Evaluation Method of Deformation Modulus of Subgrade Soils Considering Drainage Condition

Abstract

In order to improve the accuracy of pavement structural design, we examined a method to accurately estimate the deformation modulus of subgrade soils. When designing the pavement structure by the theoretical design method, if the deformation modulus of the subgrade can be accurately estimated, pavement structure thicknesses can be determined reasonably with a limited budget. For this purpose, we developed a new testing method “CTX-BE test” by combining the method of cyclic triaxial test (standardized by Japanese Geotechnical Society [JGS0542]) with that of bender element test ([JGS0544]). In this study, a series of CTX-BE tests were conducted on Toyoura sand to investigate the method of setting the deformation modulus E and Poisson’s ratio ν necessary for pavement structural analysis. The CTX-BE test was performed under undrained and drained conditions, and the shear wave velocity Vs was measured by bender element transducers after the change of effective stress with stepwise cyclic triaxial loading. Based on a series of test results, we proposed a new method for evaluating the deformation modulus and Poisson’s ratio required for pavement structural design in consideration of drainage conditions of subgrade.