Model Studies of Beams Resting on a Silt Subgrade

Models of beams of different stiffnesses resting on a subgrade of compacted micaceous silt were equipped with strain gages and loaded by various combinations of concentrated vertical loads. Investigations indicate that the pressure distribution, bending moments, and deflections are similar to those occurring under beams resting on an elastic solid. The investigation also confirms that the elementary approach using the concept of mudulus of subgrade reaction is plausible if the beams are sufficiently long. In addition, it was confirmed that the modulus of subgrade reaction depends on the relative flexibility of the beam. Only small changes were observed in pressure distribution as the loads were increased to and over the ultimate values; and little difference was found between bearing capacities of soil beneath beams of differing stiffnesses so long as conditions existed for failure in the soil occurring while beam stresses were still in the elastic range.