THESIS
2015
xiii, 104 pages : illustrations (some color) ; 30 cm
Abstract
The measurement of suction and volume change during most of the geotechnical experiments
is a challenging task due to a variety of limitations in current measurement techniques.
Currently no single equipment can cover the entire range of total suction that may be
encountered during the test. Also most of the volume measurement techniques for unsaturated
soils are either providing insufficient accuracy or having destructive approach. In spite of
having such a big importance of suction and specific volume on unsaturated soils, there is still
no perfect technology available for the measurement of these two parameters. This study aims
to develop a new economical, non-destructive and thorough technique to measure volume
change and suction in unsaturated soils. Automated digital image...[
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The measurement of suction and volume change during most of the geotechnical experiments
is a challenging task due to a variety of limitations in current measurement techniques.
Currently no single equipment can cover the entire range of total suction that may be
encountered during the test. Also most of the volume measurement techniques for unsaturated
soils are either providing insufficient accuracy or having destructive approach. In spite of
having such a big importance of suction and specific volume on unsaturated soils, there is still
no perfect technology available for the measurement of these two parameters. This study aims
to develop a new economical, non-destructive and thorough technique to measure volume
change and suction in unsaturated soils. Automated digital image processing technique was
used for the accurate and precise measurements of the soil specimen volume while a force
sensor was used to measure the soil suction.
The proposed volume measurement technique involves capturing a 360 degree view of
the specimen using a fixed camera. A structured light laser pointer was projected on the soil
specimen while capturing the 360 degree view. The laser pointer provides the reference points on
soil specimen for measurements. The high resolution images were then processed using
functions developed within MATLAB which automatically calculates the radius and height
over the entire lateral surface of specimen and hence the volume of specimen. The
computations also allowed the reconstruction of a 3D mesh model of the specimen. A
validation test on a dummy object showed that the error in radius and height measurements at
more than 75% measurement points was less than ±0.05 mm and ±0.07 mm, respectively. A
99% accuracy was achieved in the volume measurement of the soil specimen.
The measurement of suction was performed by measuring the effective stress within
the soil specimen using a force sensor called “Flexiforce sensor”. The sensor was installed in
an initially saturated soil specimen prepared at high water content. The specimen was then
allowed to air dry, and the water content was measured along with the stresses in soil at
different stages during drying. The validation for suction measurement was performed by
comparing with the SWRC determined by other authors using the conventional procedure to
the SWRC measured using our technique for the same soil. A strong resemblance in the
behaviour has been observed between the measurement by conventional technique and our
approach until the air entry value of this soil. But a drastic break in similarity was found near
the air entry value, which might be occurring because the stresses in soil no longer increases
with an increase in suction.
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