Experimental Investigation of grouted helical piers for use in foundation rehabilitation
Rehabilitation of building structures is a critical need facing numerous older urban areas. Foundations underlying many of these structures do not have adequate load capacity to support new demands expected after structural rehabilitation or superstructure replacement. Consequently, practical methods for strengthening existing foundations have the potential for significant impact. In engineering practice, both subsurface grouting and helical piers have been widely used to address these issues and provide strengthening of the foundation. If the solid shaft of a typical helical pier is replaced by a hollow shaft, then the helical piers provide the ability to deliver grout. This combined system is now termed a grouted helical pier system (GHPS). Although GHPSs have recently seen use in engineering practice, there is limited test data available to understand the mechanisms of load transfer and the potential load enhancement they provide. Small-scale model centrifuge GHPS tests provide an economical approach to simulate the working mechanisms and properties of the GHPS, avoiding costly full-scale prototype testing. In the research presented herein, grouting and pier placement tools were developed and tested on the large geotechnical centrifuge at UC Davis. Experimental methods and procedures are presented and observations regarding the developed grout bulbs under different conditions are described and analyzed. Physical observation of the test specimens indicates that average grout bulbs diameters of 0.6-1.9 times the helix diameter (Dh) are attainable in the 15-g centrifuge environment. For similar grout mixes 20-50% larger grout bulbs can be attained by only adding 0.7 MPa injection pressure. By rotating the pier during grout installation, the generated grout bulbs’ average diameter increased approximately 60-100%.
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