Signs of landslides and preventive measures
PRECAUTION: With the onset of the monsoon season, heavy rains have triggered floods and landslips throughout the country, putting lives and property at risk. In the first of a three-part series, slope management experts from Kumpulan Ikram share the steps that can be taken to address soil erosion or possible landslides
LANDSLIDES are a common natural disaster which occur along hillsides and steep slopes. A landslide, also known as a landslip, is a form of mass wasting which includes a wide range of ground movements. The main trigger factor of landslides in Malaysia is heavy rainfall which causes great damage to human lives and property.
During heavy rainfall, water percolates through the soil pore space, lubricating the slope materials to slip down and move downward under the force of gravity. In Malaysia, landslides are reported to happen mostly on man-made slopes on hillsides.
Some landslides move slowly and cause damage gradually, whereas others move so rapidly that they can destroy properties and take lives suddenly and unexpectedly. The main driving force in most land movements is gravity. However, gravity does not act alone. Slope angle, climate, slope material and water contribute to the effect of gravity as well. Furthermore, landslides tend to worsen the effects of flooding such as during the Cameron Highlands floods in 2014.
Landslides are caused by the interplay of various natural and anthropogenic factors and are often the subsequent event of rainfall. Examples of anthropogenic factors are land use and road networks which are also responsible for the increase of the vulnerability of landslides in Malaysia. The erosion can be divided into two types, namely geological and accelerated erosion.
Geologic erosion or natural erosion is due to forces of nature without the influence of man. During this process, soil and rock particles are worn away by gravity or by moving transported agents such as water, wind or ice. On the other hand, the erosion can be accelerated through human activities which disturb the state of equilibrium between geological erosion and soil formation. The removal of slope surfaces through cultivation, deforestation, overgrazing, housing development and road construction speed up the erosion.
While a landslide can theoretically occur at any elevated terrain, some areas in Malaysia are more prone to the phenomenon than others. The identification of landslide-prone areas plays an important role in avoiding or minimising the hazard and risk of these disasters. Some areas in Malaysia which are known to be landslide prone include the combination of extremely hilly terrain and highly jointed rock slopes, for example
The aftermath of the in Bukit Setiawangsa and Bukit Antarabangsa.
Is there technology to assess the risk of landslides? Yes. In order to evaluate the landslide surface displacement, a powerful tool for slope monitoring has been acquired by Kumpulan Ikram Sdn Bhd, namely Terrestrial Laser Scanning with a mission to provide high accuracy and high-speed data.
In response to the landslide hazard and risk-mitigation strategy, Kuala Lumpur Slope Information System was developed by Kuala Lumpur City Hall with the cooperation of Kumpulan Ikram Sdn Bhd in 2013. The main purpose of this system is to manage slope information through its implementation in sustainable development planning and overcoming geohazard phenomena in tropical regions such as Kuala Lumpur.
This system consists of detailed
floods in 2014. information related to slope geometry, historical failures, geology, hazard and risk map. The map of hazards and risks will display the distribution of slopes in Kuala Lumpur and categorise their hazard and risk into five levels.
Hilly terrain has been identified as the most prone area due to its rugged topography, steep slopes and drainage system. Fast-growing populations and the expansion of road networks have increased the drive to develop on such terrain, despite the engineering challenges and increased expense. While these areas have been identified as dangerous and are vulnerable to landslides, building on these slopes can be made safe with thorough study and the right engineering solutions and applications.
However, rigorous inspection and regular maintenance then become of the highest importance. The lack of maintenance of slopes and retaining walls is a major contributory factor to many landslides in Malaysia. Neglect can result in serious consequences and the cost of maintenance is far cheaper than the cost of repair after neglect. To be assured of safety, homeowners and landowners should follow a simple three-step process: Recognise, Prevent, Maintain.
RECOGNISE: Property owners should recognise the risk and signs of slipprone slopes on their land. Landslides generally occur on steep slopes with gradients of greater than
The
landslide in 2013. 30 degrees. Signs that may be observed include trees that lean in different directions; tilting fencing posts; or sunken or “lumpy” ground. “Trees with knees” are another sign, where a tree has grown in a different direction after soil shifted due to substantial erosion or a landslip event. Homeowners and landowners who see these signs should consider getting a geotechnical assessment.
PREVENT: Mitigating measures can be taken to reduce the risk and prevent landslips or landslides. Depending on the geotechnical assessment, the appropriate measures could include landscaping, drainage, grading or retaining structures.
Landscaping would involve growing the right ground cover on the slopes. Trees may not always be appropriate, as their weight could contribute to destabilising a slope.
Drainage is of the utmost importance to ensure surface water is discharged harmlessly and not over a slope.
Grading means removing earth and soil to reduce the steepness of the slope and make it a more gentle slope. Retaining structures mean putting in place structures to help improve the resisting force of the slope in order to exceed any driving force that causes soil movement. These include rubble walls, crib walls and gabion walls.
MAINTAIN: Careful periodic inspection and regular maintenance is the key to safely maintaining slopes and any retaining structures. Ideally, a log or record should be kept of inspections, especially where the slope is particularly steep.
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