Extreme variations in ground conditions which categorize karstic limestone terrain inevitably create challenges during design and installation of deep foundation systems. For example, the elevation of rock head may vary greatly over short distances, while for substantial depths below rock head, one may anticipate the presence of major solution features. Such features may be entirely open, or may be partially or completely filled with products of the limestone degradation. High capacity micropiles of the type described by FHWA (1997) have, for some years now, proved to be a technically and economically viable deep foundation system in such terrain. Frequently, they have been the only plausible solution. This adaptability is a result of the large variety of small diameter borehole drilling techniques which can be exploited to ensure penetration in such conditions, and also the fact that micropiles transfer load by skin friction. The design implication is that if certain thickness of "good" rock is encountered, then a certain pile capacity can be guaranteed. There is therefore dramatically reduced risk of piles "punching through" into a solution feature as would occur in the case of an end-bearing pile. During the last several years, the authors have been involved in the design, construction and performance testing of high capacity micropiles in karst. This paper provides an overview of these experiences and provides recommendations as to most appropriate practice. Reference is made to several recent case histories.

Despite the installation of a row of anchors in 1996, the right downstream retaining wall of Hodenpyl Dam, MI, continued to move inward and downstream. The remediation design called for installation of additional anchors. However, there were concerns about creep-induced relaxation of the anchor load over time given the existence of high-plasticity clays at the site. The solution was the installation of post grouted multi-anchors along the base of the retaining wall (Single Bore Multiple Anchors -SBMAs).SBMAs utilize several "unit" anchors within the same borehole, each with its own short efficient bond length positioned at staggered intervals along the bond zone. This staggered arrangement allows each unit load component to be transferred to the soil in a controlled manner over a discrete length of the borehole, thereby producing a very efficient load transfer mechanism. A larger factor of safety against creep is therefore attainable using SBMAs as compared to that provided by conventional tendons.One sacrificial anchor and 13 production anchors were installed. An innovative testing setup and program were developed to allow extended creep testing of the sacrificial anchor followed by load testing to 2.8 times the design load without anchor failure. This paper describes the design and construction of the SBMAs, the load testing setup, and results of extended creep load testing. 1.

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