The Impact Of Opencut Tunnel On Wind And Sand Resistance And Its Around Environment In Lin-Ce Railsay

Lin-ce railway runs through Ulan Buh desert, Yamaleik desert, Badain Jaran desert,and the vast Gobi (Hamada and Gravel desert) regions，Lince railway turns around theBadain Jaran desert and the railway is covered by opencut tunnel in the active sandy area.The opencut tunnel is a kind of linear arch construction and a new linear sand-preventionstructure. The contained structure and its large size impact the wind field and sandresistance around it, which is greatly different from the traditional sand preventionconstruction. Based on the analysis of wind-sand environmental conditions and the desertdevelopment trend in the studied area, this paper studied the wind-sand resistancemechanism of opencut tunnel with lab and field experiments. Based on the analysis ofsand size and sand dune movement, the paper1) systematically studied the impact ofopencut tunnel on its around environment;2) assessed sand resistance capability of theopencut tunnel;3) provided a methodology to prevent the entrance of the opencut tunnelbeing buried;4)constructed a sand model of preventing the entrance of the Opencuttunnel.（1）In the windward side of the tunnel,6H is the inflection point of wind speed,which does not change with the coming wind speed and direction. The high-wind-speedfield above the opencut tunnel moves toward windward direction when the wind angleincreases,which does not change with the changement of coming wind speed. At theleeward side of the tunnel, flow variaion are consistent under the different wind angle,wind shadow area increases with increasing wind speed.（2）From the analysis of the wind speed profile at both sides of the tunnel, thetunnel significantly impacts wind speed around it. At the windward side, wind speedinflection point is at the height of2H. At the leeward side, it is at the height of1H. At thewindward side, wind speed does not impact the wind profile, but impacts the size of thewind field. At the leeward side, wind direction significantly impacts wind profile and thesize of wind field.（3）The wind has been in a slow state under the vertical height of1h and has anaccelarating trend when near the tunnel.Wind speed does not impact the windreattachment distance significantly at the leeward side. According to the reattachmentdistance, wind field can be classified into three ranges: reattachment distance=1H with δ=75°~90°;, reattachment distance=2H with δ=60°~30°; flow reattachment distance=6H with δ=15°or below. （4）85%of the sand discharge concentrates in the range of0～10cm.At theleeward side, sand discharge increases with the increasing of height and80%of the sanddischarge concentrates in the range of30～70cm. The impact of wind angle on sanddischarge can be divided into the same change process with90°～60°,the similar changeprocess with55°～30°and the maximum sand discharge with15°four classes。At a samewind speed, the accumulated sand dune area and amounts near the model of tunnelincreases with the decreasing of wind angle. With the increasing of wind angle, theaccumulated sand dune area tends to be the same at both sides of the tunnel; with thedecreasing of wind angle, the accumulated sand dune area in the windward side will belarger than at the leeward side.（5）Under the impact of the tunnel, the sand size have big difference between theoutside and inside the tunnel. The sand size inside the tunnel express as coarse-grained,uniform diameter and unified distribution. The feature between the inside and outsidetunnel are significant difference. The movement direction, annual movement distance,the shape and volume of two studied sand dunes was changed, the morphology of thesand dunes closer to the tunnel was becoming typical barchan dune, and the sand dunesfurther away from the tunnel was gradually losing the morphology of typical barchandune,which reflect the significant effects of opencut tunnel on the wind and sandenvironment of region.（6）Based on the analysis results of FUZZY,Angel between tunnel and thedirection of wind should across when we construct the opencut tunnel in the desert areas.With the co-influence of dominant wind and the acceleration of wind, the tunnel will notbe buried in the recent years.（7）To prevent sand damage to the entrance of tunnel, the integrated engineeringand drip-irrigated plantation methodology should be used. The construction of sandprevention should take incount of the factor of topography, sand source, and weather.The strip-mixed vegetation with the native species of Haloxylon ammodendron andTamarix chinensis should be the best choice.