Stabilization of Retaining Wall Along Tailrace Channel of Hodenpyl Dam

A cantilever wall located along the tailrace channel of the Hodenpyl Hydroelectric Dam was undergoing significant lateral displacement. An unsuccessful repair attempt was carried out in 1996 using conventional strand tiebacks. Remediation of the movements was accomplished in 2002 by installing additional tiebacks through the wall. The tieback system selected for this project was Single Bore Multiple Anchors (SBMA), bonded into high-plasticity clays behind the potential slip surface. The SBMA system provided the desired tieback capacities in the clay with a reduced potential for long-term creep. This was the first application of post-grouted SBMA technology in the United States. The limited monitoring data collected after remediation suggests that the SBMA system has performed remarkably well. To expedite remediation of the wall, the design had to be completed in phases and adjusted according to the monitoring data obtained until the start of construction. This paper presents a description of the investigation and analyses performed for design of the remediation. It also describes briefly the SBMA system and the results obtained as interpreted from the wall monitoring performed up to this date. A companion paper by Bruce et al. (2004) describes in more detail the SBMA design and construction details for this project.