Evaluation and Analysis of Sandy Subgrade Stiffness of Transportation Systems by Continuous Surface Waves and Plate Loading Tests

New demands in societies for development of transportation networks such as highways, railroads, airports, bridges and tunnels, has caused the classic methods of subsurface and sub-base stiffness evaluating to be substituted with the advanced characterization methods rapidly. At present most methods for of stiffness parameters evaluation are based on field tests or laboratory tests on undisturbed samples in laboratories. The results of these tests are often affected by disturbance of samples and insertion effects. Values of stiffness estimated in this way can be expected to be far superior to many techniques used routinely today. For example, oedometer testing (a one-dimensional compression test), external strain triaxial testing, and penetration testing, where poor performance in predicting stiffness has been known for decades. Continuous Surface waves (CSW) method may be used to determine shear stiffness in soil or rock layers in subgrade of transportation systems. In this paper the continuous surface waves system, being used to determine stiffness parameters, is firstly introduced and then the results of field stiffness measurements carried out on a sandy sub-grade at the south of Iran (Maroon) are presented. The Continuous Surface Wave used in this testing is completely personal computer based and controlled. The surface wave source used is an electromagnetic vibrator capable of exerting a peak sine force of 498N, Fig.