Flow-momentum growth and resultant feedback from bed-sediment entrainment significantly influence the mobility of debris flows and valley topography. Existing models inadequately capture the mass and momentum growth regulated by scale-sensitive, time-dependent pore water pressure in erodible beds, which exhibit pronounced anisotropy and nonlinearity. In this study, we propose a three-dimensional, two-layer, multi-state smooth particle hydrodynamics (TLMS-SPH) model to assess the flow-momentum growth of debris flows on wet beds. Herein, an enhanced Drucker-Prager (DP) yield criterion is integrated into the Herschel-Bulkley-Papanastasiou (HBP) rheology to mitigate particle collapse induced by gravitational perturbations in steep terrains. Particularly, an efficient hydro-poro-mechanics-based pore water pressure algorithm is presented and embedded in the SPH scheme to simulate the pore pressure response. To address the size effect, we rigorously tested the method through a series of full-scale, well-documented entrainment experiments. The results demonstrate that the model effectively captures and reproduces the complex dynamics of flow-momentum growth, manifesting in erosion-induced excessive volume and mobility changes. Our method establishes a clear link between volumetric water content and pore pressure response, further underscoring its capability to delineate levee-channel and deposition morphology. This study represents the first attempt to model debris flow on beds of varying wetness from a particulate perspective.

中文翻译：

---

湿床沉积物上粘性泥石流动量增长及其反馈的两层多态 SPH 建模


流动动量增长和来自河床-沉积物夹带的结果反馈显着影响泥石流和山谷地形的流动性。现有模型无法充分捕捉可侵蚀床中由尺度敏感、时间依赖性孔隙水压力调节的质量和动量增长，表现出明显的各向异性和非线性。在这项研究中，我们提出了一种三维、两层、多状态光滑粒子流体动力学 （TLMS-SPH） 模型来评估湿床上泥石流的流动动量增长。在此，增强的 Drucker-Prager （DP） 屈服标准被集成到 Herschel-Bulkley-Papanastasiou （HBP） 流变学中，以减轻陡峭地形中引力扰动引起的粒子塌陷。特别是，提出了一种高效的基于水孔孔力学的孔隙水压力算法，并将其嵌入到 SPH 方案中，以模拟孔隙压力响应。为了解决尺寸效应，我们通过一系列全尺寸、有据可查的夹带实验严格测试了该方法。结果表明，该模型有效地捕获和再现了流动动量增长的复杂动力学，表现为侵蚀引起的过度体积和流动性变化。我们的方法在体积含水量和孔隙压力响应之间建立了明确的联系，进一步强调了它描绘堤坝通道和沉积形态的能力。这项研究代表了从颗粒角度模拟不同湿度床上的泥石流的首次尝试。