(Received 4 September 2013; accepted 21 January 2014)
Published Online: 2014
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Granular filters are used in embankment dams to protect against uncontrolled flow and internal erosion either through the embankment or the foundation. For proper performance, the filter material must not be able to sustain a crack even if the core material becomes cracked itself. Historically, the mechanism used to limit cracking potential is a restriction of no more than 5 % nonplastic fines. It has been recognized though that this requirement has not been effective in identifying cracking potential for all materials. Since the requirement is related to the exclusion of clay and silt size particles (i.e., fines) it appears to not always identify other minerals that can act as cementing agents. A supplemental test known as the Sand Castle Test was also developed, and although it did not specifically focus on detecting other binding agents it was thought to hold promise. However, since the original test lacked a precise procedure and sensitivity to some binding agents, a modification of the Sand Castle Test is being undertaken. This paper outlines the need for a new test and describes specimen preparation, Modified Sand Castle Test procedures, and results from 16 source materials from across the United States. A petrographic examination was carried out to investigate the cementing mechanisms in selected materials. Additionally, unconfined compression tests were performed on each material to help quantify the strength from cementation. The sand equivalency value was also determined for all materials to see how well it correlated with the Modified Sand Castle Test results. The Modified Sand Castle Test is shown to be a good indicator of cementation potential and correlates well with unconfined compressive strength, but to a lesser degree with sand equivalency value.
Rinehart, Robert V.
Civil Engineer, US Bureau of Reclamation, Technical Service Center, Denver, CO
Pabst, Mark W.
Senior Geotechnical Engineering Specialist, US Army Corps of Engineers, Risk Management Center, Lakewood, CO
Stock #: GTJ20130150