Study On Mechanism For Controlling Sand Hazard In Jiangbei Road And Design Method Of Sand Stabilization

The Jiangbei highway walks through the floodplain, the mesa-butte and the fan-shaped plateau caused by the branch river sediment, in the north bank of the Yarlung Zangbo River in the Shannan of the Tibet, where the sand blown by wind is very active, so the sand hazard to the Jiangbei highway is serious,and the air quality and ecological environment is more severe. Based on the investigation about the sand hazard of valley zonal distribution in high-cold region,this paper objectively analyses the application and its applicability of the common known techniques to controlling sand hazard,as well as researches the rules of the movement of the typical sand hill near the Jiangbei highway,and the application of the vegetation to controlling the sand hazard to the highway according to the special environment of the Jiangbei highway, and engineering protection techniques and the integration theory and technique for controlling sand hazard to the highway.In this paper the key technique was established elementarily for controlling sand hazard to highway on the north bank of the Yarlung Zangbo river in the shannan of the Jiangbei highway. This technique can not only help the construction of the Jiangbei highway but also offer a reference for the other highways that are threatened by the sand hazard like the Jiangbei highway in the Tibet or other area.Through the theoretical analysis, the field testing, the wind tunnel simulation, numerical simulation, sand fixation testing for the sand hazard region, this paper researches the formation mechanism and integrated control of the sand hazard in the valley pattern of high-cold region. The main research results as follow have been obtained.1.Through the investigation and data collection for sand hazard to highway on the north bank of the Yarlung Zangbo river in the shannan of the Jiangbei highway, we have grasped the meteorology, engineering geology and hydrogeology, road construction and protective material, ecological environment, distribution of eolian sand,type of eolian sand and ect along the highway, and gained the possible type of sand hazard and the distribution along the whole Jiangbei highway.Based on the study as above we analysis and conclude the damaged degree for the highway and possible scale by the sand hazard along the Jiangbei highway,which provide scientific basis for the seletion of prevention-control measures for sand hazard and the control scheme drawn up.2.Though the field testing and the wind tunnel simulation, we have carried out the research on the structural characteristics of sand drift in the natural sand surface, then determinated the key indicators including the wind speeds distribution of the local sand dune, the sand dunes erosion, roughness of surface, sediment discharge rates of sand dunes and the starting wind speed of the drifting sand. At the same time we explore moving characteristics of the grains of sand among the sand hazard in high-cold valley region, the mechanism of the sand starting by forces and the dynamics process for the formation of sand ripples, sand ridges and sand dunes, thereby the formation mechanism of the sand hazard in the valley pattern of high-cold region has been put forward.3.Using stone checkerboard as the sand barrier, there will form the inhibition low speed area of wind speed, the uplifted area of wind speed and the acceleration area of wind speed respectively in certain range of checkerboard forward and backward. Wind speed profile varies dramatically with the height increasement within 39cm to surface of sand bed. In general, the distribution of wind speed with the height obeys the law of logarithm. While sand particles at the high speed collide with stone checkerboard, some quicksand accumulates because of energy expenditure,and some quicksand changes the flow direction. Sediment discharge rates within distribution of the height are comparatively dispersive. The variation curves of sediment discharge with the height represent protruding shape, namely bigger in the middle and smaller at the both ends.So the stone checkerboards have good results for the sand prevention.4.Using geocell as the sand barrier, there will form the an increase or a decrease zone in ehthe wind speed in the front, back, top and milddle of the sand barrier.The deceleration zone consumes the kinetic energy of the wind and accelerates the energy consumption, thus the sand drift deposits here, so that the stabilization and prevention of sand has been achieved. The acceleration zone advances the wind erosion to form sand deposit on both sides of geocell and concave surface of wind erosion in the middle.Wind speed profile varies dramatically with the height increasement within 23 cm to surface of sand bed. Sediment discharge rates rapidly decrease with the increasing height. Sediment discharge rates mainly center on the low height zone.The sand protection result is good for the sand drift at the low speed.5.We have researched the charaters of sand stabilization of the vegetative sand-protecting barriers with different coverages by analyzing the coverages of different vegetative covers,as well as wind speed flow field and the distribution of sand drift at different speeds in the wind tunnel.The exponential function relationship was presented between sediment discharge rate and coverage of vegetative cover at the high wind speed.While at the low wind speed,the relationship curve can be approximately divided into two parts.At the certain wind speed the sand protection design of vegetative cover is only deminded to reach the certain critical coverage(the minimal coverage).Sediment discharge rates gradually decrease with coverage of vegetative cover increment.The grains of sand in the sand drift distribute the area within certain height limits, but the height of sand grains distribution decreases with the coverage increment.6.So far as the prevention-control for sand hazard of highway is concerned, integrated control mainly emphasize the prevention measures are set up on the basis of the the actual conditions of sand hazard and multiple prevention-control measures are combined together. Generally, based on the characteristics of sand hazard for highway, sand-moisture conditions along the highway,micro-topography of sand combined with the class of the proposed highway,the conditions of funds adequacy and the source of materials for prevention-control engineering, we will execute integrated control measures,that is to say, the engineering prevention-control should be the major measures, supplemented by vegetative measures. Though comprehensive treatments included stabilization, barrier, transportation and diversion we will thoroughly solve and lighten the sand hazard for highway to ensure the safety and unobstruction along the highway.