“Heavy rain causes landslide at Jalan Dermawan”
Due to heavy rains on 18 December 2006, a landslide occurred on 19 December at Jalan Dermawan where residents complained of hearing a cracking sound at the back of their homes at 10 am in the morning. Residents were evacuated from their homes for safety precautions. Fallen trees from the landslide covered the road which became impassable to traffic and mud and trees had also fallen into the garage areas of some of the houses. Thankfully, no one was hurt during the landslide.
This example of landslide in Singapore is caused my heavy rainfall which is one of the common causes for such movement as water plays an important role in de-stabilizing the slope. The most important effect of the water is that it increases pore pressures. This reduces the frictional forces between the soil particles and destabilizes the slope. The presence of water results in increased in weight, lubricating effect between rock layers and reduced friction between soil particles thus causing the landslide at Jalan Dermawan.
Mitigation Measures
1) Slope Drainage
Slope drainage is the cliff-face method of control which involves reducing pore pressures using drainage lines within cliff faces, field drains, gravel trenches and by intercepting overland flows. Shallow surface drains are used to intercept the overland flow while vertical drainage is emplyed to remove the water from the cliff face as well as the body of the cliff.
This method is especially useful in clay cliffs which are susceptible to slumping triggered by high water content in the clay. This method deals with the main factor of cliff face failures which is the action of water and therefore it is one of the most effective way of strengthening the cliff. However, changes in cliff hydrology can have impacts on the ecology and land uses of the cliff top. Successful drainage schemes may also result in subsidence of cliff-top land as the cliff dries out. Implementation of a comprehensive drainage network sometimes requires a considerable level of technical knowledge and expertise.
2) Cliff/Slope modification
The aim of this modification is to reduce the height of the cliff. If the height and slope angle of the cliff are decreased then there is a reduced chance of mass movements occurring as the greater slope angle and height results in an increased shear stress. Cliff modification involves blasting the upper cliff to reduce its height and very often the blast materials are used to stabilize the cliff foot as toe support.
If the blasting is done with care, the mass movements can be minimized as the shear stress caused by height is reduced. However, this method of modification can backfire and result in increased mass movements as the blasting can cause instability in the rock structure.
Due to heavy rains on 18 December 2006, a landslide occurred on 19 December at Jalan Dermawan where residents complained of hearing a cracking sound at the back of their homes at 10 am in the morning. Residents were evacuated from their homes for safety precautions. Fallen trees from the landslide covered the road which became impassable to traffic and mud and trees had also fallen into the garage areas of some of the houses. Thankfully, no one was hurt during the landslide.
This example of landslide in Singapore is caused my heavy rainfall which is one of the common causes for such movement as water plays an important role in de-stabilizing the slope. The most important effect of the water is that it increases pore pressures. This reduces the frictional forces between the soil particles and destabilizes the slope. The presence of water results in increased in weight, lubricating effect between rock layers and reduced friction between soil particles thus causing the landslide at Jalan Dermawan.
Mitigation Measures
1) Slope Drainage
Slope drainage is the cliff-face method of control which involves reducing pore pressures using drainage lines within cliff faces, field drains, gravel trenches and by intercepting overland flows. Shallow surface drains are used to intercept the overland flow while vertical drainage is emplyed to remove the water from the cliff face as well as the body of the cliff.
This method is especially useful in clay cliffs which are susceptible to slumping triggered by high water content in the clay. This method deals with the main factor of cliff face failures which is the action of water and therefore it is one of the most effective way of strengthening the cliff. However, changes in cliff hydrology can have impacts on the ecology and land uses of the cliff top. Successful drainage schemes may also result in subsidence of cliff-top land as the cliff dries out. Implementation of a comprehensive drainage network sometimes requires a considerable level of technical knowledge and expertise.
2) Cliff/Slope modification
The aim of this modification is to reduce the height of the cliff. If the height and slope angle of the cliff are decreased then there is a reduced chance of mass movements occurring as the greater slope angle and height results in an increased shear stress. Cliff modification involves blasting the upper cliff to reduce its height and very often the blast materials are used to stabilize the cliff foot as toe support.
If the blasting is done with care, the mass movements can be minimized as the shear stress caused by height is reduced. However, this method of modification can backfire and result in increased mass movements as the blasting can cause instability in the rock structure.
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