In Malaysia, approximately 60% of the total areas are coastal plains and inland lowlands of undulating terrain below 300m.
Meanwhile, about 35% of the total land consists of hilly ranges at Reduced Level between 300m and 1000m and approximately 5% consists of Mountains above 1,000m.
However, from an engineering point of view, the definition of hilly terrain should be coupled with slope gradients.
Therefore, based on the current implementation policy of hillside developments, slope terrain classification of individual development is mandatory to gauge the extent of necessary geotechnical engineering input.
However, concerns and awareness on the hazards of hillside developments only begun after the collapse of Block 1 of the Highland Towers on 11th December 1993 that killed 48 people .
Since then, numerous landslide incidents have occurred both at the surrounding areas of Highland Towers, and in other parts of the country.
On 30th June 1995, 20 people were killed in the landslide at Genting Highlands slip road near Karak Highway.
In December 2008, another large scale landslide had occurred in Bukit Antarabangsa, where five residents were killed, 14 bungalows were destroyed and 2,000 residents were evacuated from their home.
As hillside development has gained in popularity, good practice for slope engineering and slope management is vital for the formation of safe slopes both during construction and throughout the service life of the structure.
In the past decade, several projects on landslide hazard and risk assessment have been carried out by Malaysian government agencies.
These projects have been for various applications such as land use, agriculture and slope management.
The Malaysian government departments involved in landslide mitigation are the Public Works Department (PWD), Department of Mineral and Geosciences (DMG) and Centre of Remote Sensing (MACRES).
PWD is the main technical department in Malaysia and is largely involved in slope remedial works (active action) as well as the development of slope assessment and management (passive action).
The main contribution of the DMG and MACRES is to inform the government of areas prone to land sliding.
They have produced slope or terrain hazard zone maps and these are widely used by the government agencies as a guideline in the development of hilly and mountainous areas.
The road network is fundamental for socioeconomic activities and an indispensable infrastructure to transport people and materials for restoration from disaster.
In order to achieve sustainable development, it is important not only to minimize damage through rapid restoration but also to prevent damage from disaster in advance.
PLUS Expressways Group is the largest toll expressway operator in South East Asia and one of the largest in the world in terms of market capitalisation. PLUS operate the North-South Expressway.
Two incidents occur on 6 January 1996; a landslide at the North-South Expressway (NSE) near Gua Tempurung, Perak and in December 2003, a rock fall in the New Klang Valley Expressway (NKVE) near the Bukit Lanjan interchange caused the expressway to close for more than six months.
These incidents prompted PLUS to take on a stringent Environmental Policy that promotes business practices as well as products and services that are environmentally friendly and sustainable.
PLUS minimise the impact on the environment around its operation, where they continue to employ comprehensive operational controls, appropriate technology and sustainable maintenance and construction activities.
PLUS ensures more than 6,000 slopes are in good conditions along the expressway where technical assessment is undertaken to streamline the frequency of inspections.
This assessment encompasses visual inspections of the slope condition and performance based on geomorphological and geological characteristics.
In every slope repair works carried out by PLUS, the contractor must comply with the requirement of EMS in ensuring the surrounding environment and water courses are protected from any potential damage.
This requires a good drainage system and proper ground cover for the slope surface.
The Real Time Monitoring System (RTMS) helps PLUS in collecting rainfall data and monitoring the rainfall trend which relates to slope stability.
Currently the RTMS threshold is set based on the debris flow event. This system is designed to become the future early warning system for PLUS.
70 rain gauges have been installed at selected slopes along the NSE. Threshold value of debris flow has been established for all soil slopes along NSE.
Full elimination of slope failures is impossible but the impact from failures can be reduced.
In recent years, technical studies and more stringent rules gained prominence.
The Selangor government and Kuala Lumpur City Hall also updated their guidelines to include more technical analysis so as to make more well-informed decisions when approving projects.
Selangor, for one, imposed a ban on Class III and above hillside development, bringing down the permissible gradient for slope construction from 35 degrees and below to not more than 25 degrees.
The PWD is responsible for the maintenance of slopes along national roads, while the rest of country comes under the jurisdiction of local authorities, developers and private owners.
The public must also play their part by alerting the authorities when they come across early signs of a possible landslide, such as tension cracks on road surface, movements, tilting of trees and water infiltration.
Source: National Slope Master Plan, PLUS Expressway Berhad, Landslide hazard and risk assessment: The Malaysian experience; Suhaimi Jamaludin & Ahmad Nadzri Hussein (Slope Engineering Branch, PWD Malaysia); The Geological Society of London 2006 and How to Improve Slope Management and Slope Engineering Practices in Malaysia, Gue See-Sew & Wong, Shiao-Yun; G&P Geotechnics Sdn Bhd.
(this article written for 1BINA.my)