MEKANIKA TANAH I PERTEMUAN II PERMEABILITAS TANAH Oleh

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

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 Dense soil - easy to flow - difficult to flow - high permeability - low permeability 2

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

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 4

Expressing energy in unit of length: Velocity head + Total head = Pressure head + Elevation head

For flow through soils, velocity (and thus velocity head) is very small. Therefore, 0 Velocity head + Total head = Pressure head + Elevation head

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

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

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

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

10 -6 clays 10 -3 silts 100 sands Coarse Fines 11 gravels

INTRODUCTION � SUITABLE FOR SANDY SOIL, SAND OR GRAVEL WHICH HAVE BIG VOID RATIO VALUE � BASIC EQUATION :

q = 1 ft 3/hr Question : Find the permeability coefficient of sand in ft/min Bina Nusantara

TERIMA KASIH