LNOS Downstream Centinela Siphon –Sewer Rehabilitation, California, USA

ECO, as a sub-consultant to URS Corporation, designed a soil grouting program to stabilize the soils around a 100 year old large sewer tunnel. The grouting program involved the filling of voids created by the decaying old timber lagging. Furthermore, there was an extensive soil grouting program to consolidate the loosened, sandy soils above and around the sewer tunnel to prevent the structures located above the tunnel trajectory from settling. The grouting program consisted of

• void filling with a stable, slow curing cement, fly ash, based suspension grout
• frac-grouting with a stable cement based suspension grout
• permeation grouting with a microfine cement based suspension grout.

The multiple hole, multiple injection pass performed as part of the grouting program was supervised by ECO’s representatives and implemented by Hayward Baker Inc. The grouting program consisted of injecting regular cement and microfine cement based suspension grouts via steel sleeve pipes which were pushed in the formation. During the installation of these sleeve pipes, the tip pressure was recorded and monitored in real time to determine which soil horizon required treatment. The grouting operation was recorded, monitored and evaluated in real time based on ECO’s amenability theory.