Bluestone Dam Stabilization

TERRADON performed the construction engineering and structural inspection during the Phase 4 Dam Safety project at the Bluestone Dam. TERRADON performed routine inspections on all elements of the drilling platform. The steel decking was checked for deformation, section loss, confirmation that no gaps between adjacent panels exist, that all welds were performed, and that no panels were placed in such a manner that undue stresses will be introduced. TERRADON checked the stringers for deformation, section loss, and that all bolts were properly installed. All connections at the dam face were checked for proper bearing onto the concrete, and the soundness of the concrete was confirmed. TERRADON worked closely with the contractor and various fabricators to develop and approve welding procedures in accordance with AWS D1.5 for these critical items. TERRADON was intimately involved in verifying the setting of welding equipment, the travel speed, welding materials, preheat application, inter-pass temperatures and proper position. TERRADON also reviewed all ultrasonic and radiographic testing performed during the development of the welding procedure and welder qualification.

TERRADON performed a detailed analysis of the existing stringer-on-pier system that was in place when the current contractor was awarded the project. The platform system originally consisted of nine (9) HP-14×89 stringers spaced at 3’-0-3/8”. There have been a maximum of 107 pier systems installed at any given time, and the platform has been lowered 8’-0” in elevation twice, for a total of 16’-0”.

The analysis of this platform included placing multiple pieces of equipment that included, but is not limited to a 150 ton crane, a 20 ton carry-deck, and a 22.5 ton drill rig at various locations on the platform in order to determine the governing load condition for the various structural steel elements. Because of the angle of the pier column, tension forces are induced into the pier cap. These forces are transferred to the dam by way of two (2) 2” diameter Williams Forms Spin Lock anchors. It was later required for the spans in key locations to be doubled to 15.2’, while maintaining access for all equipment. In order to do this, deeper stringers (W24x84) were required. Because of this increased depth, as well as the fact that the HP14x89 stringers were still in use in adjacent locations, it was required that the new W24x84 stringers have the bottom flange and portions of the web coped at the ends. A new bottom flange, as well as bearing stiffeners was designed, and a complete fatigue analysis was performed to confirm that this was an acceptable design approach. Modifications to the column base plates were also required, adding an additional 2’ to the overall length, and performing a full penetration groove weld on the 2-7/8” thick plate. Finally, a “fender” system was developed in order to protect portions of the column that have the potential to be submerged during high water events from woody debris collisions.