Transcript Introduction to Soils - San Diego State University

Consolidation I
(CH11)
Consolidation
Process by which an
in s’ causes a deformation of a soil
mass by reducing its e (water seeps out of the voids).
How can s’ increase?
1. Water level decreases
2. A load is induced (we will consider fills)
Consolidation Physics
From Coduto 1998 (text)
Hydrostatic Pore Pressure, uh
Ground surface
Soil , g
z
hp
uh  g w  hp
“hydrostatic pore water pressure at A”
Excess Pore Pressure, ue
Pore pressure generated in excess of
hydrostatic due to an applied load.
ue is temporary
u  uh  ue
Loading Conditions
shear
LOOSE
DENSE
Soil densifies due to the change in structure (e
(water squeezes out of the voids)
)
Loading Conditions
LR: Loading rate?
shear
DR: Drainage rate? = fn (k)
DRAINED
LR
 low Water drains out, volume change, e
DR
LR
 hi
UNDRAINED
DR
Water carries load, no volume change, e = ct.
ue is generated!
Loading Conditions
Drainage rate = fn (k)
Units?
Consolidation = time - dependent
Consolidation Physics
From Coduto 1998 (text)
Consolidation Physics
From Coduto 1998 (text)
Important Conclusion
Consolidation involves a gradual
transfer of stress from the pore
water (ue) to the soil particles (s’).
Important Conclusion
Deformation occurs only if
particles experience a change in
effective stress.
Lab Testing
Consolidation test
to assess the compressibility
characteristics of clays.
Lab Testing
Board…
Field vs. Lab
From Coduto 1998 (text)
Consolidation Curve - LAB
e
eo
yield
cr
cc
sp’
s’ (log scale)
Example
Example