City of Eden Meadow Greens, Merriman Street, and Long Street Outfall Sewer Rehabilitation

City of Eden Meadow Greens, Merriman Street, and
Long Street Outfall Sewer Rehabilitation

Project Overview

Project included rehabilitation, replacement, and improvements for 8" to 12" gravity sewer outfalls and manholes in three major sewer basins for the City of Eden, NC. Improvements to manholes included replacing 8 existing manholes, and rehabilitation to 38 existing manholes. Rehabilitation methods included coating with a cementitious lining, rebuilding benches and inverts, and sealing lid frames to the manholes. Gravity sewer line improvements included replacement, point repairs, and lining. Replacement portions of the project included 1,690 LF of 12" sanitary sewer and 420LF of trenchless replacement with a 26" steel encasement pipe. The lining consisted of 8,220 LF of 8", 10", and 12" cured in place lining with video inspection, cleaning, and point repairs to these lines as needed. WKD was responsible for the design and production of plans, specifications, permitting, and bidding portions of this project. Construction administration duties included all administration, shop drawing review, and construction observation.

Boring under Golf Course

A portion of this project included the need to replace 420 LF of 12" sewer line that crosses a fairway of the Meadow Greens Country Club Golf Course. Options that were considered to perform this part of the project included lining the existing 8" line with a cured-in-place liner, replacing the line using standard open trench construction methods, or utilizing trenchless technology to install the line. Considerations for this process were the need to keep the course open for play, the presence of a large hardwood tree, small pond, cart paths, irrigation lines, and tee boxes all within close proximity to the alignment of the existing sewer line.

The option of rehabilitating the existing line was ruled out because hydraulic analysis of projected future conditions indicated that the line size needed to be increased from 8" to 12". Using standard construction methods was decided against because of the interruption to the golf course which would have included damage to the Bermuda turf grass, the need to remove and replace sections of two cart paths, and the presence of excavation equipment in the fairway.

After evaluation of the options, it was decided that utilizing underground boring would be the best way to install the sewer line across the fairway. The original design was to make two shorter bores (approximately 210 LF each) that met in the middle of the fairway. A manhole would be placed in the same pit used for as the exiting pit for both bores. The bore would take a route that would cross under the two cart paths, come within approximately 20’ of the pond, and have an average of eight feet of cover. Also important was for the 12" ductile iron pipe to stay exactly on grade, both to provide the correct slope for wastewater flow and to tie in to the existing system on the upstream side and the new system on the downstream side. Soil borings performed in the location of the bore indicated clay soils mixed with partially weathered rock. The partially weathered rock was determined to be at approximately the same elevation as the planned bore.

The contractor selected to perform the project was Sam W. Smith, Inc. based out of Eden, NC. He chose Leo Barbera owner of Horizontal Holes International, Inc. to perform the bore. Leo felt that he could perform the bore in one continuous process and eliminate the need for the middle manhole, while maintaining the necessary vertical and horizontal alignment. This situation was agreeable to the City, as it eliminated the cost of the manhole, as well as the owner of the golf course because the manhole would have detracted from the fairway.

The bore proved the presence of partially weathered rock running along the same plane as the bore itself. Every several feet the spoil would change between clay and the PWR. Adjustments were made as needed to keep the auger head from climbing out of the PWR and running in the softer clay. Vertical and horizontal alignments were checked every few feet and any needed adjustments to the steering head were made. The auger head was changed after approximately 100 LF to one with fewer bits (teeth?) that was more efficient in the PWR conditions being encountered. As needed, the bore remained on grade and exited at just the right elevation and horizontal alignment. The entire process took about two weeks, including mobilization, a couple of rain days, and waiting one day for the new auger head to arrive. The contractor, owner, and engineer were all satisfied with the results and convinced that the right process had been chosen.