The Qinghai - Tibet Railway: A Monumental Project on the Plateau
As one of the four mega projects of the 21st Century in China, Qinghai-Tibet Railway extends 1,956 kilometers from Qinghai’s provincial capital to Lasa in Tibet Autonomous Region. 960 kilometers of its tracks are located 4,000 meters above sea level with the highest point of 5,072 meters, making Qinghai-Tibet Railway the world’s highest railway and longest plateau railroad.
Construction Techniques
The Qinghai-Tibet Railway line utilizes several new techniques to endure the harsh conditions along the “Roof of the World”. With most of the track being laid at altitudes above 4,000 meters, the line crosses 550 kilometers of continuous permafrost regions and 82 kilometers of discontinuous permafrost regions. In order to overcome the problem caused by frozen soil during construction, engineers have used stone slabs to build embankments that cool without breaking up and have thrust steel tubes into the ground to transmit heat from beneath the icy surface. Because of the use of these techniques, the railway lines built on the permafrost regions have excellent quality, and trains can travel at up to 140 kilometers an hour, much faster than trains on railways in permafrost regions in other countries, whose highest travel speed is only 70 kilometers an hour. To tackle the hazard of natural disasters such as frequent earthquakes on the plateau, the route has avoided regions with active seismic activity. In the vulnerable regions that the line must go across, engineers have used rail beds rather than tunnels and bridges, and retrofitted structures to minimize the effects of any possible tremors.
Environmental Protection
The Qinghai-Tibet Railway crosses several China’s national nature reserves, where the ecological environment is sensitive and fragile. In this regard, from design, construction, operation to maintenance the Qinghai-Tibet Railway has always adhered to the concept of “environment first”. For the protection of the living environment of Tibetan antelope and other wild animals, 33 special passageways for wild animals have been established along the railway. In order to protect natural wetland, the world’s first artificial plateau wetland has been built. To protect ecological environment along the route, effective measures have been taken to prevent possible environmental pollution from train travelers—such as random garbage disposal. These unique environment- friendly design and operation concepts have made the Qinghai-Tibet Railway the first “environmental railway” in China.
Economic Impact
The Qinghai-Tibet Railway has also played a key role in promoting the economic development of the region. Qinghai and Tibet are both massively rich in natural resources, because of the operation of the railway, the region’s total capacity to move products in and resources out increases 45 times its previous level. The railway also has its most immediate impact on Tibet’s tourism industry. The railway brings more than 2.5 million tourists to Tibet in a single year, creating annual direct tourism income of more than 6 billion yuan.
The Hong Kong - Zhuhai - Macao Bridge: A World - Class Sea - Crossing
The Hong Kong–Zhuhai–Macao Bridge (HZMB) links the Hong Kong Special Administrative Region, Zhuhai City of Guangdong Province and Macao Special Administrative Region, which are geographically close but separated by water. The project is a 55-kilometre long bridge, making it the longest sea crossing in the world. With the bridge in place, travelling time between Zhuhai and Hong Kong would be shortened from about four hours to 30 minutes. The functions of the bridge are to establish a new land transport link between the east and west regions of the Pearl River and to enhance the economic development of the Pearl River Delta area. The bridge was started on 15 December 2009 and on 24 October 2018 it was opened to the public.
Construction Challenges and Uniqueness
The successful construction of HZMB has overcome a number of technological challenges, such as frequent typhoons, crisscross navigation, and in particular high environmental standards. In comparison with other sea crossing bridge in the world, HZMB possesses several engineering uniqueness.
Adoption of Tunnel Boring Machines for Sub-sea Tunnel Construction
For sub-sea tunnel construction, large diameter Tunnel Boring Machine (TBM) was used for excavation underneath the seabed. As a world record, an unprecedented 17.6 m diameter TBM, being the largest TBM in the world, had been utilized to build the 3-lane tunnel. In comparison with the traditional immersed tube method, the use of TBM for sub-sea tunnel construction created less amount of dredging and disposal of 11 mm3 marine sediment. In addition, it also saved the need to divert the existing power cables buried in ocean and helped to preserve the marine ecology, especially the Chinese White Dolphins habitat.
The Non-dredge Reclamation Method
Conventionally, seawalls of artificial island are constructed on firm foundations by replacing the soft marine mud in the seabed with sand, and this process requires dredging and dumping of a large amount of soft marine mud. However, in the HZMB project, an innovative non-dredge reclamation was developed for the construction of artificial island. The seawall was formed by sinking large diameter circular steel cells into soft marine mud with the steel cells then being filled up by sand. This approach significantly minimized the environmental impacts caused by the dredging and dumping.
The adoption of non-dredge reclamation has a number of advantages over the conventional dredge seawall construction approach. Firstly, it greatly reduces the amount of dredging and dumping of marine mud by about 22 mm3, and uses less backfilling material. Furthermore, it imposes less impact on water quality and reduces suspended particles by about 70%. All in all, adoption of non-dredge reclamation significantly reduces the impact of construction on the environment compared to the conventional dredge seawall construction method.
