Bond Stress Test on Rock Anchor in Clayey Siltstone

Wimberly, P. M.; Mazzella, S. G.; Newman, F. B.; ,

Bond Stress Test on Rock Anchor in Clayey Siltstone

by P. M. Wimberly, III, GAI Consultants, Inc, Monroeville, United States,
S. G. Mazzella, GAI Consultants, Inc, Monroeville, United States,
F. B. Newman, GAI Consultants, Inc, Monroeville, United States,

Document Type: Proceeding Paper

Part of: Geotechnical Practice in Dam Rehabilitation

Abstract:

Seventy five rock anchors with design loads of 556 to 2040 kips were required for the 1000-foot long, 125-foot high, concrete gravity, Lake Lynn Dam to comply with current FERC engineering guidelines. Alternating sedimentary rock sequences comprise the bond zone rock, with weaker claystone and clayey siltstone comprising much of the upper portion. A pre-production bond stress test was conducted on an 18-strand, 75.25-foot long test anchor having a 9.7-foot long, 7-3/8-inch diameter, cement grouted, bond zone in medium hard, clayey siltstone. Load holding for 24 hours at the maximum test load in each load cycle sequence was carried out at loads from 53.9 to 593.3 kips to observe creep behavior. Some loads were reheld after previous holding at higher loads. Shorter load holding was carried out for loads up to 831.8 kips. Significant creep movements, defined as observed anchor elongation under constant load, were observed and are a function of the applied load level and load history. This paper presents the test details and results along with observations on the current state of practice for creep testing of anchors in rock. A companion paper at this conference discusses observations during installation and testing of the 75 production anchors.

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