Industry Case Study: Lincoln Towne Centre
Challenge
Situation: The original problems consisted of both soil settlement and water leaking in the underground tunnels from the garage to the office building. The discovery indicated that the backfill around the 40' parking structure was improperly performed as the source of the problem. The owners of the property wished to stop the continuous movement and associated repairs.
Challenges: The property was in use and considered a prime office environment. The walls of the parking structure were lightly constructed and posed a risk for movement with high grout pressures in the soils. Many underground pipes and lines needed to be kept safe. The strata that was the problem soil was at the 30-45 foot depths. The dirt at the upper levels turned out to be too dense to drive a typical grout tube through by air hammer.
Solution
Solution: Drill through the upper soils using a TEI rock drill to the 30' level. Drive the grout tubes through the looser 30-45 foot deep level and inject high slump materials. Potholing around the infrastructure was done to minimize damage to it. Monitors were set at the walls near grouting operations to avoid structural damage to the walls. The waterproofing at the tunnels consisted of stabilizing the tunnel structure with grouting to keep it from moving at the connections. Urethane foam injection at the moving concrete joints, exposing the outside to apply urethane flex coating, backfill, and injection of the soils with more foam urethane
Conclusion: Some voids encountered took much more material than was anticipated. In addition, the movement of the pressure on the walls, as noted by the monitors, prevented the grout team from completely filling those larger voids. The team developed a pattern of injecting lower pressures near the wall followed up with higher pressures away from the wall, using the previous grout as a wall to protect the existing infrastructure. The project was repaired and stabilized. The structures were lifted and brought back into acceptable tolerances.
