Influence of topography on highway traffic construction

Geomorphology is the result of the interaction of internal and external forces such as structure, climate and human action. At the same time, it causes regional, especially vertical changes of atmospheric heat and moisture, which is directly related to the properties of rocks and surface sediments, as well as the distribution and movement of surface water and groundwater. Therefore, it is considered to be the most important natural factor affecting land traffic and the core of evaluating road natural conditions. Highway is directly exposed to nature, and it is a soil, stone and asphalt structure that passes through different geographical areas. After the completion of the highway, it has become a new type of artificial landform, which is constantly affected by the natural environment and destroyed by natural disasters. Xinjiang has a vast territory, "three mountains and two basins", and the terrain is complex and diverse. Mountains, plains, deserts and their secondary landforms bring obvious difficulties to highway construction and operation management. Modern geomorphic processes such as flowing water, wind, freezing and thawing, gravity and so on are strong, and landslides, flash floods, mudslides, avalanches and sandstorms caused by them can hinder or interrupt traffic and transportation, which has a great impact on highway construction.

First, the relationship between regional landform structure and highway distribution

Mountains and basins in Xinjiang are divided by deep faults, forming different geomorphic units. Geomorphic units control the distribution of highways. Affected by the above-mentioned topographic conditions of highway construction, the distribution of regional highways is as follows: ① The highway continuously crosses ditches in the piedmont plain. Because the piedmont plain is the main area of oasis town distribution and the key area of highway construction, the road network density is relatively high. National Highway 3 12 passes through the northern edge of Turpan Basin and the southern edge of Junggar Basin, and National Highway 3 14 and 3 15 extend along the northern and southern edges of Tarim Basin respectively. Due to the influence of river confluence basins in mountainous areas, highways need to constantly cross ditches and set bridges and culverts, so they are often harmed by mountain torrents and mudslides. (2) The highway goes over mountains and mountains. Tianshan Mountain separates Junggar Basin from Tarim Basin. Du (Zi Shan) -Ku (Car) Highway, Wu (Lumuqi)-Yan (Mao) Highway and Ha (Mi)-Ba (Li Kun) Highway pass through Tianshan Mountain. National highways 3 14 and 2 19 cross Kunlun Mountain to connect Pakistan and Tibet respectively. ③ The highway crosses the desert. 2 16 National Road crosses Gurbant Desert, and Luntai-Minfeng Highway crosses Taklimakan Desert (Figure 9- 1). Because the plants in desert areas are sparse or poor, there are sandstorm hazards such as road wind and sand. ④ Xinjiang highway has a long mileage, circuitous routes and a large proportion of trunk lines. Restricted by topography and water resources, oasis towns are scattered and the highway mileage between towns is long. The average distance from Urumqi to cities (states) is 742km, the distance between counties is 1 12.3km, and the distance between townships is 35km. The length of highway in Xinjiang is about 3.28× 104km, and the highway density is only 2.69km/ 100km2 after deducting the barren desert Gobi 44. 1km2.

Second, the impact of landform types on highway traffic construction

The landform conditions of highway construction in Xinjiang are complex, and the landform types of highway engineering are diverse (Figure 9-2). In highway engineering construction, landform types such as mountains, hills, plains and deserts have great influence on highway route direction and project cost, and the types of topographic external forces are closely related to the formation of various highway diseases, such as winding routes in mountainous areas, high project cost, easy occurrence of highway diseases such as landslides and collapses, straight highway routes in plain areas, low cost, and mountain torrents and mudslides at the foothills.

Figure 9- 1 Geomorphological Structure and Highway Distribution in Xinjiang

(1) Ordinary

Plains are distributed in basins and valleys, and are mainly formed by the accumulation of water carriers and lakes in rivers and gullies. Including swamps, lake plains, alluvial plains, flood plains, dry erosion plains, ice water plains, etc. The terrain is flat, the slope is generally less than 3, and the fluctuation is between 0 and 0~20m, which is convenient for highway survey, design and construction. There are abundant sand and gravel resources, and Gobi can use local materials, but the alluvial plain is soft and lacks sand and gravel. The high groundwater level in oasis area is easy to cause soft subgrade and frost boiling; There are salinization hazards in some areas; Subgrade in loess distribution area is prone to collapse; Some areas are short of water and windy and dusty, and at the edge of desert, the road surface is easy to accumulate sand, which hinders traffic. There are many dusty weather in Yecheng, Yutian and Ruoqiang in spring and autumn, which has a certain impact on road traffic. Bridges across rivers and ditches are vulnerable to mountain torrents and mudslides. There are many clay materials in fan edges and depressions, and the degree of salinization is strong, so the highway subgrade is easily affected. The plain composed of Paleogene and Neogene mudstone has high clay content and high salinity, which softens the mud when it meets water. Snow on the road often hinders the smooth flow of traffic in winter. In the tuyere area such as Alashankou, strong winds in spring and autumn have a bad influence on traffic. Mountain torrents and mudslides occur from time to time in summer, which will hinder traffic.

(2) Desert

Mainly located in Junggar basin and Tarim basin, it is formed by wind erosion and aeolian sand deposition. Including sand, sand piles, sand dunes, sand dunes and other types. Dunes are complex in shape, including crescent, honeycomb, fish scale, beam nest, dendritic, pinnate sand ridge, chain and star dunes. According to the vegetation coverage of sand dunes, they can be divided into fixed sand dunes, semi-fixed sand dunes and moving sand dunes. The desert topography fluctuates from 0 to 50 m, with the maximum of 200 m m m, the sand dunes fluctuate, the sand is loose, and the lack of sand and gravel for road construction has a bad influence on road construction; Gurbantunggut Desert is dominated by fixed and semi-fixed sand dunes, with low vegetation coverage and fragile ecology, which is prone to quicksand accumulation on the road surface and affects traffic. Taklimakan Desert is dominated by mobile sand dunes, and Kumutage Desert is a mobile desert, with few or no plants. The sand dunes move quickly, and quicksand often accumulates on the road to block traffic. There are more dusty weather in spring and autumn every year, which has a certain impact on highway traffic.

Figure 9-2 Geomorphological Types of Highway Engineering in Xinjiang

(3) Hills

Mainly distributed in the eastern Junggar Basin and the eastern Tianshan Mountains, the elevation is generally between 700 ~ 2000m, which can be divided into: ① micro-hills, including low hills (r < 100 m) and Zhongshan hills (r =100 ~ 200 m); ② Heavy hills (r > 200 m). The climate here is dry and short of water, mainly dry erosion. Hills are composed of bedrock, and exposed rock mass and debris are all over the slope; Quaternary loose gravel layer is accumulated in the valley depression, and desert vegetation such as ephedra, Haloxylon ammodendron and salsola grows, and plants such as reeds and tamarisk are exposed in the spring water. The hilly terrain fluctuates 5 ~ 200 m, and the topography of the depressions between hills fluctuates slightly, resulting in a large amount of excavation and filling in highway construction; Hilly bedrock is hard, which is an excellent building material for road construction, and loose sediments in depressions between hills are harmful to salinization. There are mudslides and sandstorms, and there are occasional flash floods and mudslides in the main ditch. Due to drought and water shortage, road construction, maintenance and transportation management are very difficult.

(4) Mountain area

It refers to Altai Mountain, Tianshan Mountain, Kunlun Mountain and West Junggar Mountain, with elevation > 1000m, fluctuation > > 100m. According to the different characteristics of geomorphic external forces, it can be divided into: ① low mountains, which are found in Altai Mountain [altitude (h) 1000 ~ 1500m], Tianshan Mountain (h < 1700m), Kunlun Mountain (h < 29000m) and West Junggar Mountain (h < Terrain fluctuation is 20 ~1200m. The amount of excavation and filling in highway construction is very large; There is collapsibility problem in loess area; The plain of intermountain basin is relatively flat, mainly composed of sand and gravel, which is convenient for road construction, and the local groundwater level is high, so the swamp and saline-alkali have adverse effects on highway subgrade. There are aeolian silt on some slopes of Kunlun Mountain, which is easy to collapse because of its porosity. The steep slope area is prone to collapse and breakage; Mountain torrents and mudslides are prone to occur in summer, which hinders or interrupts traffic. ② Zhongshan is mainly distributed in Altai Mountain (h = 1500 ~ 2400 m), Tianshan Mountain (h = 1700 ~ 3000 m) and Kunlun Mountain (h = 3000 ~ 4000 m), with forests and grasslands, which are mainly eroded by running water. The mountain is high and steep, the valley is deep, the terrain is undulating, and the terrain conditions for road construction are very poor; The road slope is unstable and prone to landslide and collapse; Collapsibility exists in loess distribution area; There are many landslides in summer, and snow and avalanches often block traffic in winter, most of which are blocked. ③ Alpine mountains, mainly distributed in Altai Mountain (H > H>4000m), Tianshan Mountain (H>4000m) and Kunlun Mountain (H > 4000m). The bedrock of mountain peaks and steep slopes is exposed, and alpine meadows grow on gentle slopes and flat land, mainly because of freezing. High altitude, cold and lack of oxygen, poor road construction conditions and difficult transportation; Freeze-thaw action in mountainous areas has an impact on subgrade stability, and debris flow and frost boiling in summer are unfavorable to highway traffic. In winter, heavy snow and avalanches often hinder the smooth flow of traffic. The enclosure period is longer in winter.

Third, highway diseases caused by geomorphic processes.

From Paleogene to Pleistocene, due to the continuous subduction of the Indian plate to the north, the mountains rose rapidly and overthrusted to the basin, forming a landscape pattern of "three mountains and two basins" in Xinjiang. The neotectonic movement in this area is active, with strong earthquakes in mountainous areas and volcanic eruption in Kunlun Mountain. In recent 30 years, the uplift rate of the main ridge in the northern Tianshan Mountains is greater than10 mm/a. Due to the great difference in the height of the mountain basin, the modern geomorphological process from the center of the basin to the surrounding mountains is wind erosion → flowing water accumulation → dry erosion → flowing water erosion → glacier freezing, in which wind, flowing water, freezing and thawing and gravity have great influence on the highway, mainly causing highway diseases such as sandstorm, mountain torrents, mudslides, landslides and collapses. Modern human activities, such as the construction of reservoirs, cause the decrease of water sources in the lower reaches of rivers, leading to the death of plants, the intensification of wind, excessive logging, indiscriminate digging of medicinal materials and overgrazing, leading to increased soil erosion, resulting in highway sand damage and mudslides.

Geomorphological process has a great influence on highway construction, resulting in many types of highway diseases (Table 9- 1). Mainly include: ① Landslide: mainly seen in Yili area and Kuitun River basin in the west of Tianshan Mountain, with broken rock mass, extensive loess distribution and a lot of precipitation. For example, the loess in the middle section of Zeketai-Nileke Highway is deep, and due to the artificial digging of licorice and the continuous rainfall from April 29 to May 2002, a large landslide occurred, and the landslide spread 5km along the ditch, resulting in the middle section of highway traffic. On July 19, 2003, three landslides caused by heavy rain blocked the traffic on the section of K4757-K4758 of Guozigou, 3 12 National Highway. (2) Collapse: It can be seen everywhere on mountain roads, which is very harmful. Lutu (Lufan)-Urumqi (Lumuqi)-Da (Huangshan) Expressway is located in Baiyanggou section, and the bedrock along the highway is broken, which is in danger of landslide, so we have to adopt the measures of hanging nets to protect the slope. On July 5, 1997, the mountain on the side of No.5 bridge in the trunk ditch section of National Highway 3 14 collapsed, blocking traffic for 7 hours. In mid-July, 2003, the "Tuwuda" Expressway was forced to close to 12h due to landslide caused by precipitation. (3) Mountain torrents and debris flows: widely occurring in Altai Mountain, Tianshan Mountain, Kunlun Mountain-Altun Mountain and foothill plain, mainly formed by high-temperature melting of ice and snow and rainstorm and flood. The Aragou, Duku Highway, Barentai-Hejing Highway, Shufu-Bulunkou Highway, Sangong River and Shuimogou River on the northern slope of Tianshan Mountain are disaster-prone areas, and disasters occur in spring and summer every year, with obstacles or traffic phenomena in between (Figure 53). For example, 1996 floods interrupted expressways11times, destroyed expressways 633km 1998 floods interrupted 53 highways, washed away 24 road culverts1places and washed away 329 kilometers of roads. On July 13 ~ 15, 2003, it rained continuously in Urumqi, and many roads such as K33km, K34km and K69~73km on the provincial highway 103 line were washed away by mountain torrents and mudslides, trucks were buried by mudslides, and hundreds of vehicles were blocked. The road at K 164 ~ 165 km of national highway 3 14 was washed away by mountain torrents and mudslides, and the traffic on the southern Xinjiang line was interrupted. On February/7, 2004, due to the rising temperature and 8 hours of continuous rainfall, a mudslide occurred in Jinghe County, and 7 sections of 3 12 national highway were washed away, resulting in traffic interruption16 hours, and more than 800 vehicles were blocked. On July 2, 2005, due to the sudden rainstorm, the roadbed between National Highway 3 15k 2743+500-k 2744+000 was washed away by the flood, with a length of 850m, a width of 1.5m and a depth of 1.6m: On that day, On June, 2065438 10/0, nearly 600m section of National Highway 31-K2902, heavy rain fell in Tarim Basin of Xinjiang, and floods occurred in some areas, resulting in K2810 of National Highway 3 15 between shache county and Yengisar County. On June 23rd, a snowmelt flood occurred in the mountainous area at K2 122km of 3 15 National Road in Minfeng County, which washed away the road section with a width of nearly 50m and a ditch depth of about 10m, causing thousands of vehicles to stay. On the same day, 557 kilometers of desert roads in Minfeng County were also destroyed by floods. On July 6th, the section of Tashkurgan County 150km was triggered by flash floods, resulting in the damage of two roadbed of more than 30 meters, and more than 200 passing drivers and Chinese and foreign tourists were blocked. ④ Sandstorm: In spring and autumn, the climate is dry and windy. In addition, Xinjiang and foreign countries such as Kazakhstan are exposed, and wind erosion blows up a lot of dust to form sandstorms, which affects the driver's sight and has a negative impact on traffic safety; Due to wind accumulation, the traffic in the desert oasis belt and the highway crossing the desert is blocked by the accumulated quicksand pavement, such as the downstream section of Tahe River on National Highway 2 18, the southern edge section of Tarim Basin on Line 3 15, and the eastern desert highway in Karamay, Junggar Basin, and the road traffic is not smooth (photos 57 and 58). ⑤ Boiling: Mainly seen in areas with high groundwater level in oases. Snowmelt water and artificial irrigation water in spring cause the groundwater level to rise, and the soil turns into mud to boil, which hinders the smooth traffic. ⑥ Freeze-thaw: Cold in winter in mountain areas is easy to cause subgrade frost heaving or pavement frost cracking; The melting of frozen soil in summer makes the road muddy. ⑦ Snowstorm: There are frequent snowstorms in Brzin, Jimunai, Laldun, Aikendaban and other tunnels in the Tianshan Mountains; At Guozigou and Gongnaisi Avalanche Station in Yili, avalanches often block or interrupt highway traffic. For example, in February 1985 and 15, an avalanche occurred in No.3 ditch of Gongnaisi Avalanche Station, with the road buried 20 meters long and the snow on the road surface 6 meters thick; 1February 27, 996 to the following year1October 3, 65438+ continuous heavy snow in northern Xinjiang. The thickness of snow in plain area is 40 cm, and that in mountainous area is 1 ~ 2 m. The snow damage is serious, and more than 450 vehicles on National Highway 2 16, 2 17 and 38007 are blocked. 20 10, 65438+ 10, 17, an avalanche occurred at K474 1km+200m of the original national road 3 12 in Guozigou, Yili, which washed away the factory building of the seventh section of Guozigou-Huocheng Expressway. On 26th, an avalanche occurred at the intersection of National Highway 2 18 and National Highway 2 17 in xinyuan county, and a jeep was buried, killing five people. On 20 10, heavy snow fell continuously in Altay and Tacheng areas, and most road traffic was interrupted. ⑧ Earthquake: The neotectonic movement in this area is active, with 34 main active faults. In history, earthquakes with Ms≥8 occurred in Fuyun and Manas, and earthquakes with M ≥ 8 occurred in 200 1 1 in no man's land of Kunlun Mountain in 2000+0. On February 24th, 2002, Bachu-. Destructive earthquakes happen occasionally, but they are destructive, and they will also cause landslides, collapses, floods, mudslides and other concurrent disasters caused by reservoir dam break, which is very destructive to highways. 9. Sandstorm: In Xinjiang, especially in southern Xinjiang, it often occurs in spring and autumn, which has a great impact on highway traffic. For example, on May 8, 2007, Hotan was hit by a sandstorm, and the visibility from Yutian to Hotan of National Highway 3 15 was less than 10m m. Without exception, all vehicles were driving slowly with their headlights on. 20 10 There was a sandstorm in Kashgar on September 5, and the visibility in the urban area was only about 100m, so the vehicles could only drive slowly.

Table 9- 1 Types and Characteristics of Highway Diseases in Xinjiang

① The number of people affected by the disaster in 2000 is still short, and some information is incomplete, so it is only a rough statistic.