Falling Head Conductivity
Oklahoma State University
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This procedure covers the measuement of
saturated hydraulic conductivity by the falling head method. The
only special equipment needed is the test column. A burette is
used as the supply reservior and the measured data is simply the
burette volume at various times.
Hydrology and Hydraulics, by D. McWhorter and D.K. Sunada. Pages
- Flexible wall column with fittings (Column,
membrane, 2 end plates, 2 support plates, 2 wire screens, 2 bolts,
6 washers, 6 wing nuts, 2 water end connections, 1 vacuum connection.)
- Glass beads or oven dried sand of various
- Packing rod, ruler, and spoonula,
- Meter stick
- Plastic beaker
Procedure for Column Packing
- Weigh column and fittings. Include all
- Draw vacuum on membrane and measure column
inside diameter and length. Measure height of interior support
plates. Calculate volume based on inside diameter, and length,
less the height of the support plates.
- Place end support plate and wire screen.
- Note particle size of material used.
- If the sand is smaller than #50 place
a filter paper on bottom screen.
- Pack column with soil in lifts, no greater
than 5 cm in height. Tap column to settle sand into place. Carefully
remove enough sand to place last support plate.
- Carefully assemble column with bolts,
washers and wing nuts.
- Weigh packed columns with all fittings
- Measure diameter of burette and calculate
- Measure distance between burette maximum
burette volume and calculate change in head with respect to volume.
- Mount burette, fill with test solution,
and run water out of line.
- Slowly allow solution to fill column.
- Disconnect effluent line, mount it over
beaker for running, and measure its height.
- Run about one pore volume through column
to work out air. Turn-off and refill burette.
- Record height of drip point above counter
or floor depending on your set up, hdrip.
- Record burette capacity, Vmax
and length between the zero and the maximum graduations, Lb.
- Record height of the burette maximum-volume
graduation above counter or floor, hmax.
- Start column and timer.
- Record burette volume and time for a minimum
of six readings.
- Share results with other lab groups.
With the data collected determine the following
- Dry bulk density of column packing, rb
Dry weight of soil / CV
where CV is the volume of the column.
- Column pore volume, PV, determined
PV = CV * (1- rb/rg )
where rg is the
mineral density and is assumed to equal 2.65 gm/cm3
for sand and glass.
- Calculate the differential head loss,
Dhi for the various time reading with,
is the height of the burette's maximum volume, hdrip
is the height of the drip point, Vmax is the
maximum volume of the burette, Vi is burette
volume at time ti, and Lb
is the burette length.
- Mean measured conductivity of the material
is given by,
where K is the hydraulic conductivity,
a is the area of the reservoir, A is the area of
the column, Dho is the initial head loss at time, t =
Provide Introduction, Procedures,
and Results of the experiment. Discuss measured
conductivity relative to material and packing density. The results
should contain a plot of ti versus Ln(Dho/Dhi). The
plot should be a straight line with a slope of aL/AK.
Units are to be reported in the cgs system,
(centimeters, grams, and seconds). Variable dimensions are:
L, h: cm