<p><p><h2>Project Summary/Scope:</h2><div>An emergency repair of two roadways was conducted after a sinkhole formation was observed in a nearby storm-water retention pond and under the travel lanes of the two highways. Subsurface Conditions: The site was underlain by engineered fill and quarry run shot-rock placed on residual silty sand soils. The depth to bedrock was an average of 16.8 meters with a minimum of 7 meters and a maximum of 24 meters.</div><div> Compaction grouting was chosen to seal the bedrock and densify the overlying soils. A 10-foot square shaped spacing pattern was chosen based upon previous experience in the area. Secondary injections were delayed 24 hours. Design mix had to be a low slump, low mobility, permanent material capable of being pumped at 41 bars. An unconfined compressive strength of 42.2 kg/cm²and a maximum slump of 50 mm were specified. The stopping criteria were defined as 3.45 MPa or a ground heave of 3 mm.</div><div></div><div>Construction had to take place without closing the roadways to vehicle traffic. Most of the construction within the extents of the lanes took place at night. Grout holes were placed on angles underneath the highway when possible to limit closing the lanes to traffic. 90-mm casings were installed with a diesel hydraulic track drill. The casing was advanced using a top air hammer and air flushing. Drilling stopped when the casing was advanced 1.5 meters into bedrock. Grout was pumped through 76-mm inside diameter high pressure grout hoses. A trailer-mounted pump was used with rates averaging from 15 to 90 L/min. Grout was mixed on site and at a ready mix plant. The bottom-up method was used, staged in 1-meter increments. The casing was extracted in the first meter to allow for the grout to expand into any voids.</div><h2>Performance Monitoring:</h2><div>A typical 30-cm slump test was used as the sole field test for this project. Mix designs were verified on site to assure they complied with the established criteria. Heave monitoring was continuously performed throughout the project. Grout logs kept by the grout technician were reviewed. They contained grout pressure, volume, and time information. Particular attention was paid to the secondary grout injections as a means of evaluating the grout’s effectiveness.</div><div></div><div>Overall, the grouting effort increased from primary to secondary injections by 27%. The volume intake on the secondary injections was 43% less for route 85 and 10% less for I-70.</div><h2>Project Technical Paper:</h2><div>Blakita, P.M. and Johnson, R. (1997) “Design and Construction of a Compaction Grouting Program to Remediate a Highway Over Karst,” Proceedings of Geo-Logan Conference, ASCE, pp 54-61.</div><h2>Date Case History Prepared:</h2><div>November 2012</div></p></p>