⇒1D flow & fully saturated soil
⇒Re ≤ 1
⇒ laminar flow
⇒fine grounded soil ,not for gravel
⇒{V = Ki} & {q = KiA} i = ∆h/L
V→discharge velocity or superficial V or avg velocity
⇒Vs = V/n = Ki/n
★Vs > V
⇒ coeff of percolation Kp = K/n
⇒ coeff of Transmissibility T = KH ,H←thickness of aquifer
★coeff of absolute permeability / intrinsic permeability: Ko = Kμ / γw (cm² or m²)
Factor affecting K:
⇒K ∝ D10²
⇒K ∝ e³/ 1+e ∝ e²
⇒K ∝ γw/μ
⇒K ∝ 1/impurties
⇒K ∝ DOS
⇒K ∝ Temp ∝ 1/μ
⇒K ∝ 1/ρsoil
⇒K ∝ size ( less size → high compressibility)
⇒K ∝ 1/compressibility
⇒– σ↑ : e↓ : K↓
Determination of K:
A} laboratory methods
A.1) constant head method :
⇒coarse graind soil & pervious soil like sand & gravel
⇒K = QL/thA ( Q=kia)
A.2) Falling/variable head m:
⇒fine soil & impervious soil like clay
⇒K= (aL/Ato) x (2.303log(h1/h2))
B} Field test:
B.1) Pumping out :
⇒large Area
⇒homogeneous coarse grain soil
⇒radii of influence: R = 3000d √K (sichardts formula)
B.2) Pumping in:
⇒small Area
⇒economical bu less reliable
C} Indirect method :
i) from consolidation data
ii) from particle size & Specific surface area
⇒kozeny - Carman equation :
K = (1/c) x (γ w/μ) x (e³/1+e) x D10²
⇒Allen Hazen's formula :
K = CD10² cm/s C=100,D10→cm
⇒Louden's formula :
⇒Tarzaghi's eqⁿ
K= 200e²D10²
⇒consolidation eqⁿ :
K = CvMvγw
★{K1/K2 = tanϕ1 / tanϕ2}
Gravel > 1cm/s →very pervious
Sand = 1 to 10⁻³ →Pervious
Silt = 10⁻³ to 10⁻⁶ →poorly pervious
Clay < 10⁻⁶ cm/s →Impervious
Kh = ΣKiHi / ΣHi
Kv = ΣHi / Σ(Hi/Ki)
★(Kh > Kv)
eff permeability k' = √(Kx.Kz)
Tags :
SOIL and FOUNDATION
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