**Acknowledgements**

The authors would like to thank University of Malaya (UMRG-RG042-09SUS, RG120-11SUS, RG019-09AET, PV084-2012A, PV052-2011A), Slope Engineering Branch of Public Works Department Malaysia, Ministry of Science, Technology and Innovation (SF16-02-03-6013) and Ministry of Higher Education (FP070-2010A) for the research grants throughout this project.
