垭口、山前丘陵地段风动力环境与敦格铁路沙害形成机理研究

Passes and piedmont hills are typical geomorphic landforms along the northwest railway. Afterwards, the landscape patterns and the terrain variations will cause spatial differentiation of airflow field, and then nonuniform gradient flow occurs, which will affect the near surface aeolian sand transport processes. The railway sand hazards become severe and distribute concentrate as passing through passes and piedmont hills, while it worsens the situation because of the lack of in-deep study of sand hazards formation mechanisms in complex geomorphic environments. Given this circumstance, the project will select Dunhuang-Gomuld Railway, adjacent to the eastern edge of the Kumtagh Desert, as our target to study the flow field structures and the characteristics of dynamic wind environments at passes and piedmont hills through series methods such as field insitu gradient investigation, wind tunnel experiments and numerical simulation. This study aims at revealing the sand hazards mechanism of Dunhuang-Gomuld Railway by clarifying the effects of nonuniform gradient flow on near surface aeolian sand transport processes, and establishing two-dimensional theoretical mode of aeolian sand erosion and deposition processes at the two sides of railway embankment. The study has theoretical significance and practical values which is not only to clarify the near surface aeolian sand dynamic processes of up and down flow environments and to complete or to rich the study of blown sand physics, but also to reveal the sand hazards mechanism over complex geomorphic terrain, both which contribute to providing theoretical references of the selection and reasonable arrangement of sand control measures of sandy railways.

垭口、山前丘陵是西北铁路沿途的典型地貌单元。由于景观格局、地形差异造成局地流场的空间分异，以及由此产生的非均匀梯度流将影响近地表风沙输移过程。铁路途经垭口、山前丘陵地段风沙危害较为严重且分布集中，对复杂地形环境铁路沙害形成机理缺乏深入研究。鉴于此，本项拟选择毗邻库姆塔格沙漠东缘的敦格铁路，通过野外定位梯度监测、风洞实验与数值模拟等方法，研究垭口、山前丘陵地段流场结构与风动力环境特征，阐明非均匀梯度流对近地表风沙输移影响过程，建立路基两侧风沙蚀积过程的二维理论模式，揭示敦格铁路沙害形成机理。此项研究，不仅可阐明上升和下沉两种气流环境近地表风沙动力过程，完善和丰富风沙物理学研究内容；而且有助于揭示复杂地形环境铁路沙害形成机理，为沙区铁路风沙防治措施的选择和合理布局提供理论依据，为“丝绸之路经济带”沿线基础设施互联互通提供重要保障，具有重要的理论意义和实践价值。

本项目基于敦格铁路沿线风沙危害现状，通过野外监测、风洞实验、数值模拟等手段，分析了敦格铁路沿线下垫面性质、近地表物质组成和气候特征等；阐明了垭口、沟谷和丘陵地段风动力和流场结构特征；揭示了复杂地形环境铁路沙害时空分布及成因；利用三维地貌激光扫描仪定期监测铁路路基两侧风沙蚀积动态变化，评价了铁路沿线防沙体系的防护效益，提出了典型路段沙害防治原则与建议。受本项目资助发表研究论文9篇，其中，SCI收录论文5篇；获批授权发明专利10项；培养硕士研究生2人和博士研究生2人；项目负责人分别获甘肃省专利奖（R1）和青藏高原青年科技奖（第11届）；在敦煌铁路沿线建立了3个野外固定风沙观测场。.主要结论包括：（1）垭口地段输沙势DP为481.09 VU，属高风能环境，合成输沙方向为115.19°，方向变率为0.69；山前丘陵地段输沙势DP为260.73 VU，属中风能环境，合成输沙方向为72.25°，方向变率为0.12；沟谷地段输沙势DP为80.86 VU，属低风能环境，合成输沙势为19.75 VU，方向变率为0.24。（2）铁路路基两侧2 H范围内风沙蚀积过程及粒度形态特征差异较大，路基迎风侧粒度分选性和峰度均高于背风侧，气流在路基两侧空间分异显著，集流加速区以风蚀为主，路基边坡积沙范围间于-1~1H，风季积沙厚度可达6.3 cm。（3）路基迎风侧减速区为1~1.4 H，背风侧回流区为1~2 H；桥梁迎风侧减速区较小，背风侧较大，增幅可达63%；气流在垭口内形成减速区，减速区从迎风侧山体边坡2/3处至背风侧山体坡中，垭口底部风速最小；路基背风坡气流降幅大于迎风坡，且背风侧存在回流区，气流所携带的大量沙粒沉降在背风侧。本项目研究不仅揭示了敦格铁路沙害的形成机理，丰富了铁路风沙灾害与防治研究内容，为沙区铁路风沙防治措施的选择和合理布局提供理论依据，具有重要的理论和实践意义。