Shoring Sets the Mark
Like many other communities across the country, Springfield, OR, is in the process of upgrading its aging sewer infrastructure to keep pace with growth and new development. This means replacing miles of sewer lines and manholes, as well as installing new lift stations.
One recent lift station installation project was unusual due to the sheer enormity of the structure: a poured-in-place behemoth measuring 35 feet by 29 feet, 37 feet tall.
Two bores and pipe runs were needed for the new lift station to handle the increase on the sewer system from a new hospital. Safely installing the structure posed several unique challenges as the 41-foot by 35-foot square pedestal for the structure needed to be set at a final grade of 41 feet deep.
Emery and Sons of Stayton, OR, won the job as low bidder by working closely with Nigel Guisinger from D.P. Nicoli Inc. — a shoring and piling supplier in the area — to design a shoring system that used Efficiency Production's Universal Slide Rail System in the exclusive ClearSpan configuration.
"We were competing with three other contractors for the job, and I'm sure we would not have been low if we didn't bid with Slide Rail," said Tim Janesofsky, Emery and Sons' estimator and project manager.
Guisinger met with Emery and Sons and concrete subcontractor Marion Construction, and settled on a final ClearSpan system that was 46 feet by 50 feet square with a depth of 41 feet; the largest four-sided Slide Rail System ever designed, according to Efficiency Production Vice President of Engineering, Mike West.
"We've always said that in theory, ClearSpan can have unlimited size, and this excavation proves that a 50-foot-wide pit is not just theory," said West. "Other manufacturers' clear span configurations need to be installed with cumbersome cross-members. Only Efficiency's ClearSpan system is never encumbered by cross-members at any time."
"Dig and Push" System
Efficiency's Universal Slide Rail is a component shoring system composed of steel panels (similar to trench shield sidewalls) and vertical steel posts. The system can be used in a variety of configurations in addition to ClearSpan, such as small four-sided pits, or in a linear Multi-Bay configuration to install lengths of pipe over 40 feet.
Slide Rail is installed simultaneously as the trench or pit is excavated by sliding the panels into integrated rails on the posts — either double or triple rails depending on needed depth — and then pushing the panels and posts incrementally down to grade as the pit is dug; a process commonly referred to as a "dig and push" system.
D.P. Nicoli, Inc. worked closely with Hans Vermeulen, owner of J.M. Turner Engineering, to come up with a final, stamped, site-specific shoring plan for the large pit. Two internal and one external waler were required to get the calculations to work out for the submittals. Guisinger then consulted with Efficiency's West to design the custom walers. There was a bore pit located on the south end of the large pit that was also shored with Efficiency Slide Rail.
Wayne Toney was Emery and Sons' on-site foreman. His crew had installed Efficiency Slide Rail from D.P. Nicoli on numerous Emery and Sons projects, and he has a very good working relationship with Bruce Ellis, D.P. Nicoli's Senior Slide Rail Specialist.
"The nice thing about working with Wayne is that he has a lot of common sense as well as experience," said Ellis. "He also really knows Slide Rail, so any problems that creep up when installing or removing the system are quickly dealt with."
D.P. Nicoli, Inc. is a member of the local NUCA chapter. Emery and Sons is also a member, and Bill Martinak, Emery's owner, is the current president.
Limited Access Problems
The excavation site had very limited space to stage product, so deliveries were coordinated to keep excess product to a minimum. The pit was located just 30 feet off Harlow Road, a major five-lane arterial in Springfield. A senior center was only 75 feet from the pit on one side, and a driveway into an apartment complex was less than 10 feet from the other side of the excavation.
The tight quarters of the excavation site essentially eliminated the option of sheet piling. The disturbance created by the vibration or piling machine would have been very disruptive to the residents living next to the project.
Before starting to dig, Kirk St. Claire Welding was brought on site to fabricate the custom ClearSpan walers. Two-inch-thick steel plates were welded to 24-inch by 162-pound grade 50 wide flange beams. All welding and fabrication on the walers was inspected. These beams were bolted to the Efficiency patented waler corners, which were used on the external and internal walers. St. Claire Welding also was called on to weld corner supports on the inside walers to help get the proper depth rating for the system.
Dewatering wells were installed around the parameter prior to digging. The top 12 feet was sandy clay, which turned to a very dense hard-packed cobble. The water table was around 10 feet. An internal pump was also used to control the water in the work area.
Before actually digging the pit, the excavation was benched down the first 8 to 10 feet. The pit was dug out with a Link Belt 290 excavating the inside, while a Komatsu 600 trackhoe loaded trucks and drove the slide rail posts and panels. After setting slide rail panels into the outside slotted rails of the posts down to 12 feet, the 290 was tracked out, and a John Deere 80C was lowered into the pit to complete the excavation.
The remaining panels were installed into the two inside "open face" rails of the 32-foot triple-rail posts to obtain the final grade needed for the lift station. Efficiency Production's Slide Rail is unique in that it is installed and removed incrementally, which allows the trench to be properly shored throughout the entire installation or removal process, always protecting workers from a trench wall collapse.
Story and photos courtesy of Efficiency Production Inc.