Enhancing the Capacity of Belled Caissons with LMG: A Case History

The owner of a parking garage in Baltimore, Maryland, wanted to increase parking capacity by adding two additional supported levels. Adding two new levels of parking increased the loading on the existing belled caisson foundation by 42 to 102%. There was only limited data available regarding original foundation construction, specifically describing only depth, diameter and capacity of the caissons. The task at hand was to assess the available capacity and, if needed, provide a method for increasing the capacities of these foundations. A load-testing program was developed where the existing caisson was loaded to the maximum increased load values plus a safety factor. Due to unacceptable performance under this testing, a Limited Mobility Grouting (LMG) program was implemented at this location to enhance the pile bearing materials. The shaft was retested with significantly improved performance. Based on this performance, the remainder of the columns where increased loading was an issue was treated with similar LMG injection around and under shafts. This paper discusses the site investigation, load testing method, LMG program, and pre- and post-load test results.