by Mike Fernandez

The Natt McDougall Company (NMC) of Portland, Oregon has been working on an extremely challenging project that involves trenching through a Union Pacific railroad yard. The project is part of the City of Portland’s $7,750,000 Columbia Slough Consolidation Conduit Project "Segment 3" that will divert sewer and storm flows from entering the Columbia Slough during wet weather and redirect it to a treatment plant before it enters the Columbia River. McDougall was awarded the job of installing 7000 feet of 72" reinforced concrete pipe and several structures to depths of 17 feet for the new combined sewer overflow system.

NMC installed the 7,000 feet of pipeline through the Kenton railroad yard adjacent to 6 tracks while crossing under two bridges in the process. They successfully excavated and installed the pipeline within 10 feet of operating tracks, and continued along in other limited right-of-way areas parallel to the remaining tracks where accessible widths were as narrow as 24 feet! Several other impediments such as highway bridge underpinnings, existing utilities, surrounding buildings, and excessive concrete bedding presented significant challenges. Vibration during the installation process was also a major concern as it posed a high risk for structural damage to the buildings and railroad tracks. Although faced with tough conditions, NMC was able to successfully complete the railroad yard section of the job 4 months ahead of the contract deadline, with no settlement problems, or damage claims from the railroad or building owners!

Recognizing the consequences of excavating under the difficult circumstances, NMC evaluated the project specs required by the City, the building owners, and the Union Pacific Railroad and then researched their trench shoring options. The job called for type III shoring (equivalent to shoring for type "C" soil conditions) to protect the surrounding structures as well as the railway against settlements greater than 3/8 of an inch. McDougall realized that driving sheet piling was not a reasonable solution since vibrations during installation would be unacceptable. McDougall saw an ad in a local trade publication for Efficiency Shoring Systems of Oregon and contacted Scott Kellerman for a trench shielding solution. Kellerman recommended Efficiency Production, Inc.’s Shore-Trak^TM cross trench utility shielding system (2 - 20’ long guide frames with 40 - 2’ wide x 17’ long steel panels), a 1024 HT6 (10’ high x 24’ long x 6" thick) heavy-duty steel trench shield, and a 624 XLD (6’ high x 24’ long x 4" thick) steel trench shield.

Efficiency’s P.E., Nathan Bone, quickly provided engineering calculations for submittal to the project owners. Frank Buehler, City of Portland’s Resident Engineer, welcomed the Shore-Trak system as a positive method of shoring that achieved stringent type III requirements. These requirements were a major concern to the City who carried insurance for the project. Efficiency provided a field demonstration of the Shore-Trak. Following the field test, McDougall was convinced that he had made the right choice in selecting Efficiency’s Shore-Trak system. "We are very pleased," stated McDougall. "Efficiency’s engineers provided an outstanding design and were very supportive, and Scott Kellerman was helpful at bid time. Efficiency also committed to an extremely tight delivery date and met it."

The Shore-Trak was installed in the narrow type III designated areas with conventional trenching equipment. The trench was benched at approximately 5 feet deep and about 8 feet wide. The guide frames were then positioned in the trench to receive the 2’ wide x 17’ long Shore-Trak panels that slide vertically through slots in the guide frame and can be locked in place at the necessary heigth above cross trench utilities and other obstructions (refer to photo). As the pipeline installation progressed the individual panels were pulled out concurrently while backfilling the trench. The guide frames were then "leap-frogged" ahead in the trench and the panels were inserted again. This innovative Shore-Trak system successfully maintained a safe working distance from the adjacent railroad tracks without disturbing the track foundation! McDougall commented on the advantages of the system, "It saved money in that it could be installed as part of the trench operation. There were 10 locations totaling over 2,000 feet along the line where type III shoring was called for by engineers and the City. We would have had to pre-drill, drive soldier pile, or sheet pile as a separate, more costly operation in advance of pipe laying in those narrow areas."

In linear sections that were not designated as type III, nor had cross trench utilities, NMC used Efficiency’s 1024 HT6 and 624 XLD trench shields. NMC used Link Belt 5800, 3900, 3400 excavators, a 100 ton Lima Crane, a Komatsu 450 loader, a Powerscreen Plant, and numerous dump trucks for the excavation and installation of the shoring system and related pipeline.

NMC also used the Shore-Trak in 4-sided configurations when installing manholes that had 3 or 4 pipes running from them. Again, the panels were positioned at the necessary heigth to accommodate the intersecting pipes. NMC’s Project Superintendent, Scott Zorza, found the Shore-Trak system to be so versatile that he found ways to use it for 5 other individual structures where they had planned to use soldier piling. This ability to adapt the system to different situations made installations simpler, increased pipeline production, and saved money!

NMC’s project manager, Al Saye, maintained an excellent relationship with all of the groups using "partnering" sessions to resolve issues. When problems surfaced, NMC’s Saye, Scott Zorza, and Mike McDougall, the City’s Frank Buehler, Justin Gough, and Neil Choate, KCM engineer Phil Roppo, Union Pacific, and Efficiency’s Kellerman and Bone would confer to discuss the issues and find solutions to the problems. These cooperative partnering sessions were crucial in the success of this extensive project!

The Natt McDougall Company was originally founded in 1932. They constructed dams and railroads until 1960. The company was re-founded in 1988 and presently works on pump stations, pipelines, fish facilities, dams, and heavy civil construction jobs in Oregon & Washington. NMC is also a member of the Associated General Contractors’ Oregon-Columbia and Washington chapters.

Shore-Trak system installed along tracks while railyard remains operational.		Excavation continues in system between tracks and buildings.