Proceedings of DFI-India 2018: 8th Conference on Deep Foundation Technologies for Infrastructure Development in India, (DFI)
Single Bore Multiple Anchor Systems (SBMAs) in Challenging and Variable Ground Conditions
Antonio Marinucci, Ph.D, MBA, P.E., M.ASCE, Devon Mothersille, B.Eng, Ph.D., C.Eng, FICE and LETAPAEWE
Single bore multiple anchors (SMBAs) are ground anchors that incorporate multiple individual unit tendons of varying lengths, which are installed within a single borehole. Decades of research and practical applications have demonstrated that this configuration facilitates greater efficiency of load transfer to the surrounding ground. Unlike conventional ground anchors, especially in heterogeneous and variable ground conditions, the design of SBMAs can be optimized because the bond length of an individual unit anchor can be designed individually, thereby utilizing and maximizing the inherent strength of the ground. Historically, SBMAs have been used for both permanent and temporary earth support systems, and, where project circumstances dictated, SBMAs have been installed with removable tendons, which permitted the complete removal of the prestressing steel strand (at the end of the anchorís design service life). The installation of SBMAs is congruent with that of traditional ground anchors, and the testing protocol is similar regardless of anchor type. However, unlike conventional ground anchors, the stressing of SBMAs can require a different set up, whereby separate hydraulic jacks are hydraulically synchronized to stress each individual tendon simultaneously so that each unit anchor receives the same load. This paper will provide a general overview of the design, installation, and testing of permanent, temporary, and removable SBMAs along with the applicability for their use and the benefits afforded from using this type of anchoring system. The paper will also present and discuss applications in different ground conditions and test results via mini case histories where SBMAs have been implemented worldwide. The use of specially developed tablet-based software that allows real-time analysis and data management of the anchor testing process will also be presented with reference to SBMAs. Finally, it will be shown that, depending on the ground conditions and project requirements, it is possible that SBMAs can double the capacity of conventional anchors, thereby generating substantial savings in program time and cost.
|article #3182; publication #1050 (India2018)|