A new approach to estimate the bearing capacity of driven piles

Although the problems associated with the repeatability of the standard penetration test (SPT) measurements have long been recognized, SPT results are the basis of many direct methods to estimate the axial capacity of driven piles. In this paper, a new approach is proposed to estimate the bearing capacity of driven piles in various soils, based on soil SPT values estimated from cone penetration test (CPT) data and soil behavior index, Ic. A databank consisted of results of 63 full-scale pile load tests has been compiled. Thirty-eight cases have been employed for calibration and 25 for validation. CPT records were converted to N60 values using a popular equation. Calibration was conducted using multilinear regression and pile bearing capacity was correlated with the estimated SPT values. Depending on the soil type, different pile bearing capacity coefficients are suggested for unit base and shaft resistance. The current method was compared with other methods using the log normal distribution, which showed that the current method exhibits the least average error. The average error of the current method was found to be −2% and the probability of accurate prediction with a ±10% error was found to be equal to 45%. Applying the new method to the 25 verification cases showed an error of 3% with a probability of 34.1% in prediction with error of ±10% showing that this approach could be successfully employed to estimate the bearing capacity of piles in different soil types.