Marcus originally used a “shotcrete” method to shore part of the excavation, which didn’t stand up against Michigan’s wet and saturated soil in portions along the trench wall.
In underground and utility construction, a contractor must always be ready to pivot to a Plan B when unexpected challenges arise. Flexibility and ingenuity is essential. This was true for Willmar, Minn.-based Marcus Construction, which recently completed installing a 74 x 16 ft.-long (22.6 x 4.9 m) pour-in-place auger “alley pit” vault at the Anderson-Webberville Dry Storage Elevator in Webberville, Mich.
Marcus’ efforts included overcoming one particular plan-changing; flexibility and ingenuity-testing; trench shoring challenge.
The excavation for the alley pit vault was unusual in that though relatively shallow — 16 ft.-deep (4.9 m) — the long trench needed to be dug two-thirds outside and one-third inside an existing building. The outside portion of the trench was open cut and sloped back to OSHA regulated standards determined by the soil condition, in this case C-60 soil requiring a 1 to 1.5 angle of repose. The inside portion of the building, about 40 ft. (12.2 m) of 16 ft.-deep (4.9) excavation, was cut with vertical walls which required appropriate and safe shoring.
Marcus originally used a “shotcrete” method to safely firm up the walls of the inside-the-building portion of the excavation. Unfortunately, the shotcrete didn’t stand up against Michigan’s wet, saturated, and often described “nasty” soil in portions along the lower wall of the trench.
Marcus needed to audible quickly on a new shoring option in order to keep the project on schedule and on budget.
Alternate Shoring Option Needed Fast, Alternate Shoring Option Quickly Found
The first course of action for Marcus was to consult with Hosford Brothers Concrete in East Lansing, Mich.; a company Marcus had subcontracted to excavate and pour-in-place the vault. Hosford immediately recommended that they call local excavation contractor Woodhull Construction, who Hosford felt confident could come up with a new plan quickly and put it in place.
“I told them that the only conceivable shoring system that could work for the conditions and parameters, like working inside a building, was a Slide Rail System,” said Mike Smith, Woodhull Construction’s owner and operator. “The very next thing I told them was that if you wanted to know anything about Slide Rail, you call the Slide Rail experts at Efficiency Production.”
Efficiency Production Draws-Up Slide Rail System Solution, Quickly Approved
Rod Austin, Efficiency Production’s Senior Slide Rail installer and special operations shoring division specialist, took the call from Marcus.
“Fortunately, we’re located about 30 minutes from Webberville so after a quick site visit, we were able to get Marcus 3D CAD drawings and a detailed plan on how Slide Rail would get them back on schedule,” said Austin. “We were able to get all of that to them in just a couple of hours.”
Those plans and drawings went to Marcus Construction Project Manager Mike Heinen for approval. “I got the new shoring plans very quickly, and even with a quick change we were able to green-light the switch to Slide Rail right away,” said Heinen. “Efficiency [Production] was very efficient and effective.”
Local Excavation Contractor Installs Slide Rail Inside and Outside Building
For Woodhull’s efforts, they were subcontracted by Hosford to install the Slide Rail System with installation assistance from Efficiency’s Austin; plus Tim Hurst and Mark Mitchell, also shoring specialist in the Special Operations Shoring Division.
“I had heard a lot about Slide Rail but hadn’t used it before so I was excited to get the opportunity to install it. Having experience with Slide Rail may open up some new avenues of business in the future,” said Smith.
Efficiency’s Universal Slide Rail is a component shoring system comprised of steel panels (similar to trench shield sidewalls) and vertical steel posts. The versatile system can be used in a variety of configurations, such as small four-sided pits; large unobstructed working pits as big as 50 x 50 ft. (15.2 x 15.2 m) with Efficiency’s ClearSpan System; or in a Multi-Bay configuration to install tanks, long lengths of pipe, and to shore boring and microtunneling pits.
Slide Rail is installed simultaneously as the trench or pit is excavated by sliding the panels into integrated rails on the posts 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. Woodhull used a Cat 345 and smaller Case CX160 excavator to install the Slide Rail components, plus they had a John Deere 310 backhoe and Cat mini track-loader in support.
Slide Rail System Installed With Two Inches to Spare
For the Webberville vault project, Austin designed a highly modified Linear Multi-Bay configured Slide Rail System that required very exact dimensions to make the shoring system work inside the building.
“We actually started by backfilling much of the excavation inside the building where the shotcrete had failed. This enabled us to first push in sheeting against the far trench wall which we braced with a 26 ft. (7.9 m) waler I-beam,” said Austin.
“Then, we needed to install two different size systems; one an 18 ft.-wide (5.5 m), 20 ft.-long (6.1 m) bay inside the building; and then a narrower 14 ft.-wide (4.3 m), 24 ft.-long (7.3 m) two-bay system. The narrower system which was about half inside and half outside the building enabled us to get around an existing support pier which ended up about two inches from the outside panel.”
In a linear Multi-Bay configured system, 8 ft.-tall (2.4 m) panels are installed first in the outside slotted rail of the posts; then another set of 8 ft.-tall panels are installed into the inside “open-face” rail of the post creating a grade depth of 16 ft. (4.9 m). Efficiency Production is the only Slide Rail manufacturer to offer an open-face rail design on their Slide Rail posts which greatly reduces the potential of the panels binding against the soil.
Multi-Bay also utilizes Efficiency’s exclusive Parallel Beams that roll up and down the slotted rail on the inside face of the linear posts and have spreader collars — like trench shield sidewalls — which pin standard trench box spreaders. This versatility enabled the widths of the two systems to be altered by simply using two different lengths of spreader pipe. In this case, 16 ft.-long (4.9 m) spreaders were used on the wider, 20 ft.-long (6.1 m) inside system; and shorter 12 ft. (3.7 m) spreader pipe on the narrower two-bay system.
“[The Slide Rail] worked great and really kept the project moving. I’m not sure what else we would have done because there was no overhead room for sheet piling,” said Marcus’ Heinen, who flew in from Minnesota for a couple of days to observe the Slide Rail installation.
Marcus Construction, established in 1956, is a family-owned construction company that uses design-build, general contracting and construction management delivery methods. Marcus’ national projects include liquid chemical and dry fertilizer and flat grain storage; plus educational, commercial, health care, financial and industrial facilities. For more information, visit www.marcusconstruction.com
Woodhull Construction, located in Laingsburg, Mich., has been a mid-Michigan general contractor since 1991. They are members of the Association of General Contractors (AGC). Since 1994, family owned and operated Hosford Brothers Concrete Inc. has been providing residential and commercial concrete services in Michigan. They are members of the American Builders Association. For more information, visit hosfordbrothers.com.
Efficiency Production, Inc., “America’s Trench Box Builder,” provides a wide selection of standard and custom trench shielding and shoring systems. Efficiency’s versatile products are designed specifically for safe and cost effective installation of utility systems and infrastructure improvements. All products are P.E. certified to meet OSHA and MIOSHA requirements.
For more information, visit www.efficiencyproduction.com