Strain History and Short-Period Aging Effects on the Strength and Cyclic Response of Fine-Grained Coal Refuse

This paper presents an experimental investigation on the effects of strain history and aging on cyclic response and resistance of fine-grained coal refuse (FCR) using large-scale shaking table tests. The FCR specimen was slurry-deposited in a membrane-lined laminar shear box and subjected to three shaking events on a 1-g shaking table. Sensors were used to measure the FCR's dynamic response during shaking, and a piezocone penetrometer (CPTu) was used to measure soil resistance and estimate the cyclic behavior of the FCR specimen before and after each shaking test for time intervals up to 97 days. Based on the CPTu tests, the freshly deposited FCR specimen was classified as sensitive fine-grained soil after deposition and self-consolidation. An irregular pore pressure pattern was measured during and after the shakes due to heterogeneity of the FCR specimen. The FCR specimen experienced cyclic mobility and pore pressure redistribution, indicating that the material may be vulnerable to large deformations after cyclic loading. Cone tip resistance immediately after the first shaking event showed limited strength loss due to the original loose structure of the FCR. Each shaking event progressively densified the FCR specimen and increased the cyclic resistance. However, the FCR specimen remained susceptible to cyclic softening and flow liquefaction. The FCR specimen was classified using the CPTu data as clayey silt to silty clay after two shakes and 97 days of aging. Cone tip resistance increased over 100% by 97 days after the second shaking event with a rate of strength increase slower than the rate observed for clean sand in an earlier study. The increase in CPT tip resistance over time was quantified, and an equation to estimate the undrained shear strength of FCR as a function of normalized tip resistance and time after a shaking event was developed and calibrated.