Sheet Cover

In this picture, the hazards of mass movement are mitigated with the covering of the slope using a large sheet waterproof material, often made from canvas or plastic. This helps to prevent landslides, flows and heaves. In this case, the slope may be exceptionally vulnerable to slope failure and may therefore require the placement of such a material over it.

The removal of this mechanism of mass movement is essential to hazard mitigation because water adds weight, lubricates slope materials and increases pore water pressure.

Water and sand or soil grains are drawn together by capillary attraction. This attraction is a result of surface tension where exposed surface of liquids contract to the smallest possible area. If too much water comes in contact with a slope and its materials, the soil becomes saturated and may turn into a slurry that can flow down the slope.

Another important aspect of the mechanism of water in the study of this particular slope is that of the reduction of shear strength. Water can reduce shear strength in 6 ways. However, for this slope only a few are relevant. Firstly, it can reduce the natural cohesiveness as water will push the soil clumps or sand grains further apart and reduce friction. It can also add weight by filling the pores of sedimentary rocks which are highly porous. Lastly, it can also dissolve materials and break down the materials that bind the rock together.

The sheet can also prevent rainsplash and raindrop impact, which has the capacity to erode soil, sand and fine regolith, leading to the mass movement process of soil creep.

With the sheet cover in place, water from precipitation will fall on the sheet and slide down to the bottom of the slope where there is a drain that will channel the water away. This allows for the slope to remain relatively dry, especially during times of heavy thunderstorms or extended periods of rain.

This form of mitigation is also essential because much of the roads and highways had to be constructed through an area with exceptionally hilly and undulated terrain. As such, most of the slopes still exist and may have also become weakened during the course of the construction because of the removal of materials that may have been supporting the slopes.

Done By : Wesley Teo, 2AD2