**6. Landslides prevention and control**

Initially, the materials with a huge volume of water in the convex part of the slope begin to slide and roll over the concave part and finally on a fairly regular part (settlement areas). The extraordinary rapid movement of sediment and water destroys and buries people and houses, and finally due to the non-cohesive nature of slope materials, the slide terminates as dry flow. The steps involving the development of landslides (**Figure 5**) can be summarized

• Due to torrential rain, rainwater starts to infiltrate into the slope materials increasing pore

• On top of hills, crown cracks developed and those cracks allow more and more water to

• Landslides initiate when threshold for shear resistance is exceeded by pore water pressure.

• The resulting pore water pressure exceeds the shear resistance of the slope materials.

as follows:

water pressure.

infiltrate into the materials.

140 Engineering and Mathematical Topics in Rainfall

**Figure 5.** Stages of development of landslides.

The choice of landslides prevention and control measures depend upon the geological condition, physiography, available technology and above all the socioeconomic condition of the people. Important landslides prevention and control methods are [11] as follows:

Avoid method: If slope is extremely hazardous and landslides control measures are expensive, complete avoidance of the area is the only sustainable solution.

Water control method: Usually, rainwater infiltrates into the slope materials and makes them exposed to landslides. Proper management of rainwater through drainage from the slope instead of infiltration into the soil can significantly reduce landslide vulnerability. This can be realized by afforestation and building suitable drainage structures on slopes.

Excavation method: A slope turns out to be vulnerable when the natural angle of the slope becomes higher than the angle of internal friction of slope materials. The main objective of excavation method is to stabilize the slope by modification of the slope angle so that the internal friction angle of slope materials is higher than the slope angle.

Retaining structure: Structures that can be used for slope stability are buttresses, retaining walls, shear keys, guide walls, and so on.

The best prevention method for Chittagong area might be complete avoidance of hazardous slopes. A second option might be excavation method which suggests reforming the slope so that the slope angle becomes less than the angle of friction of slope materials. Thirdly, retaining structures like retaining wall, guide walls or buttresses can be constructed to protect the slopes from further landslides. However, if we could harness the modern communication and information technology to provide an in-advance warning prior to an incidence by developing real-time landslides early-warning system, then that should be one of the best options at least to save lives.
