Physical Model Tests Evaluating Transparent Viscous Debris Flow Impact on Bridge Piers Using Particle Image Velocimetry
Quantifying the impact force of debris flows on bridge piers is crucial to ensuring the safety of bridges in mountainous areas.A transparent debris flow modeling technology based on particle image velocimetry(PIV)was proposed to address the inability of existing modeling methods to visualize the interaction between a debris flow and bridge pier as well as the fluid movement characteristics inside the debris flow.A set of transparent debris flow models was designed using two transparent mineral oils(550 USP white oil and 68 # engine oil)with different apparent viscosities to create two corresponding transparent debris flows.Twenty-one groups of impact tests were subsequently conducted using these two types of transparent debris flows under three slope conditions with three bridge pier cross sections(square,rounded end,and round).The results indicated that the dimensionless impulse height h/H gradually increased with the increase in the Froude number Fr,and the impact force was related to the cross-section of the bridge pier as well as the Reynolds number Re and the Fr of the transparent debris flow;when the section shape remained unchanged,the impact resistance coefficient Cd decreased with increasing Re and Fr.The change in the apparent viscosity of the transparent debris flow had less effect on the relationship between the surface flow velocity and flow depth for piers with rounded end and round sections,and greater effect on that for piers with square sections.The surface velocity of the transparent debris flow significantly increased after passing the piers,with the most significant increase occurring for round piers and the least significant increase occurring for the rounded end piers.Outside the pier-affected area,the surface velocity of the transparent debris flow in the vertical direction(y-direction)exhibited an"inverted U-shaped"distribution that was large in the middle and small on both sides;in the range of pier,the surface velocity exhibited an"M-shaped"distribution.
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