A Failure Mechanism around Axially Loaded Sockets in Weak Rock

Pouyan Asem, Joseph F. Labuz

Research output: Contribution to journalConference articlepeer-review


This paper is concerned with the failure mechanism predicted from the cylindrical cavity expansion model for a rock mass around the sidewalls of axially loaded sockets. The failure mode, which depends on the initial lateral stresses, load-induced radial stresses, and tensile strength of the rock, is critical to identify so that the axial capacity and stiffness of the foundation can be determined. A comprehensive database of in situ load tests, specifically drilled shaft, anchor, and plug load tests in weak rock provides validation of the model. The initial lateral stresses in the rock mass are estimated using the coefficient of earth pressure and knowledge of the average vertical stresses at each load test elevation. The back-calculated shear stress-shear displacement relationships for socket sidewalls in each load test are used to calculate load-induced radial stresses developed on the socket sidewalls. The tensile strength is obtained from tabulated ratios of uniaxial compressive strength to tensile strength and knowledge of the measured compressive strength. The failure mechanism around the socket sidewalls is analyzed by applying the Fairhurst (parabolic) failure criterion. Theory shows that the rock mass generally fails by circumferential tension, which is in agreement with field observations.

Original languageEnglish (US)
Pages (from-to)198-209
Number of pages12
JournalGeotechnical Special Publication
Issue numberGSP 321
StatePublished - 2020
EventGeo-Congress 2020: University of Minnesota 68th Annual Geotechnical Engineering Conference - Minneapolis, United States
Duration: Feb 25 2020Feb 28 2020

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© 2020 American Society of Civil Engineers.

Copyright 2020 Elsevier B.V., All rights reserved.

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