Final answer:
Overpressurized pore water causes slope failure by reducing the friction between sediment particles, which can lead to landslides. Factors such as heavy rains, earthquakes, and volcanic activity contribute to this overpressurization. Effective drainage is essential to mitigate such risks.
Step-by-step explanation:
Overpressurized pore water in a pile of sediments can cause slope failure because it reduces friction between particles. When sediments become saturated with water, weak slopes can fail due to the loss of effective stress that holds sediment particles together. This is because the water pressure within the pores of the sediment counteracts part of the gravitational force that contributes to the friction and stability of the slope. When grains of sediment are surrounded by pressurized water, they are more likely to slide past each other, leading to slope failure or landslides.
Multiple factors can contribute to the overpressurization of pore water, such as heavy rains, snowmelt, accumulation of rain or snow, and human activities like stockpiling of materials. Compaction and cementation reduce porosity by bringing the grains closer together, but if water is trapped, the pressure in the pore spaces may increase. Particularly, earthquakes and volcanic eruptions can also create stresses or add loose materials that make slopes more prone to failure when combined with pore water overpressurization.
Therefore, effective drainage can help to mitigate the risk by allowing water to escape from the soil, reducing the possibility of creating pressurized conditions that trigger slope failures.