Journal of Geotechnical and Geoenvironmental Engineering

Several tailings dam failures have highlighted the potential for instability under prevailing drained conditions, which can be represented in the laboratory using constant shear drained (CSD) loading. In this study, the mechanical response of three mine tailings gradations (coarse, intermediate, and fine) from a tin ore tailings storage facility subjected to CSD loading were evaluated. The experimental results were interpreted using the critical state soil mechanics framework and different instability criteria. Salient findings include the following: (1) the onset of instability in initially loose specimens was dictated by a tradeoff of volumetric strain components (i.e., elastic and plastic), which in turn governed the evolution of the dilatancy and plastic modulus, key properties for modern constitutive models that were also investigated in this study; (2) dense-type instabilities may occur for initial states above the critical state line; this response was observed in the fine tailings due to their compressibility and initial state before CSD stress relief; (3) variable rate tests suggested that drained creep in the intermediate tailings made the second-order work instability criterion unattainable; variable rate effects were manifested in the postinstability responses of the intermediate and fine tailings but not in those of the coarse tailings; and (4) existing instability criteria perform similarly when applicable, but they also have limitations. In this context, a new criterion is proposed by modifying an existing criterion. This study advances the understanding of the mechanical response of mine tailings, under nonstandard stress paths.

When the temporary backfilled subgrade is not sufficiently compacted, the result is low stiffness of the track system. Excessive deformation of railway tracks under the action of freight trains will aggravate track wear and reduce service life. However, traditional reinforcement technology to increase the stiffness of the track system is sometimes limited due to requirements of working space, efficiency, and little disturbance of the normal operation of the existing railway. Battered grouted helical piles (BGHP) are a kind of strengthening technology that has little influence on the existing railway and high construction efficiency. This paper presents a field case study of the implementation of BGHP to reinforce the freight railway subgrade. The paper evaluates the effect of the BGHP on the dynamic response of the treated subgrade. The subgrade soil was initially characterized by cone penetration tests at one location before BGHP reinforcement. The subgrade dynamic deformation modulus was measured before and after BGHP installation. In addition, the acceleration and velocity time histories of the subgrade were monitored during the passage of a freight train before and after BGHP reinforcement. The field measurement showed that the vibration acceleration, velocity, and displacement of the subgrade all decreased while the dynamic deformation modulus of the subgrade increased after BGHP reinforcement. Further, the vibration level reduced remarkably, mainly in the frequency band of 44.7 to 56.2 Hz, and the distribution of the normalized accumulated energy of velocity and acceleration was significantly influenced after BGHP reinforcement. The findings from this case study are of practical value to the emerging application of the freight railway subgrade reinforced by BGHP.