The writer believes that too much has been taken for granted in connection with earth pressures and resistance; and that, far too often, observations of the results of natural laws have been set down as phenomena. He believes that, both in experimenting and observing, the engineer will frequently find what is being looked for or expected and will fail to see the obvious alternative. He may add that his own experiments and observations may be criticized for the same reason, and he asks, therefore, that all possible light be thrown on this subject. A comparative study of much of our expert testimony or of the plans of almost any of the structures designed in connection with their bearing upon earth, or resistance to earth pressure, will show that under the present methods of interpretation of the underlying principles governing the calculations and designs relating to such structures, the results vary far too widely. Too much is left to the judgment of the engineer, and too frequently no fixed standards can be found for some of the most essential conditions. Until the engineer can say with certainty that his calculations are reasonably based on facts, he is forced to admit that his design must be lacking, either in the elements of safety, on the one hand, or of economy, on the other, and, until he can give to his client a full measure of both these factors in fair proportion, he cannot justly claim that his profession has reached its full development. Table 1 gives approximate calculations of pressures on two types of tunnels and on two heights of sheeted faces or walls, due to four varying classes of materials. TABLE 1.--PRESSURES ON TYPICAL STRUCTURES UNDER VARYING ASSUMED CONDITIONS. [Illustration: Key to Table of Pressures, etc.] _h_ = exterior height, _l_ = exterior width, { [delta] = depth of cover, that is, { _D_{E}_ = earth, and _D_{W}_ = water depth, [phi] = angle of repose, and, for tunnels _D_{W}_ > _D_{E}_ a depth _l_ [phi] = ----- ( 45 deg. + ------- ) 2 2 _W_{E}_ = weight of 1 cu. ft. of earth = 90 lb.; _W_{W}_ = weight of 1 cu. ft. of water = 621/2 lb. Conditions: 1 = normal sand, 2 = dry sand, 3 = supersaturated firm sand with 40% of voids, 4 = supersaturated semi-aqueous material, 60% aqueous, that is, 60% water and aqueous material.