(II) Expressways in canal towns and coastal areas

The crisscross rivers, gullies and streams, together with scattered rice fields and fish ponds all over, are typical of the landscape to the south of the Yangtze River. They make lovely canal towns but meanwhile pose special difficulties for highway construction there. The Shanghai-Jiading Expressway constructed in December 1984 was the first expressway in mainland China and an experimental highway. The typical soil texture in Shanghai is soft soil, with the water content in the surface soil higher than the optimal level for soil base compaction and thus not easy to dry. The Shanghai-Jiading Expressway passes through several sections based on the ground of soft soil and silt. In other words, you can neither simply squeeze out the water nor dry it. It is like building a highway on “tofu.” Therefore, how to treat soft ground and control ground subsidence became a vital issue. In the early stage of the Shanghai-Jiading Expressway construction, a series of sci-tech research projects were carried out, such as the Stability Research of Building High Embankments on Soft Ground” and “Research on Application of Geotextile in Expressway Construction.”

i. Soft ground treatment as a stumbling block

In the canal towns to the south of the Yangtze River, the highway pavement should be appropriately higher than the natural ground,leading to increased load on the roadbed, excessive ground settlement, and poor stability, which undermines the stability of bridge structures and pavement structures. The embankment of the Shanghai-Jiading Expressway at the height of 2.5 meters and above accounts for 70% of the total length. Under the premise of ensuring quality and keeping to the schedule, the builders adopted three methods in line with the height of fill and the geological conditions, namely the natural settlement method, fly ash and soil interval filling method, and bagged sand drain preloading drainage consolidation method.

Soft ground treatment is arguably the crux of expressway construction in the riverine areas. The canal towns to the south of the Yangtze River need a large number of expressways. As a result of the rapid economic development, the Yangtze River Delta and the Pearl River Delta became the main battlefields for early expressway construction. In the early 1980s, China concentrated its efforts on studying and promoting heavy compaction standards to control the degree of subgrade density. However, this method is time-consuming and labor-intensive. Facing an urgent need for soft ground treatment technology, the builders widely applied such measures as replacement foundation, sand blanket, and plastic drainboard for soft ground treatment. In this way, they built expressways with distinctive features in canal towns to the south of the Yangtze River.

Today, it seems that the soft ground treatment is no longer a problem. We dedicate a special section to the expressway in canal towns and coastal areas to display a unique landscape.

During the construction of Shenyang-Dalian Expressway and Beijing-Tianjin-Tanggu Expressway, the Ministry of Communications began to mull over the construction of Shanghai-Nanjing Expressway(CCCC Second Consultants Co., Ltd., the CCCC First Highway Engineering Co. Ltd., CFHEC, and CCCC Second Highway Engineering Co. Ltd.). Shanghai and Nanjing are key cities in the Yangtze River Delta, with several well-developed medium-sized cities and hundreds of rivers. Due to the doubts over expressway construction and a massive demand for funds, this expressway was not among the first to be built. In 1990, the state approved the development and opening up of Pudong District in Shanghai, which became an impetus for the construction of the Shanghai-Nanjing Expressway, followed by the approval of the State Council in 1991. The expressway is designed for a total length of 274 kilometers, mainly in Jiangsu Province. The initial plan was to build the eastern section before the western section. When construction started, Jiangsu Province decided to speed up the progress by building the two sections simultaneously. However, the ambition was still constrained by funds. Simultaneously, the cost of expressway construction has jumped from 15 million yuan to 25 million yuan per kilometer. Apart from bank loans, Jiangsu Province raised some funds in the cities along the route. More importantly, in 1992, Jiangsu set up a company based on the expressway under construction. The company issued stocks and bonds to raise funds, which introduced a market mechanism into the expressway construction for the first time. In 1996, the Jiangsu section of the Shanghai-Nanjing Expressway was completed two years and three months ahead of schedule. In addition, the engineering quality reached an excellent level. The overall engineering quality was top-notch in China and the engineering quality of the soft ground treatment in the riverine areas met the highest international standards, which showed that expressway design, construction and management in China reached a new level. Furthermore, this expressway is distinctive in that it brings large-scale construction projects closer to the people. The expressway passes through relatively developed areas and requires large-scale land requisition and demolition. However, as the expressway meets the universal and urgent aspiration of the public, the land requisition and demolition were supported by the people. There was a story about this. After hearing about the construction of the Shanghai-Nanning Expressway, the pupils of Erchen Primary School, Dasi Township, Jiangyan District, Taizhou in northern Jiangsu Province, donated all their pocket money, a total of 20.1 yuan,, to the project. The expressway headquarters returned the money but appreciated their kind offer. It is reported that in the later stages of expressway construction, people nearby went to visit the project and even the elderly people with limited mobility asked people to take them there just for a look.

ii. Living examples of expressways in canal towns

There are many expressways in the riverine areas in Zhejiang Province. Shanghai-Hangzhou-Ningbo-Wenzhou Expressway is a vital communication line in the province, passing by a large number of cities such as Jiaxing, Hangzhou, Shaoxing, Ningbo, Taizhou, and Wenzhou. The Shanghai-Hangzhou-Ningbo section is the first expressway in Zhejiang Province, the “golden line” connecting Zhejiang with Shanghai, and the main line linking Ningbo with Zhoushan Port. It was completed and opened to traffic at the end of 1998. The Ningbo-Wenzhou section was completed around 2007. Its construction involved the treatment of various types of soft ground. Based on the study into the hydric-soil-containing performance of soft plastic-fluid plastic, combined with a series of technologies, a reinforcement plan for the high embankment on the soft ground alongside the mountain came into being. In addition, an in-depth study into the settlement of the expressway on the soft ground was conducted, followed by corresponding methods for design and construction. Generally speaking, the surcharge preloading and vacuum induced preloading technologies that combine preloading with plastic drainboard are widely applied.

The Guangzhou-Shenzhen-Zhuhai expressway is a typical example of expressways on the alluvial plain in the delta region. The alluvial plains are often densely covered with river networks and crisscross ditches, allowing only boats to flow through large or small watercourses. The soft ground soil usually contains organic matters and voids, which can be roughly analogized to plasticine. Therefore, soft ground treatment is a compulsory course for expressway construction on soft ground.

The Fuding-Ningde Expressway in Fujian Province is an example of a coastal expressway built on a soft ground of coastal plains and tidal flat areas along the beach. Such soft ground features low strength, large deformation, and a long time for consolidation, easily leading to a relatively large settlement. A special construction plan on coastal soft ground was made from the beginning of the design, proposing to adopt varying approaches for different soil textures, including excavation and replacement, throwing stones to packing sedimentation, and blasting silt-removal. The expressway was completed in 2003, and its construction plan for the rockfill subgrade was later promoted throughout the country.

After 2010, large land areas were reclaimed through dredger fill in coastal areas in Tianjin and Hebei Province and different types of expressways were constructed on these reclaimed soft ground, requiring extensive application of soft ground treatment techniques. Caofeidian, under the jurisdiction of Tangshan City in Hebei Province, is an isolated island on the sea. At an ideal water depth, Caofeidian is perfectly suitable for port construction. At the beginning of the 21st century, Caofeidian became the focus of port construction and development in Hebei Province and even the whole country. However, first and foremost, it requires a highway leading to Caofeidian on the ground of large areas of saline-alkali soil, deserted beaches, and even “fresh” soft soil filled with sediment in the sea. The builders used bagged sand as a foundation to build the highway. There was also a twist in the process.During the earthworks, the roadbed once disappeared after a night of strong winds and great waves, leaving builders no choice but to restart from scratch.

For the sake of expressway construction, the support capacity of the foundation could be improved through a variety of soft ground treatment techniques. However, given the uneven distribution of various types of hydric soil, if the problem cannot be solved as a whole, the geological settlement at various sections will cause the depression and cracks of the road surface. Generally speaking, heavy-load tamping can be applied to dig out and replace the hydric soil, or the approach of riprap can be applied to change the roadbed completely. However, these approaches require either a long time or a large amount of materials such as rocks, bagged sand, and geotextiles. Therefore, with the advancement of technology, rapid drainage technology has begun to be widely applied. In recent years, due to extensive application in large scale land reclamation through dredger fill, the technology of rapid reinforcement of soft soil has gradually matured. For example, in some processes, a layer of woven cloth is laid on the surface of the hydric soil before laying the main drainage pipe and branch drainage pipes to form a grid-like horizontal drainage channel, which forms a closed loop with the vertical drainage channel. Then, after paving the non-woven fabric and sealing membrane, water is pumped by a water pump for drainage and reinforcement of the soft soil.

iii. Expressway upgrading in canal towns

Similarly, these highways also face the problems of retrofitting and reconstruction.

For example, the traffic volume of the Shanghai-Nanjing Expressway was close to saturation after a few years of operation, failing to meet the needs of economic and social development. In fact, this situation had been foreseen since the beginning of preparing for its construction, but due to various limitations, it was decided at the time to reserve tens of thousands of mu (a unit of area, one mu equals to about 0.0667 hectares) of land on both sides of the highway, in preparation for the future expansion of lanes at a lower cost. Since the beginning of the upgrading project of the Shanghai-Nanjing Expressway in 2003, the traffic had not been interrupted at all, which is the first time in the history of expressway construction in China. In only about two years, the upgrading project was completed and the whole line was opened to traffic in 2006. The upgraded Shanghai-Nanjing Expressway has eight wide lanes in two ways, facilitating smooth traffic flow. In charge of the upgrading project, the CCCC Second Highway Engineering Co. Ltd. took the lead in China to retrofit it into an eight-lane expressway without interruption to traffic. Well-developed temporary plans for traffic control, diversion, and dispersion were made for the early, middle, and later stages of the upgrading project. By making the best use of the existing traffic engineering facilities, combined with the characteristics of the highway network along the route, the CCCC Second Highway Engineering Co. Ltd. carried out research into particular topics, implemented dynamic design at all stages, and set up complete temporary traffic engineering facilities to ensure the smooth progress of both upgrading project and traffic operation.

The traffic volume of the Shanghai-Hangzhou-Ningbo Expressway has been increasing at an annual rate of about 15% since its opening. The reconstruction project will expand the four lanes to eight lanes, which is equal to building another “Shanghai-Hangzhou-Ningbo” line. Among them, 90% of the expressway for reconstruction involves soft ground treatment. In response, a series of countermeasures for soft ground treatment, such as embankment piles, powder sprayed piles, and plastic drainboards, was widely adopted to reinforce the soft ground.