Environmental Engineering Reference
In-Depth Information
F
F
σ 1
σ 1
σ 3
σ 3
P
P
σ n
σ n
S
(a)
(b)
F
F
S
σ 1
P
P
P
S
S
σ 3
P
σ n
(c)
(d)
F
σ 1
P
S
F
σ 3
P
S
σ n
σ n
(e)
(f)
FIGURE 3.23
Some field conditions involving failure by rupture: (a) foundations; (b) retaining structures; (c) slopes;
(d) ground anchors; (e) wall anchors; (f) embankments.
Undrained or drained conditions: It relates to the ability of a material to drain under
applied stress and determines whether total or effective stresses act.
Loading direction: Forces applied parallel to weakness planes, as represented by stratifi-
cation in soils, foliation planes, or joints in rock masses, will result in lower strengths than
if the force is applied perpendicularly. Compressive strengths are much higher than ten-
sile strengths.
Displacement and normal stress: In some cohesive materials, such as overconsolidated fis-
sured clays and clay shales, the strain at which the peak stress occurs depends on the nor-
mal stress level and the magnitude of the peak strength varies with the magnitude of
normal stress (Peck, 1969) as shown in Figure 3.24. As strain continues the ultimate strength
prevails. These concepts are particularly important in problems with slope stability.
φ
The stresses acting on a confined specimen of dry cohesionless soil, either in the ground or
in a triaxial testing device (see Section 3.4.4) , are illustrated in Figure 3.25. p is the applied
stress,
Angle of Internal Friction
σ 3 (in testing p is termed the deviator stress
σ d ). As stress p is gradually increased, it is resisted by the frictional forces acting between
σ 3 is the confining pressure, and
σ 1
p
 
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