As you may have guessed by now, the question set up by Means (1976) and Davis and Reynolds (1996) is used to illustrate the concept of lithostatic or confining pressure. Such stresses act uniformly in all directions at a given point at the base of a column of rock (Figure 5).
For example, to solve the question what is the lithostatic stress at point P along the base of the granite cube in Figure 3, we use the equation lithostatic stress = rgh, substituting for r , 2700 kg/m3, for g, 9.8 m/sec2, and for h, 1500 m. The resulting answer is the same as we calculated in Chapter 3.4. But, what if point P is also subjected to a modest horizontal stress oriented East-West?