A joke on the Sichuan-Tibet Northern Line! What is particularly difficult about the construction of the Queershan Tunnel?

"The peak that an eagle cannot fly to" - Que'er Mountain.

It is the highest highway crossing in Sichuan. It is covered with ice and snow in winter, with extreme temperatures reaching minus 40°C. Natural disasters such as avalanches, mudslides, and landslides are severe. Traffic is often interrupted due to snow, with an average of 7 crossings every year. It snows every month, and the deepest snow can reach 3 meters!

On the Sichuan-Tibet Line, Queer Mountain is always a topic on the minds of passing drivers and is a staple on the Northern Sichuan-Tibet Line.

The Northern Sichuan-Tibet Line starts from Chengdu. The main carrying section is National Highway 317, passing through Malkang, Luhuo, Garze, Dege, Jiangda, Qamdo, Leiwuqi, Dingqing, Baqing, Suo After the county, it reaches Nagqu, and after converging with National Highway 109, it reaches Lhasa. This becomes the Great Northern Line. Among them, in Luhuo, you can take the provincial highway to Kangding Xinduqiao and Qamdo to Bangda. The other sections overlap with National Highway 318. This is called Sichuan-Tibet Xiaobei Line.

Therefore, no matter which way you go, Queer Mountain on National Highway 317 will always be a natural chasm. Whether you walk or not, the mountain is there, neither close nor far.

On September 26, 2017, the Queershan Tunnel was officially opened to traffic, indicating that this line on National Highway 317 for many years has become history. Que'er Mountain, with an altitude of 6,168 meters and the pass at an altitude of 5,050 meters, was once "the most dangerous and the highest in Sichuan and Tibet".

China Railway No. 1 Engineering Group Co., Ltd. undertook the construction of the tunnel exit section. The contract starting and ending station numbers are K344+500-K349+200, with a total length of 4.726 kilometers. You have to climb over Queer Mountain and fight from the inside out.

China Construction Fifth Engineering Group Co., Ltd. is responsible for the construction of the entrance section of the tunnel. The starting and ending pile numbers of the contract are K34240-K344+500, with a total length of 4.231 kilometers. It is to be drilled inward from the direction of Manigange.

What is the difficulty?

We have overcome technical difficulties in the construction of extra-long highway tunnels in high-altitude areas, including frozen soil, water gushing, faults, rock bursts, ventilation and oxygen supply, etc.

Quier Mountain in Garze Dege is located on the 317 National Highway on the northern line of the Sichuan-Tibet Highway. The main peak is 6,168 meters above sea level. It is covered with snow for up to 8 months every year. The mountain is high and the road is dangerous, and it is cold and hypoxic. It is called "the first danger in Sichuan and Tibet". In order to further open up the Sichuan-Tibet transportation artery, it took 15 years for the Queershan Tunnel to start project demonstration and be completed and opened to traffic.

The Queershan Tunnel is located on National Highway 317 (Northern Sichuan-Tibet Highway) between Garze and Dergegangtuo. It is about 900 kilometers away from Chengdu in the east and 150 kilometers away from the Tibetan boundary in the west. The total length of the tunnel is 7,079 meters. , is a key control project of National Highway 317, and is a rare high-altitude extra-long highway tunnel in the world.

The tunnel has a total length of 12.995 kilometers and the entrance is 4,378 meters above sea level. It is the highest ultra-long highway tunnel in the world. Among them, the tunnel is 7.079 kilometers long and the approaches at both ends are 5.916 kilometers long. The tunnel has a net width of 9 meters and a net height of 5 meters. It has two lanes in both directions. It adopts the second-class highway standard and has a design speed of 40 kilometers per hour. The total investment is 1.15 billion yuan. The program demonstration and feasibility study were started in 2002, construction started in September 2012, and it was officially opened to traffic on September 26, 2017.

The construction of the Queershan Tunnel not only overcomes difficulties such as high cold, hypoxia, lack of materials and manpower, but also solves construction problems caused by uncertain factors such as collapse, water inflow, and rock bursts caused by the complex geological conditions in the tunnel area. . After five years of hard work and more than 2,000 people participating in the construction, this extremely difficult tunnel was finally built.

The mountain is high and the road is dangerous: "Crossing Que'er Mountain in winter is like going through the gate of hell"

The main peak of Que'er Mountain is 6,168 meters above sea level. The mountain is desolate all year round and the wind is biting. Due to the high altitude, even passengers passing through Queershan will suffer from altitude sickness, let alone the "stationed" construction workers.

Quer Mountain is the main passage of National Highway 317 into and out of Tibet from the mainland. The highest point of Queershan Highway is 5,050 meters above sea level, and the road is closed due to ice and snow for half of the year. The road conditions are very poor, and it is common to accidentally fall into an ice hole, not to mention overturning or falling off a cliff due to slippery roads. It stands to reason that under normal circumstances, a shuttle bus leaves at 6 a.m. and can arrive at 5 p.m. after covering a distance of 589 kilometers. But emergencies often happen here, and the shuttle bus is delayed until 3 o'clock the next day to reach its destination.

Therefore, Que'er Mountain is known as "the most dangerous place in Sichuan and Tibet", and there is a local saying that "going to Que'er Mountain in winter is like going through the gate of hell".

The lowest temperature here is minus 20 degrees Celsius, the humidity is only 40%, the intensity of ultraviolet rays is 3-4 times that of the plain areas, and the artificial efficiency is less than half that of the plain areas.

The temperature difference between the inside and outside of the cave can reach 70 degrees

There is a saying among the workers: "The wind blows the stones away, grass does not grow all year round, you take three breaths every step, and wear cotton-padded jackets in summer." A vivid portrayal of the climate in Ershan. In extreme weather, the outdoor temperature at the tunnel entrance can reach minus 40 degrees. Extreme cold is also a major dilemma faced by the construction of the Ershan Tunnel.

In winter, due to the work of mechanical equipment, the temperature in the tunnel can reach more than 30 degrees, forming a temperature difference of nearly 70 degrees with the outdoors. It can be said to be a "two heavens of ice and fire." Concrete, in particular, cannot meet construction standards in low-temperature environments. Equipment similar to "floor heating" is occasionally installed under the equipment where concrete is stored to keep the material at about 20 degrees.

There is a shortage of materials and manpower, and the logistics supplies "cannot keep up"

During the project construction, many materials need to be purchased from Chengdu, which is more than 900 kilometers away, and multiple buildings with an altitude of 4,000 meters must be climbed along the way. In the mountains above, there are many construction sections along the way, and the traffic conditions are extremely poor. Poor traffic conditions directly led to a lack of materials and manpower and difficulties in the delivery of logistical supplies - in the early days, most of the daily supplies needed by construction workers relied on Chengdu. Later, transportation improved, and some supplies were transported by Derge.

Five years of construction, five years of line selection and exploration - "Ten years of sharpening a sword"

The line selection of Queershan Tunnel is also a big problem - after all, the altitude is fixed , not only is it easy to be blocked by snow, but the function of shortening the distance of the tunnel will be reduced, which is counterproductive; if it is chosen low, it will increase the length of the tunnel and increase the difficulty of construction.

So, the engineers personally surveyed, climbed over Queer Mountain, collected data, and designed multiple plans such as 2 kilometers, 4 kilometers, and 7 kilometers, and set up the entrance and exit points among the multiple pre-selected plans. , established meteorological observation stations respectively, and spent a year observing and recording meteorological element data in four seasons at different altitudes, and based on the records, they speculated and simulated the actual conditions of extreme climate.

In the end, the design team set the tunnel length at 7 kilometers, designed the entrance of the Queershan Tunnel at an altitude of 4,373 meters, and the exit at an altitude of 4,250 meters. The tunnel is high in the middle and low on both sides. This design is mainly to prevent water accumulation in the tunnel and ice formation in the tunnel due to water accumulation. Engineers chose the entrance of the tunnel on the ridge, taking advantage of the natural terrain to avoid avalanches and snow on the top of the mountain from sealing the entrance.

Although the construction period of the Queershan Tunnel is 5 years, from the beginning of the design, it took a full 10 years of project research, geological exploration, meteorological observation, tunnel measurement and design, etc.

Plateau Hypoxia

Altitude sickness was mentioned earlier. The average altitude of the Queershan Tunnel entrance is more than 4,200 meters. The oxygen content in the air is equivalent to 58% of that on the plain, while the oxygen content deep in the tunnel is lower than 53% of that on the plain. . In order to increase the oxygen concentration in the tunnel, the construction unit adopted various methods such as setting up oxygen bars, setting up oxygen supply pipes, adding oxygen to the ventilation pipes, and carrying oxygen bottles at all times.

However, even with the above measures, it is still not safe enough. After all, long-term high altitude work has a great impact on the health of employees. Initially, they were given a vacation once a year, but after physical examination, it was found that many employees had severe hemoglobin It exceeded the standard, so it was adjusted to a half-yearly leave. Ancillary facilities such as entertainment rooms and hot spring baths (there is a hot spring not far from the tunnel exit) have also been built to ensure the physical and mental health of construction workers.

The altitude sickness of the machine is a bit "scary" and may even cause black smoke pollution

According to experience, for every 1,000 meters of altitude increase, the atmospheric pressure decreases by 10%, and the power loss of the internal combustion engine is compared to that on the plains. The index dropped by 8%-12%, and the efficiency of aerodynamic equipment dropped by 10%-13% compared with the plain index. In low-pressure and low-temperature environments, mechanical equipment often encounters difficulty in starting at low temperatures. The mechanical efficiency is only about 50-60% of that in plain areas, and fuel consumption may increase significantly. The efficiency of aerodynamic equipment dropped to half of its original value, and the mechanical failure rate was 2-3 times that in plain areas.

While the power of mechanical equipment decreases, the oxygen content in the intake air of the diesel engine is insufficient due to the lack of oxygen on the plateau. The diesel is not fully burned after high-pressure atomization, causing a large amount of black smoke to pollute the air. The altitude sickness of the machine is even more "scary".

To address the problem of black smoke pollution caused by reduced equipment power and insufficient diesel combustion, three solutions have been adopted:

First, add an oxygen pipe to the intake air filter , by increasing the oxygen intake of the diesel engine by carrying oxygen bottles in the machinery itself, thereby achieving the purpose of improving fuel utilization and reducing black smoke emissions;

The second is to add a filter device to the exhaust pipe of the mechanical equipment. In order to achieve the purpose of improving the exhaust gas of mechanical equipment;

The third is to add additives to solve the problem of insufficient combustion.

Landsins and water gushing also seem to be common occurrences in tunnel construction

The Queershan Tunnel has passed through the fracture zone many times, and the surrounding rock levels have changed greatly. The surrounding rock conditions are better, including granite. Category 1, but the tunnel crosses 4 fault zones and belongs to weak surrounding rock. During construction, it will encounter disasters such as water inflow, debris material gushing out, collapse, and rock burst.

How to avoid landslides?

In order to solve these construction problems, when excavating the weak surrounding rock on the plateau, the upper and lower step method and the reserved core soil method are used to reduce the impact on the surrounding rock. of disturbance. In order to avoid landslide accidents, excavation steps are strictly controlled, and vibration blasting and loosening blasting are used to reduce disturbance to the surrounding rock.

When carrying out cross-section excavation construction, it is not only necessary to ensure that the clearance and structural dimensions of the tunnel meet the project requirements, but also the deformation caused by the initial support must be taken into consideration. For the calculation of reserved deformation, various factors such as surrounding rock grade, section size, support conditions, etc. must be considered, and reasonable adjustments should be made according to the different environments.

During support, the weak surrounding rock is anchored through the pipe shed and the leading small conduit; the surrounding rock is reinforced by grouting the leading small conduit. The grouting slurry is usually pure cement slurry or mixed with water glass to achieve the purpose of strengthening the surrounding rock. When protecting weak surrounding rock, choose foot-locking anchors for reinforcement. The locking anchor technology is a new type of structure composed of anchors, concrete surfaces and anchor plates. Before tunnel excavation, the anchors are driven into the arch foot through the arrangement of the locking anchors, and the anchors are used to The slab protects and reinforces the weak surrounding rock to form a composite structure. The locking anchor can enhance the bearing capacity and stability of the rock mass so that the locking anchor can effectively play its role and prevent safety hazards such as collapse due to deformation of weak surrounding rock or insufficient bearing capacity.

How to solve the problem of water inrush?

The Queershan Tunnel passes through three large fault fracture zones. Near the fault fracture zones and influence zones, the rock mass is broken, cracks develop, and the cracks are not connected. Good, there is a large space for groundwater storage. The granite between the faults has a relatively complete rock mass, poor fracture connectivity, and relative water isolation. Therefore, the tunnel site area is a series of hydrogeological structures with alternating water supply and water isolation, controlled by network fractures.

The construction unit adopted the method of water drainage + grouting to effectively solve the problem of water inflow. Rely on scuppers, weep holes, and pumps to drain the accumulated water in the tunnel to lower the groundwater level in the tunnel. At the same time, through grouting reinforcement, the moisture content of the rock layer is reduced, and the permeability coefficient of the surrounding rock is reduced to limit the amount of water seepage in the rock layer in the tunnel. Finally, the loose rock mass reinforced by grouting is used to block the groundwater seepage channels, thereby achieving the purpose of controlling water surge. It must be pointed out that because the Queershan Tunnel has a low entrance and exit and an arc shape with a slightly higher altitude in the middle of the tunnel, the tunnel has a natural drainage function.

How convenient is it for the tunnel to open to traffic?

The beautiful natural scenery of Ganzi Prefecture is very attractive to self-driving enthusiasts, but many people hear that they have to climb Queer Mountain. All gave up this plan.

Now, the Queershan Tunnel has opened up a new golden channel for self-driving tours in western Sichuan, shortening the mileage by 20 kilometers and saving two hours of driving time. Veteran drivers can travel through Queershan in only 10 minutes!

What are the humanized designs of the tunnel?

The Queershan Tunnel has created many miracles in design and construction. From the perspective of highway use, there are also rich cultural landscape settings and many humanized designs.

◆Import Kamba culture? Export the road-building spirit of the 18th Army

From the entrance to the exit of the Queershan Tunnel, careful passers-by will find that there are unique landscapes at the entrance and exit. design. The entrance is themed "Holy Kham, Colorful Derge". Sculptures of Southern Tibetan Medicine, Tea Horse Road, King Gesar and others stand beside the entrance of the tunnel. They are made of bronze and Tibetan compatriots holding hadas in their hands are singing and dancing to welcome visitors from all directions.

At the exit, the theme is the soldiers of the 18th Army opening the Queershan Highway. The soldiers built the road while marching, using natural stone reliefs, which are integrated with the entire mountain and are completely natural.

◆An oxygen-making station is set up at the entrance of the anti-high-reflection tunnel

In addition to the landscape, the tunnel also adopts many humanized and environmentally friendly designs. The oxygen generating station during the construction process will be retained, and an oxygen generating station will be set up at the entrance and exit of the tunnel to provide oxygen supply services to tunnel construction personnel, management personnel, passing drivers, and tourists.

The curve design of the route in the tunnel can not only prevent driver fatigue caused by long-term straight driving, but also prevent heavy snow from being blown directly into the tunnel by the wind.

At the same time, in order to prevent groundwater from freezing, the drainage ditch is more than two meters lower than the road surface. In order not to damage the environment, the entire vegetation was transplanted during the construction and moved back again after the construction was completed. During the design and construction, the roadbed of the approach roads at both ends of the tunnel was also deliberately raised as a whole to digest the waste residue from the tunnel.

Honors Received

In 2018, the Queershan Tunnel became the first road tunnel project in China to be shortlisted for the International Tunnel Association's "Annual Engineering Award", and eventually won the "Oscar Award" in the tunnel industry ——The Brunel Trophy marks that China’s highway tunnel survey, design and construction levels have successfully ranked among the top in the world.

Conclusion

After the Queershan Tunnel is completed, it will not only avoid 3 avalanche sections (47,000 meters) and 6 debris flow sections (2,220 meters), but also reduce the accumulation of snow in winter. The section with snow thickness greater than 1.5 meters has been reduced by about 22 kilometers. More importantly, after the Queershan Tunnel is officially opened to traffic, it will only take more than 10 minutes for vehicles to pass through Queershan, instead of having to detour on the dangerous mountain road for more than two hours, and it will no longer be like the old road. The road is closed for half a year every year, so that it can be connected throughout the year.

This article comes from the author of Autohome Chejiahao and does not represent the views and positions of Autohome.