Section By: Bill Maloney

     Faced with rapid growth that strained their current water supply capabilities, the Somerset Water Service in Somerset, KY decided to construct a new intake structure on the shore of Lake Cumberland. The site included several challenging characteristics including:

• Lake level fluctuations of as much as 90'
• Very hard limestone geology with calcitic geodes
• An existing above grade intake structure located within 200' of the new intake, which precluded blasting

     After a thorough review of intake design options, lead designer Beuren Garten of H. K. Bell Consulting Engineers, Inc. in Lexington, KY designed a simple, cost effective, fixed screen intake, which could be installed with mechanical excavation technology. Prior to construction, the University of Kentucky Department of Civil Engineering constructed a scale model of the new intake.

     Levels in Lake Cumberland fluctuate on a seasonal basis, meaning construction of the shaft has to be completed prior to spring 2000, when the water will rise above the current 720' site elevation. General contractor Building Crafts, Inc. began site construction in July 1999 as soon as the lake elevation allowed for access to the site.

     Piling was installed on the lakeside to allow for construction of the new shaft site location pictured on the left. The old intake structure is pictured on the right. The crane in the lake is excavating for 6' airblast piping which will clear away any build up on the screen.

     A piling cell was excavated to start the shaft. The 17.75' ID, 2' thick, reinforced concrete coping section was then installed into bedrock at a depth of 28'. This portion of the project was completed between August and October, 1999.

     The 17.5' diameter shaft was excavated by first drilling a pilot hole. This 17.5' hole was reamed out to full diameter in one pass by a dome reamer designed and fabricated by North American Drillers, Inc. The same reverse circulation techniques employed in their mining work were used to circulate the cuttings into a pit on site. Reaming rates averaged a remarkable 1 hour to cut and remove 9 yards of material per foot. The shaft was drilled to a total depth of 67' in November.

     Before lining, the shaft was dewatered and the walls scaled for safety purposes. The rock was self supporting, allowing the reinforced floor to be poured in an open hole. A 47' ID flanged port for the microtunnelling process was fastened to the shaft wall at the bottom of the shaft with rock bolts.

     Shaft forms were custom made 16'ID, 10' long used for North American's mining work. A two stage work deck was utilized inside the forms which allowed the lining process to be completed in December of 1999.

     SEC Associates was contracted to microtunnel the 36" ID RCP line out into the lake, a distance of 208' from the shaft. The machine used a pressurized slurry system to allow it to daylight into the already excavated trench in the lake. Once tunneling began in March of 2000, it took only 7 days to complete the 208' line despite geology ranging from soft clays to flint. The slurry lines were removed from the tunnel and the tunnel was plugged at the shaft end. Water was then pumped in to balance the pressure on both sides of the head to make it safe for divers to go into the lake and remove the machine from the end of the RCP. Once the head was on the barge a cap was placed over the lake end of the RCP and the tunnel drained. A 36" valve was bolted to the port at the bottom of the shaft and the cap removed to complete this portion of the project.

     The 45' extension of the shaft to get above the 100 year flood elevation was completed in June. Pump and electrical installation work were then followed by startup of the new intake in October 2000.

     This is the second intake structure of this type for North American Drillers, Inc. having been involved in the Bluestone Lake Intake Shaft near Hinton, WV. This 10 MGD intake also utilized a combination of shaft drilling and microtunneling techniques to install a new intake structure in a pristine park setting. (Maloney, Smith and Tuneblom, 1999) Bluestone Lake Intake Shaft, Rapid Excavation and Tunneling Conference Proceedings, Orlando, FL. (Chapter 41 p. 753-760)