New Ragged Mountain Dam

New Ragged Mountain Dam Project is located in Albemarle County, Virginia approximately 4 miles west of the City of Charlottesville. The project includes construction of a new earthen dam along with an adjacent tunnel system and raw water pipeline that will serve as the principal spillway for the new dam structure. The new dam will stand almost 100 feet in height, and it is being constructed to increase local water supply by raising the normal reservoir pool by approximately 30 feet, as currently planned, with future expansion capability up to an additional 12 feet. The new raw water pipeline will convey raw water to the existing water treatment facilities near the University of Virginia campus as part of the public water supply system.

The project required the completion of more than 137 acres of tree and related debris removal on steep, mountainous terrain with restricted access around perimeter reservoir. Controlled burning methods with forced-air, burn boxes were utilized for the reservoir clearing work resulting in a significant reduction of smoke emissions and improved air quality as compared to more conventional burn methods.

Approximately 500 linear feet of tunnel through bedrock is required for new principal spillway and raw water pipeline. Additionally, an approximate 100-ft tall, concrete intake tower with new operations building at the top and pre-fabricated steel bridge will be constructed to house and access a new 36″ D riser pipe which feeds the new raw water pipeline.

Foundation improvements for the new dam include deep foundation grouting to 100+ foot depth to create a “grout curtain” beneath the dam centerline. Our specialty grouting subcontractor was required to pump grout into drilled holes to fill and seal existing rock cracks and crevasses located deep beneath the existing ground surface. Additionally in areas of highly fractured rock, a soil-cement-bentonite (SCB) cutoff wall was installed up to 40 feet in depth by a specialty SCB subcontractor. An excavated, trapezoidal keyway section approximately 10′ deep and up to 50′ wide to be comprised of select clay (soil) core material will also be situated along the same “grout curtain and SCB” alignment to complete cutoff system into existing ground at foundation level.

Thalle is currently postured to begin construction of the complex internal drainage system comprised of horizontal blanket and vertical chimney drains to collect, convey, and monitor seepage through the new dam. In conjunction with drain construction, Thalle will use specialized “zone” embankment construction techniques to place approximately 95,000 cubic yards (CY) of select clay core and 500,000 CY of embankment shell material in order to create a composite-soil dam embankment with impermeable clay inner-core section and sound, competent, outer structural shell. Select core and structural shell materials (soils) will be obtained from on-site borrow areas.

Additional elements of work include demolition and removal of portions of the existing dams and appurtenant structures; improvements to the adjacent I-64 highway embankment including specialty slip lining and grouting of 8′ x 8′ box culvert beneath I-64; a rock-cut auxiliary spillway that will be built to allow emergency reservoir lowering during extreme storm events; and a variety of finish work for complete facility such as geotechnical instrumentation, site security, process control and monitoring, asphalt pavements and landscape systems.

Thalle will self-perform most work on this project including earthwork and new pipeline construction. Additionally, Thalle will form and pour approximately 1,500 CY of cast-in-place concrete in connection with new intake tower, operations building, downstream access vault, auxiliary spillway, retaining walls and concrete ditch sections.