Many special fittings, such as the Tee base manhole, were manufactured by Hobas to meet the Elmsford project requirements. Click here to enlarge image"We performed a hydraulic analysis of the sewer, comparing present conditions to the new relined sewer, and even with the decreased diameter found negligible decreases in flow capacity," said Chris Patackis, environmental engineer with the New York office of the engineering firm.
The smooth, Manning's .009, interior of the CCFRPM pipes allows for substantial flow recovery in most sliplining applications.
The pipe can be inserted in high or low flow and pushed up stream or down. In this case, the segmented, gasket-sealed pipes allowed for live insertion.
"There was no option to bypass flow from this interceptor sewer and at times the flow was within six inches of the crown of the pipe," said Richard Palmer, PE, with Northeast Remsco Construction, of Toms River, N.J.
The pipe also gave the contractor flexibility in the pushing directions and pit locations. This was a great benefit since the existing 66-inch line made several direction changes and varied in diameter along the project alignment. The line was located 15 feet deep along several highly traveled roadways requiring that the installation pit locations be chosen carefully.
The project was rather complex even though it was fairly small, consisting of 936 linear feet of 60-inch and 124 feet of 54-inch pipe plus a variety of closures and fittings. Because of the complexity and other reasons, the Westchester Department of Public Works required that a Hobas representative be available on site during the entire project. Hobas field service personnel were there at the beginning of the job and representatives including the area manager were in constant contact with the contractor to provide assistance when it was needed.
"There were lots of obstacles to overcome on this project," Palmer said.
Aside from the alignment changes, and poor condition of the host pipe, another obstacle was the removal of the broken pieces of concrete from within the host. A previous failure in the line had driven large pieces of concrete downstream during high flow conditions. The contractor needed to remove the debris to prevent future blockage of flow and to facilitate installation of the liner pipe.
A third obstacle appeared when the contractor discovered that the host pipe had an alignment change near the originally planned pushing pit. A new pit was constructed and Hobas provided several short pieces with closure couplings to reline the bend. The balance of the push was completed from this pit.
Once installation was complete, the line was grouted and inspected. The annulus at each end of each pipe run was bullheaded. Then, cellular grout was pumped into the annular space between the host pipe and the sliplined pipe. A post-construction video inspection and videotape were required to verify the complete and proper installation of the pipe. The project was started in December 2003 and despite the winter weather, the project was substantially complete by February 2004.
About the Author: Kimberly Paggioli, PE, is Marketing Manager with Hobas Pipe USA. Keith Kelly, PE, is a Vice President at Camp Dresser & McKee. Paggioli may be contacted by calling 800-856-7473.