Particle interaction inside debris flows: Evidence through experimental data and quantitative clast shape analysis

Results of analytical experiments related to the dynamic behavior of debris flows are presented. Particle interaction and the amount and type of fines content present in the matrix, aspects that govern debris flow behavior, are studied via the morphological evolution of constituent particles. Four different mixtures of water and sediment with compositions resembling debris flows were prepared and put into a rotating drum, known as a Los Angeles standard abrasion machine, and studied at different time intervals. For each sampling time, quantitative shape analysis was performed using three morphological coefficients, MC2, MC3–8, and MC30–34. Coefficient MC2 gives information about particle ellipticity. MC3–8 is related to basic irregularities at a macro scale, such as roundness. MC30–34 is related to microscale irregularities like surface texture. Coefficient MC3–8 was shown to be very sensitive to silt content in the matrix, and coefficient MC30–34 to the presence of clay. All three coefficients point to the fact that changes in shape between granulometric classes are gradual and follow a power law. Coarse granulometric classes acquire more circular and smooth profiles while small particles maintain their irregular profiles. This phenomenon is the result of clast interaction processes within mixtures. Clast collisions between particles produce comminution of the coarsest fractions, while finer particles fracture along their entire surface. The rate at which these changes occur is related to the type of fine sediment present in the matrix. Changes in particle shape are an important tool for revealing internal dynamics because they are related to clast interaction and affect sedimentation processes inside these flows. This type of experiment, although not on a real scale, provides important physical information for understanding the phenomena that occur inside debris flows, enabling the study of a variety of textural parameters and their changes at regular time intervals. The experimental patterns observed offer new insights into clast–clast interaction, rounding and comminuting theory, with important implications for understanding rheological behavior and kinematics of flows and related hazards.

► Influence of fines content on particle interaction was studied via shape evolution.
► Shape evolution is a function of particle size and matrix composition.
► Clast collisions produce comminution of the coarsest clasts.
► Smaller particles fracture along their entire surface.
► Patterns observed offer new insights on clast interaction and comminuting theory.