On June 11, 2002, a 150-foot wide and 60-foot deep sinkhole collapsed in Pine Hills, near Orlando, Florida. The Pine Hills Sinkhole was the largest sinkhole to occur in Central Florida in the past 20 years. The collapse swallowed approximately 10,000 cubic yards of earth, sidewalks, light fixtures, a sanitary sewer and several large oak trees in less than 2 hours. The rim of the sinkhole came within a few feet of the shallow foundations of 2 three-story apartment buildings. Observation and subsequent geotechnical analysis showed that the sinkhole slope supporting the buildings was subject to imminent failure, and if a slope failure were to occur, it would likely result in a complete loss of the structures. The weather forecast predicted heavy rainfall, which could further destabilize the steep sand slope. Immediate action was taken to prevent slope failure, including the rerouting of stormwater roof drains and placement of a 30 mil-thick PVC liner over the slope adjacent to the buildings. A detailed geotechnical investigation including Ground Penetration Radar, electronic Cone Penetration Test soundings and Standard Penetration Test borings was immediately implemented to develop geotechnical parameters for remedial design. Due to critical time constraints, a chemical grouting program was conducted concurrently with the investigation to provide temporary stabilization of the building foundation soils from undermining due to the adjacent sinkhole. Settlement and cracking of the building slab foundations and walls were observed within a few days after the sinkhole collapsed, and the settlement and cracking accelerated with time. The permanent design solution for stabilizing the building foundations, and adjacent sidewalks and utilities, was installation of a Giken Wall using the Press-In installation method. The 200-foot long wall was located between the sinkhole and the buildings. The wall was comprised of 3-foot diameter interlocking steel pipe piles that were 50 feet in length. The combined internal auger and Press-In installation methodology allowed the wall to be constructed adjacent to the sensitive sand slope with negligible ground disturbance. The building movement was arrested by construction of the Giken wall and the building foundation stabilization was complete within 1 month after the sinkhole occurred. The relatively minor damage to the structures was then repaired and tenants have returned to occupy the buildings
