Cat® Earth Pressure Balance Machine Successfully Conquers Beijing Subway Construction Issues

According to Ming Unity Record, “Yuyuantan is a beautiful lake area surrounded by willows and wild birds.” In spring, Yuyuantan Park, located in Beijing’s Haidian District, turns into a garden of blossoming flowers. Tourists reveling in the beauty of the flowers might not realize that an extremely challenging construction project was being conducted 30 meters under the bed of Yuyuantan East Lake. There, an enormous Cat® Earth Pressure Balance (EPB) Machine was excavating a tunnel.

Planned in the 1990s and launched in 2007, Beijing Subway Line 9 starts from Guogongzhuang (South) and extends to the National Library (North). At a length of 16.9 km, Subway Line 9 has 13 stops, including Beijing West Railway Station, Yuyuantan and Diaoyutai. As scheduled, Subway Line 9 will officially open in September 2012. However, the project ran into an unprecedented challenge tunneling the section under the Yuyuantan East Lake. 

Originally, a conventional EPB Machine was going to be used to bore a tunnel under Yuyuantan East Lake. However, the engineering difficulties went far beyond anything the planners had imagined. 30 meters under the lake is a layer of soil littered with more than 160 boulders with diameters greater than 1.5 meters, creating more than 100 high-risk areas. A normal EPB Machine needs to change its disk cutters after every 160-180 meters of excavation. In 2007, the company in charge of the undertaking, Beijing Urban Construction Group (BUCG), opened bidding worldwide to find partners for the project. However, many bidders withdrew after discovering the adverse geological conditions of the Yuyuantan East Lake section. Caterpillar eventually won the bidding due to its abundant experience overcoming such challenges and outstanding technology. After beating out the competition, Caterpillar was able to make an enormous contribution to the construction of Subway Line 9.

The EPB Machine (full name: Earth Pressure Balance Tunnel Boring Machine) is a piece of professional tunnel excavation equipment that consists of optical, mechanical, electrical, hydraulic, sensor and information technologies that all work in concert. It is capable of excavation, soil transportation, tunnel assembly and deviation error correction. The Cat EPB Machine has been widely utilized in constructing tunnels for subways, railways and highways. It has also been employed in highly difficult and customized municipal and hydropower projects because of its ability to meet extremely high reliability standards. For instance, 45% of Beijing Subway construction has been done by Cat EPB Machines, which has improved efficiency by 8 to 10 times compared with traditional tunnel construction. Additionally, tunnel boring by an EPB Machine does not lead to any large scale demolition, noise, soil collapse, or traffic disruption.

The giant boulders under Yuyuantan East Lake presented the most serious obstacle to tunnel boring. “The EPB Machine can wear down quickly and may get stuck in the section,” said Shang Xiaomin, head of BUCG and in charge of Beijing Subway Line 9 construction. To overcome the challenge, Caterpillar Tunneling Canada Corporation  provided a customized 6.28-meter EPB Machine named Diamond. Diamond was the first such EPB Machine used in China and contained world leading technologies. The steel cutter was 50% stronger than that used in the “Bird’s Nest” National Stadium. The cutter consisted of 159 knives and rollers equipped on a two-storey high round steel disk. Diamond easily broke through hard sediment and boulder layers like a submarine cruising in the ocean and immediately. It successfully solved the tunnel boring issue and created a 2.4-kilometer tunnel under Yuyuantan East Lake.

On April 10, 2012, the Diamond EPB Machine broke out of the ground around the northeast corner of Navy General Hospital after creating the southern and northern sections of Subway Line 9. Supported by the Cat EPB Machine, BUCG successfully overcame unprecedented engineering difficulties and completed a crucial stage of construction. When Subway Line 9 is completed, it will optimize traffic conditions in the western part of Beijing and in the areas around Beijing West Railway Station and Fengtai District. It will also facilitate investment and improve living standards in urban Beijing.