Caissons Socketed in Sound Mica Schist

The behavior of long caissons socketed in sound mica schist is examined with an emphasis on load distribution within the socket. Load tests were conducted on 14 pairs of caissons, 24 in. (61.0 cm) or 30 in. (76.3 cm) in outside diameter and cased to the top of sound rock. Socket lengths varied between 20 ft and 30 ft (6.1 m to 9.1 m). Very high bond stresses were mobilized within the socket at very small deflections. However, the distribution of bond stress within the socket was highly nonuniform, with the maximum stresses occurring near the top of the socket. The shape of the distribution was found to be in good agreement with theoretical solutions which assume linear elastic behavior. The maximum measured bond stress within the socket was 218.3 psi (1,504 kPa), with corresponding vertical deflection of 0.029 in. (0.73 mm). At the maximum mobilized bond stress the socket was still responding in a linear elastic manner which implies that even greater bond stresses could be mobilized had the socket been subjected to greater loads.