and summarized graphically in figure 7.58 (Gray, 1978). the figure shows that for typical root area ratios (0.05 to 0.15 percent), the amount of apparent cohesion or shear increase provided by the live or fresh roots is in the range of 0.5 to 2.5 pounds per square inch. the theory of root reinforcement is discussed in detail by barker (1986), Gray (1978), and Waldron (1977). figure 7.59 shows how root strength can be incorporated into stability analyses.