Dynamic Cone Penetration Tests for LiquefactionEvaluation of Gravelly SoilsMichael H. TalbotDepartment of Civil and Environmental Engineering, BYUDoctor of PhilosophyIn North American practice, the Becker Penetration Test (BPT) has become the primary field test used to measure penetration resistance of gravelly soils. However, this test is expensive and uncertainties exist regarding correlations and corrections for rod friction. As an alternative, the dynamic penetration test (DPT) developed in China has recently been correlated with liquefaction resistance in gravelly soils. The DPT equipment consists of a 74 mm diameter cone tip driven by a 120 kg hammer with a free fall height of 100 cm using 60 mm drill rod to reduce friction. The DPT is a very rugged, economical device, capable of penetrating dense gravel layers. During DPT field investigations following the 2008 Wenchuan earthquake in China, liquefaction resistance was correlated with DPT blow count.Dynamic Cone Penetration tests (DPT) tests were also performed adjacent to Becker Penetration test (BPT) sites at Pence Ranch, Whiskey Springs, and Larter Ranch in Idaho where gravel liquefaction was observed during the 1983 Mw6.9 Borah Peak earthquake. Companion DPT tests were performed using an automatic hammer at two energy levels, namely the energy specified in the original Chinese standard and the energy typical of SPT testing which would be easier to use in practice. Companion testing was undertaken to determine if the cone could be driven in gravelly soil with more standard drilling equipment available to geo-professionals. The second energy level also offers the potential to provide more resolution on the soil layering. PDA measurements were made to determine the energy transferred to the cone rods and the statistical variation in the energy transferred.Additionally, companion DPT tests were undertaken at the downstream toe of Millsite Dam near Ferron, Utah, where gravelly soils are predicted to liquefy in an earthquake. Two energy levels were used, one using an automatic hammer and the other a manual donut hammer. The blow counts from the BPT and DPT correlated reasonably well for gravels using the automatic hammer, but poor correlation was obtained with the donut hammer. Liquefaction resistance for the BPT and DPT soundings were also in reasonable agreement for gravel layers suggesting that the DPT can provide liquefaction hazard evaluations more economically than the BPT using direct correlations with field performance.Correlations suggest that the standard energy corrections developed for the SPT can be used for the DPT. In general, the liquefaction resistance from the BPT and DPT correlated reasonably well when using the 30% probability of liquefaction resistance curve developed for the DPT.Keywords: Michael H Talbot, liquefaction, Chinese dynamic penetration test, gravelly soils.