Landslide dams are formed mostly in V-shaped valleys, with poor stability and a high risk of failure. Once landslide dams fail, they may cause floods or debris flows that endanger lives, property, and infrastructure downstream. Therefore, it is important to evaluate the stability immediately once a landslide dam is formed. The geometry of a landslide dam is the most critical to its stability assessment. However, the complex terrain and geomorphological conditions in the disaster area often make field surveys difficult. Aerial photography and satellite imagery technology are usually limited by poor weather conditions, which bring severe restrictions to the timely acquisition of the geometry of a landslide dam. In this paper, a discrete element simulation model was proposed and verified by two experiments, and then a series of numerical simulations were performed to investigate the geometry and formation process of landslide dams under different topographic factors including the motion path dip-angle, the river bed inclination, and the angle between valley slopes (valley angle). The results show that the geometry and formation process of landslide dams are significantly affected by the topographic factors. According to the results of comprehensive numerical analysis, a simple predictive model for landslide dam geometry in V-shaped valleys was established, and two landslide dams with data collected from early events were employed to validate the predictive model. Based on the easily accessible topographical factors, the proposed model accomplished the fast prediction of landslide dam geometry. This research provides a vital basis for the stability evaluation of landslide dams and can be used for the disaster emergency response before the dams break.

滑坡大坝主要形成于V形山谷中，稳定性差且有很高的破坏风险。一旦滑坡坝失灵，它们可能会导致洪水或泥石流，危及下游的生命，财产和基础设施。因此，一旦滑坡坝形成，立即评估稳定性很重要。滑坡坝的几何形状对其稳定性评估最为关键。但是，受灾地区复杂的地形和地貌条件常常使实地调查变得困难。航空摄影和卫星图像技术通常受到恶劣天气条件的限制，这给及时获取滑坡坝的几何形状带来了严重的限制。本文提出了一个离散单元仿真模型，并通过两个实验进行了验证，然后进行了一系列数值模拟，研究了滑坡大坝在不同地形因素（包括运动路径倾角，河床倾角和谷坡之间的夹角（谷角））下的几何形状和形成过程。结果表明，滑坡坝的几何形状和形成过程受到地形因素的显着影响。根据综合数值分析的结果，建立了一个简单的V型谷滑坡坝几何预测模型，并利用两个从早期事件中收集到的数据对滑坡坝进行了验证。基于容易获得的地形因素，该模型完成了滑坡坝几何的快速预测。