Deformation and shear strength of rockfill materials composed of soft siltstones subjected to stress, cyclical drying/wetting and temperature variations

• Deformation mainly develops in drying and heating process.
• The ultimate degradation strain was estimated to be 16.4%.
• Strength reduction was significant after combined weathering.

In this paper, the authors studied the deformation and shear strength behavior of an argillaceous siltstone used as rockfill material for the 261.5 m high Nuo Zha Du core wall rockfill dam in south-western China. As the soft siltstone was poorly cemented and easily disintegrated on exposure to water, it was considered to be susceptible to weathering. The long term behavior of rockfill is of major concern. Laboratory experimental research was initiated to investigate the deformation and shear strength behavior of the soft siltstone under stress, drying/wetting and temperature variations. The results highlighted that the combination of stress, water- and thermal weathering greatly intensified material degradation, in terms of softening in wetting, cracking in drying–heating and localized structural collapse under stress adjustment. The weathering deformation mainly developed in the drying and heating process and accumulated with weathering cycles. In this study, the ultimate degradation strain was estimated to be 16.4%. Strength reduction was found significant after combined weathering. However, compression and particle breakage induced densification of the weathered argillaceous siltstone may enhance the strength under high stress.