Mass Movements in Singapore

Mass movement is the downward movement of material such as rock regolith and soil on slopes, under the influence of gravity, without erosive agents like wind water and ice. The various types of mass movement in Singapore are, fall, slide and heave.
 

ROCKFALL

Rockfall took place on the steep walls of the Quarry at the Bukit Timah Nature Park. This steepness (50 to 90 degrees) greatly exceeded the angle of friction and the internal strength was overcome, resulting in rock fall. Factors affecting this movement are the presence of joints, faults and fissures that allow weathering processes such as thermal disintegration and water pressure in pores or joints to occur.

SOIL CREEP

Soil creep is the gradual and continuous movement of soil down a hill slope under the influence of gravity. Damp soil and trampling by animals and humans can result in soil creep. The creep is evident from the tilting of trees. Due to Singapore's hot and wet climate, the process of wetting and drying is common, and as the soil dries, a crack may result from contraction. When it rains again, this crack will be filled with material from upslope and a net movement downslope takes place.

LANDSLIDE

A landslide is the movement of rock and regolith where the masses of materials retain their coherence while sliding. Landslides are common in Singapore because abundant rainfall, characteristic of tropical weather, makes rock structures vulnerable to weathering. Water accumulated at the base of the impermeable layer increases the weight and lubricating effect between layers of rock. This reduces the friction between soil particles and rock layers, resulting in the negative loss of pore water pressure.

Landslides can also be caused by human activities when piles in soft clay are subjected to lateral forces induced by horizontal soil movements from nearby construction activities such as deep excavations, tunnelling and approach embankments.
 

Case Study 1: 2007 Landslide Incident

On 11 January 2007, heavy downpours in Singapore caused soil near the Bukit Batok MRT Station's tunnel to loosen, releasing a landslide. Other than the Bukit Gombak area, landslides were also reported in Westlake Avenue off Thomson Road, Parbury Avenue off Upper East Coast Road, and Jalan Girang in the Braddell estate.

This damaged property and affected families who had to be evacuated from their homes.

Case Study 2: Collapse of Nicole Highway

The Nicoll Highway Collapse occurred on 20 April 2004 when a tunnel, being constructed for a MRT line collapsed. It caused a cave-in and brought the highway and surrounding land down into it, forming a ravine 30m deep. This was the result of the weakening of the underlying soil due to construction.

Singapore’s Mitigation Strategies

Hazard mapping

Singapore engineers define the areas of potential landslide activity and mass wasting hazards on a map. If used properly in the planning process, hazard mapping reduces the risk of landslides by keeping people away and preventing any construction from taking place on the slope. Measures are also taken to stablise weak slopes.

Monitoring and interpretation

Engineers monitor and interpret slide movements that result from rainfall. Instruments are used to detect ground movements and ground-water pressure.

Slope drainage reduces pore water pressure by introducing drainage lines within a cliff face to intercept overland flow and remove water from the cliff’s surface and body. Slopes are also covered by a large sheet of durable plastic to prevent mass movement.

Terracing

Terracing lowers a slope's gradient and makes it more stable.        

   

One example of Mitigation in Singapore
 


Parts of Pulau Ubin was subjected to aggressive soil erosion in 2000. Picture A has a steep sided slope and after heavy rain, the sand will become saturated and turn into a slurry and flow downslope. Not only that, water is heavy and the infiltration of water into the soil will also cause mass movement to occur. Water flowing through rocks can dissolve some of the materials that bind the rock together. The removal of cementing materials decreases the cohesion of rocks and saps some of the slope strength, preparing it for mass movement.

After 2 years of vegetation


 
Bushes and small light weighted plants are planted on the slopes to absorb water, decreasing the saturation limit of the slope material. It also bind together soil particles and hold soil to bedrock with their roots reducing the likelihood of rapid or mass wasting of a slope. 
 

i have a terweeble stomach ache and have been spending ages trying to get this to work. (: