CHINA IS CHUGGING AHEAD with large-scale construction projects, both domestic and international, that guarantee to kick-start business, bolster trade routes and safely connect people from all corners of their borders. According to the country’s ministry of transport CNY 5 trillion (USD 750bn) will be spent in transport infrastructure over the next three years.
To put this into perspective, there is signifi cantly more spending on infrastructure in China than in the US and Europe combined. According to a new study by the McKinsey Global Institute (MGI), the US and Europe saw spending fall as a share of gross domestic products (GDP) from 2008 – 2013 to 2.5 percent annually. Whereas the MGI report shows China's strength in infrastructure spending. The country spends an average of 8.6 percent of its GDP in infrastructure.
One of the country’s latest projects is the Shen-Zhong Link project. The Shen-Zhong Link is a CNY 30bn (USD 4.76bn) coast-to-coast link that connects the cities of Shenzhen and Zhongshan. The project is part of a wider upgrade in and around Guangdong and the Pearl River Delta. It aims to create a more direct connection between the west and the north part of the river while reducing traffi c through Guangdong.
“There’s only one major crossing in the north currently in operation, close to Guangdong with a bridge across the Pearl River. There is also a crossing in the south in Hong Kong, which is around 70km away. So when this new crossing is built it will cater up to 90,000 vehicles a day. I think some 50 percent of it is heavierthan- normal vehicles. There’s a lot of traffi c of goods going from east to west,” says Michael Tonnesen, chief tunnels specialist from Cowi.
THE COMPETITION
In 2015, the Advanced Work Offi ce held an international design competition in which competitors were challenged to come up with a state of the art crossing for the Shen-Zhong Link Project. The engineering consulting group Cowi and the architect Dissing + Weitling, both based in Denmark, were recently announced the winner. “The competition process is often the way in China; to see if there are good ideas and development in Europe or other countries in the world that they can benefit from, and developments they haven’t seen before. China is always eager to see new things being developed or practiced in the industry,” says Tonnesen.
Cowi states that the key parameters for the design competition were aesthetics, functionality and price. “Key parameters were laid out, and there was a reward, so you get money to provide designs. There are times when there is not a design contract given afterwards, but maybe you get points for putting in a proposal when you’ve won the competition. This happens in China. In Europe this doesn’t normally happen.”
The design competition was a two stage approach: During stage one the key issue for the overall crossing (tunnel, islands and bridges) was architectural appearance of the overall link and to carry out an initial comparison of different options for the key elements of the crossing. This began in October 2015 and lasted until mid January 2015. “The focus here was to make the tunnels look aesthetically nice when they come out into the islands,” says Tonnesen.
During stage two the focus was on the technical description and details. The recommended solution was documented through a number of analysis. “This lasted from February this year to the end of March and included the big suspension bridge, another smaller suspension bridge, two artificial islands and the immersed tunnels.”
However, a Chinese designer was appointed for the actual design of the Shen-Zhong Link in April this year. While infrastructure development is a top priority for China, there are a number of challenges for foreign entities doing business in the country. One of the biggest hurdles to entering the Chinese market for engineering design, construction and consultancy is the need to obtain the requisite qualifications, which are quite stringent in the eyes of foreign companies. Another challenge for foreign companies is the need to understand the local market and the different roles of key players and stakeholders within that market. Any new business to China would be advised to partner with a local company. This is an effective way to navigate differences in the regulatory system, tax laws, contract negotiation, employment practices and corporate culture.
“The Chinese company is cracking on with the design of the tunnel and bridges at the moment,” says Tonnesen. “They will go through a selection phase themselves, choosing the right solution for the tunnel. Once it has gone through the various design phases, and it has gone out for contractors to bid on – and then it has been through an adjustment afterwards to suit the means and measures of the contractor – we will be able to do an independent review and checking of all the design.
“That’s what these international consultant companies were bidding for. Cowi won the bid for owners consultant together with three Chinese consultant companies: Shanghai Municipal Engineering Design Institute (Group); China Railway Tunnel Survey & Design Institute; and CCCC First Highway Consultants. So we will continue on the project during design and construction.”
PROJECT SCOPE
The complete link will be 24km long and consist of two artificial islands, one of which will contain a 15,000 sq m conference hall as well as offices and restaurant facilities; two bridges; and the world’s widest immersed tunnel with eight traffic lanes in dual directions. The proposed concept is a post-tensioned segmental tunnel consisting of 31 elements in total, a typical element being 185m long and the widest being up to 70m wide. The width of the road bore varies from 19m to 38m.
Immersed tunnels are becoming far more common in recent years, with continuous development of construction techniques and technologies that overcome challenging conditions and minimise risk. Immersed tunnels have historically been seen as a third option behind bored tunnels and bridges, but are now becoming longer, deeper and more competitive with boundary pushing projects such as the Swedish-Danish Øresund Link and the Busan-Geoje fixed link in South Korea already completed.
The decision to build an immersed tunnel rather than a bored tunnel was, Tonnesen says, driven by the desired size of the tunnel. “We will have two by four lanes corresponding to a total of eight lanes along the new crossing to cope with the predicted road traffic. The immersed tunnel was considered to be less risky and costly compared to an option with a number of bored tunnels to accommodate the eight lanes including hard shoulders.
“In addition, at the east end of the tunnel it was required to connect the tunnel with a north south running highway on a low level bridge located in the Pearl River Delta. For the immersed tunnel this interface was easier to accommodate compared to a bored tunnel.”
Immersed tunnels can be laid in poor ground conditions that would cause major risks to building bridge foundations or driving through a tunnel boring machine. However, Tonnesen says that the project still pushes the boundaries of what is technically possible.
“To minimise the water blocking and impact on current and sedimentation in the river due to the new crossing, is one of the key elements to be assessed. The Island in middle of the Pearl River, used as transition between the tunnel and the bridge part of the crossing, is one of the elements having an impact on water blockage, water current and sedimentation. The length of the island will be shorter and thereby preferred with an immersed tunnel compared to a bored tunnel,” says Tonnesen. “The demand on the structural capacity to get it to work is really on the limits. We are exploring options such as steel tunnels, because the normal reinforced concrete is just on the limit of being feasible.” The tunnel will be constructed on a soft seabed requiring soil improvement to prevent the elements from settling, and in rough, open waters under deep navigation channels trafficked by the world's largest ships. In addition, the tunnel will be placed in a deep excavated trench and after it has been in use for a few decades, layers of sediment up to 20m thick will accumulate above it. The sediment combined with water pressure from above will impose enormous forces on the tunnel’s central sections. “This will happen over time and we have to design for this,” says Tonnesen. “Water tightness of the tunnel structure is also a key issue, as we have to address the risk of earthquakes in the region. The project bears a lot of similarities to the project we have been involved with in South Korea.”
The Busan-Geoje fixed link in South Korea involved the construction of an 8.2km motorway connecting Busan, Korea’s southernmost and second largest city, to the island of Geoje. It included the construction of a 4km immersed tunnel with two 170m long cut and cover sections at both ends. Similarly to what is expected on the Shen-Zhong Link project, due to soft soils the tunnel foundation included soil improvement (sand compaction piles and cement deep mixing). Towards the western landfall the tunnel elements were placed inside a sub-sea embankment above the existing seabed.
However, it’s the Hong Kong-Zhuhai- Macao Link (HZM Link) project that Cowi was deeply involved in, which is currently under construction, that Tonnesen says bears even more similarities to the Shen- Zhong Link project. The HZM Link is a six-lanes highway connection crossing the Pearl River Delta between Hong Kong and the city of Zhuhai, mainland China, and Macao on the western side. The overall length of the bridge and tunnel crossing is more than 40km.
“We know how to do this type of construction in the area; we know that siltation is a key issue and sometimes during the year you get a lot of deposits from upstream up the river. We had to be mindful of this for the HZM Link, a connection crossing the Pearl River Delta between Hong Kong and the city of Zhuhai in mainland China and Macao on the western side. You have to focus on avoiding risk for the contractor later; making sure that everything is clean before putting in the foundation layer, and before you put in the tunnel elements. You will need to monitor it carefully so you don’t get any delays in the construction,” says Tonnesen. “But, it’s difficult to really know what the Shen-Zhong Link project will end up being, as ultimately it’s the Chinese companies designing it”.
