This from LC.com
Drilling problems to delay dam repair beyond 2012
January 19, 2011
Drilling problems to delay dam repair beyond 2012
By BILL MARDIS, Editor Emeritus
Commonwealth Journal The Commonwealth Journal Wed Jan 19, 2011, 07:00 AM EST
Remedial work at Wolf Creek Dam continues unabated during an unusually cold and snowy winter and the U.S. Army Corps of Engineers said the foundation remedial contract is approx-imately 44 percent complete. However, delays caused by drilling problems in a critical area near the concrete section of the dam are expected to push completion of the remedial project beyond the previously announced date of December 2012. The latest project update issued by the Corps said 289 protective concrete embankment wall (PCEW) panels and 186 secant piles have been inserted in the 4,000-foot earthen section of the dam. PCEW panels create a stabilizing wall in the earthen section of the dam ahead of drilling for the secant piles that form the permanent concrete barrier wall. The Commonwealth Journal has been unable to determine how many panels and piles are involved in the entire project but engineers have said enough concrete is required to build a 5-foot-wide sidewalk all the way from the dam to Washington DC. When remedial work is done, the earthen section of the dam will be fortified with three concrete walls: The original diaphragm completed in 1979 to stop a more serious leak that developed in the late 1960s; the protective concrete embankment wall; and the permanent barrier wall. Corps engineers say this will be a perpetual fix for the seepage-plagued, 60-year-old dam. The Corps announced in August 2005 that an outside panel of experts had classified Wolf Creek Dam in high risk of failure. Treviicos Soletanche JV, a French-Italian firm, was awarded a contract to install a permanent barrier wall in the dam and in January 2007 the lake level was lowered about 40 feet to relieve pressure on the troubled structure and facilitate repairs. Engineers have decided a new method of drilling is necessary to form a barrier wall in Critical Area 1, a 200-foot-wide spot near where the earthen section joins the concrete monolith. Drilling in this critical area will be done through double-wall steel casings so as not to disturb the cavern-laced structure. Special equipment to drill through these casings must be designed and manufactured, another cause for delay. “(Drilling through casings) will isolate the cave and cutoff trench material outside the casing from the effects of the construction activities inside the casings,” explained Michael Zoccola, chief of Civil Design for the Nashville District. “Once the hole is drilled to the design depth it will be filled with concrete as the casing is removed. This approach will be slower but it satisfies concerns regarding dam safety and constructability. The dam is monitored around-the-clock, seven days a week and instrumentation data and observations show no abnormalities in stability of the dam, the Corps said. The permanent barrier wall is being formed by drilling overlapping 50-inch-diameter holes extending 275 feet from the work platform to a more stable stratum of limestone rock below the dam. The larger holes are drilled following an 8-inch pilot hole. Although final design of equipment for modified construction in Critical Area 1 is still under way, Hendrix said each section of the double-wall steel casings will probably be about 10 feet long. A special casing rotator will be use to “screw down” the casing. Hendrix said pilot holes for drilling through the casings will be 9 inches in diameter and the overlapping larger holes to form the barrier wall will be 60-64 inches in diameter, about 10 to 14 inches larger than regular holes for the permanent wall. The Corps and the general contractor are in the proposal and negotiation stage of a modification to the contract to install cased secant piles in the cave and core trench area of Critical Area 1. Negative impacts to project cost and completion schedule are expected, and final impacts will be released upon completion of the contract negotiations, the Corps said. That’s Corps-speak for saying they will tell us how much the remedial costs will rise above the previously estimated $584 million, and how much longer beyond December 2012 it will take to finish the job. The main culprit for delay is Critical Area 1, honeycombed with caverns in its limestone base. Reports indicate when the dam was constructed before and after World War II, caves in the limestone rock were filled with clay that has washed out since Lake Cumberland was impounded. Subcontractor Hayward Baker Inc. (HBI) continues drilling and grouting the rock foundation below the cave and core trench features in Critical Area 1. HBI has completed a line of holes to close an area between the ends of the upstream and downstream grout lines. Baker is currently drilling steep angled holes at the west end of the work platform to tie in with the grout lines drilled from the gallery beneath the concrete dam in 2007. Engineers have told the Commonwealth Journal that caverns 40 feet in width are beneath the dam. The critical area near the concrete portion of the dam refused to accept grouting and has been the main reason the lake level has been held lower than normal for four years. No change is expected in the lake level until the main barrier wall is in place in this 200-foot area. Treviicos Soletanche JV continues to install the protective concrete barrier wall and the main barrier wall in all areas except Critical Area 1.
Thanks for the update.