包兰铁路沙坡头段风沙运动规律及其与防护体系的相互作用

Interaction between Sand Blown Activity and Protection System in Shapotou Section of Baotou-Lanzhou Railway

包兰铁路沙坡头段是穿越流动沙丘最长，受到风沙危害最为严重的路段，自建成运营45a以来，其有效而稳定的防护体系受到世人的关注和公认。通过前期23a的防沙实践和后期22a的监测证实：①该地区存在着一个较为稳定的风沙流场，具有三组不同风向，主风向为W-NNW，次主风向为NE—E、WSW—S，此种风沙流场格局具有明显的季节变化，是塑造格状沙丘形态和造成对铁路危害的重要因素。②沙丘移动过程表现为格状沙丘主梁沿主风向前后摆动，以缓慢的速度向前推移，其移动量为2～5m·a^-1，造成风沙危害的最直接的原因是格状沙丘副梁的迅速前移，22a平均移动速度为0．527m·a^-1。合成移动方向为318．6°（NW→SE）。③从理论上考虑，前移的沙体是一种对防护体系的潜在威胁，即可能在固沙带前缘形成高大的沙堤掩埋防护体系。可是，实际上随着防护体系的建立和逐步的完善，不但有效的保障铁路的安全，而且同时也抑制了年总输沙量的25％；并改变了风沙流场的某些性质或作用，进而控制了风沙活动的方向与活动强度。在迎风坡的风蚀和背风坡的积沙致使沙丘高度相应的降低，这种变化规律具有从流沙区向固沙区逐渐衰减的趋势。

Shapotou section of Baotou-Lanzhou Railway is the longest section of railway traversing moving dunes and suffered from very severe blown sand harms. The stable and effective protection system has always been regarded and recognized by people for 45 years since it was built. The former 23 years sand control practice and the later 22 years monitoring demonstrated that： ①These region exists a relative stable sandflow field and has three different wind directions, namely main wind direction W-NNW, sub-main wind directions NE-E and WSW-S. This kind of sandflow filed is the main factor shaping the configuration of reticulate dunes and harming railway with obviously seasonal changes. ②The moving process of sand dunes is manifested as that the main girder of reticulate dune sways along the main wind direction, with a slow forward speed of 2～5 m·a^-1. The most direct reason of forming wind-sand harm is the rapidly moving of subgirder of reticulate dune, with an average moving speed of 0.＇527 m·a^-1 during the 22 years. ③Theoretically, the forward moving sand body latently menaces the protection system and may forms a high sand bank at former sand-fixed belt and then buries the protection system. However, as the protection system being built and gradually being improved, the characteristics of sandflow field will be altered and the direction of sandblown activity and its intensity also will be controlled.