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Permeability: Soil Mechanics Laboratory

General
background information

The objective of the permeability test is obviously to determine the permeability of the soil.  Soil permeability is used to calculate drainage.  For example, perimeter drains around a building and infiltration through a dam or landfill structure.

The rate at which water flows through a soil is proportional to the hydraulic gradient and is expressed by Darcy's Law as:

Darcy's Law

Darcy's law

The coefficient of permeability varies with the type of soil and conditions.  It is influenced by:

  1. Size and shape of the soil particles
  2. Void ratio
  3. Temperature
  4. Degree of saturation

Empirical methods to estimate permeability using Hazen equations:

Hazen equations

for sands:

k = CD102
k = coefficient of permeability (cm/sec)
C = 0.4 to 1.2, typically 1.0

D10= grain size of 10% passing (mm)

for estimating flow through graded sand filters (clean sands and gravels):

k = D60D10
k = coefficient of permeability (cm/sec)
D60= grain size of 60% passing (mm)

D10= grain size of 10% passing (mm)

Several different laboratory testing methods can be performed to more accurately determine permeability, including constant-head and falling-head types.   For our purposes, a falling-head test will be performed.  The falling-head test essentially consists of measuring change in head and quantity of flow over time as follows:

Falling head test

Falling head equation

Error considerations

Several errors could have affected the test results:

  • air trapped in sample or sample not 100% saturated;
  • soil was washed from the sample;
  • some of the head loss occurred in the apparatus rather than in the sample;
  • not starting and stopping stop watch at correct point;
  • sample settling during test;
  • sample disturbed by flowing water at inlet;
  • difficulty of accurately measuring heads relative to tail water and significant figures

 

Apparatus
Get a bigger hammer

 

Permeameter (1/30 cf volume) apparatus
Burette stand
Meter stick
#4 sieve
Stopwatch
Pan
Tamper

 

Procedure
Get a disk!

 

 

Procedure / Data Sheets [right-click | "save target as" xls]

References

Holtz, Kovaks and Sheahan (2011), section 7.4

Holtz and Kovaks (1981), pages 199-245.

Das (1998), chapter 5, starting on page 159.

Gorrill (1998), pages 17-20, 59.

Bowles (1986), pages 93-105.

[full citations]


crestlogotiny.jpg (2k) Manion, William P. (wmanion@(nospam)maine.edu "Soil Mechanics Laboratory Course CIE 366." University of Maine, Civil and Environmental Engineering Department, Orono, Maine.  04 January 2011 02:33 PM.  http://www.civil.maine.edu/cie366/.