Grouting to Control Deep Foundation Settlement

An 18-story reinforced concrete building under construction in South Florida reached 16th floor level when significant differential settlement presented an unanticipated foundation problem. The foundation consisted of a structural mat supported by 14-in. concrete piles 24 to 75 ft long. Surprisingly, the longest piles were within the area of greatest settlement. Investigation revealed a previously undisclosed semi-cavernous zone from 120 to 175 ft below ground surface, and level surveys using deep benchmarks confirmed that zone to be the source of movement. Injection grouting first accelerated and then controlled the settlement, allowing the building to be completed on schedule. Temperature probes and weekly precise level surveys were key control devices contributing to the correction of the problem