Foundations for embankment dams are often composed of soft rocks and/or strongly weathered rocks. Rocks of these kinds usually have low strength and are very susceptible to slaking. Therefore, foundation surface of such rocks should often be covered with shotcrete before an embankment to be prevented from slaking. For the excavationmanagement of rock foundation of this kind, in addition to the conventionalmethods, such as visual observation and hammer blow, the development of a quick and accurate excavationmanagementmethod is strongly required. In this study, we have investigated the applicability of needle penetration test to verify design strength of soft rock foundations for embankment dams. We firstmade needle penetration tests at a dam site, and estimated unconfined compressive strength. Secondly, we performed the triaxial compression tests of the undisturbed samples collected from the dam site. From these results, we finally concluded that a needle penetration test could be used as a quick and accurate verificationmethod of design strength of dam foundations composed of soft rocks.
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