settlement_of_shallow_foundations_on_granular_soils (Lutenegger ang DeGroot)

EXECUTIVESU~RY
This report presents the results of a research project undertaken to provide a comprehensive
state-of-the-art review of the procedures used by the geotechnical engineering profession to estimate
the settlement of shallow foundations resting on granular soil deposits. A comprehensive review was
made of the literature in order to sunnarize all of the existing design methods available and to
assemble reported case histories involving documented settlement of shallow foundations on
granular deposits. A Windows-based PC operated software package was developed which
incorporates the majority of the connon design methods and allows the operator to predict
settlement of a proposed foundation using the available methods. The results of the work are
presented in this report and accompanying Appendices that comprise the overall final report.
A stand alone Computer Program Users Appendix presents background of the progranning
language and a description of the software development. A users manual is included which provides
step-by-step instructions on how to operate the software. The use of the software is illustrated in
this Appendix by showing examples of calculated settlements for the FHW A footing load tests
recently performed at Texas A&M University and other published cases. Additionally, in the final
report a comparison is presented between the predicted settlement of a 3 m by 3 m footing using
connon SPT and CPT methods and actual settlement.
A standalone Case Histories Appendix contains a compendium of reported case histories
involving settlement of shallow foundations resting on granular soil deposits. The compilation is
limited to cases involving field large scale plate and footing tests and full size structures and is
separated into several categories including tanks, mats and rafts, small footings (1m <B <3m) and
large footings (3m< B <6m). Each case history includes a reference for the data, reported foundation
geometry, reported soil conditions and properties, and reported load and settlement observations.
The case histories serve to allow a check of full-scale performance on the accuracy of a given
prediction method.
Recommendations are given at the end of this report for improvements in site
characterization and improvements in settlement analyses. It is anticipated that the implementation
of these recommendations will produce a better approach to the evaulation of settlements of shallow
foundations on granular soils.
The results of the project indicate that a number of methods are outdates and should not be
used in predicting settlements. Other, more modern methods, appear to give more reasonable
approaches and results. The results presented in this report should enable design engineers to
formulate exploration programs better suited for evaluating settlement and should allow more
reliable settlement estimates to be made. This will allow more frequent use of cost-effective shallow
foundation systems in lieu of more expensive deep foundation systems for transportation related
structures such as highway bridges.
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