Development of a Test to Determine Cementation Potential of Embankment Dam Granular Filter Material – Results of Phase III Research

Granular filters are used in embankment dams to protect against internal erosion either through the embankment or the foundation. For proper performance, it is required that the filter material not be able to sustain a crack during embankment settlement or seismic loading. Historically, the mechanism used to limit cracking potential is a restriction of no more than 5% non-plastic fines, and this requirement is easily measured with the standard soil tests for grain size distribution (gradation) and plasticity (Atterberg Limits). Unfortunately, material meeting this requirement has been observed to cement, and hence has cracking potential. More robust test procedures are needed in order to better quantify the desired material properties (cementation potential), and to this end, modification of the Vaughan and Soares Sand Castle Test has been undertaken jointly by the Bureau of Reclamation and U.S. Army Corps of Engineers. This report presents the third phase of the research, describing specimen preparation and test procedures and results from 16 source materials from around the United States. All materials met ASTM C-33 fine aggregate gradation requirements as well as the additional requirement of less than 2% fines. Additionally, unconfined compression tests were performed on each material to help quantify the strength gain from cementation. The Sand Equivalency Value, which further quantifies the amount and characteristics of the clayey portion of a material, was also determined for all sources 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. Petrographic analysis aided in understanding the cementation mechanisms. A discussion is presented describing how the tests results could be carried forward into practice.