Quality Control of Caisson Foundations

This paper deals with the quality control methods and procedures, which were employed for foundations of a steel frame high-rise building, involving twenty-five (25) stories above level and two (2) below street parking levels. The main building tower is supported on fifty-two (52) drilled straight shaft caisson members bearing within sound shale formation. The installed lengths of caisson members range between approximately 160 feet (48.8 m) and 170 feet (51.8 m). Bearing diameter of the individual caissons varies between 3 feet – 8 inches (1.1 m) and 6 feet – 10 inches (2.1 m). The caissons were installed at the base of an approximately twenty-five (25) foot depth excavation below street level. The field control included proof testing and visual examination of all excavations for drilled straight shaft caissons, plumbness evaluation using laser alignment equipment, and comprehensive concrete placement control operations. Statistical analysis of concrete strengths and post-construction evaluation of the in-situ caisson concrete density and strength supplemented the inspection operations. The comprehensive inspection program furnished sufficient information to assure the design team and owner of the integrity of the foundation system.