A soil sample is taken from the midpoint of the clay layer of Example 6.8-that is, from a depth of 6 m. If the pore pressure parameter Au for unloading is 0.90, estimate the effective vertical and horizontal stresses acting on the sample just before testing in the laboratory. Assume ∅' for the clay is 25 deg. (Hint: Draw elements with stresses similar to Fig. 12.36, and use the definition of stress increments in Appendix B.3.) (After G.A. Leonards.)?