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

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

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

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

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

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

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.

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

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)

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

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

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

TERIMA KASIH