Assessment of the Posttunneling Safety Factor of Piles under Drained Soil Conditions

Marshall, Alec M.; Franza, Andrea; Jacobsz, Schalk W.

Abstract

The need to tunnel closely beneath piles is increasing due to the development of urban areas. This poses a risk to the stability and serviceability of overlying structures (e.g., buildings, piers, and piled embankments). The impact of tunneling on piles is usually assessed using a displacement threshold, yet this provides no information about the posttunneling pile safety factor. Knowledge of a pile’s safety factor under serviceability or extreme loading conditions is important, especially if future repurposing of the associated superstructure is a possibility. Tunneling can reduce the safety factor of a pile up to the point of geotechnical failure (i.e., when the pile capacity reduces to that of the applied load), yet little guidance is available to enable a straightforward means of assessing the posttunneling safety factor of a pile. This paper aims to address this shortcoming by providing design charts based on an analytical tunnel-single pile interaction approach that provides a means of determining a posttunneling pile safety factor. The methodology and design charts are applicable to drained soil conditions and include for the effects of the initial pile safety factor, the pile installation method [displacement (driven and jacked), nondisplacement (bored) with only the shaft capacity, and nondisplacement with base and shaft capacity] and varying water table depths. In the paper, as a validation exercise, analytical predictions are compared against data from geotechnical centrifuge tests designed to model both displacement and nondisplacement piles in sands, including a variety of tunnel–pile relative locations and initial pile safety factors. For a specified design value of a posttunneling pile safety factor, the design charts enable a quick assessment of the safe location of a pile or a tolerable tunnel volume loss considering ground parameters, water table position, pile installation method, and initial safety factor.

Citation

Marshall, A. M., Franza, A., & Jacobsz, S. W. (2020). Assessment of the Posttunneling Safety Factor of Piles under Drained Soil Conditions. Journal of Geotechnical and Geoenvironmental Engineering, 146(9), Article 04020097. https://doi.org/10.1061/%28ASCE%29GT.1943-5606.0002348

• Journal Article Type: Article
• Acceptance Date: May 15, 2020
• Online Publication Date: Jul 15, 2020
• Publication Date: Sep 1, 2020
• Deposit Date: May 13, 2020
• Publicly Available Date: Jul 15, 2020
• Journal: Journal of Geotechnical and Geoenvironmental Engineering
• Print ISSN: 1090-0241
• Electronic ISSN: 1943-5606
• Publisher: American Society of Civil Engineers
• Peer Reviewed: Peer Reviewed
• Volume: 146
• Issue: 9
• Article Number: 04020097
• DOI: https://doi.org/10.1061/%28ASCE%29GT.1943-5606.0002348
• Keywords: Geotechnical Engineering and Engineering Geology; General Environmental Science
• Public URL: https://nottingham-repository.worktribe.com/output/4430160
• Publisher URL: https://ascelibrary.org/doi/10.1061/%28ASCE%29GT.1943-5606.0002348
• Additional Information: Received: 2018-10-29; Accepted: 2020-05-15; Published: 2020-07-15