DFI Journal - The Journal of the Deep Foundations Institute

Volume 16, Issue 1, April 2022
DOI: 10.37308/DFIJnl.20210408.235

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Side Resistance of Drilled Shafts in Weak Fine-Grained Sedimentary Rock
Article Type: Research Paper

Stark, T., Baghdady, A., Osouli, A., Shoup H., & Short, M.

Abstract

Load transfer mechanism in side resistance of rock socketed drilled shafts has been studied for the past four decades using results of axial load tests and theoretical methods. Various models for prediction of side resistance have been proposed. Only few studies (e.g., Horvath et al. 1983; Rowe and Armitage 1987; Hassan et al. 1997, Miller 2003, Abu-Hejleh et al. 2003) have been completed on socket side resistance of drilled shafts in weathered and fractured fine-grained rock. These studies, however, were based on only a limited number of load test data. A survey of current predictive models has been conducted. This survey shows most of the current models include strong and intact rocks in their databases. Almost all of the current models use a power function to correlate side resistance of rock socket to rock unconfined compressive strength. A database of side resistance of large diameter drilled shafts in only weak fine-grained rocks, such as, weak shales, mudstones, and siltstones (i.e., Intermediate Geomaterial first introduced by O’Neil et al. 1996, Hassan et al. 1997, and O’Neill and Reese 1999) has been complied in this study. The range of weak rocks considered herein corresponds to an unconfined compressive strength of 0.48 to 4.8 MPa. Analysis of this database shows that a linear model best predicts the side resistance of drilled shafts in weak fine-grained sedimentary rocks.

Keywords:
rock socketed drilled shafts, side resistance, weak fine-grained sedimentary rocks, unconfined compressive strength