Load–displacement behaviour of socketed piers—Hamilton General Hospital

Abstract

Monitoring the settlement behaviour of full-scale drilled pier foundation that are in service is seldom possible. This report describes the instrumentation and monitoring program for three of the drilled pier foundations socketed into weak shale used for the Hamilton General Hospital addition, and presents and summarizes the data collected over a period of almost 2 years.The three socketed piers were constructed so that each had different load support conditions. Pier P5 was conventional, and supported loads through shaft resistance in the soil and rock and end bearing in the rock. Pier K3 was similar except shaft resistance in the soil was eliminated by installing a sonotube casing in the upper portion of the shaft. Pier P3, which also had a sonotube casing, was constructed with a void apparatus at the base to eliminate end bearing resistance so that support was achieved only through shaft resistance in the rock socket.Instrumentation included multiple-point rod extensometers, with remote readout, to measure vertical displacements at the top of the pier, top of the rock, and bottom of the socket. Load cells, reinforcing bar load cells, and concrete embedment strain gauges were also installed in an attempt to determine load distribution in the pier foundations.Under approximately full dead loading, less than 3 mm (1/8 in.) settlement has been observed. The settlement and bottom load cell data suggest that very little of the applied loading (less than 5%) has been transferred to the base of the socket. Key words: rock-socketed piers, settlement, load transfer, weak shale, instrumentation, monitoring, full-scale foundations.