Portable tilting table testing results for friction angles of bedding surfaces of sandstones in Highwood Pass, Alberta

Sliding of rock masses along penetrative discontinuities cam be simulated by rock blocks slide along inclined planes. Shearing strengths along penetrative discontinuities are determined by friction and cohesion along the sliding planes. Determination of friction angles of rocks and discontinuities is essential for evaluation of stability of rock slopes. The use of direct shear boxes requires careful transport of specimens from the field, cutting rocks to specified shapes, lapping rock surfaces if necessary and spending at least a day to test a sample. Since Hoek and Brary (1974) first suggested that the angle of friction could be obtained from a simple tilt test when a clearly defined failure surface existed, friction angles of artificial rock surfaces and natural discontinuities have been tested by Cawsey and Farrar (1976), Barton and Choubey (1977), Bruce et al (1988) and Cruden and Hu (1988). Hencher (1976) discussed advantages and limitations of tilting tables. Testing rocks in the laboratory using a tilting table requires transportation of rock samples from the field and, generally, cutting of rock samples in the laboratory. Only a limited number of rock samples can be tested if the working site is far from a highway. Rock samples may be broken when they are sawn. In order to conduct as many tests as needed in the field, a portable tilting table was designed by the author and built in the Department of Civil Engineering workshop at the University of Alberta. The tilting table was used to test friction angles of bedding surfaces of sandstones in the Highwood Pass, Alberta. A report on the tilting table is given here. The construction of the tilting table and the test procedure are given first, followed by test examples of the rocks of Highwood Pass. Then a discussion of the testing results and the table itself is given