Construction, construction, construction. Road construction as far as the eye can see. This is probably what residents in Columbus, Ohio, think when they travel practically anywhere. And due to the multi-year Interstates 70/71 Columbus Crossroads project, much of the freeways in downtown Columbus will be under construction into the next decade.
With a civil project as large as the 70/71, a lot of the construction is not just road paving and bridge reconstruction; it is the installation or rehabilitation of underground utilities such as the miles of pipes for gas, water, and sewers. Though perhaps a little less high-profile, these out-of-sight infrastructure projects are just as important.
Taking on one of these behind the scenes – though no less extraordinary – infrastructure projects was SHELLY & SANDS, Inc. (SSI) based in Zanesville, Ohio. SSI were low-bidder on an Ohio Department of Transportation (ODOT) project to install a new sewer system that diverts water from a large existing sewer line through four hydrodynamic separators that clean storm-water runoff before it is discharged into the Scioto River.
This was not an easy excavation project. It was in fact, four different excavation projects; each a different depth; some with different soil condition; some with existing crossing utilities to navigate; and each having different sized pipes, structures, and manholes to install within. Complicating matters further was the fact that the Best Management Practices (BMP) sewer project needed to be installed over a length of one block that was bordered narrowly between a western section of the I-70/71 corridor and an apartment building.
Shoring Required for Challenging Excavation Site
All four excavation points were deeper than 5 feet and required a trench protection system per OSHA regulations. “The first thing we considered were trench boxes; possibly using the equipment that we had in our fleet or we could easily rent,” said Brian Snode, SHELLY & SANDS’ Project Superintendent. “But we realized with the soil conditions and the existing utilities that were in the ground, plus the surrounding buildings; dropping in a box just wasn’t going to work.”
“Also with the highway and the apartment on each sided, we realized we couldn’t vibrate in any sheeting or drive-in a lag wall,” Snode continued. “So when we got down to it, really the only thing that would facilitate our need was a dig-and-push shoring system.”
Contractor Chooses Unconventional Slide Rail System
“Dig and Push” is a process most commonly associated with installing a Slide Rail System. Slide Rail is installed by sliding steel panels (similar to trench shield sidewalls) into integrated rails on vertical steel posts – an outside slotted rail first, then an open-face rail on the inside – then pushing the panels and posts incrementally down to grade as the pit is dug.
Snode, however, had little experience with Slide Rail Systems. Needing help, he contacted his friend Jeff Riddle at Baker Corp for some ideas. “We’ve worked with SHELLY & SANDS many times before, and have a good relationship with the company and with their personnel,” said Riddle, Baker Corp’s Branch Operations Manager. “So after looking at Brian’s project parameters, I knew that an Efficiency Production Slide Rail System would work; maybe the only thing that was going to work.”
Added Snode, “When Jeff started showing us how Efficiency’s Slide Rail System works, and the versatility of the system to change depending on ground conditions, well it was refreshing to see that they had a different shoring option for us.”
Awaiting ODOT Approval
However, it wasn’t just the contractor that had to be convinced on the effectiveness of the Slide Rail System. Snode and Riddle needed to also convince ODOT that it would work in the difficult site conditions, and meet their safety requirements. “We went over the entire installation and removal process with ODOT; how Slide Rail actually works and how it meets their safety guidelines for underground construction,” said Riddle.
Slide Rail is considered a positive shoring system. It maintains constant pressure against the sides of the excavation and requires no over-digging. This prevents possibly undermining or disturbing the surrounding foundations of buildings, roads, or other structures. A positive shoring system is a critical requirement for approval from most states’ Department of Transportation – including Ohio’s – for any underground construction.
SSI Begins Work on New Sewer from Bottom to Top
Sufficiently assured that Slide Rail met all safety requirements, ODOT gave SSI the green light to begin work on the new gravity-flow sewer. They started from bottom to top; or downstream to upstream; or literally from the bottom of the hill at Short Street to the top of the hill at 2nd Street.
Pit 1 reached down 32 feet to uncover and reroute an existing sewer line. Utilizing the same Slide Rail components from the first excavation, Pit 2 was dug and shored for the installation of the four deep pre-cast sump manholes, which contain the hydrodynamic separators.
Pit 3 widened and lengthened the shored space just by adding a few more Slide Rail components, which allowed SSI to install inflow and outflow vaults and four 18-inch intake/outtake lines. “That’s where the manifold separates the water through the four deep sump manholes and through the screening process to clean it before it reenters the new piping that we built into Short Street,” Snode explained.
Lastly, Pit 4 was excavated for an 18 x 11 x 28-foot-tall pre-cast chamber that intersects a 96-inch existing storm sewer and diverts the flow through a more conventional 42-inch line down to the treatment structures. Pit 4 – the largest of the four excavations – was shored with a 29 x 38 x 32-foot-deep ClearSpan configured Slide Rail System.
“Jeff and I looked at the ClearSpan pit at least eight times and actually had to redesign it on the fly,” said Snode. “Because the big 96-inch line was not in the exact location indicated in the plan, plus everything was right in the middle of the street... It was a challenge but we were able to overcome all of that because of the flexibility of Efficiency’s Slide Rail System.”
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