Cyclic Shear Response of Cemented Paste Backfill

A constant-volume direct simple shear (DSS) apparatus was used to characterize the liquefaction resistance of cemented paste backfill (CPB) prepared using unclassified fine-grained tailings. The effects of curing age, cement content, and initial void ratio (also expressed through initial solids content of the mixture) on the resistance to liquefaction were investigated. Higher cement contents, longer curing periods, or higher initial solids contents were found to increase CPB liquefaction resistance in a consistent manner. The commonly used 100-kPa unconfined compressive strength (UCS) rule of thumb for CPB liquefaction susceptibility, as originally adopted from lightly cemented sands, was found to be conservative under a large earthquake-induced cyclic stress ratio (CSR). For two different mixes, a UCS of approximately 70 kPa was found adequate to resist liquefaction under a CSR typically generated by a maximum ground acceleration of 0.3 g. For the samples tested, a UCS of 70 kPa was found to correspond to a shear wave velocity of 220 m/s, which may be a more convenient criterion for assessing liquefaction resistance, given the potential for in situ measurement. (C) 2016 American Society of Civil Engineers.