Stabilizing a ‘Mann’-Sized Sinkhole

On Sept. 21, 1988, a sinkhole suddenly developed beneath a transmission/distribution effluent pipeline on Mann Road in Orange County, FL. Initially it measured 30 ft in diameter and 8 ft deep near the center, but three weeks later, with corrective deep grouting barely started, the sinkhole abruptly expanded to 50 ft and 20 ft deep. The prestressed concrete pipeline lay unsupported for 50 ft and the vertical extent of the ravelled zone measured some 125 ft below ground. The remediation team relied on two unique techniques, one for the short-term and one for the long-term, to stabilize the soil and sinkhole. A cement grouting program, which consisted of injections into the soil at depths of 125 to 20 ft, was implemented in the short-term. Shallow depth chemical grouting was completed in Sept. 1989 to stabilize the sinkhole in the long-term.