SGER: Development and Verification of In-Flight Grouted Helical Pier Placement Technique for Use in Foundation Rehabilitation Investigations

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Abstract American usage of ground improvement and ground reinforcement (GIGR) techniques has exploded in popularity over the past 10 years. Despite widespread adoption, analysis of such techniques remains non-standardized, especially when multiple GIGR systems are used concurrently or in conjunction with existing retaining walls and foundations. As American cities age, rehabilitation of existing geotechnical installations will further popularize usage of these techniques. Despite this growing popularity, an accurate, robust method for design of such systems does not exist. Key to the development of such design methods is the understanding of underlying load transfer mechanisms, supported by experimental efforts. Such studies help substantiate the applicability of new emerging field-employed methods while providing a database for model evaluation. To this end, in this project, we focus our study on the issue of rehabilitation of pile groups in urban areas when either (1) site conditions or geology preclude transfer beams usage, (2) the removal of existing piles may destabilize nearby structures, or (3) where sustainability is being promoted through building reuse. Our emphasis is on developing the necessary centrifuge tools to support the needed experimental investigations, which will enhance our understanding of the mechanisms of load transfer of these rehabilitation systems. Specifically, this project will develop helical pier placement and in-flight grouting techniques and tools for the University of California, Davis NEES centrifuge facility. Such techniques and tools will be useful not only for foundation improvement and rehabilitation, but also for the broader category of ground improvement studies. The work plan has three primary objectives: (i) develop suitable in-flight grout placement tools and techniques to simulate the improved foundation systems, (ii) conduct one centrifuge series to verify the capability of the grouting method and employ it for load capacity enhancement of one pile group foundation, and (iii) enable much needed links with international researchers to benefit from previous and ongoing research during (i) and (ii) and collaboratively disseminate findings. In-flight grout placement will be explored using either fixed grout stations (stations placed at one-g, with grout deployed at N-g), or robot-controlled placement of grout or a combination of both. The new robot arm being constructed through the NEES project makes the later technique a plausible alternative to explore.BROADER IMPACTS OF THE PROPOSED WORKIn terms of technical contribution, if successful, this work will provide the foundation for the broader geotechnical centrifuge user community to apply in-flight grouting techniques, greatly expanding the capabilities of physical model testing. Further, the foundation rehabilitation solution investigated, and the completion of one series of centrifuge experiments will help substantiate its use, and provide guidance for subsequent testing needs. The unique international collaboration, as well as involvement with European initiatives (RUFUS), further strengthens the broader reach of this work. Finally, this proposal involves a team of junior level researchers (two of whom are female), with a dedication towards recruiting a diverse population of research students, for involvement in this project.