Available at: https://digitalcommons.calpoly.edu/theses/3388
Date of Award
6-2026
Degree Name
MS in Civil and Environmental Engineering
Department/Program
Civil and Environmental Engineering
College
College of Engineering
Advisor
Robb Moss
Advisor Department
Civil and Environmental Engineering
Advisor College
College of Engineering
Abstract
This research addresses the analysis and design of double cased piles. Bay Area Rapid Transit (BART) runs a large rail system both above and below ground that connects the entire Bay Area. BART requires that all new constructions avoid transmitting axial load to their tunnels from adjacent piles. If piles fall within the zone of influence, builders must install double cased piles. Double casing is where there is an extra casing around the pile, with an air gap between them. The air gap prevents load from transferring to the outer casing. The length of this casing is called the isolation zone. This zone extends to a depth that keeps the BART tunnel outside of the zone of influence. This, however, creates a section of the pile that has no soil support, weakening the pile both axially and laterally. Static axial load test data on a single-cased pile (L-29) and double cased pile were used to confirm an RSPile model soil parameter. These piles were taken from a project on a residential building in close proximity to a BART tunnel. Analyses run with the recommended geotechnical design parameters by Langan Engineering under-predicted the measured pile-head displacement for the double-cased pile, so t-z curves back-calculated from load test strain-gauge data were used in place of the design parameters. Lateral response, for which no field load test was available, was first validated against Broms' Method on a single-cased equivalent of L-29 and then extended to the double-cased configuration. The calibrated model was used to perform a study across pile diameters of 16, 18, 20, and 24 inches and isolation casing lengths up to 15 feet. Two non-dimensional design relationships were developed for axial loading. A displacement factor (DF) defined as the ratio of cased to uncased pile-head displacement at the same load, and a maximum load factor (MLF) defined as the ratio of cased to uncased capacity. Lateral displacement factor curves were also developed for isolation casing lengths up to 9 feet. The resulting design charts are recommended for preliminary estimation of axial and lateral response reductions for double-cased piles.