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Purpose: The critical speed of a railway track is the speed at which the vibration occurs at the largest magnitude. Thus, its identification is necessary to prevent derailments and damage to the rail tracks. The present study attempted a three-dimensional finite element analysis of a typical ballasted rail track under a single moving wheel load at different speeds to evaluate the critical speed. Methods: The track's ballast, subballast, and subgrade layers (substructure) were modeled as elastoplastic material with material damping and radiation damping (infinite layers). Track response was recorded in the form of stress, displacement, velocity, and acceleration responses to identify the critical speed of the rail track. Different parameters were analyzed to find the critical speed, such as the method of applying moving load, the material model of the primary load-carrying layer (ballast), the effect of boundaries, and the type of data extracted from the output databases. Parametric studies were performed on material damping and stiffness of track substructure layers to see their effect on the track's dynamic response. The effect of shear strength parameters (cohesion and friction) of the subgrade was also analyzed to examine their effect on the critical speed of the rail track. Results and Conclusions: The study shows that the combination of vertical velocity, stress, and acceleration trends can be used to identify the critical speed of the rail track. Young's moduli of substructure do not show direct proportionality with the critical speed. The damping ratio has a small but noticeable effect on the critical speed, while the increase in shear strength of the subgrade increases the critical speed. A phase-lag was observed as the speed transitions from subcritical to supercritical. The critical speed from the finite element analysis shows a good agreement with the shear and Rayleigh wave velocities calculated from empirical approximations. [ABSTRACT FROM AUTHOR]

Purpose: Dynamicimpact factor (DIF) is the ratio of dynamic and static wheel load. It determines the effect of dynamic load on a rail track based on several empirical formulations given in the literature. These formulations are developed under a low-speed range of about 50 km/h on old tracks. Thus, their reliability for rail tracks under higher speeds up to 200 km/h needs to be validated. Methods: A three-dimensional dynamic finite element analysis is performed on a ballasted railway track for this purpose with elastic and elastoplastic material models, radiation damping, and material damping. A pressure-loaded areal patch was moved at a constant speed to simulate the load motion. A parametric study was performed on train speed, track modulus, and wheel diameter. A regression analysis was performed on the output data, and a DIF formulation was developed as a function of speed and track modulus. Results and Conclusions: The relationship calculated from the numerical study suggested a higher DIF than the existing relationships in the literature. Additionally, the difference between the existing DIF formulae and the present study increases with speed. It was inferred that at higher speeds (>150 km/h), the elastoplastic behavior of the rail track causes higher vibration as compared to lower speeds (<50 km/h), where dynamic vibrations are generally under elastic range. [ABSTRACT FROM AUTHOR]

In this study, the response of soft clay was assessed during electrokinetic consolidation. The laboratory-based experimental study was conducted in a custom-designed test set-up focusing on soft clay’s engineering and physicochemical response during and at the end of the electrokinetic consolidation. Six electrokinetic consolidation tests were performed under self-weight for 24 h with different voltage gradients. The operational response was investigated by monitoring the electric current and the power consumed during the test. Further, the variation of ohmic heating, volumetric water content, and water potential was continuously measured. The efficacy in enhancing the engineering response is analysed by investigating cumulative discharge, surface settlement, water content, and undrained shear strength of the soft soil. At the end of the test, the effect of electrochemical reactions in altering the soft clay’s pH, microfabric, and mineral phases was investigated. Finally, the quantification of the surface crack was investigated, and their dependence on the applied voltage gradient was established. The study results show substantial enhancement in the engineering characteristics of soft clay. It significantly accelerates the dewatering efficacy, increases the undrained shear strength and surface settlement, and reduces the water content of the soft clay irrespective of the applied voltage gradient. The electrokinetic consolidation increases the temperature of the soft clay. The measured surface cracks give the crack intensity factor of 1.95, 2.10, and 2.15% for the applied voltage gradient of 0.05, 0.10, and 0.15 V/mm, respectively. [ABSTRACT FROM AUTHOR]