Experimental investigation of grouted helical piers for use in foundation rehabilitation

Building rehabilitation is critical for numerous older urban areas, many of which have inadequate foundations to support new demands. Consequently, development of practical methods to strengthen existing foundations is crucial. In engineering practice, both subsurface grouting and helical piers have been widely used to address these issues by strengthening the foundation. If the solid shaft of a typical helical pier is replaced by a hollow shaft, then helical piers provide the ability to deliver grout. It is hypothesized that these grouted helical pier systems (GHPS) could address foundation strengthening needs. However, there is limited test data available to understand the mechanisms of load transfer and the potential load enhancement they provide. In this paper, grouting and pier placement tools were developed and tested on the large geotechnical centrifuge at the University of California, Davis. Experimental methods and procedures developed are presented, and observations regarding the formation of grout bulbs under different conditions are analyzed. Physical observation of the test specimens indicates that average grout bulb diameters of 0.6-1.9 times the helix diameter (Dh) are attainable. For similar grout mixes, 20-50% larger grout bulbs can be attained by adding just a modest amount of injection pressure.