Horizontal Pressures on Retaining Walls Due to Concentrated Surface Loads

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Iowa State College of Agriculture and Mechanic Arts, 1938 - Retaining walls - 79 pages
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Retaining walls of various kinds, used to restrain earth masses against lateral flow, are among the commonest and oldest types of structures which engineers are still called upon to design. The engineering literature is replete with theories and accounts of experiments relating to the overturning forces which the retained earth imposes against these structures. Meanwhile, there has been little study of the magnitude and distribution of overturning forces due to loads applied over limited areas on the backfill surface. Designers have had to be content to assume an equivalent uniformly distributed load or surcharge to substitute for the actual load situation. The purpose of this research was to measure the magnitude and distribution of the horizontal forces transmitted to a retaining wall through a gravel backfill by a concentrated wheel load applied at the backfill surface and at various distances back of the wall. Also, measurements were made of the distribution of normal pressure due to a line load parallel to the wall, and a method proposed for determining the magnitude and distribution of horizontal pressures due to an area load adjacent to the wall. A new hypotheses of horizontal pressures on retaining walls due to an earth backfill is suggested, based upon a consideration of the elastic solid characteristics of the fill. Pressure measurements were made on actual retaining walls 6 ft. high and 15 ft. long, by means of stainless-steel, friction ribbons and Goldbeck pressure cells. A heavily loaded truck was used to apply the concentrated loads. The parallel line load was obtained by placing the two rear wheels of the truck on a heavy timber resting on the backfill surface parallel to the walls. The measured pressures were found to be distributed in accordance with the Boussinesq law of distribution of a concentrated load through an elastic medium, but the magnitudes of the pressures were two or three times as great as those calculated by the classical Boussinesq equations. The greater divergence occurred when the loads were applied close to the retaining walls. Considerably more research is needed to correlate the stress-distribution characteristics of various kinds of backfill materials with physical properties of the soil, and to determine the effect of the relative rigidity of the wall and backfill. Also, experimental evidence is needed to confirm or disprove the proposed theory for determining normal pressures due to area loads and surcharges, and to indicate the merit of the new hypothesis of horizontal pressures due to fill materials.

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