Sewer Tunnel Collapse: A Case History

In June 1993, a massive "sinkhole" developed in a surface parking lot of a hotel facility located in the Piedmont Geologic Province of Georgia. The hole was the result of the soil erosion associated with a failed, 4-meter diameter combined sewer tunnel. Two fatalities occurred with the collapse. The subsequent forensic study uncovered a series of contributing factors, including a disregard for site history during the planning stage of the development, mis-application of the use of geogrids in the design of a "safety net", mis-interpretation of the signs of impending failure in both the preventative maintenance inspections conducted by the city and forensic studies conducted by consultants immediately prior to the collapse. The paper discusses the planning and design process, the technical inadequacies of the design, and the involvement of consultants and engineers leading up to the time of the collapse.