Testing and Evaluation of High Capacity, Multi-Strand Rock Anchors for Lake Lynn Dam

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


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. To evaluate the potential for creep occurring, a pre-production bond stress test was conducted on a test anchor having a bond zone in medium hard, clayey siltstone. Significant creep movements, defined as observed anchor elongation under constant load, were observed. A companion paper at this conference discusses observations during installation and testing of the pre-production anchor. For the production anchors, multi-load step performance (creep) testing of 8 anchors to 133 percent of their design loads and single-load step proof (creep) testing of 67 anchors to 125 percent of their design loads were carried out. After load lock-off, initial lift-off tests on all anchors and later lift-off tests on 12 anchors were performed to assess the ability of the anchors to maintain the loads. Testing was generally done in accordance with procedures for performance and proof testing outlined in the PTI Post Tensioning Manual (1990), with performance testing modified to reflect the more appropriate detailed PTI (1990) creep test procedures. This paper presents the results of the testing and evaluation of the 75 anchors. Creep elongation was noted during testing for 74 of the 75 production anchors. Testing at sustained loads was continued for 10 to 330 minutes until the observed creep rate met the project requirements.

Subject Headings: Load tests | Anchors | Concrete dams | Gravity dams | Rocks | Creep | Rockfill dams | Lakes

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