ARKANSAS BRIDGE FOUNDATIONS. LABORATORY INVESTIGATION

A review of laboratory testing for bridge foundation design is presented with discussion of application and errors. Testing is primarily composed of classification, shear strength, and consolidation tests. The AASHO and Unified Soil Classification systems are the most widely used systems. Mechanical analysis, hydrometer analysis, and the Atterberg limits are the tests required for classification. Classification test results are insufficient for use as design values. Shear strength testing is done by direct shear, unconfined compression, vane shear, triaxial, and plane strain tests. Triaxial testing with back pressure allows test variations which simulate actual field conditions. Plane strain and residual shear tests can simulate field embankment conditions effectively. Laboratory vane shear devices can be used for testing of samples in sampling tubes. The standard consolidation test yields a good estimate of settlement. The controlled gradient and controlled-rate-of-strain consolidation methods, both of which use back pressure, give improved results, decrease testing time and make data reduction easier.