An underground utility contractor encountered loose fill after initial exposure of an open trench excavation. A hydrovac was used to vacuum excavate the trench daylighting locates when fill began to collapse into the trench from beneath the sidewalk and road.

From the perimeter of the trench, parallel holes were drilled at 3-foot intervals, at alternating depths of 10 feet and 5 feet. 1/2 inch brake lines were driven into the subgrade using a hammer drill, to the correct depth. 60 litres of cement grout were injected into the drilled holes through the brake lines, permeating into the loose fill, binding with the fill to form a cement stabilized base.

Cement grout injection using MME Multiurethanes microfine cement and superplasticizer, 1/2 inch brake lines, four cement pumps, and a mixer 22E were used to stabilize the backfill along the perimeter of the open trench. The stabilization program eliminated the potential for collapse of the open trench, allowing for the utility contractor to continue the excavation operation without incident.