ALKALI-SILICA REACTIVITY AT ROANOKE RAPIDS DAM INVESTIGATION, DESIGN, REMEDIAL CONSTRUCTION AND SAFELY MANAGING CONCRETE GROWTH

摘要

Roanoke Rapids Dam is a 72-foot high, 3,050-foot long concrete gravity dam with four 26MW power generating units located on the Roanoke River in North Carolina. The South Non-Overflow Section (SNOS) of the dam is approximately 581 feet long and was designed with an upstream curving south abutment. Recent instrumentation history indicated accelerated deformation, increased seepage, and increases in uplift pressure in the SNOS. An investigative program performed by Gannett Fleming, Inc. from 2006-2008 discovered significant cracking along several monoliths of the SNOS and concluded that the dam was experiencing concrete growth due to Alkali-Silica Reactivity (ASR). The ASR caused the dam to expand in the longitudinal direction resulting in a downstream force component that cracked and “rocked” the curved section downstream. Partial sections above the cracking were determined to be unstable during the design flood (PMF). HDR Engineering was (HDR) contracted by Dominion to perform detailed engineering for a crack grouting and anchoring system. Downstream grout leakage during construction led to the discovery that cracking extended horizontally almost completely through the structure, then continued downward sub-parallel to the downstream face. This led to an immediate re-evaluation of dam stability and implementation of temporary structural measures to allow construction to proceed safely. Crack grouting and anchor installation was completed in May 2010. Since completion, HDR has prepared a state of the art finite element model (FEM) to predict future performance of the structure and help Dominion determine if and when additional remedial measures may be required. The FEM will continue to be used in conjunction with the existing instrumentation program to periodically re-evaluate and update performance predictions. This presentation will provide a brief review of the project, discuss the unique challenges of the crack grouting and anchor installation and summarize results from the ongoing instrumentation and FEM performance evaluation.