| At certain depths during driving of large diameter displacement piles, rebound greater than 0.25 inches occurs, followed by a small permanent-set after each hammer blow. This phenomenon is called high pile rebound (HPR). HPR soils may stop the pile driving and result in a limited pile capacity. The overburden depth at which HPR occurs is typically greater than 50 ft. In some cases, rebound leads to pile damage, delaying of the construction project and foundations redesign.;The objective of this research was to develop a geotechnical engineering protocol that would allow the geotechnical engineer to identify soil properties and strata which might cause HPR before pile driving begins (i.e., during the design phase of the project).;A total of 172 test piles at 138 pier locations, including 102 large prestressed concrete piles (PCP) and 70 low displacement steel H-Piles, were evaluated so as to select the HPR sites where geotechnical data could be collected. Based on available geotechnical data, 21 PCP piles at eleven sites were chosen for this investigation. The H-piles did not experience any HPR problems and thus were not studied.;All HPR piles were driven into saturated, fine silty to clayey sands and sandy clays or fat clays. A complete subsurface investigation was conducted after all HPR piles were installed. It included Standard Penetration Testing (SPT), retrieval of disturbed samples, lab testing to produce basic geotechnical index properties, plus Cone Penetrometer Testing (CPT) with pore water pressure measurements. A total of 43 SPT test borings and 27 CPT soundings were performed and evaluated. Pile Driving Analyzer (PDA) data from all the test piles was reduced to a deflection versus time to enable both the maximum and final displacements per blow to be used in calculating rebound. Maximum displacement and inspector set (iSet), recorded during installation of the test piles, was used to develop several promising correlations between pile rebound, or inspector set and SPT blow counts (NSPT), fines content, and CPT.;In soil conditions where the NSPT values were 15 blows/ft or less with a fines content of 25 percent (i.e., analyses include 21 piles at eleven sites), the rebound was less than 0.25 inches and yielded an acceptable pile permanent-iSet of up to 3 inches. When the NSPT values were between 15 and 40 blows/ft with a fines content of 25 to 40 percent, the pile rebound varied between 0.25 and 0.6 inches but still produced an acceptable permanent-iSet. As the N SPT exceeded 40 blows/ft with a fines content greater than 40 percent, the pile rebound was greater than 0.6 inch accompanied by a small or zero (i.e., unacceptable) permanent-iSet.;Where piles experienced excessive HPR with zero or minimal permanent-iSet at 8 piles, the CPTu pore water pressure (u2) yielded very high positive values of more than 20 tsf. However, at the two sites (i.e., 4 piles) where the pile rebounded, and was followed by an acceptable permanent-iSet, the measured CPTu u2 ranged between 5 and 20 tsf, the u2 exhibited values of less than 5 tsf at two piles where no rebound detected. Direct linear correlations between CPTu u2 and rebound were produced with strong linear correlations with regression coefficients R2 of 0.6 or higher. In these cases, the permanent-iSet decreased and rebound increased as u2 increased. Rebound versus either u2 or u2/hydrostatic pressure (uo) pressure produced a linear plot through the origin, indicating rebound would equal approximately 2.5 % of the CPTu u2 or 5.5 % of the u2/uo. Therefore, these correlations between CPTu pore pressure and rebound allow identification of soils that produce HPR.;Most non-HPR soils on these charts were in zone 6 (clean sand to silty sand). The most promising chart was developed by Schneider et al. (2008), and classified HPR layers as 1a and 1b (silt and clays) with Δu2/ σνo of greater than 1, while non-HPR soils were plotted in transitional soils, zone 3 (sand), with Δu2/ σνo of less than 1. Comparison of these results with classifications from laboratory tests were in excellent agreement with CPT soil type, and therefore the CPT can be a useful tool in evaluation of HPR soils.;A variety of methods were shown to be effective in predicting HPR and the correlations developed in this study allow the geotechnical engineer to predict if HPR will occur at a proposed site, where high displacement piles are to be driven using a single-acting diesel hammer. The correlations showed that permanent-iSet and rebound were a direct function of N SPT and fines content or friction ratio Rf and pore pressure u2 of the soil at the pile tip. The design equations and corresponding nomograph developed provide a methodology that allows for the prediction of HPR during the design phase. (Abstract shortened by UMI.). |
