This study proposes a reliability-based design (RBD) procedure to evaluate the allowable load for augered cast-in-place (ACIP) piles installed in predominately granular soils based on a prescribed level of reliability at the serviceability limit state (SLS). The ultimate limit state (ULS) ACIP pile-specific design model proposed in the companion paper is incorporated into a bivariate hyperbolic load-displacement model capable of describing the variability in the loaddisplacement relationship for a wide range of pile displacements. Following the approach outlined in the companion paper, distributions with truncated lower-bound capacities were incorporated into the reliability analyses. A lumped load-and resistance factor is calibrated using a suitable performance function and Monte Carlo simulations. The average and conservative 95 percent lower-bound prediction intervals for the calibrated load-and resistance factor resulting from the simulations are provided. Although unaccounted for in past studies, the slenderness ratio was shown to have significant influence on foundation reliability. Because of the low uncertainty in the proposed ULS pile capacity prediction model, the use of a truncated distribution had moderate influence on foundation reliability.Author Keywords: ACIP piles; Reliability; Serviceability limit state; Statistics; Design INTRODUCTIONA suitable foundation design will satisfy the strength limit or ultimate limit state (ULS) as well as the serviceability limit state (SLS), which is often associated with the allowable displacement or angular distortion of a structure. At present, the ULS has received considerably more attention in reliability-based design (RBD); however, the SLS is often the governing criterion for many foundation alternatives (Becker 1996;Wang and Kulhawy 2008; Zhang et al. 2008;Uzielli and Mayne 2011). Phoon and Kulhawy (2008) incorporated the accuracy and uncertainty of the Meyerhof (1976) method for estimating shaft resistance of drilled shafts to make assessments of reliability at the SLS for augered cast-in-place (ACIP) piles. However, the Meyerhof method was originally developed to predict the capacity of driven displacement piles and then modified for use with drilled shafts, which are constructed differently than ACIP piles.Additionally, Phoon and Kulhawy (2008) neglected toe bearing resistance when estimating ACIP pile capacity, resulting in a biased and considerably variable model (Phoon et al. 2006). Phoon et al. (2006) noted that models specific to ACIP piles needed to be developed (Phoon et al. 2006).The goal of this study is to use the ACIP pile-specific ULS design models presented in the companion paper (Reddy and Stuedlein 2016) to investigate reliability-based SLS design of ACIP piles installed in predominately granular soils. Those case histories described in the companion paper characterized with high quality load-displacement (Q-δ) curves were used to investigate foundation reliability at the SLS. First, an approach to link the ULS capacity models ...

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The use of augered cast-in-place (ACIP) piles for transportation infrastructure requires an appropriate reliability-based design (RBD) procedure. In an effort to improve the accuracy of an existing design model and calibrate appropriate resistance factors, this study presents a significantly revised RBD methodology for estimating the shaft and toe bearing capacity of ACIP piles using a large database consisting of static loading tests in predominately granular soils. The proposed design models are unbiased, as opposed to those currently recommended. Based on the reasonable assumption that a finite lower-bound resistance limit exists, lower-bound design lines are developed for shaft and toe bearing resistance by applying a constant ratio to the proposed design models. Resistance factors are calibrated at the strength or ultimate limit state (ULS) for ACIP piles loaded in compression and tension for two commonly used target probabilities of failure with and without lower-bound limits. For piles loaded in compression, separate resistance factors are calibrated for the proposed shaft and toe bearing resistance models. The inclusion of a lower-bound limit for piles loaded in tension results in a 24%–50% increase in the calibrated resistance factor. For piles loaded in compression, the application of a lower-bound limit results in a 20%–150% increase in the calibrated resistance factor, and represents a significant increase in useable pile capacity. Although the impact of a lower-bound limit on resistance factor calibration is directly dependent on the degree of uncertainty in the distribution of resistance, this effect is outweighed by the type of distribution selected (i.e., normal, lognormal) at more stringent target probabilities of failure due to differences in distribution shape at the location of the lower-bound limit. A companion paper explores the use of the revised ULS model in a reliability-based serviceability limit state design framework.

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Instrumented static loading tests present an effective tool for appropriate engineering of piled foundations. Whether instrumented or not, considerable effort can be expended to determine the interpreted failure load developed during the loading test, and the determination of an appropriate capacity is often subject to regulatory review and discussion, which may be complicated by the large number of interpretation methods available and the large range in interpreted capacities that could result. This paper focuses on the differences in the interpreted failure load for augered cast in place (ACIP) piles and seeks to determine which methods are suitable and which methods are inappropriate for the interpretation of ACIP piles. First, a review of various capacity interpretation methods is provided with emphasis on those methods cited in the International Building Code (IBC, 2012). Then, an ACIP pile case history database used to illustrate differences in interpreted capacity is described, followed by the presentation of the resulting differences. Recommendations for and against the use of several failure load interpretation methods are made. This paper emphasizes the importance of both the interpretation of the failure load as well as the consequence of a particular methodology on displacement -a critical performance measure.