Piezocone Penetration Testing in Florida High Pile Rebound Soils

Abstract Contractors and engineers have experienced pile installation problems while driving high displacement piles with single-acting diesel hammers at Florida Department of Transportation (FDOT) construction sites located throughout the Central and Panhandle regions of Florida. At certain depths during pile driving in saturated soils, rebound exceeding 1 inch (25 mm) was experienced, followed by a small permanent-set during each hammer blow. High pile rebound (HPR) may cause false refusal to occur, stopping the pile driving and resulting in a limited pile capacity. In some cases, rebound leads to pile damage, delaying of the construction project and foundation redesign. In this paper, the response of HPR is investigated using cone penetrometer testing (CPT) and a pile driving analyzer (PDA). PDA data, which yielded the amount and the depth where rebound occurred, produced the pile movement per blow, Nineteen Piezocone soundings were performed at seven FDOT sites in Florida, of which five sites experienced a rebound greater than 0.6 inches (15 mm), one site yielded rebound of 0.35 inches (9 mm), and one site’s rebound was less than the FDOT limit of 0.25 inches (6 mm). In order to improve the knowledge about the soil types producing HPR, a traditional geotechnical investigation on grain-size distribution and soil plasticity allowing for classification using Unified Soil Classification System (USCS) was conducted. Piezocone data were interpreted using the CPT and CPTu soil behavior type (SBT) charts proposed by Schmertmann (1978), Robertson (1990) (i.e., Q-Fr, Q-Rf, and Q-Bq), Eslami and Fellenius (2004), and Schneider et al. (2008). Comparison with classification data from laboratory tests was in excellent agreement with the CPT soil type, indicating that the CPT is a useful tool in evaluation of HPR or “large quake” soils. Correlations between rebound and CPTu data were developed showing that rebound is a direct function of both friction ratio Rf and pore pressure u2.