The influence of geological factors on rocks and rock masses 29decreasing stress at constant strain. We might be considering processes
which occur very rapidly, in particular, stress waves travelling through the
rock. These could be caused by natural processes, as in earthquakes, or by
artificial processes such as blasting or mechanical excavation using picks,
discs or button cutters. Hence, throughout the time range from milliseconds
to millions of years (say, 16 orders of magnitude), the engineer should have
some understanding of rate effects. These time aspects will be discussed
further in Chapter 13.