戈壁大风区近地表沙砾起动与输移动力过程研究—以兰新高铁烟墩风区为例

Lanzhou-Xinjiang High-speed Railway passes through the gobi area with strong wind, where wind speed is very high, sand or gravel particles bounce in a higher layer and the impact damage on railway is also significant. Upright sand fence made of cement even can not prevent the saltating particles leaping over it, resulting in sand deposition on the railway track, thus greatly threatening to the safety of train operation. The dynamic mechanism of sand and gravel entrainment and transport is the key scientific problem for the control of wind-blown sand hazards in gobi areas along Lanzhou-Xinjiang High-speed Railway. In view of this, this project takes Yandun as a study area and attempts to conduct studies on dynamic processes of entrainment and transport of sand and gravel over gobi by field observation and wind tunnel tests, aiming to reveal the dynamic mechanism of sand and gravel initiation; to establish the vertical structure of sand and gravel flux and kinetic energy and thus to reveal the feedback mechanism between wind-blown sand and gravel flux and their kinetic energy; to build aeolian transport equation to quantify sand and gravel transport intensity and saltation height and to elucidate the degree of damage of sand and gravel to structures of Lanzhou-Xinjiang High-speed Railway. Thus, this project can provide a scientific basis for the prevention and control of wind-blown sand and gravel in gobi area with strong wind along the Lanzhou-Xinjiang High-speed Railway.

兰新高速铁路穿越的戈壁大风区具有风力大、沙砾弹跳高和冲击破坏力强等特征，沙砾弹跳入侵挡风墙，造成轨道积沙，已严重威胁到动车的安全运营。戈壁沙砾起动与输移动力机制是兰新高铁戈壁大风区风沙砾灾害防治亟待解决的一个关键科学问题。本项目以兰新高铁烟墩风区为例，通过野外观测与风洞实验，研究戈壁大风区近地表沙砾起动与输移动力过程，阐明戈壁大风区不同粒径沙与砾起动的动力机制，建立戈壁大风区近地表风沙砾流固体流量与能量垂直结构模式，揭示风沙砾流不同高度固体流量与能量的互馈机制，构建不同类型戈壁近地表输沙砾通量模型，量化不同风速条件下不同类型戈壁风沙砾输移强度和沙砾跃移高度，进而利用跃移沙砾能量界定其对高铁构筑物的破坏程度，为兰新高铁戈壁大风区风沙砾灾害的防治提供科学依据。

兰新高铁戈壁大风区沙砾跃移弹跳高，且具有很强冲击破坏力，挡风墙也难以阻止沙砾弹跳入侵，造成轨道形成大量积沙，已严重威胁到动车的安全运营。本项目以兰新高铁烟墩风区为例，通过野外观测和风洞实验，开展戈壁大风区沙砾起动与输移动力过程研究，旨在为兰新高铁戈壁大风区风沙灾害的防治提供科学依据。.通过研究，得出了以下主要结论：（1）砾石覆盖度是戈壁床面沙粒起动风速的主要影响因素：10-50%砾石覆盖度戈壁床面，沙粒起动风速随砾石覆盖度增加呈直线增大，而当砾石盖度达到50%及以上时，沙粒起动风速受砾石覆盖度的影响程度显著降低；（2）砾石的起动受砾石粒径和沙源供给度的共同影响，砾石起动风速随砾石粒径增加呈对数规律增大，当达到一定沙源供给度时，起动风速随砾石粒径的增加其增幅变缓；（3）实地风沙观测结果表明，戈壁大风区近地表风沙砾流质量通量和颗粒数随高度增加均遵循指数递减规律，其中，K2828处戈壁90%的沙量集中于地表以上26-34 cm范围内，K2813处90%的沙量集中于地表以上84 cm范围内；（4）戈壁大风区风沙砾流动能通量随高度增加遵循Pearson VII曲线，并在近地表0.09-0.15 m高度范围内存在最大动能通量密度，最大值介于8.8×10-4~3.6×10-3 J m-2 s-1之间；本研究首次揭示了戈壁风沙流动能通量垂直分布规律，取得了创新性研究成果，为戈壁大风区兰新高铁构筑物风蚀危害防治提供了科学依据；（5）兰新高铁烟墩风区戈壁输沙率可用类Owen输沙率公式来表示，输沙率Q与u(u2-ut2)成正比；利用风况资料和实测年输沙量对输沙率公式的预测效果进行了检验，确定了标定系数，最后对兰新高铁烟墩风区K2828处2017-2019三年输沙量进行了计算，计算的K2828处年输沙量介于31.5-155.4 kg/m之间。研究结果为兰新高铁烟墩风区沙害防治提供了科学依据。