This purpose of this project is to provide a new effluent discharge line from the Lemay Wastewater Treatment Plant to an outfall structure on the west bank of the Mississippi River.
SAK’s scope of work included continuing tunnel excavation where a previous tunnel contractor stalled. Approximately 381 linear feet of tunnel excavation was required up to an existing junction chamber designated as JC-9. SAK utilized a Robbins 94-218 tunnel boring machine (TBM) to excavate the tunnel to a finished diameter of 11’-3”. Tunnel excavation commenced on 04/14/11.
Upon completed of tunnel excavation, non-explosive and explosive rock excavation methods were then employed to widen the TBM excavated tunnel to a 16 foot diameter horseshoe shape in order to accommodate installation of the 132 inch diameter concrete carrier pipe.
Non-explosive rock excavation occurred for a total length of 252 linear feet beneath an active railroad yard. The Cardox system was used to fracture rock by non-explosive means. Once past the limits of the railroad, SAK switched to explosive rock removal methods in order to expedite the tunnel excavation and widening process.
After all tunnel excavation and support activities were completed, pipe installation commenced. Jacking methods were used to install the 132 inch diameter by 12 foot long sections of concrete pipe within the tunnel. The annulus space between the pipe and tunnel wall was then filled with a low density flowable grout, thereby locking the tunnel pipe in place. Final connections between the tunnel pipe, JC-9, and the surface installed (open-cut) pipe were made and the outfall was activated on 01/20/12.