Estimation of the axial side shear resistance of drilled shaft rock sockets is directly
related to the unconfined compressive strength of the bedrock. Commonly, the
mean unconfined compressive strength value is calculated from a range of
laboratory test results and is used to estimate the side shear of the bedrock. This
paper presents the results from a full scale axial load test performed on an 8.5-feetdiameter
drilled shaft rock socket, and compares measured side shear values to
estimated values for two different rock strata. Measured side shear values
correlated well with the design value calculated for the “strong” rock stratum, but
did not correlate well with the design value calculated for the “weak” rock stratum.
The mean unconfined compressive strength was used to calculate the side shear
in both strata, but review of the laboratory data indicates that this value may not
have been appropriate for the weak stratum due to a large variation in the
laboratory test results. Also included in this paper is a discussion of the subsurface
conditions, the laboratory test results, and the methodology used to design the
drilled shaft rock sockets for axial and lateral resistance.
Author: Paul J. Lewis & David R. Scherer, Gannett Fleming, Inc.
Publisher: DFI