range of climatic and soil conditions. It can also grow in infertile soils, limestone soils or loam. Vetiver grass has been widely cultivated in many tropical and subtropical regions of the world for soil and water conservation, land rehabilitation, and embankment stabilization. Vetiver grass has deep roots (2-4 m) and adapts well under extreme conditions of temperature, soil, moisture, soil acidity, and alkalinity. The role of Orange Jasmine and Vetiver grass in minimizing rainwater infiltration, for improving the stability of slopes, was investigated on a soil slope in Singapore with its tropical climate. Two slope sections, covered with Orange Jasmine and Vetiver grass, were instrumented with tensiometers, installed at different depths within the slope, and a rainfall gauge. The instruments were connected to a real-time monitoring system to study the pore-water pressure, the rainfall, and the groundwater level in the slope throughout a one-year period. The pore-water pressure characteristics within the slope sections covered with Orange Jasmine and Vetiver grass are analyzed and presented in this paper. The analyses indicate that both Orange Jasmine and Vetiver grass played a significant role in reducing rainwater infiltration into the slope, minimizing the loss of matric suction, and hence, the shear strength of the soil during rainfall and, as a result, maintained the stability of the slope. Vetiver grass and Orange Jasmine appeared to be similar in effectiveness in terms of reducing the rainwater infiltration into the slope. © 2014 The Japanese Geotechnical Society. Production and hosting by Elsevier B.V. All rights reserved. Source


Rahardjo H.,Nanyang Technological University | Satyanaga A.,Nanyang Technological University | Leong E.-C.,Nanyang Technological University | Ng Y.S.,Housing and Development Board | Pang H.T.C.,Housing and Development Board
Engineering Geology | Year: 2012

Rainfall-induced slope failures are commonly observed in residual soil. Due to weathering, the residual soil properties vary with depths, especially in tropical countries, such as: Singapore. Therefore, it is important to characterize the properties of residual soil with depth. Index properties, soil-water characteristic curve and saturated and unsaturated shear strength tests were carried out on residual soils from sedimentary Jurong Formation, Bukit Timah Granite and Old Alluvium in Singapore. The variations of residual soil properties in Singapore were determined from the laboratory test results and evaluated as a function of soil inherent variability. Typical, upper and lower bounds of soil properties for the residual soils in Singapore were described using confidence interval approach and coefficient of variation (COV) in this paper. The variations in residual soil properties can be incorporated in design based on risk or reliability approach. The COV of index and engineering properties of residual soils in Singapore indicate that residual soils from Bukit Timah Granite and Old Alluvium are coarser than residual soil from sedimentary Jurong Formation. The particle size distribution of residual soil from Old Alluvium is more uniform than that from Bukit Timah Granite. On the other hand, the particle size distribution of residual soil from Bukit Timah Granite is more uniform than that from sedimentary Jurong Formation. The shear strengths of residual soils from Bukit Timah Granite and Old Alluvium are higher than that from sedimentary Jurong Formation. © 2012 Elsevier B.V. Source


Rahardjo H.,Nanyang Technological University | Santoso V.A.,Nanyang Technological University | Leong E.C.,Nanyang Technological University | Ng Y.S.,Housing and Development Board | Hua C.J.,Housing and Development Board
Journal of Geotechnical and Geoenvironmental Engineering | Year: 2012

A capillary barrier as a cover system is a two-layer system of distinct hydraulic properties to prevent water infiltration into the underlying soil by utilizing unsaturated soil mechanics principles. This paper illustrates the application of the capillary barrier system on a slope that experienced shallow slip failures to prevent future rainfall-induced slope failures. In this study, the capillary barrier system was designed as a cover system for residual soil slopes with a steep slope angle under heavy rainfall conditions of the tropics. The capillary barrier system was constructed using fine sand as the fine-grained layer and granite chips as the coarse-grained layer. Both layers were contained in a cellular confinement system. The slope was instrumented with tensiometers and piezometers. The tensiometers were installed at different depths from about 0.5 m to 2.0 m below the slope surface. An adjacent original slope without the capillary barrier system was also instrumented using tensiometers to investigate the performance and effectiveness of the capillary barrier system in reducing rainwater infiltration and maintaining negative pore-water pressure in the slope. The detailed installation of a matric suction measurement device is discussed comprehensively in this paper. The measurement results showed that the capillary barrier system was effective in maintaining the negative pore-water pressures during rainfalls, particularly on the crest of the slope. © 2012 American Society of Civil Engineers. Source

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