Research Highlight

The effect of mud slurry on reducing flow resistance of coarse particles in debris flow is well studied by the Institute of Mountain Hazards and Envir

Pubdate:2017-11-24    From: ANDF    Views:

Two-phase fluid models have been increasingly employed in dynamic simulation of debris flow. In such models, the fluid phase is comprised of water and fine particles homogeneously dispersed in water, while coarser particles constitute the solid phase. Recent research has revealed that the solid phase plays a dominant role in the movement of debris flow. However, the fluid phase also has important influence on the magnitude of debris flow resistance. First and foremost, buoyant weight of the coarser particles is reduced by the fluid phase, the bulk density of which could be significantly greater than water. In addition, it is likely that the internal frictional coefficient of the coarser particles would become smaller because they are embedded in the slurry. Moreover, solid particles might be fluidized due to the existence of a high excess pore fluid pressure. Dr. Hongjuan Yang from the Institute of Mountain Hazards and Environment, Chinese Academy of Sciences, has conducted a series of laboratory experiments to investigate the role of the fluid phase in debris flow.

The sediment in debris flow covers a wide range of particles in size, varying from clay minerals to boulders. As a result, it is of importance to determine the critical particle size between the fine fraction and the coarser part, which is closely related to the bulk density of the fluid phase and the volume concentration of the solid phase. A method has been proposed to determine the critical particle size based on particle size analysis. Analyses show that this parameter in Jiangjia Gully, Yunnan Province, China, increases exponentially with the bulk density of debris flow. Moreover, natural angles of repose were measured for the gravel materials resting in air, in water, and in mud slurry separately. It indicates that the mud slurry has no significant effects on the frictional coefficient of the gravels. Furthermore, rheological tests were taken using a vane rheometer to measure the torque-time response of sand particles within mud slurries of varying solid concentrations at different rotational speeds. It was found that the effect of the mud slurry on decreasing flow resistance of sand particles becomes more significant at higher rotational speeds or for more concentrated slurries because the excess pore fluid pressure is easier to maintain at higher shear rates or within more cohesive slurries.

 

The results of research works have been published on International Journal of Sediment Research (2014, 29(1): 83-91) and Powder Technology (2017, 310: 1-7)

 

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Graph   for the determination of critical particle size (D0) on the basis of sediment particle size analysis in   two positions of a debris flow

The   relationship between critical particle size (D0) and bulk density of natural debris flows (ρm) in   Jiangjia Gully, Yunnan Province, China

 Natural angle of repose of gravels in different media in degree

Test number

In air


In water


In mud slurry

Average

Standard   deviation


Average

Standard   deviation


Average

Standard   deviation

1

41.95

1.77


42.15

1.53


42.66

2.77

2

40.47

1.08


41.28

2.78