Sammis Power Plant
Stratton, Ohio
RECON negotiated a sole-source contract to design and install the Limestone Unloading Pit (LUP) at the Sammis Power Plant. The LUP is 60-feet long by 60-feet wide, and its walls extend to depths greater than 50-feet below grade. To deliver limestone, loaded trains will pass over the top of the LUP, supported by the 42-inch thick reinforced concrete “diaphragm wall”. The project is a portion of the Air Quality Control Project that will introduce lime slurry into the Plant’s coal-fired furnaces, to reduce future sulfur emissions and to eliminate “acid rain”.
Diaphragm Walls
Diaphragm walls are excavated using the slurry trench method. This method involves excavating a narrow trench that is kept full of slurry. The slurry exerts hydraulic pressure on the trench walls and acts as shoring to prevent collapse of the excavation. The excavation is performed in panels using a crane and clam bucket, between temporary concrete guide walls to maintain alignment and verticality. Slurry is pumped to the excavation to keep the slurry level near the surface. Following the excavation of a panel, temporary metal templates are secured on the guide wall at the ends of the panel, and end stop beams are placed to form the panel ends and are driven with a small vibratory pile hammer.
Reinforcing steel cages were fabricated, hoisted with a support crane using a spreader, and positioned over the guide walls at the precise location and orientation for installation. The cage was carefully lowered into the panel excavation between the end stops. Rollers were placed on both faces of the cage to maintain the required separation between the cage faces and the excavation sidewalls. Concrete was placed into the excavation using tremie pipes to complete the diaphragm wall panel. The process was repeated for each panel to create the permanent walls of the LUP.
Scope of Work
The scope of work also included:
- Designing and performing dewatering, as necessary;
- Excavating material from inside the LUP and Tunnel structure and installing temporary bracing;
- Removing and disposing of excavated materials;
- Performing jet grouting for internal temporary soil retention for grade changed in the LUP;
- Designing and constructing reinforced concrete base slabs and tie-in to slurry walls; and
- Installing grade beam and anchor bolts for conveyor and shaker installation.
Construction Issues
Construction was complicated due to the close proximity to the Ohio River, as well as the groundwater and associated geology, including sloping rock. In addition, the LUP was constructed within 20 feet of an active mainline railroad.
The final structure was created to be virtually water tight and included cantilevered walls to depths of 50 feet, capable of supporting the railroad loads beside, and over, the LUP