Table of Contents
Pressure/Tensiometer Sensors in an Engineered
Dam Failure Experiment Don Baker, Postdoctoral Associate USDA-ARS
Hydraulics Engineering Research Lab Stillwater, OK
In an overtopping experiment an earthen
dam is built and then caused to fail, usually by the erosion
caused by water passing over unprotected soil.
Since this kind of failure happens with
working dams that have had reservoirs full for some time, the
experimental reservoir is kept partially filled for some days
before the experiment.
The phreatic surface
SEEP2D Phreatic Surface Solution
Measure Phreatic Surface with Peizometer/tensiometer
Peizometer-Tensiometer Tube
Design for Measuring Bulk Conductivity
Building an Embankment in a Flume
Mark the height of the next lift, 6 inches
Dump dirt in the flume
Level the dirt
Roto-till the clumps out
Fine level
Two passes with the vibratory compactor
Compact the edges
Recheck lift height Get ready for another
cycle
Auger a 2 1/4 inch hole
Tamp in 1 inch dry soil to protect the
porous cup from the concrete floor
Add about 4 to 6 inches of mud
Insert tube and twist into mud
Tamp in several inches of dry soil to
avoid bentonite contamination near the porous cup
Fill and tamp the rest of the hole with
a mixture of soil and 30% bentonite
Clean up bentonite mix, avoiding conductivity
changes in inflow or outflow
Shave inflow and outflow surfaces off
flat
Install soil retention screen
Install weir to set inflow head at 4.6
feet
Gravel pack between screen and weir to
hold inflow pipe and soil
Outflow screen and 6-inch v-notch weir
Bows added against wind
First flow over the inflow weir
Initial tensiometer responses to inflow
head
Outflow weir w/ level sensor
Outflow weir
Diurnal variation in sensor readings
Diurnal variation in sensor readings
Sensor 1&3 readings w/o sun shield
Sensor 1&3 readings w/ sensor 1 sun shield
Reduced diurnal variation in Sensor 1
Stove pipe sun shield on sensor 1
Post mortem shows that the probe had
good hydraulic contact with the soil and the bentonite mix formed
a good seal against vertical flow above it.
Manometer tube sensor calibrations in
tower
Two 6 psi and four 15 psi sensors on
manometer sight tube
Sensors and instrument shack installed
at dam
South sensors, 27S, 19S, 15S and 9S,
one day after 4.5 foot fill of reservoir
Sensor response to filling of reservoir
Sensor responses to filling of reservoir
SEEP2D solution for phreatic surface
(blue) and (uncalibrated) estimates of phreatic surface from
sensor readings just before the reservoir was raised to overtopping,
about 12 days after the initial flood.
Sensor response to overtopping and failure
Sensor response to overtopping and failure
Camera 2 Time Lapse
0830 hrs: Overtopping begins, note wet
dirt lower down where grass is stripped off
0836: Exposed dirt is eroding
0851: Head cut is wider
0918: Head cut is wider yet
0957: Head cut is about 1/3 overtopping
width
1012: Mass failure on the right
1030: Head cut more than half width of
overtopping flow
1103: Head cut is full width of overtopping
flow
1257: More mass failure on the right
1351: Reservior drops as breach jet begins
on right about 0.7 from left to right
1354: Mass failure on right undermines
I-beam pad, breach jet stronger, tailwater higher
1357: Breach jet bigger, reservoir lower,
tailwater higher
1453: Near the end, breach jet smaller,
reservoir lower, tailwater lower
Dam safety officials cheering the mass
failures
Ours are volunteers
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