Pipe Grouting for Discharge and Intake Tunnel Closure

Pipe Grouting for Discharge and Intake Tunnel Closure

Project Description

Pipe Grouting Dimensions:  1,450 linear ft of 13 ft diameter discharge tunnel plus multiple intake tunnels of varying sizes. Total volume filled: 10,965 CY.

Description of Work:

 Geo-Solutions completed the closure of Steam Station Discharge and Intake tunnels using a cement-bentonite (CB) grout mix. In total it took 7,735 CY of grout to fill the discharge tunnel, 3,061 CY to fill the intake tunnels, and 169 CY to fill the storm drain pipe to the north of the plant, totaling 10,965 CY.

Mixing of the CB was performed using Geo-Solutions’ specially designed continuous mixing plant equipped with a density meter to monitor the mix. The mixing was completed in a two phase process. First the bentonite slurry was mixed by introducing dry bentonite to water using a venturi flash mixer which hydrates the bentonite initially. The bentonite slurry was then pumped into a series a paddle mixer frac tanks to mix and hydrate the slurry even before it was pumped to holding tanks.

For the second phase, the hydrated bentonite slurry was pumped into the mixing plant and Portland cement was added into the mix plant using an auger equipped silo. Cement was added until the mixture reached its target density and then was pumped to the voids.

The CB was initially pumped into the discharge tunnel through a port located at the east end of the plant’s basement. Pumping continued through this location for 8 days before that port filled up and plugged off. HDPE pipe was run under the tracks and road and connected to the second port drilled in the hillside closest to the discharge gates. Pumping then resumed from this port until the discharge tunnel was filled.

After the discharge tunnel was completely filled, Geo-Solutions began filling the intake tunnels underneath the plant building. A total of 10 intake tunnels were filled. All tunnels were topped off and Geo-Solutions tore down to demobilize.