Study on the Modified Coefficient of Dynamic Penetration Rod Length

Dynamic penetration test (DPT) is one of those widely applied to in situ test techniques. The rod length during operation could be as large as hundreds of meters, calling for length modification in practical applications. Two major methods were proposed in the most recent specifications for the modification of dynamic penetration rod length. These two methods were based on Newton elastic collision theory and elastic rod waving theory, respectively, and derived totally different correction coefficients. How to apply rod length modifications to the results of dynamic penetration tests has become a major issue that affects the reliability of its application. In this study, indoor model tests were conducted to evaluate the length corrections. A variety of heavy dynamic penetration models was conducted on sand and gravel soil with different rod lengths (2.0 m, 8.9 m, 16.4 m, 23.4 m, 30.0 m, and 36.0 m). The modification coefficient of heavy dynamic penetration rod length was obtained from these experiments. The results indicated that the modification coefficient for the length of penetration rod followed the description of Newton elastic collision theory, and was independent of the material properties.