Factors encouraging the rock slope instability

Slope stability refers to the condition of inclined soil or rock slopes to withstand or undergo movement.

a. Surface Water:

Surface water is that water which is found available either through heavy rainfall or from other water resources traversing from one place to another through the ground surface. Such water may be sailed or filtered from surface to underground causing shallow failure.

b. Ground water:

Ground water is that water which is being under the surface of the ground. It increases pore water pressure at depth causing the plane failure.

c. Lithology

Development of weak rocks such as fractured slates, phyllites and schists are highly susceptible to instability. Even presence pf calcareous interlayer in these rock increases porosity and vios formation owing to leaching and dissolution. Furthermore inter bedding and alteration of hard and soft rocks are other causative factors.

D. Rock structure

Intense folding, faulting and thrusting rock are highly vulnerable to sliding. Presence of many joint sets and fractures on rocks also lead to failure. Randomly oriented and stress relief also lead to failure,

e. Weathering:

Himalayan rock belongs to warm temperate and subtropical climatic zone. These climates are susceptible to disintegrate and decompose rocks in short time . Deep weathered rocks could not stand properly and any one agent such as rain, wind, glacier,etc. may wash away these rocks to low land. Nepal Himalaya constitutes phyllites and schists predominately. For example: when phyllites come in contact with water, sericite minerals present in it decompose vary fast and become hazardous in the point of view from instability.

Other factors are  slopes,  bank undercutting, precipitation, seism and added weight .