Because the earth has been freshly cut and will not be kept open long enough to break up the cohesiveness of the banks it is customary to reduce the assumed pressure by dividing by 2, 3, or 4, according to the natural cohesiveness of the material. The cohesiveness of sand is not great, therefore the pressure will be assumed as one-half of the amount given by the formula, or _p_ = 18_h_. 2. _Thickness of Sheeting and Spacing of Rangers._—It is desirable to use the same thickness of sheeting throughout the depth of the trench. Computations should therefore be commenced at the bottom of the trench where the pressures are the greatest and the thickest sheeting will be required. It is necessary to determine by trial a spacing for the rangers and a thickness of sheeting so that the sheeting is stressed to its full working strength. Having determined the thickness of the sheeting at the bottom, the remainder of the computations consists in determining the spacing of the rangers. In the example the lower ranger will be assumed as 3 feet from the bottom of the trench and the distance to the next ranger as 4 feet. The intensity of pressure at 22 feet 9 inches is 409.5 pounds per square foot. The intensity of pressure at 26 feet 9 inches is 481.5 pounds per square foot. The distribution of pressures is shown by the diagram on Fig. 111. The maximum bending moment is slightly below the point midway between the rangers and for a 12–inch strip is 10,500 inch-pounds. Assuming 3 inch sheeting the maximum fiber stress is: _f_ = _Mc_⁄_I_ = (10,400 × 1.5 × 12)⁄12 × 27 = 568 pounds per square inch. The working strength of yellow pine as given in Table 59, is 1200 pounds per square inch. Thinner sheeting should therefore be used. TABLE 59 WORKING UNIT STRESSES FOR TIMBER