Stability of Slopes in Civil Engineering point
slopes of earth are of two types
1. Natural slopes2. Man made slopes
The slopes whether natural or artificial may be
1. Infinite slopes2. Finite slopes
Slope stability -
It is very important in design and construction of earth dam. the result of slope failure can often be catastrophic, involving the loss of property and many livesCauses of Failure of Slopes
1.Gravitational Forces2. Seepage Forces - forces due to seepage water.
3.Erosion of the surface of slopes due to flowing water
4.The sudden lowering of water adjacent to a slope
5. Forces due to earthquakes
Erosion n the surface of a slope may be the cause of the removal of a certain weight of soil, and may thus lead to an increased stability as far as mass movement is concerned. On the other hand, erosion in the form of undercutting at the toe may increase the height of the slope, or decrease the length of the incipient failure surface, thus decreasing the stability.
When there is a lowering of the ground water or of a free-water surface adjacent to the slope,for example in a sudden draw-down of the water surface in a reservoir there is a decrease in the buoyancy of the soil which is in effect an increase in the weight. This increase in weight causes increase in the shearing stresses that may or may not be in part counteracted by the increase in shearing strength,depending upon whether or not the soil is able to undergo compression which the load increase tends to cause . If a large mass o f soil is saturated and is of low permeability, practically no volume changes will be able to occur except at a slow rate, and in spite of the increase of load the strength increase may be inappreciable.
The shear strength of soil is assumed to follow Coulomb's law
s = c + σ. tan ϕwhere,
c' - effective unit cohesion
σ' = effective normal stress on the surface of rupture = (σ - u)
σ - total normal stress on the surface of rupture
u - pore water pressure on the surface of rupture
u - pore water pressure on the surface of rupture
ϕ' = effective angle of internal friction.
2. Factor of safety with respect to cohesion. This is termed the factor of safety with respect to height.
FACTOR OF Safety
stability analysis, two types of factors of safety are normally used.
They are
1. Factor of safety with respect to shearing strength.2. Factor of safety with respect to cohesion. This is termed the factor of safety with respect to height.
