Mississinewa Dam foundation and remediation

The Mississinewa Lake Dam is located in northern Indiana on the Mississinewa River, 7.1 miles above its confluence with the Wabash River, approximately 65 air miles northeast of Indianapolis, Indiana. At spillway crest level the pool extends up the Mississinewa River a distance of approximately 31 miles. The Mississinewa Lake project consists of an 8000 feet long earth fill embankment, having a maximum height of 140 feet, a gate controlled outlet works along the base of the left abutment, and a 1550 feet wide uncontrolled, open cut spillway through the right abutment. The embankment consists of compacted impervious fill with a downstream compacted random fill section, and a 36-foot crest with a top elevation of 797. The embankment was completed in 1967, and the dam was placed in full operation in 1968.

Construction of the left abutment included an impervious cut-off trench with dental treatment into competent limestone. The right abutment was founded on glacial outwash materials overlying solutioned limestone with a shallow inspection trench. Prior to completion, the project was placed into emergency operation in 1966. During this episode, a boil carrying embankment material formed on the downstream toe of the right abutment. Remedial grouting was ineffective, but relief wells and filtered toe drains were effective. By 1974 the embankment had completed its post-construction consolidation of approximately 0.3-feet. In 1988, project personnel noticed an anomalous "low spot" in the guardrail on the crest of the dam. Re-evaluation of the data from the surface displacement monuments confirmed that 200-400 feet of the dam was continuing to settle about 0.035-foot per year. The crest elevation in the settlement zone is currently 0.6-feet lower than the rest of the dam and continues to settle. The foundation conditions, settlement history, instrumentation data, reasons for the settlement, and current plans for remediation will be the focus of this presentation. 11 pp.