Environmental Engineering Reference
In-Depth Information
Elapsed time, min
0
30
60
90
120
150
180
210
240
0
Preapplied matric suction:
−
100
150 kPa
200 kPa
200
−
250 kPa
300 kPa
350 kPa
400 kPa
450 kPa
500 kPa
550 kPa
−
300
−
400
−
500
−
600
Figure 4.22
Comparison of applied and measured matric suctions on Regina clay using Uni-
versity of Saskatchewan direct high-suction range tensiometer (from Guan and Fredlund, 1997).
Elapsed time, min
0
30
60
90
120
150
180
210
240
270
300
0
−
50
Preapplied matric suction:
100
−
−
150
150 kPa
200 kPa
−
200
−
250
300 kPa
−
300
−
350
400 kPa
−
400
−
450
−
500
Figure 4.23
Comparison of applied and measured matric suctions on reconstituted silt using
University of Saskatchewan direct, high-suction tensiometer (Guan and Fredlund, 1997).
slight drift in the recorded suctions when the preapplied
matric suction exceeded 300 kPa. A matric suction of
300 kPa corresponded to a degree of saturation of about
38% for the silt specimen.
Differences between applied matric suctions and the mea-
sured negative pressures were less than 5%. The accuracy
of matric suction measurements appear to have been lim-
ited in part by the accuracy of the transducer in the high-
suction tensiometer. The response time of the high-suction
probe to a change in the applied matric suction was on
the order of seconds. The fast response of the high-suction
tensiometer is attributable to the rigidity of the chamber
of the suction probe and the high degree of saturation of
the soil.
The mini probe developed by Meilani et al. (2002) was
successfully used to measure suction up to 400 kPa along
a triaxial specimen. Suctions on the order of 400 kPa were
maintained for about 15 h while suctions of 200 kPa were
maintained without cavitation for about 155 h (i.e.,
6 days).
The time period over which a particular matric suction can
be maintained is believed to be related to factors affecting
the diffusion of dissolved air through the water in the high-
air-entry disk.
Figure 4.24 shows the results from one experiment where
the soil specimen was subjected to a net confining pressure
of 25 kPa and a matric suction of 100 kPa. The matric suc-
tion of 100 kPa was achieved by applying an air pressure
of 290 kPa to the top of the soil specimen. The water pres-
sure at the bottom of the specimen was then lowered from
290 to 190 kPa. The difference between the air and water
pressures then produced a matric suction of 100 kPa which
remained in the soil specimen for 130 h until the shear-
ing of the specimen was complete. The use of the mini
high-suction probe meant that the matric suction in the soil
specimen could be directly measured without use of the axis
translation technique.
∼
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