15 AUGUST 2005
drainage should be designed to divert water away from trenches.
Factors Controlling Stability of Sloped Cut in Some Problem Soils
PRIMARY CONSIDERATIONS FOR SLOPE DESIGN
Field shear resistance may be less than suggested by laboratory tests. Slope failures
may occur progressively and shear strengths reduced to residual values compatible
with relatively large deformations. Some case histories suggest that the long-term
performance is controlled by the residual friction angle which for some shales may be
as low as 12 degrees. The most reliable design procedure would involve the use of
local experience and recorded observations.
Strong potential for collapse and erosion of relatively dry material upon wetting. Slopes
in loess are frequently more stable when cut vertical to prevent infiltration. Benches at
intervals can be used to reduce effective slope angles. Evaluate potential for collapse
as described in UFC 3-220-10N.
Significant local variations in properties can be
expected depending on the weathering profile from parent rock. Guidance based on
recorded observation provides prudent basis for design.
Considerable loss of strength upon remolding generated by natural or man-made
disturbance. Use analyses based on unconsolidated undrained tests or field vane
Talus is characterized by loose aggregation of rock that accumulates at the foot of rock
cliffs. Stable slopes are commonly between 1-1/4 to 1-3/4 horizontal to 1 vertical.
Instability is associated with abundance of water, mostly when snow is melting.
May settle under blasting vibration, or liquify,
settle, and lose strength if saturated. Also prone to erosion and piping.