Study On Local Failure Analysis And Improvement Of Protective Measures For Desert Highway

The sand control system is an important means of avoiding sand damage on desert highways,but with the increase of service time,the sand control system will break down to different degrees,which greatly affects the safe operation of the line.To this end,this paper relies on the Zhongwei section of the Wuhai-Maqin Highway project,and through on-site research,unmanned aerial tilt photography and numerical simulation and other technical means,clarifies the characteristics of the wind and sand environment in the Zhongwei desert section of the Wuhai-Maqin Highway,calculates the degree of damage to the sand control system,analyses the causes of damage,optimises the deployment form of sand control measures,and evaluates the improved sand control system’s sand control system,which provides technical reference for the design and maintenance of highway sand control projects.The main conclusions are as follows:(1)Analysis of the wind and sand dynamic environment characteristics of the Wuhai-Maqin HighwayK160+000～K182+000 of the Wuhai-Maqin Highway is located at the southern edge of the Tengger Desert,and the sand dune type is mainly flowing sand dunes.The annual average wind speed in the area is 2.18m/s,and the annual average wind speed of sand initiation is6.20m/s;the annual sand initiation wind is variable,and the dominant wind direction is mainly northwest and southeast wind;the annual sand transport potential is 16.42 VU,which is a low wind environment;the synthetic sand transport direction RDD is 175.07°,and the sand material is transported from northwest to southeast direction;the directional variation index RDP/DP is 0.29,which is a high wind direction variation.It is a high wind direction variability,the wind condition in this region is complex and there are multiple transport directions.(2)Analysis of the local breakdown of the desert highway sand control systemUnmanned Aerial Vehicle(UAV)was used to take aerial photographs of the sand control system of some sections of the Wuhai-Maqin Highway,and the actual points of the project were reviewed in conjunction with the site,and the accuracy of the tilt photography met the specification requirements.In the desert highway sand control system,the outermost sand barrier fence is particularly damaged,the more inner the sand control measures,the less damaged the sand fixing measures are,and the degree of damage is positively correlated with the deployment time.The causes of breakage are mainly wind,the characteristics of the sand control system itself and the natural environment;the forms of breakage are sand burial,wind erosion and overturning in the short term,and in the long term,the ageing of materials can also cause breakage.(3)Research on the response of existing sand control measures to wind and sand flow under sand dune conditionsCFD numerical simulations were used to analyse the wind and sand flow response patterns of lattice dunes with(without)sand control measures.Under the original terrain conditions,the wind speed of the sand-carrying wind is higher at the secondary beam of the lattice dune,and the blocking effect of the dune on the wind and sand flow is weaker,so the sand particles can easily move across the dune to the back side,which endangers the safety of the road.When sand-blocking measures are placed on the top of the dune,the wind speed is greatly reduced and the low-speed zone is increased;however,the sand-blocking measures are subject to stronger wind effects,and at the same time,the sand particles on the top of the dune tend to move along the slope,which will easily lead to the sand-blocking measures not being buried deep enough and then overturning,making the sand-blocking fence broken.When 1m x 1m sand-blocking measures are installed,a large number of eddies appear inside the sand-blocking measures,resulting in lower wind speeds near the surface,higher velocity zoning and better sand control;the volume fraction distribution of sand grains is related to both the topography and the installation of sand-blocking measures,and the distribution of sand grains has the characteristics of "progressivity" and "transferability".(4)Research on the improvement of desert road sand control measuresWhen sand-blocking measures are placed on the slope of the dune,the overall wind speed of the sand-carrying wind is reduced by about 17%～74% compared with that at the foot of the slope,and sand particles can be deposited near the sand-blocking measures,which in effect increases the burial depth and makes the sand-blocking measures less likely to overturn.When the spacing between sand-fixing measures is different,the speed zoning basically remains the same.When the spacing is 2.0m,the increase of wind speed between the mounds is not obvious,and the sand-fixing effect is good;but when the spacing is greater than 2.0m,the sand-fixing effect is not obvious.The overall sand control efficiency is slightly less than before the improvement,about 5% lower,but the service life of the sand control system is greatly extended.