The main objective of the Phase II research is to address the knowledge gaps identified in the Phase I study to improve reliability, performance, and safety of transportation infrastructure (e.g., embankments/structures) supported by RIs.  The detailed objectives include: (1) gathering full-scale test data for RI serviceability and failure limits, (2) improving analytical methods for load and deformation calculations, (3) evaluating installation-induced soil displacements and potential damage to adjacent RIs and structures as well as soil property changes, (4) evaluating load-displacement behavior of single RI versus group RIs under walls/embankments, (5) investigating RI behavior under walls versus slopes, (6) evaluating lateral load capacities of RIs with and without steel rebars, (7) improving/developing an analytical method for slope stability with RIs, and (8) developing guidelines for construction specifications and instrumentation.

This Phase II project is comprised of seven major tasks:

 Task 1: Developing Full-scale Field Test Program

Based on the findings from the Phase I study, a full-scale field test program will be developed to fill the gaps of knowledge and practice identified and collect additional data to be used for validating and improving existing design methods or developing new design methods. A test site has been tentatively selected in Lawrence, Kansas and existing geotechnical information for the test site has been collected.

Task 2: Performing Additional Site Characterization

Additional insitu and laboratory tests will be performed on the selected test site to better determine geotechnical engineering profiles and quantify soil and rock properties. Embankment fill

Task 3: Constructing Test Embankment and Quantifying Installation Effects 

Conduct field tests to evaluate installation effects of rigid inclusions by the drilled displacement method. The evaluation will include, but is not limited to, ground movements and excess pore water pressures at different distances and depths, changes in soil properties (e.g., density, strength, and modulus) with two different rigid inclusion spacings and installation sequences.

Task 4: Evaluating Load-Displacement Responses of RIs

Perform field loading tests on RIs without and with steel reinforcements under vertical and lateral loads to evaluate the load-displacement responses of RIs and the effect of steel reinforcements in RIs.

Task 5: Assessing Global Performance

Construct a 20-ft high full-scale test embankment (consisting of a vertical wall on one side and a steep slope on another side) with a geosynthetic-reinforced load transfer platform on installed RIs. The test embankment, the load transfer platform, and selected RIs will be instrumented with sensors and monitored to evaluate the global performance including load transfer (e.g., load distribution between RIs and soils, downdrag forces, and tensile forces in geosynthetics), differential settlements between RIs and soils, lateral displacements of RIs and soils, and stability of side slope/wall. Numerical analyses will be performed to supplement the full-scale experimental program.

Task 6: Standardizing Design Approach

Based on the results from the installation effect study in Task 3, the RI loading tests in Task 4, and the full-scale field testing and the numerical analyses in Task 5, the design methods identified in the Phase I study will be validated and improved so that they can be standardized for the design and evaluation of RIs for transportation infrastructure projects.

Task 7: Developing Construction and Instrumentation Specifications

Develop a specification for implementing RIs in transportation infrastructure projects, especially for embankment and retaining wall support and guidance (performance-based) specifications that provide the DOTs (along with FHWA and NHI) a means to perform quality assurance (e.g., inspection and testing) and instrumentation during and after construction.

At the conclusion of this project, three deliverables will be produced:

i.                 A new, standardized design method or new recommended factors and input values that account for soil conditions, installation technique, and installation effects to be included into design computations for nominal axial, lateral, and flexural resistance of single and grouped RIs.

ii.               Guidance (performance-based) specifications that provide the DOTs (along with FHWA and NHI) a means to perform quality assurance (e.g., inspection and testing) and to evaluate the findings therefrom. The guidance specifications will be developed such that they would apply, be common, and be applicable to the various construction methods used to install RIs.

iii.             The report will provide recommendations and guidance for incorporation into (a) AASHTO bridge specifications, (b) state DOT project specifications, (c) future updates of FHWA guidance documents (e.g., GEC-8 and GEC-13), and (d) applicable NHI training courses.

The required commitment for the Phase II study is $1,800,000. Participants are requested to contribute $45,000/year for four years from each state.

Contractors may provide in-kind contributions to install rigid inclusions in the field.