3491
Enhanced Soil Characterization through Advances in Imaging Technology
Caractérisation approfondie de sol grâce aux progrès du traitement d'image
Ohm H. S. & Hryciw R. D.
University of Michigan, USA
ABSTRACT: The particle size distribution of coarse-grained soils is traditionally determined by sieve tests. However, image-based
techniques may soon replace sieving as they are cleaner, faster and less expensive. A major impediment to adoption of images for soil
characterization is the wide range of particle sizes in a typical specimen. With current technology particles spanning two orders of
magnitude in diameter can be sized from a single image. However, as camera technology advances, the range of sizes that can be
analyzed with a single image increases. Two new systems, the Sedimaging (for 2.0 mm to 0.075 mm particles) and the Translucent
Segregation Table (TST) (for 75 mm to 2 mm particles) rapidly segregate the particles by size prior to image capture. However,
unlike previous image-based methods, these tests do not require that particles be physically detached from one another. The
Sedimaging test requires a camera resolution and lens magnification that can achieve at least 3 image pixels per particle diameter
(
PPD
) and the TST requires a minimum
PPD
of 9. The minimum
PPD
s must be achieved while capturing entire specimens in the
camera’s field of view. Extention of the systems to silt sized particles is explored.
RÉSUMÉ : La distribution granulométrique des sols grossiers est traditionnellement déterminée par tamisage. Cependant, des
techniques d’analyse d’image pourraient bientôt remplacer le tamisage car elles sont plus propres, plus rapides et moins coûteuses.
L'obstacle majeur à l'adoption des technologies d'imagerie pour la caractérisation des sols est la large gamme de tailles de particules
dans un échantillon typique. Avec la technologie actuelle, la taille des particules qui peuvent être analysées avec une seule image est
de deux ordres de grandeur. Deux nouveaux systèmes, Sedimaging (pour des diamètres de 2,0 mm à 0,075 mm) et la Table de
Ségrégation Translucide (TST) (pour des diamètres de 75 mm à 2 mm) peuvent rapidement séparer les particules par taille avant la
capture d'images et il n’est plus nécessaire que les particules soient physiquement isolées les unes des autres. Le test Sedimaging
nécessite une résolution de la caméra et de l'objectif d’au moins 3 pixels de l'image par diamètre de particules (
PPD
) et le TST
nécessite un minimum
PPD
de 9. Le
PPD
minimum doit être atteint tout en capturant un specimen entier dans le champ de vision de
la camera. La possibilité d’appliquer ces systèmes aux particules de limon est explorée.
KEYWORDS: Particle size distribution, Soil characterization, Imaging technology
1 INTRODUCTION
The most fundamental characteristic of soils is its particle size
distribution. For the coarse soil fraction, the size distribution and
subsequent soil classification are determined by sieve analysis.
However, sieves and shakers are costly and it takes time to
remove jammed soil particles from the sieve openings. The fines
fraction must be determined by wet sieving and specimens must
be dried and weighed several times. Sieving is also noisy while
generating vibrations and air-borne particulates (Ohm et al.
2012). Cleaner and faster image-based methods have emerged as
alternatives to sieving. They have the potential added benefit of
providing particle shapes and roughnesses.
Several image based particle sizing systems are commercially
available. In all such current systems, the particles have to be
“detached” from one another prior to photographing. In static
techniques, the particles are spread on a flat surface. Two
systems that use the static approach are the Aggregate Image
Measurement System (AIMS) (Fletcher et al. 2003) and the
University of Illinois Aggregate Image Analyzer (UIAIA) (Rao
and Tutumluer 2000). Both systems analyze particle sizes and
shapes of fine aggregate (sand) and coarse aggregate (gravel). In
dynamic techniques, particles drop from a moving conveyor belt
into a camera’s field of view. A CAMSIZER
®
(Brown et al.
2005) uses such a conveyor belt system with two cameras at
different magnifications. Masad and Tutumluer (2007) provide
details of these and other commercial devices.
Taking advantage of recent advances in camera technology
and image analysis methods, two new image-based analyzers
were developed that do not require physical separation of
particles. For sand particles smaller than 2 mm, the system is
called
Sedimaging
. For larger sands and gravels, a
Translucent
Segregation Table
(TST) is used. The two systems are briefly
described in this paper with emphasis on the critical role that
high resolution digital cameras have made to their development.
The minimum particle sizes that can be analyzed by the two
systems using different camera resolutions are compared and
extention of Sedimaging into the silt-size range is explored.
2 RECENT ADVANCES IN IMAGING TECHNOLOGY
Since their commercial introduction in the late 1990’s
digital
single lens reflex
(DSLR) cameras have rapidly increased in
resolution as measured by image megapixels (MP). Figure 1
shows the resolution history of two commercial lines, DSLR
cameras by Nikon and medium format
digital camera back
(DCB) cameras by Leaf. DSLR cameras reached 36 MP in 2012,
while DCB cameras had already achieved 80 MP in 2010. Since
DCBs cameras are very expensive, DSLR cameras are currently
used in the Sedimaging and TST systems.
Many particulates such as pills, agricultural products and
even biological cells are digitally imaged. However, they do not
possess a very wide range of sizes and therefore, advances in
image resolution is not as critical for their respective industries.
., Hryciw R.D
