★consolidation is fⁿ of eff stress but not total stress
i) initial → expulsion of air
Si = qB(1 - μ²)/Es ∝ If
ii) primary →excess pore water due to ↑ total stress. , time dependent
⇒ ∆H/H = ∆e/1+eo
⇒∆H = mv ∆ ⁻σHo = {CcHo/1+eo}log(
iii) secondary → plastic readjustment (due to creep) , constant eff stress.
⇒significant only for Highly plastic soil.
★Temp ↑ : rate of consolidation ↑
★Oedometer test / consolidation test :
1D consolidation (zero lateral strain )
max pore water pressure will at centre
★odometer : distance in vehicle.
⇒Routine consolidation test (lab) : specimen t = 20mm , dia = 60mm
⇒general settlement formula {∆H/H = ∆V/V = ∆e/1+eo}
⇒e = wG(S=1) ,∆H = Hi - Hf , ∆e = eo-ef
1.} compression index (Cc)(coeff of compression) : a constant value
Cc ∝ LL
Cc = 0.009 (LL-10)← undisturbed & medium sensitivity.
Cc = 0.007(LL-10)←Remoulded & low to medium sensitivity.
Cc = ∆e/log(σ2/σ1) ∝ ∆H
Cc = 0.115Wn
2}Coeff of compressibility (Av) : variable not constant
Av = strain/stress = ∆e/∆σ ←m²/kn
1D & ∆σ = small then Av = constant.
3} coeff of vol compressibility (mv)
mv = Av/1+eo
★eo ↑ : ultimate settlement ↓
TERZAGHI 1-D CONSOLIDATION TEST.
→ only for 1-D
→analysis to behaviour of spring piston model
→homogeneous & isotropic soil
→fully saturated , laminar flow ( Darcy law valid)
→speciman t = 60mm
→e vs σ relation is linear
→rate of change of pore water with time
δu/δt = Cv x δ²u/δz² (u=γwh)
⇒Coeff of consolidation :
{Cv = K/mvγw = k(1+eo)/Avγw } ←cm²/s
→determination of Cv:
a} casagrande method ( logarithm of time fitting method)
Cv ∝ 1/LL ∝ 1/plasticity & Cc ∝ LL ∝ plasticity.
b} Taylor's m (square root time fitting )
Taylor curve much suitable as compared to casagrande m.
TIME FACTOR
Tv = Cvt/d². d = H (1 way drainage) & d= H/2 (2 way drainage)
Tv = πu²/4 (u ≤ 60%)
{ T50 = 0.196 , T90 = 0.848 , T60 = 0.287 , To =0 }
u = ∆h/∆H = (eo - e )/(eo - ef)
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