Measurements of surface settlement, changes in piezometric levels and earth pressures were undertaken on a 10-ft diameter tunnel that passed through extremely sensitive and moderately over-consolidated Leda clay in Ottawa. The instrumentation is described, and the results are given for a period of 5 years, from 1 year before construction until 4 years after completion. Results of the measurements are compared with those obtained from a tunnel of similar size in Detroit clay. Because of the method of construction there was opportunity to conduct measurements on both the rather flexible temporary steel lining and the more rigid permanent reinforced concrete lining.Very little surface settlement was measured owing to overconsolidation of the clay and the method of construction. The tunnel had considerable influence on the piezometric regime in the clay, acting as a drainage sink. Earth pressures were in accordance with previous measurements on tunnels, with vertical pressures approaching the full overburden pressure.