Important progress has been made on the Gaoligongshan Tunnel of the Dali-Ruili Railway.

On July 30, a new breakthrough was achieved in the construction of the Gaoligongshan Tunnel on the Dali-Ruili Railway, the world's first super project to cross the Hengduan Mountains. The parallel adit of the tunnel's inclined shaft has broken through to the tunnel's entrance end, solving the construction challenges of reverse-slope drainage and large water inflow at the inclined shaft, and taking another solid step toward early completion of the "last section" within China of the China-Myanmar international corridor on the western route of the Pan-Asian Railway under the Belt and Road Initiative.

The Gaoligongshan Tunnel has a total length of 34.538 kilometers and crosses 19 active fault zones. Its complex geological conditions are rarely seen anywhere in China, encompassing almost all adverse geological conditions and major risks in tunnel construction. The construction difficulty is second to none, and it is known as one of the "most difficult tunnels in the world to build," currently holding nine records in the history of tunnel construction. Among them, the 3,870-meter-long inclined shaft of the Gaoligongshan Tunnel is the longest inclined shaft on a railway in China. To this end, the Yunnan Company of the Yungui Railway and the contractor China Railway Tunnel Group have consistently adhered to dynamic design and on-site control as key measures, working together to overcome difficulties and advance the project in an orderly manner.

Important progress has been made on the Gaoligongshan Tunnel of the Dali-Ruili Railway.

Due to the active geological structures, complex geological features, extremely high in-situ stress and abundant groundwater of the Gaoligong Mountains, builders have had to constantly face a series of major risks and severe tests during construction, including large water inflow, high ground temperature, large deformation and easy collapse. The inclined shaft has a daily water inflow of 33,000 cubic meters, enough to fill 17.5 standard swimming pools. Affected by high ground temperature, the average temperature of the inflow water reaches above 38°C, and the working area above the tunnel even reaches 42°C, far exceeding China's 38°C orange high-temperature warning threshold. The average humidity inside the tunnel exceeds 99%. Builders have to work continuously in such a hot and humid environment, akin to长期 taking saunas in a sauna room; the stuffy and damp construction environment has caused builders to develop eczema all over their bodies.

To improve the on-site working environment of high temperature and water inflow, the Yunnan Company of the Yungui Railway and the China Railway Tunnel Bureau have repeatedly joined forces with design, supervision and other units, invited industry experts to conduct on-site diagnosis and consultation, continuously optimized the gallery ventilation scheme and increased ventilation volume. For local high-temperature water inflow sections, grouting plugging was carried out, a special platform for "local fan jet ventilation plus ice block cooling" was set up, and high-power fans and mechanical refrigeration equipment were purchased to effectively solve the problem of cooling the tunnel face. 1.5 million yuan was invested to build an ice factory with a daily output of 60 tons to meet the on-site demand for nearly 60 tons of ice per day for cooling.

At the same time, for the health of the workers, tunnel workers were promptly organized to undergo comprehensive physical examinations at hospitals, domestic dermatology experts were invited to provide online consultations for the workers, and professional testing institutions were commissioned to conduct detailed tests on water inflow, tunnel gases and other factors. On the basis of increasing ice blocks and equipping cooling equipment to lower the temperature by 5-6°C, the 4-hour work shift was adjusted to 2-3 hours to speed up worker rotation and avoid prolonged work under high temperatures. The site was also equipped with a construction site clinic, dermatology medicines, high-temperature emergency medicines, and heat-relieving drinks such as salt water and herbal tea for the workers, actively improving the working environment.

Affected by bedding planes, eccentric pressure and extremely high in-situ stress, the initial support of the inclined shaft deformed severely, the sprayed concrete cracked and fell off, and local arch frames twisted into "Z" and "S" shapes, squeezing the already formed tunnel smaller, with wall rock intruding more than 1 meter into the tunnel, resulting in narrow and deformed working space. For large-deformation sections, builders optimized the construction plan, adjusted support parameters, improved processes and methods, shortened the closure time, adopted double-layer or even three-layer and four-layer arch frames, implemented initial support reinforcement and secondary lining, and increased monitoring and measurement frequency, forming a set of large-deformation control technical measures to prevent further deformation of the surrounding rock. According to statistics, deformation and local collapse caused by high in-situ stress alone have led to 11 suspensions of work for treatment.

Important progress has been made on the Gaoligongshan Tunnel of the Dali-Ruili Railway.

The height difference between the inclined shaft of the Gaoligongshan Tunnel and the tunnel entrance is 429 meters. The breakthrough of the parallel adit's small mileage end with the entrance end has solved the construction problem of reverse-slope drainage in the ultra-long inclined shaft that had plagued builders for six years, avoided the risk of tunnel flooding that could be caused by large water inflow, and created favorable conditions for accelerating the construction of the Gaoligongshan Tunnel.

After the Dali-Ruili Railway is completed and opened to traffic, the travel time for the more than 700-kilometer journey from Kunming to Ruili will be reduced from 9 hours by road to 5 hours by rail. This is of great significance for accelerating the development of the southwest region, promoting connectivity between China and Southeast Asian and South Asian countries, supporting the Belt and Road Initiative, and revitalizing the "Southern Silk Road."