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CCEER-10-02: Laboratory Study to Assess Load Capacity Increase of Drilled Shafts through Post Grouting
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Date
2010-01-01Type
ReportAbstract
While post grouting of the base of a drilled shaft is an acknowledged means of mobilizing
shaft base resistance at low values of displacement, much uncertainty exists among
engineering professionals as to the conditions under which this option may be entertained.
The impact of diverse factors such as soil gradation and soil relative density, overburden
pressures, and grouting methods utilized need to be properly understood. Furthermore, the
complete benefit of post grouting, as a means of economizing construction expenditure,
can only be realized when it is factored into the project at the design stage. For
consideration of post grouting as a viable alternative, the designer must be able to
effectively predict the load � displacement behavior of both the grouted and ungrouted
shafts for direct comparison of one to another. Therefore, an effective numerical model
capable of providing shaft base resistances at increasing levels of displacement is required.
This report presents experimental and analytical research work carried out towards
developing a numerical model capable of predicting shaft base load � displacement
response with and without post grouting and a step-by-step procedure that is suitable for
designing drilled shafts incorporating the post grouting option.
Included in this report is the development and use of the large scale testing chamber,
model shaft, grouting apparatus and instrumentation utilized to study the different factors
affecting the usefulness of post grouting. The model shafts were tested in two types of soils
each prepared at two different relative densities for both the ungrouted and grouted shaft
tests. The developed soil deposition method is unique in enabling preparation of soil to
uniform relative densities fairly accurately. Experimental results obtained include the
variation in pressures induced during grouting as well as the load � displacement behavior
of ungrouted and grouted shafts. These show definitive proof of the increase in resistance
as a result of post grouting. The analytical model was developed based on refinement of
the shallow foundation model and provides variation in loading resistance with base
displacement. This model was calibrated using the experimental data obtained and
accuracy demonstrated using case histories. The numerical model unload � reload loop was
also obtained to enable prediction of the grouted shaft load � displacement behavior.
Description
Report No. CCEER-10-02
Permanent link
http://hdl.handle.net/11714/7169Subject
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