High Capacity Micropiles in Karst: Challenges and Opportunities

Abstract

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.

Integrated Underground Analyses as a Key for Seasonal Heat Storage and Smart Urban Areas

“…In particular, the implementation of micropiles in karst terrain involves the combination of two complex systems like drilling and grouting with advanced tools. In complex geological contexts, for example, Taylor et al [22] verified the high capacity of micropiles under karstic geological conditions and proposed universally applicable recommendations; while Bivens and Siegel [23] illustrate that micropiles can be very effective, considering both time and money, when the installation approach and quality controls are tailored to the project conditions.…”

Use of Micropiles for Foundations of Transportation Structures Final Report

“…Typically, they are 100 to 300 mm in diameter (4-12 in) with lengths up to 30 m or more (Bruce et al 1999). When micropiles are installed in competent rock within a reasonable depth below the ground surface, they are capable of resisting very large loads (Traylor and Bruce 2002;Bedenis et al 2004a and2004b).…”

Micropiling in Karstic Rock: New CMFF Foundation Solution Applied at the Sanita Factory

“…The intriguing selection of a foundation system in karst is a challenge particular to each project as was recently reported by many professionals like Dotson, D.W (2003), Brinker, F.A (2004), and Siegel, T.C (2005). The use of high capacity micropiles to solve foundation problems in karstic formations was successfully adopted and published in recent years by Traylor, RP et al(2002), Dotson, D.W et al (2003), and Uranowski, D. et al (2004). The behavior of micropiles under vertical loads in rock have been recently evaluated by Cushing, A.G(2004).…”