1. MEKANIKA TANAH I PERTEMUAN II PERMEABILITAS TANAH Oleh :
Arwan Apriyono
PROGRAM STUDI TEKNIK SIPIL JURUSAN TEKNIK
FAKULTAS SAINS DAN TEKNIK UNSOED
TAHUN 2011

2. INTRODUCTION
What is permeability?
A measure of how easily a fluid (e.g., water) can pass through a porous medium (e.g., soils)
water
Loose soil
- easy to flow
- high permeability
Dense soil
- difficult to flow
- low permeability

3. Hukum dalam Konsep Permebilitas
INTRODUCTION
Hukum dalam Konsep Permebilitas
Hukum Bernoulli
(Aliran Gas dan Fluida)
Hukum Darcy
(Aliran Air pada Media Porous)

4. Bernoulli’s Equation 1. Kinetic energy 2. Strain energy
The energy of a fluid particle is made of:
1. Kinetic energy
fluid particle
- due to velocity z
2. Strain energy
- due to pressure
datum
3. Potential energy
- due to elevation (z) with respect to a datum

5. Bernoulli’s Equation Velocity head + Pressure head + Elevation head
Expressing energy in unit of length:
Velocity head +
Total head =
Pressure head +
Elevation head

6. Bernoulli’s Equation Velocity head + Pressure head + Elevation head
For flow through soils, velocity (and thus velocity head) is very small. Therefore,
Velocity head +
Total head =
Pressure head +
Elevation head
Total head = Pressure head + Elevation head

7. At any point within the flow regime:
NOTES
At any point within the flow regime:
 Pressure head = pore water pressure/w
 Elevation head = height above the selected datum

8. NOTES
If flow is from A to B, total head is higher at A than at B.
water A B
Energy is dissipated in overcoming the soil resistance and hence is the head loss.

9. length AB, along the stream line
Hydraulic gradient (i) between A and B is the total head loss per unit length.
water A B
length AB, along the stream line

10. Darcy’s Law
Velocity (v) of flow is proportional to the hydraulic gradient (i) – Darcy (1856)
v = k i
Permeability
or hydraulic conductivity
unit of velocity (cm/s)

11. Permeability Values (cm/s)
10-3
10-6
100
clays
gravels
sands
silts
Coarse
Fines

12. CONSTANT HEAD (TINGGI KONSTAN)
INTRODUCTION
CONSTANT HEAD (TINGGI KONSTAN)
SUITABLE FOR SANDY SOIL, SAND OR GRAVEL WHICH HAVE BIG VOID RATIO VALUE
BASIC EQUATION :
Bina Nusantara

13. EXAMPLE 1 q = 1 ft3/hr Question :
Find the permeability coefficient of sand in ft/min
Bina Nusantara

14. TERIMA KASIH