The Lhasa–Linzhi Railway is located in the sandy area of the South Tibet valley, with high elevation and cold temperature. The Xierong section is a bridge section where blown sand hazards are severe. However, the disaster-causing mechanism of blown sand hazards in this section is currently unclear, thereby hindering targeted sand prevention and control. To address this problem, the wind dynamic environment of and causes of sand damage in this section are investigated through the field observation of the locale and a wind tunnel simulation experiment. Results show that the dominant sand-moving wind direction in the Xierong section is SSE. The wind speed, frequency of sand-moving wind, sand drift potential (DP), and maximum possible sand transport quantity (Q) in this section are relatively high during spring (March to May) and low during other seasons. The yearly resultant sand transport direction (RDD, RA) is SW. The angle between the route trend of this section and the sand transportation direction is 30°–45°, and the sand source is located in the east side of the railway. During spring, sand materials are blown up by the wind, forming blown sand flow and movement from the NE to SW direction. Increased wind speed area is formed between the top of the slope shoulder of the windward side of the bridge and the downwind direction of 3H, causing blown sand erosion. Meanwhile, weakened wind speed areas are formed within the distance of -3H at the upwind direction and from the downwind direction of the 3H to 20H of the bridge. These areas accumulate sand materials at the upwind and downwind directions of the bridge, thereby resulting in blown sand hazards. This research provides a scientific basis for the prevention and control of sand damage in the locale.

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Wind Dynamic Environment and Wind Tunnel Simulation Experiment of Bridge Sand Damage in Xierong Section of Lhasa–Linzhi Railway

Using the plane alignment design of the Wuhai–Maqin highway as the background of this study, based on the Fluent–Euler two-fluid model, the response law of the wind–sand flow to the embankment under different angles, different curve radii, and different surface windward factors were studied. Additionally, the accuracy of the numerical simulation was verified by the distribution of sand accumulation on the embankment site. The results show that when the wind–sand flow passes through the embankment, and when the angle between the wind direction and the straight embankment gradually decreases from 90° (vertical) to 0° (parallel), the speed-division range is correspondingly shortened. Under the influence of plane alignment, the diversion effect leads to a certain difference in the flow-field structure at different positions of the line. The convex windward embankment has the effect of dredging the wind–sand flow outward. The concave windward embankment has the effect of gathering the wind–sand flow inward. The dredging and gathering effects of the flat curve on the wind–sand flow decreases with the increase in the radius. In the plane linear design, line direction should be parallel to the dominant wind direction as much as possible. If a flat curve needs to be set, the convex windward curve should be given priority, and a large radius curve should be selected as much as possible.

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Numerical Simulation Research on Plane Alignment Parameters of Desert Highway

Damage will appear in the wind-break wall under the effects of many factors. The wind-break wall may be destroyed when the damage is accumulated to some extent, which may cause accidents. To identify damage within the wind-break wall structure, the Wavelet Packet frequency bands energy ratio spectrum analysis of the virtual impulse response function of responses to the wind-break wall was performed under the effects of excitation. Based on the damage sensitivity analysis of subfrequency bands, a further updated Wavelet Packet frequency bands energy ratio spectrum was proposed. To reflect the damage information sensitively, the feature bands, which were more sensitive to damage, were selected via the threshold value ε0. Then, the Wavelet Packet damage feature vector and damage identification index, which can reflect damage information of the wind-break walls sensitively, were proposed. A damage identification method for wind-break walls was proposed. To verify the validity of this damage identification method, the vibration tests on a pile plate wind-break wall were performed. Damage within the wall was identified via the method. The tests results show that the damage feature vector is a zero vector and the value of damage index is zero, when the wind-break wall is not damaged. The damage feature vector is a nonzero vector and the value of damage index is positive, when the wind-break wall is damaged. Thus, the damage state of the wind-break wall can be detected via the damage feature vector and damage index. With increase of damage accumulated within the wall, the damage intensity and the value of the damage index increase. The quantitative relationship between the damage index and damage intensity is established. The damage intensity can be calculated reversely, when the damage index is available. Thus, the damage intensity of the wind-break wall can be identified via the quantitative relationship between the damage index and damage intensity. In addition, the damage index value of the measuring point, which is much closer to the partial damage, is much larger. The damage index value of the point, which is located at the partial damage, is the largest. Thus, the damage location of the wind-break wall can be diagnosed via the characteristics of damage index for different measurement points. Thus, the damage state, damage location, and damage intensity of the wind-break wall can be identified via this damage identification method.

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Damage Identification of Wind-Break Wall Structures based on the Further Updated Wavelet Packet Frequency Bands Energy Ratio Spectrum

The wind-blown sand disaster on the railway has a very important negative influence on the economic development of traffic networks in desert areas. While there are some engineering protection measures for railway sand deposition, they are far from satisfactory in terms of economic efficiency and protection performance. Therefore, it is still of great practical significance to explore novel measures for actively preventing sand deposition on railway tracks in desert areas. In this article, the laws of sand deposition on single and dual tracks were studied with the help of field experiments. On this basis, it can be seen that the deposition of sand on the rear track can be effectively reduced by placing various types of baffles on the track. Field experiments were designed to study the change law of sand deposition ratio in front of the tracks caused by placing baffles of different cross sections. The results show that placing a 45° inclined baffle on the track can reduce the volume of sand deposition by up to 42%. The findings in this paper can provide scientific guidance for the design of new desert railways or novel protective measures for railway sand deposition.

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Experimental Research on Sand Sediment Protection on Railway Tracks

The Lan-Xin Railway II from Lanzhou to Xinjiang is the first high-speed railway which passes through the strong wind zones in the world, and it passes through the famous "Yan Dun", "Hundred Miles", "Thirty Miles" and "Dabancheng" wind zones. The total length of the railway is more than 462.4 kilometers, accounting for 65.1${\%}$ of the total length of railway in Xinjiang. Strong winds can do great harm to the operation, maintenance and transportation of railways. In order to resist the damage of strong wind to train, a large number of wind-break walls were built along the Lan-Xin Railway II. The wind-break wall reduces the strong wind damage, but brings a new disaster caused by sand sedimentation. To solve the problem of this engineering practice, this paper puts forward the idea of setting up the second retaining wall at different positions on the leeward side of existing wind-break wall to reduce sand particles sedimentation. The wind tunnel experiment was employed to simulate the wind-sand flow environment. Three typical configurations are considered: 1) single wind-break wall; 2) two walls and the second one locates at the top of the leeward slope of subgrade; 3) two walls and the second one locates at the foot of the leeward slope of subgrade. The decrease rates of the horizontal velocity, number density, horizontal transport flux and deposition rate of sand particles at the height of 0.1 m after the second wall are respectively 8${\%}$$\sim $12${\%}$, 51${\%}$$\sim $69${\%}$, 20${\%}$$\sim $73${\%}$ and 26${\%}$$\sim $38${\%}$, by comparing to the case without the second wall. It is found that the second retaining wall at the foot of the leeward slope of subgrade is optimal. The research result of this paper is helpful to optimize the preventing sand sedimentation measures of existing railway lines and towns in the strong wind zone.

Huang Ning

Papers

Wind-tunnel experiment on sand deposition mechanism and optimal measures of wind-break wall along railway in strong wind area