Development of an in-situ shaker for evaluating railway earthworks

The geotechnical and geodynamic characteristics of railway earthworks under train loading are important quantities for railway and geotechnical engineers, but difficult to quantify. Characterizing the anticipated settlement and dynamic properties of compacted fills after earthwork construction, but before track laying, is advantageous, because modifying construction after laying the track is significantly more expensive. The difficulty in measuring these indices arises from the need to perform cyclic loading that realistically simulates the frequencies and magnitudes induced by trains. To address this issue, this paper introduces a novel shaker designed to apply cyclic loads similar to those of trains. The paper first presents an outline of the design requirements for the shaker, followed by the development of a theoretical dynamics model to aid mechanical design. This model is used for examining various shaker configurations, especially their performance under different potential testing conditions. The shaker's final design includes dual eccentric rotors that excite an adjustable-mass counterweight, complemented by a lateral support frame to counter horizontal movement and ensure vertical excitation. Once the shaker is built, it is used to evaluate newly constructed mudstone earthworks near a railway line. A method for estimating the dynamic stiffness and damping of earthworks is proposed, which uses data from frequency sweep test data from the shaker. Outputs from the dynamics model show close alignment with the field results. Finally, a method for designing the shaker configuration according to the desired loads is proposed.