Environmental Engineering Reference
In-Depth Information
80
Refill the tensiometer
70
60
50
40
30
Tensiometer
failed due to
cavitation
20
Sensor #18
Tensiometer
10
0
0
500
1000
1500
2000
2500
Time, h
Figure 4.63
Drying and wetting soil suction readings taking hysteresis in calibration curves
into account when using thermal conductivity suction sensors (from D.G. Fredlund et al., 2000b)
.
was used. The results show that the soil suction measure-
ment made using the thermal conductivity suction sensor
agrees well with those measured by the tensiometer. Some
differences occurred because of the water cavitation in the
tensiometer.
of 4.25 after calibration. Another three thermal conductivity
suction sensors were placed in a solution of sodium hydroxide
(NaOH) with a pH value of 10.9. The sensors remained
submerged in acid and base solutions for 3 weeks after which
time the sensors were recalibrated.
Typical calibration and recalibration curves for one of the
thermal conductivity suction sensors are shown in Fig. 4.64.
The results showed that the original calibration and recalibra-
tion curves were essentially the same after submergence in
the acid solution for 3 weeks. Similar results were observed
for the thermal conductivity suction sensors immersed in the
NaOH solution as shown in Fig. 4.65. Figure 4.66 shows
the results of regression analyses performed on all six ther-
mal conductivity suction sensors. While the tests continued
for only 3 weeks, the results showed negligible differences
between the initial calibrations and the recalibration values
for all sensors.
4.2.9.9 Effect of Chemicals on the Thermal
Conductivity Suction Sensors
It is possible that in situ monitoring might be required
under adverse acidity and alkalinity conditions. The effect
of adverse chemical conditions was studied by Shuai et al.
(2002). Following saturation, the thermal conductivity
suction sensors were calibrated as increased suction values
were applied in a calibration cell. The thermal conductivity
sensors were calibrated from zero suction to 400 kPa.
Three thermal conductivity suction sensors were sub-
merged in a hydrochloric acid (HCl) solution with a pH value
400
380
360
340
320
300
280
260
Water
HC (pH = 4.25)
240
10
6
1
10
100
1000
10,000
100,000
Suction, kPa
Figure 4.64
Initial and recalibration curves for University of Saskatchewan thermal conductivity
suction sensors subjected to HCl (pH 4.25) for 3 weeks (after Shuai et al., 2002).
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