Physico-mechanical performance of debris-flow deposits with particular reference to characterization and recognition of debris flow-related sediments

To characterize and recognize the debris flow-related deposits, the physico-mechanical performance of four deposits from the Dongyuege (DYG), Shawa (SW), Jiangjia Gully (JJG), and Gengdi (GD) debris flows in southwest China is investigated through laboratory analyses and tests. The four debris-flow materials can all be remolded into coherent, homogeneous cylinders with high densification and strength–porosity of 25%–36%, mean pore-throat radius of 0.46–5.89 µm, median pore-throat radius of 0.43–4.28 µm, P-wave velocity of 800–1200 m/s, modulus of elasticity of 28–103 MPa, unconfined compressive strength (UCS) of 220–760 kPa, and cohesion of 65–281 kPa. Based on the comparison in slurryability and formability among debris-flow deposits, granular flow deposits, fluvial deposits, residual lateritic clay and loess, whether a sediment can be cast into competent cylinders for physico-mechanical tests can be regarded as a diagnostic evidence of old debris-flow deposits. The discrepancy in physico-mechanical properties among the four debris-flow deposits suggests that the combination of foregoing physico-mechanical parameters can characterize assembling characteristics of debris flow-related sediments including grain size distribution, mineralogy, and accidental detritus. Four deposited sediments above can be surprisingly classified as hard soil-soft rocks according to UCS, and the hard soil-soft rock behaviors can advance the further understanding of debris flows.