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The Metropolitan St. Louis Sewer District (MSD) is planning to construct a new larger force main to parallel the existing Caulks Creek force main to provide more capacity and redundancy. However, recent failures in the existing force main caused MSD to rehabilitate a section of the existing force main as soon as practical before additional failures occurred. The existing force main, a 24-inch ductile iron line, had shown signs of internal corrosion resulting from localized high points where air had become trapped. Gas from the sewage created the air pockets, which are extremely corrosive to ferrous metals. The area of immediate concern consisted of approximately 1,000 LF, where additional failures were expected prior to the planned installation of the proposed new line.
Due to difficulty obtaining additional work easements in the project area, it was determined that the most timely and cost-effective solution to mitigate the existing corrosion was to utilize the existing 24-inch ductile iron force main alignment. Because of the operational importance of the existing line, it was not possible to take the force main out of service for any length of time. Accordingly, an in-place rehabilitation of the line proved to be faster and more economical, while still providing the long-term performance required. A temporary bypass system was therefore required to continue service, handling the existing flows for the duration of the rehabilitation effort.
|Pipeline Details and Project Summary|
|Project:||Caulk's Creek Phase VI-A - Infrastructure Repair Project|
|Use:||Sewer Force Main Slipline|
|Location:||Missouri River Bottoms - Chesterfield, MO|
|Pipe:||1,000 LF of 20-inch DR25 Fusible C-905®|
|General Contractor:||Bates Utility, Weldon Springs, MO|
|Engineer:||Crawford, Murphy & Tilly, Inc. - St. Louis, MO|
|UGSI Contact:||David Reuter - (816) 518-5162 firstname.lastname@example.org|
The rehabilitation was competitively bid with the following options:
1. 20-inch DR25 Fusible C-905® pipe installed via sliplining;
2. 24-inch DR11 HDPE installed via swagelining; and
3. A fully structural cured-in-place option.
Tim Tappendorf of Crawford, Murphy & Tilly, Inc. stated, "Based on the dimensional constraints of the host pipe and the required operational performance, Fusible PVC® pipe provided an excellent option for the project." When bids were opened, all of the bidding contractors selected the Fusible PVC® pipe option, based on ease of construction and overall economic advantage.
The Fusible PVC® pipe was installed in two separate runs at lengths of 300 LF and 700 LF. Each installation was quick and smooth. According to Kris Bates of Bates Utility, "The pull-in of the Fusible PVC® pipe was the easy part of this job." Upon completion of the pulls, the line was pressure tested at 100 psi for four hours. The annular space between the existing 24-inch ductile iron line and the new 20-inch Fusible PVC® pipe was grouted, reconnections to the existing line were made, and the line was brought back into service.