Singapore, Singapore
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Hartono E.,National University of Singapore | Leung C.F.,National University of Singapore | Shen R.F.,National University of Singapore | Chow Y.K.,National University of Singapore | And 3 more authors.
Physical Modelling in Geotechnics - Proceedings of the 8th International Conference on Physical Modelling in Geotechnics 2014, ICPMG 2014 | Year: 2014

Centrifuge model study was carried out to investigate the effects of tunnelling beneath piled foundation in soft clay. Tests were performed on a single pile with its toe at three meters above the tunnel crown and located at various distances from the tunnel centre line. The induced pile axial load transfer and bending moment profiles due to tunneling are examined in this paper. It was found that the induced axial load transfer due to tunnelling changes considerably for a pile located directly above tunnel crown, at tunnel edge and at two tunnel diameters away from the tunnel centre line. © 2014 Taylor & Francis Group.


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.


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.


Rahardjo H.,Nanyang Technological University | Santoso V.A.,R.J. Crocker Consultants Pte Ltd. | Leong E.C.,Nanyang Technological University | Ng Y.S.,Housing and Development Board | And 2 more authors.
Canadian Geotechnical Journal | Year: 2013

A capillary barrier is a two-layer cover system having distinct hydraulic properties to minimize water infiltration into the underlying soil by utilizing unsaturated soil mechanics principles. In this study, a capillary barrier system was designed as a cover system for a residual soil slope to maintain stability of the slope by minimizing infiltration during heavy rainfalls in the tropics. The capillary barrier system (CBS) was constructed using fine sand as the fine-grained layer and recycled crushed concrete aggregates as the coarse-grained layer. The coarse-grained layer is commonly constructed using gravels or granite chips. However, due to scarcity of aggregates and in consideration of environmental sustainability, recycled crushed concrete aggregates were used as the coarse-grained layer in this project. The suitability of recycled crushed concrete aggregates as a material within the coarse-grained layer of a CBS is subject to the hydraulic property requirement. For comparison, another CBS was constructed using fine sand as the fine-grained layer and a geosynthetic (Secudrain) as the coarse-grained layer. The performance of each constructed CBS on the residual soil slope was monitored using tensiometers installed at different depths - from 0.6 to 1.8 m below the slope surface - and a rainfall gauge mounted on the slope. An adjacent original slope without the CBS was also instrumented using tensiometers and piezometers to investigate the performance and effectiveness of the CBS in reducing rainwater infiltration and maintaining negative pore-water pressures in the slope. Real-time monitoring systems were developed to examine pore-water pressure, rainfall, and groundwater level in the slopes over a 1 year period. Characteristics of pore-water pressure distributions in the residual soil slope under a CBS with recycled crushed concrete aggregates and in the original slope during typical rainfalls are highlighted and compared. The measurement results show that the CBS was effective in minimizing rainwater infiltration and therefore, maintaining stability of the slope.


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.


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.


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.


Santoso V.A.,Nanyang Technological University | Rahardjo H.,Nanyang Technological University | Leong E.C.,Nanyang Technological University | Ng Y.S.,Housing and Development Board | Tam C.P.H.,Housing and Development Board
Unsaturated Soils: Theoretical and Numerical Advances in Unsaturated Soil Mechanics - Proceedings of the 4th Asia Pacific Conference on Unsaturated Soils | Year: 2010

Horizontal drains have been used extensively for preventive and repair works of slopes. Horizontal drains have been found to be effective in lowering groundwater table to increase the stability of slopes. The ideal location of horizontal drain is at the toe of the slope in order to optimize the thickness of unsaturated zone from the horizontal drain to the ground surface. However, the ideal length of the horizontal drain has not been fully investigated, particularly for residual soil slopes. In this study, the effectiveness of different lengths of horizontal drains in sedimentary and granitic residual soils is investigated. Typical soil-water characteristic curves and permeability functions of the soils were used in performing seepage analyses of water flow through unsaturated soil slope with horizontal drains. It appears that the length of horizontal drain affects water flow through unsaturated soil slope and consequently stability of the slope under heavy rainfall conditions. Results of slope stability analyses indicate that the horizontal drain installed to the critical slip surface provides the ideal length of horizontal drains in residual soil slopes. In addition, soil properties also influence the effectiveness of horizontal drains in maintaining stability of slopes. © 2010 Taylor & Francis Group, London.


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
Soils and Foundations | Year: 2011

Changes in the pore-water pressure of unsaturated soil slopes due to rainwater infiltration comprise a crucial factor which affects the shear strength of soils and may trigger slope failures. Two residual soil slopes in two main geological formations in Singapore, the Bukit Timah Granite and the sedimentary Jurong Formation, were fully instrumented. Real-time monitoring systems were developed to examine the pore-water pressure, the rainfall and the groundwater level of the slopes for over a year. The characteristics of the pore-water pressure distributions in both slopes during rainfall were highlighted and compared. The monitoring results indicate that the residual soil slope of the Bukit Timah Granite has a thicker unsaturated zone due to a deeper groundwater table than the residual soil slope of the sedimentary Jurong Formation. A higher permeability of the residual soil of the Bukit Timah Granite results in more rapid changes in negative pore-water pressure due to rainwater infiltration than the residual soil of the sedimentary Jurong Formation. Therefore, the residual soil slope of the Bukit Timah Granite differs from the residual soil slope of the sedimentary Jurong Formation in the changes in shear strength and the variations in the factor of safety during rainfall. The differing characteristics of the pore-water pressure responses during rainfall for these two residual soil slopes are analyzed in the present study based on the results of field measurements and numerical analyses.


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
Soils and Foundations | Year: 2011

In tropical and subtropical regions, shallow landslides often occur in residual soil slopes. Short-duration, high-intensity rainfall will increase the pore-water pressure. As a result, the shear strength of the soil in the slopes decreases and the stability of the slopes is affected. In this study, horizontal drains were installed in a residual soil slope in Singapore in order to improve the stability of the slope. The slope was instrumented with tensiometers and piezometers to investigate the effectiveness of the horizontal drains as a slope stabilization method against rainfall-induced slope failures. The variations in water table elevation and matric suction in the slope due to rainfall events were monitored. In addition, numerical analyses of the seepage into the slope brought about by the rainfall were carried out, and the results showed a reasonably good agreement with the data obtained from field measurements. The field measurement results indicated that horizontal drains were indeed effective for lowering the water table and for increasing the stability of the investigated slope. Therefore, horizontal drains are considered to be a useful and economical method for improving the stability of residual soil slopes against rainfall.

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