Effect of Competent Caliche Layers on Measuring the Capacity of Axially Loaded Drilled Shafts Using the Osterberg Test

Abstract

This study investigates the effect of the location of an O-cell hydraulic jack along the length of a drilled shaft in a full-scale Osterberg test performed in soils containing layers of caliche. The location of the hydraulic jack with respect to caliche layers influences the measurements obtained from the Osterberg test and the subsequent interpretation of drilled shaft capacity. In this study, drilled shaft capacities were derived utilizing data from 30 Osterberg full-scale field load tests in soils containing caliche layers. The hydraulic jack was placed at the midpoint of the drilled shaft length. Additionally, the Osterberg test data was used to calibrate a numerical model by Plaxis finite element software for drilled shaft analysis. Using the calibrated model, several scenarios of hydraulic jack location were simulated. The scenarios included hydraulic jack locations at several distances above and below a caliche layer. The results of the simulations indicate that in cases where the O-cell was installed far from the caliche layer, the Osterberg tests results showed lower pile resistance capacity compared to the top-down test. However, in cases where the O-cell was installed close to the caliche layers, the Osterberg tests results showed comparable pile resistance capacity compared to the top-down tests. This study recommends installing the hydraulic jack as close as possible to the caliche layers for more reliable interpretation of the Osterberg field tests which leads to a cost-effective design approach by reducing the required shaft length.

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