LARGE-SCALE MODEL TEST OF DRILLED PIER IN SAND

A technique is presented for assessing the magnitude of skin friction for pier foundations in sand. The technique employs the results of interface direct shear tests between sand and the construction material; the results are presented in hyperbolic equation form. The test pier was 16 in. (407 mm) in diameter and 15 ft (4. 6 m) long. The test pier was heavily instrumented with Carlson stress meters, electrical resistance strain gages, and calibrated hydraulic rams on the top and bottom of the pier. Comparisons of predicted and measured values of skin friction showed agreement within 5%. Bonded resistance strain gages on the vertical steel reinforcement are the most reliable instrumentation method. The magnitude of skin friction for ″point bearing″ piers in sand in prototype installations may approach 20% - 30% of the total load capacity.