Design of inclined loaded drilled shafts in high-plasticity clay environment.
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2011-05-01
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Abstract:Drilled shaft foundations are principally used to support many structures such as bridge piers, towers,
buildings, transmission towers, and roadway cable barriers. This research focuses on the use of drilled shafts
in the cable median barrier systems which play an important role in protecting people’s lives due to cross-over
collisions on highways. During December 2006 to February 2007, several failures of 3-cable median barrier
(TL-3) were observed in Kaufman County near Dallas without any traffic-related vehicular impacts.
Preliminary investigation of failures showed that failed drilled shafts were located in high plasticity clay.
Causes of failures are attributed to cold temperature induced shrinkage in the cables that increased in the
tension in them, soil saturation due to long periods of rainfall and small sizes of drilled shafts used. Various
sizes of drilled shafts were established and constructed in an environment similar to the one in which
foundation distress was observed. Geotechnical sampling and laboratory testing were performed, and a new
test setup for the application of an inclined tensile loading on drilled shafts was designed to simulate the
loading under real field conditions. The capacities of different sizes of drilled shafts from field test were tested
and measured under this setup. Once good simulation was obtained, the models are used for various
foundation dimensions and various undrained shear strengths of soils which, in turn, provided results that are
used in the development of foundation design charts. Additionally, construction guidelines and
recommendation for periodic maintenance are provided in this report.
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