Behavior of a Soil Mass Under Dynamic Loading

For the initial stages of a major research project concerned with the distribution of stress and strain in multi-layered pavement systems subjected to dynamic surface loading the work described was limited to direct loading of a single layer of silty clay contained in a pit 8 ft sq by 5 ft deep, in which were buried instruments capable of measuring stress, strain and deflection under dynamic conditions. The basis for design of the instruments used in this work is outlined and a novel strain cell is described. To carry out this work under dynamic conditions it was necessary to design a loading system that was capable of delivering a single pulse of up to 5 tons with a variable duration; details are given of the pneumatic system that was developed. The initial layout of instruments to enable principal stresses and strains to be obtained is described. Tests were designed to determine stress and strain patterns set up for a variety of uniform surface contact pressures and rates of loading and the results obtained are compared with existing theories for stress distribution and surface deflection in a linear isotropic elastic half space. In addition, the relationship between apparent in situ soil modulus and applied stress is compared with results obtained from cyclical laboratory compression tests.