Now showing 1 - 2 of 2
  • Publication
    Grouted helical piers for use in foundation rehabilitation : centrifuge testing
    Rehabilitation of building structures is a critical need facing numerous older urban areas. Many of these structures are supported on pile groups, which do not have adequate load capacity to support the demands expected after rehabilitation or superstructure replacement. Consequently, practical methods for strengthening existing foundations are of paramount concern. Recent studies have focused specifically on the use of grouted helical pier systems to strengthen pile group foundations, thereby substantiating their potential as a technique for load capacity enhancement (see companion paper by Laefer and Manke, 2006). However, these scaled studies were conducted at one-g level, resulting in soil confining stresses lower than those expected in the field. Thus, further verification through numerical modeling; full-scale experiments, or centrifuge testing is needed. This paper presents preliminary issues related to developing tools to support centrifuge testing of grouted helical pier systems. For this study, models for a 15-g centrifuge test were first explored at the one-g scale. With the small-scale model piers, a variety of grout types and pier installation methods were considered for the design and evaluation of the centrifuge tests. Based on the findings from this one-g testing, a preliminary centrifuge testing plan is presented.
  • Publication
    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.