REGIONAL DISTRIBUTION OF INSITU HORIZONTAL STRESSES IN ROCKS OF SOUTHERN ONTARIO

Some structures built in different rock formations in Southern Ontario have been subjected to various degrees of distress. These case histories include heaves of quarry bottoms, buckling of concrete lining of canal floors, cracking of concrete lining of tunnels at the springline, and long term movement of the walls of unsupported excavations. Inference from these case histories, together with direct measurements of in situ stresses, indicate that high horizontal stresses exist in the Silurian and ordovician rocks. The magnitude of the maximum stress in the horizontal plane varies from 6-14 MPa depending on the depth and rock type. Excavations in rock relieve the in situ stresses. The stress relief serves as an initiating mechanism for time-dependent deformation to occur leading to the process loosely termed as 'rock squeeze'. It appears, therefore, that due consideration must be given to this prevalent phenomenon for the design of underground structures in rock in this region. Refs.