The effects of valleys on the strength of rock materials at depth

Most investigations of the effects valleys have on rock properties have been performed where surface excavations occurred in a valley. The impact valleys have at depth into the bedrock has been limited to borehole measurements of hydrologie conductivity, various models of stress distribution, and empirical relationships with roof instability of underground coal mines. This investigation used core from borings extending below and adjacent to bedrock valleys. Laboratory measurements of strength, slake durability, and P-wave velocities were compared amongst the cores. Test results show that the strength of samples of bedrock below valleys ranges from 10 to 26% less than adjacent or shallower areas of the valley. This work also shows that the deeper parts of the valleys have a greater effect on the bedrock strength.