The impact of wide-graded debris flow on sediment-trap dams in the Tibetan Plateau: an experimental study

In the Tibetan Plateau, pronounced topographical relief (steep mountains and deep valleys) coupled with intense weathering processes generates highly fragmented slope surfaces, creating debris-flow source materials with exceptionally heterogeneous grain-size distributions. These conditions frequently produce debris flows that exhibit extraordinary impact forces which cause severe damage to sediment-trap dams. Through 27 sets of flume experiments that systematically varied the particle-size distribution ( d max ), bulk density ( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" id="IM1" overflow="scroll"> <mml:mi>γ</mml:mi> </mml:math> ) and flume slope ( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" id="IM2" overflow="scroll"> <mml:mi>θ</mml:mi> </mml:math> ), this study investigates the impact mechanisms of wide-graded debris flows on sediment-trap dams. The results demonstrate that debris-flow interactions with sediment-trap dams occur through three distinct phases: (1) impact run-up, (2) rotational backflow and (3) depositional back-silting. Lower bulk-density flows exhibited greater run-up heights and more pronounced phase differentiation. Measured impact forces ( F ) showed an inverse relationship with bulk density ( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" id="IM3" overflow="scroll"> <mml:mi>γ</mml:mi> </mml:math> ↑→ F ↓), while displaying positive correlations with both slope gradient ( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" id="IM4" overflow="scroll"> <mml:mi>θ</mml:mi> </mml:math> ↑→ F ↑) and maximum particle size ( d max ↑→ F ↑). This occurs because higher- <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" id="IM5" overflow="scroll"> <mml:mi>γ</mml:mi> </mml:math> flows experience increased internal shear resistance, resulting in a reduction in velocity. Steeper slopes enhance kinematic energy, while larger particles generate more concentrated momentum transfer during impact. Sensitivity analysis revealed that d max exerts dominant control over impact dynamics compared to <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" id="IM6" overflow="scroll"> <mml:mi>γ</mml:mi> </mml:math> and <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" id="IM7" overflow="scroll"> <mml:mi>θ</mml:mi> </mml:math> . These findings provide critical insights for sediment-trap dam design in high-altitude debris-flow mitigation systems.