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An NTU Digital Project
Unsaturated Soil Mechanics for Sustainable Urban Living


Prof Harianto Rahardjo
School of Civil and Environmental Engineering
College of Engineering

View Prof Harianto Rahardjo’s publications

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Dr Alfrendo Satyanaga Nio
Senior Research Fellow
School of Civil and Environmental Engineering
College of Engineering

Unsaturated Soil Mechanics
First and Second textbooks


New book
Unsaturated soil guidelines cover

NTU Library Resources



Research @NTU on Unsaturated Soil Mechanics for Sustainable Urban Living in Singapore

Singapore is located in a tropical region where abundant rainfalls and high temperatures provide conditions for rapid and thorough insitu chemical and mechanical weathering of rocks. The active weathering process gives rise to deep residual soil profiles. In tropical regions, residual soils commonly exist in an unsaturated state with negative pore-water pressures. The negative pore-water pressures contribute additional shear strength to the unsaturated soils. Numerous studies have indicated that many slopes often fail during and after periods of heavy rainfalls in Singapore. Trees also tend to be overturned under similar conditions. Infiltration of water into the soil occurs during rainfall, reducing negative pore-water pressures and reducing the shear strength of the soil. The end result is the failure of many slopes and the uprooting of trees during heavy rainfalls. The assessment of stability of slopes and trees needs to take into consideration the mechanics and properties of unsaturated soils and the flux boundary conditions related to the imposed climate (i.e., rainfall infiltration, evaporation and transpiration across the ground surface). The application of unsaturated soil mechanics to geotechnical engineering is generally considered to be beyond classical soil mechanics and it is usually ignored by engineers. Unsaturated soil mechanics is becoming increasingly important as engineers become aware that global climate change concerns can be taken into consideration when analyzing the dynamic inter-action between the environment and near-ground-surface soils.

As Singapore moves towards a more liveable, and more sustainable city, carefully planned and executed research must be carried out to optimise land and resource utilisation. Over the past two decades, the School of Civil and Environmental Engineering (CEE) at NTU has embarked on several collaborative research projects which have attempted to provide state-of-the-art solutions to overcome problems imposed by inter-actions with the environment and the environmental changes and resource limitations. The cutting edge research in unsaturated soil mechanics conducted @ NTU has been a major contributor to the realization of the sustainable city blueprint for Singapore in facing challenges associated with global climate changes.
Objectives of Research   Research Collaboration Projects NTU & PWD  |  Research Collaboration Projects NTU & HDB-BRI  |  Research Collaboration Projects NTU & NParks  |  Research Collaboration Projects NTU, BCA & SLA | About this Digital Project

New *  UTM Engineering Distinguished Lecture Series, 30 June 2020. “Sustainable Urban Development” by Professor Harianto Rahardjo   Slides | Video

New *  Research Collaboration Projects between NTU, Building Construction Authority (BCA) and Singapore Land Authority (SLA)


New * Mercer, K., Rahardjo, H., & Satyanaga, A. (2019). ”Unsaturated soils guidelines – Volume 1: Soil water characteristic curves for materials classified according to the unified soil classification system.” Australian Centre for Geomechanics.

New * Rahardjo, H., Leong, E. C., Satyanaga, A., Gofar, N., Zhai, Q., Mohamed, H., Wong, J. L. H. Tan, S. T., Wang, C. L., Lim, H. V., Kew, J. H. and Seow, W. K. (2018). “Geobarrier system for use in underground structure”. Geotechnical Engineering Monograph. Research collaboration between Nanyang Technological University and Housing Development Board, Singapore.

Slope failure at Bukit Batok 2006  Tree failure

Typical layout of slope instrumentation  Effect of climate on tree stability

Cross-sectional view of the shear box and the pressure chamber for direct shear test  Effect of climate on tree stability



Collaborators & Funders