Geotechnical Engineering Circular No. 9 Design, Analysis, and Testing of Laterally Loaded Deep Foundations that Support Transportation Facilities

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12 LATERAL LOAD TESTS
The behavior of deep foundations under lateral loads is often difficult to predict accurately, especially with limited published material models that may not correlate well with local geologic materials. Lateral load tests can provide site-specific information that can be used to develop site-specific p-y curves, develop or verify a project design and/or be used in future designs in the same geologic formations. Lateral load tests reduce the uncertainty and potential risks associated with the design, and may result in more efficient (lower cost) foundations. Documenting and publishing lateral load test results also adds value to the overall industry by enabling other practitioners and researchers to benefit from the testing without having to incur the significant cost of implementing a test program
12.1 CONSIDERATION FOR PLANNING LATERAL LOAD TESTS
Lateral load tests can be used to fulfil three functions
1. To develop site specific parameters/p-y curves and investigate performance for development of the foundation design,
2. To verify the adequacy of the foundation design during construction through proof testing, and
3. For research and documentation purposes, to further the state of practice. This chapter has its focus on static lateral load testing of single full scale foundation elements for use by the designer. Guidance is provided on the planning and execution of static lateral load tests, including aspects of testing and monitoring, approaches to data reduction, and analysis and derivation of p-y curves for use in design. The p-y method is used for detailed analyses of laterally loaded deep foundations. Other more simplified methods (i.e., Broms method) would not require full scale load testing, and design methods of similar or more complex application (strain wedge method or numerical modeling) would be used in addition to the p-y method. Much of the discussion, in particular with regard to test setup and instrumentation, is based on testing of individual driven piles and drilled shafts, but the same principles apply to other types of deep foundations. Testing of pile groups under lateral loads is rarely done in practice, given the significant costs that are not typically justified, even on major projects. Accordingly, this topic is not addressed in detail. A guide specification for lateral load testing of a single deep foundation element is provided in Appendix Di b Lateral Load Tests for Design
A lateral load testis performed to measure the load-deflection performance of a deep foundation element pile or drilled shaft) for the anticipated means and methods of construction, and for the ground and groundwater conditions of a site. For lateral load tests performed during design, preliminary analyses using available data, including p-y curves, is necessary in order to develop the load test program. Information needed to plan a lateral load test includes subsurface conditions, foundation element type, depth, planned test loads and loading intervals, performance criteria, and expected performance.

176 For structures where lateral loads govern the design, lateral load tests provide a means to investigate and confirm key issues or design inputs such as deflection versus load performance, required minimum depth, and depth and magnitude of maximum bending moment for reinforcement design. There may also be opportunities to optimize the design by developing site-specific p-y curves from the test that may demonstrate higher lateral capacities compared to the standardized p-y models available in published references or software programs. In addition, it maybe possible to develop different p-y curves for Service Limit State and Strength Limit State design cases (which maybe based on different limiting deflections, which may allow further refinement in the design. The decision to implement a lateral load test program should consider the following issues Engineering time and cost for planning and design of the test program, preparation of contract documents, monitoring the load tests, and to reduce and evaluate the load test results Cost for implementing the load test program, including equipment mobilization, materials, instrumentation equipment, and test frame materials and setup Cost of sacrificial foundation elements for testing (foundations for lateral load tests are typically not performed on production piles or shafts because they are likely to be loaded beyond the service limit deflections and possibly beyond the deflections used to define the strength limit Cost of load reaction system, including the installation of reaction piles or drilled shafts Costs for supervising and conducting the load tests, and professional services for instrumentation installation and monitoring during the load test, and for preparing the load test report Costs of supplemental subsurface exploration and in-situ testing at the site of the lateral load tests to correlate with the p-y curves derived from the test and The potential cost savings that maybe achieved in the event that the lateral load tests result in stiffer p-y relationships than standardized relationships would suggest. (This task requires assumptions regarding a reasonable expectation of increased soil stiffness, and foundation analyses to estimate the potential savings in foundation arrangement and cost associated with this increased soil stiffness.

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