Climbing the "Everest" of Engineering
—— Construction Record of the Luding Dadu River Xingkang Grand Bridge on the Ya'an-Kangding Expressway

On the morning of October 10, construction workers at the C15 contract section of the Ya'an-Kangding Expressway were beaming with joy as the Luding Dadu River Xingkang Grand Bridge successfully completed the final layer of concrete pouring for the anchor plug body in the right tunnel of the tunnel-type anchorage, marking the completion of construction for this world's longest tunnel-type anchorage, which is 159 meters long.
The Xingkang Grand Bridge, invested by Sichuan Transportation Investment Group Co., Ltd. and constructed by Sichuan Road and Bridge Construction Group Co., Ltd., has a total length of 1411 meters. Its main bridge is a 1100-meter single-span steel truss suspension bridge. It is one of the key control projects of the "one bridge and one tunnel" on the entire Ya'an-Kangding Expressway and is known as the "First Bridge in Sichuan-Tibet."

Overcoming Difficulties: Bridge Construction Achieves Initial Success
　　Driving along National Highway 318 deeper into the Tibetan region, one can see the surging Dadu River like a galloping horse. Just past the Luqiao Tunnel, the main pier and cable towers of the Dadu River Grand Bridge come into view, standing tall between the cold mountains, exuding majesty. From the viewing platform, one can enjoy even more captivating scenery: the cable towers on both banks complement the emerald Dadu River, modern technology and beautiful scenery enhancing each other, adding grandeur to the magnificent landscape. Since construction began, this place has attracted many people to stop: photographers love the light and shadow of the mountains, water, and bridge; technical experts are fascinated by the ingenious design of the grand bridge; and tourists can feel the grand atmosphere of the motherland's development here...
As an old saying goes: "The great river and natural moat were considered limits in ancient times." The "great river and natural moat" became an insurmountable "limit." In the construction of the Dadu River Grand Bridge, five "extremely" challenges must be faced: "extremely complex terrain, extremely complex geology, extremely harsh climate, extremely fragile ecological environment, and extremely difficult construction."
In the early stage of the grand bridge construction, in order to explore the construction access road on the Ya'an side, the Ya'an-Kangding Company organized designers, supervisors, and construction personnel to carry a day's water and dry food on their backs in the early morning, take fishing boats to the opposite slope foot, and climb the rocks to survey the access road route. The terrain on the Ya'an side is very steep, with a slope of 35 degrees, and engineering personnel faced the risk of falling at any time. At the same time, due to the broken surface on the Ya'an side and the frequent strong winds and heavy rain in Luding, the newly marked access road route was often destroyed by landslides and mudslides the next day, and the route had to be re-selected. After nearly half a year of exploration, a rugged construction access road was finally paved, allowing the project to proceed smoothly. This is just one episode in the construction of the grand bridge.
One of the challenges that must be faced in the construction of the grand bridge is the complex wind field environment. The wind field environment in the bridge site area is very complex, with turbulent strong winds all year round. The maximum wind speed can reach 32.6 meters per second, equivalent to a Category 12 typhoon. When the wind blows, sand and stones fly, completely portraying the true scene of "flat sand vast and yellow reaching the sky." Strong winds greatly interfere with engineering construction: concrete pouring quality and weld quality cannot be controlled, lifting equipment and construction elevators are difficult to use, and the risks of falling objects and high-altitude operations are extremely high. Even the installation of corrugated steel webs weighing tons on the main tower crossbeam may pose a risk of overturning. To solve the problems caused by turbulent strong winds and complex wind fields, the Ya'an-Kangding Company required engineering personnel to collect detailed meteorological data, set up wind speed monitoring points, establish a weather chart, and deeply analyze the wind operation patterns in the bridge site area. Then, they studied construction plans overnight and finely optimized the design for the wind field environment. If strong winds affect project quality and increase operational risks, construction is carried out when wind speed is low; if wind affects weld quality, windbreak sheds are set up and welding rods are preheated; if corrugated steel webs may overturn, rigid anti-overturning support frames are erected... In short, all means are used to overcome the various disadvantages of the complex wind field.
After more than two years of construction through wind and rain, the participating parties have overcome the "ancient limit" of dangerous mountains and extreme climate, and the grand bridge construction has achieved initial results: the mysterious world's longest tunnel-type anchorage has been completed, the 188-meter-high cable towers on both banks have been successfully capped, and the huge gravity anchorage has been 92% completed.

Pioneering and Innovating: Technological Achievements Bear Fruit
　　The famous bridge expert Mr. Mao Yisheng once said: "Many mountains and rivers make road construction difficult, and the difficulty lies in building bridges." Bridge construction is difficult because the bridge construction process is very complex and requires high technological innovation. Since the start of construction, the Tibetan Plateau Expressway Company, the Ya'an-Kangding Company, and the construction units have realized this. They attach great importance to technological innovation and have joined forces with universities and research institutions such as Southwest Jiaotong University, Wuhan University of Technology, and the Yangtze River Scientific Research Institute of the Yangtze River Water Resources Commission to organize special teams for scientific and technological research. So far, they have successfully applied for 8 national utility model invention patents, and it is expected that more than 20 subsequent technical and process innovations will be made, providing strong technical support for the construction of the grand bridge.
Among all the completed parts, the technological innovation achievements of the mysterious world's longest tunnel-type anchorage are particularly prominent. The tunnel-type anchorage on the Ya'an side is 159 meters long, more than double the length of the world's second-longest tunnel-type anchorage (78 meters) of the Wanzhou Yangtze River Fourth Bridge; the vertical height difference reaches 95 meters, equivalent to a 33-story building; the excavation volume of a single tunnel is 20,866 cubic meters, and the schedule pressure is enormous. To solve the excavation problem, the Tibetan Plateau Expressway Company and the Ya'an-Kangding Company attached great importance to the feasibility of the plan, organized experts for plan review multiple times, and organized supervisors and construction parties to actively carry out scientific and technological research. The project innovatively adopted the double-track mucking method for the first time, achieving an average daily excavation volume of 52 cubic meters and an average daily advance of 0.4 meters, nearly doubling the excavation efficiency compared with similar bridges in China.
After excavation is completed, the next problem to solve is the transfer, installation, and precise positioning of high-strength steel tie rods. Due to the terrain environment, the anchorage tunnel is very narrow and relatively enclosed, and general lifting equipment such as tower cranes and truck cranes cannot operate. However, with the joint efforts of the Tibetan Plateau Expressway Company, the Ya'an-Kangding Company, and all participating parties, they have proposed a series of practical invention innovations such as "A Simple Device for Rapidly Threading Super-Long Steel Tie Rods and Its Operation Method," "Layout System and Operation Method for Rapidly Transferring Steel Tie Rods in Super-Long, Large-Inclination Tunnel Anchors," and "Rapid Installation System and Operation Method for Steel Tie Rods in Super-Long, Large-Inclination Tunnel Anchors." During construction, they explored favorable conditions and used the cross passage of the Luding Tunnel to safely and efficiently transfer steel tie rods with a translation system. After entering the tunnel anchor work area, they installed a cable lifting system inside the tunnel for steel tie rod installation. During installation, manual coordination with chain hoists was used for precise fine-tuning, achieving the transfer, installation, and precise positioning of high-strength steel tie rods in the narrow, enclosed anchor tunnel.
Another representative process innovation in the construction of the grand bridge is the waterless underwater concrete pouring for manually excavated piles. Due to geological conditions and construction constraints, the 100 pile foundations of the 3# and 4# main piers of the grand bridge all adopted manual excavation. Among them, the pile foundation of the 4# main pier on the Kangding side is as deep as 60 meters. In addition, the Kangding side has a huge Quaternary Upper Pleistocene moraine layer underground. If the traditional dry pile pouring method were used, construction would face three difficulties: the height difference of 60 meters makes it impossible to guarantee the safety of construction personnel; the concrete gas at the bottom of the pile foundation is highly irritating and affects the health of construction personnel; and the concrete pouring time is long, construction efficiency is low, and quality is not easily guaranteed. After repeated surveys, demonstrations, and tests by the Ya'an-Kangding Company and relevant participating units, they innovatively proposed the waterless pouring method for dry piles. After construction was completed, the pile inspection report showed that all 100 pile foundations of the main piers were Class I piles. Compared with the traditional dry pile pouring method, the waterless pouring method has the following advantages: first, it eliminates the need for layered pouring and vibration, eliminating the safety risks of manual work under the hole; second, it eliminates the need to inject water into the hole, providing greater safety for the highly permeable alpine moraine layer; third, the pouring time is shortened from 24 hours to 8 hours, doubling efficiency, and quality is easily guaranteed.
Not long ago, three academicians from the Chinese Academy of Engineering visited the Dadu River Grand Bridge for research. When interviewed by the media, they could not help but say: "The Ya'an-Kangding Expressway is a dream awaited for a thousand years, and its construction difficulty and complexity are comparable to climbing the Everest of engineering." As a key chapter in this dream, this bridge carries many expectations. It is an artery bridge for the economic development and prosperity of the Tibetan region, and also a microcosm of the development of modern bridge design and construction techniques in China.