GREEN LANE GETS GREEN LIGHT: PARAMETER SENSITIVITY IN GRAVITY DAM STABILITY ANALYSIS

摘要

This paper includes a case history of the evaluations of Green Lane Dam, a 103-ft high concrete gravity dam constructed in the mid 1950s. In 2000, the Pennsylvania Department of Environmental Protection (PADEP), Division of Dam Safety expressed concerns regarding the dam's ability to safely pass the Probable Maximum Flood (PMF) based on current meteorologic and hydrologic criteria. Initial stability analyses of the structure indicated that the dam did not meet stability criteria under the increased PMF loading condition and would require strengthening. In 2004, Aqua Pennsylvania engaged Schnabel Engineering to provide subsurface investigations and preparation of design documents for a rock-anchoring program. The subsurface exploration, laboratory testing, detailed hydraulic analyses, and a thorough review of construction documents and photos indicated that the following factors significantly contributed to stability of the structure: 1. The unit weight of the concrete was higher than expected 2. Tailwater levels during the PMF were higher than assumed in previous analyses 3. The dam was "keyed" into the rock foundation Stability analyses incorporating these factors and considerations showed that the dam meets Army Corps of Engineers' criteria and that stabilization is not required. This paper focuses on the results of the field investigations and stability analyses, illustrates the significance of parameter selection in gravity dam stability analysis, and presents a dam safety story with a happy ending.