Physical Properties of Rock, Soil and Water
Coulomb equation
1.
dry soil
o
u is atmospheric
o
c = 0
o
S = normal stress * tan phi
2.
wet soil
o
c > 0, u <0
o
effective normal stress = normal stress  (u) = normal stress + u, that is water
increases the normal stress (adds weight to the soil)
o
s = c + normal stress * tan phi
3.
saturated soil
o
u > 0
o
S = c + (normal stress  u) tan phi
Note
•
when c = 0 (# 2 above), tan phi = shear strength/ normal stress, when shear strength =
shear stress,
i.e.
at the critical stability threshold (failure is imminent)
•
therefore, tan phi = shear stress/ normal stress = W sin theta / W cos theta = tan theta
•
or tan phi = tan theta,
i.e.
slope angle (theta) is governed by friction (phi)
Factor of Safety
shear strength/ shear stress
•
= 1, critical threshold
•
< 1, slope instability
•
> 1, slope stability
Atterberg limits
behavoir of fine sediment:
plastic limit
water content at the transition from solid to plastic behavior, measured when a wet thread
of fine soil begins to crumble
liquid limit
This preview has intentionally blurred sections. Sign up to view the full version.
View Full Document
This is the end of the preview.
Sign up
to
access the rest of the document.
 Fall '10
 JayMuza
 Geology, Erosion, Force, Atterberg limits, Shear strength, normal stress

Click to edit the document details