Technical Description:
• CON/SPAN
® B-Series Bridge System
• Span: 32’
• Rise: 11’
• Length: 18' and 72’
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While Erlen Group (EG) was opening a new limestone mine, more material was taken inadvertently from one side than the other leaving a large spalled area above the entrance. Since the location will eventually be used for commercial purposes, the damage needed to be repaired. Black & Veatch (B&V), the project's engineer, recommended relining the entrances.
“Taking into consideration our current operation of limestone mining and the long term plan toward underground, secure storage, we wanted entrances that were structurally sound for safety and that had an aesthetically finished look for our long term plans,” stated Terry Quick, P.E., Engineering Manager of EG.
Several options were considered, but it was decided that a 32' span x 11' rise CON/SPAN® B-Series Bridge System, 72' in length, was the best solution for its aesthetics,
strength and similar installations in the area.
Even though the west tunnel was not damaged, it was also relined with a 32' span x 11' rise x 18' long CON/SPAN so that both entrances maintained a similar look.
Before the tunnels were relined, pedestal wall foundations were poured about 10’ outside of the mine. The foundations in the east tunnel
extended about 62’ into the mine until they were past the damaged area and only about 8’
inside the east, undamaged tunnel.
The CON/SPAN arch units were set on rollers and then, once they were inside the mines, they were pulled into place. Steel plates had been added to the keyway so that rolling the 25 ton units was possible. Once each unit was in place, it was jacked up, the rollers were removed and then the unit was lowered back into the keyway.
The biggest challenge of the project was determining the proper amount of clearance for the rollers, while also minimizing the final clearance as much as possible and in turn, reducing the amount of cellular concrete flowable fill needed to fill in the gap. In order to accomplish this, B&V worked with a local company to acquire a 3D scan of the tunnels. The scan was then used to create a model of the tunnels and liners so it could be studied before the actual installation occurred. The result was that the pedestal walls were designed a bit wider
than necessary to accommodate the jack and rollers.
In the end, the project was a great solution for the site, and EG and B&V were satisfied with the outcome.
“After considering several options including steel frame and shotcrete, metal plate and frame structures and the concrete liners, we decided that precast concrete CON/SPAN structures were the best option for the finished look, structural integrity and competitive pricing," concluded Quick. "The overall composite design by B&V using the concrete pedestal walls, the CON/SPAN structures as a liner and the cellular concrete flowable fill in the gaps between the liners and the mine tunnel roof provided us with the structural strength and finished look we wanted.”
Technical Description:
• CON/SPAN
® B-Series Bridge System
• Span: 32’
• Rise: 11’
• Length: 18' and 72’
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