mod2 Flashcards
Zone I
initially high rate of settlement and excess pore pressure - undrained behaviour occurs at the very beginning
Zone II
transient behaviour - partial drainage
settlement rate reduces over time
Zone III
‘drained’ behaviour occurs here - excess pore pressure has dissipated
Isochrone property 1
The slope of the isochrone at any point is proportional to the hydraulic gradient magnitude
due/dz = gammaw * i
Isochrone property 2
the overall compression, W, measured at the surface of the sample at a given consolidation time t, is equal to 1/Eo’ times the area swept out by the isochrone
First Stage of Consolidation
L < d
W = deltastressv / Eo’ * sqrt(4/3 * cv * t)
Second Stage of Consolidation
L = d W = d * sigmav / Eo' * (1 - 2/3 exp(1/4 - 3cvt/d ) )
Cv for sand
infinity
Cv for silt
10 ^ -6 m2/s
Cv for clay
10 ^ -8 m2/s
area outside of parabola
x * y / 3
Cv relationship with soil permeability
increases
- higher permeability means water flows out of sample quicker
Cv relationship with stiffness Eo’
increases
- stiffer soil implies smaller compression (settlement) for a given increment of land
- this in turn implies that a smaller amount of water needs to be expelled
R
degree of consolidation
R = W / Wult
- gives idea of how much settlement out of the total expected has taken place at a particular time
- first stage: R <= 1/3
T
Time factor
T = cv * t / d^2
- gives comparison of a particular length of time for consolidation relative to the total time expected for complete settlement
- first stage: T <= 1/12
