Michigan, USA 2007-2010
A pre-excavation grouting program to facilitate the sinking of 2 large diameter caissons was designed by ECO, assisting NTH. There were several formidable challenges to these projects. Vast volumes of water under artesian pressure were encountered in the weathered rock and in the Contact Zone overlying the limestone formation. As a result, the grouting program had to deal with a highly variable Contact Zone and a pervious rock formation. The presence of H2S made matters even more interesting.
A double row of grout holes around the perimeter was installed. Prior to drilling the grout holes into rock (approximately 100 feet below surface), the Contact Zone was grouted first. This was done via OCSP’s: large diameter sleeve pipes with barrier bags strapped around the sleeve pipes. The Contact Zone was grouted in multiple passes using cement based suspension grout but predominantly acrylamide based solution grout. The grouting operation (monitored and assessed in real time) continued until the hydraulic conductivity in all zones in all holes had been reduced to less than 1 Lugeon. At that time, the holes were extended into the rock formation. A cement grouting program was performed via the primary holes on the outer row of grout holes. The secondary holes on the outer row and all the holes on the inner row were grouted with acrylamide.
The execution of the grouting operation was directed by ECO, assisted by NTH Consultants, Ltd. The residual hydraulic conductivity of the grouted rock and Contact Zone on Contract 7 was less than 0.01 Lugeon. Virtually the same result was achieved in Contract 8, with the exception of one in-filled semi vertical feature. The Specialist Grouting Contractor on this project was Layne GeoConstruction.