The Guizhou Expressway Development Corporation is currently undertaking construction of the Chongxihe to Zunyi Expressway (known as the ChongZun Expressway), part of the Chongqing to Guizhou Roads Development Project through the central mountainous region of Guizhou province in China (Figure 1). The ChongZun Expressway will provide approximately 118kms of new grade-separated dual two-lane expressway, from Chongxihe in the north to Zunyi in the south.
Approximately 19km (or 16%) of the route is to be in tunnel, with 11 of the 17 construction contracts including tunnelling works. The longest of these tunnels is 4107m and the shortest 115m. Depth of rock cover ranges from a few meters to approximately 370m. Many of the tunnels are located at high levels in mountainous areas, at between 900m and 1100m elevation, and connect directly with bridges or high embankments. These tunnels have become known as the ‘tunnels in the sky’. Access for tunnel construction in these remote high-level locations has been a major consideration.
Construction commenced in July, 2002, and is scheduled for completion in October 2005. The contracts were open to international tendering, but without exception all contracts were awarded to Chinese companies.
Each tunnel will have two separate tubes, each carrying two lanes of traffic in one direction, except where constructed as ‘double arch’ tunnels, where a single excavation is made for four lanes of traffic with a central dividing wall.
In general, each tunnel tube was driven simultaneously from both portals, although some of the shorter tunnels were driven from one portal only. During the peak construction period (2003/2004), approximately 55 tunnel drives, with a total tunnelled length of over 38kms, were being excavated at the same time. The scale of tunnel construction therefore probably has few parallels elsewhere in the world at the present time.
The total cost of the civil works for the expressway, including many major bridges, the tunnels, and upgrading of 740km of feeder roads, is approximately US$834M. The project is jointly funded by the Asian Development Bank, the Ministry of Communications of the Peoples’ Republic of China, the Guizhou Provincial Government, and domestic commercial banks.
The preliminary and detailed designs were prepared by the Guizhou Institute of Transportation Survey and Design. Halcrow China Ltd was appointed by the Corporation as the international consultant to assist with construction supervision and contract management, and to provide expert technical assistance and specialist training in areas such as tunnel construction and safety, quality assurance, electrical and mechanical installation, and tunnel asset management.
Geology
The project is located at the junction of the northern mountainous region of Guizhou and the southern edge of the Sichuan basin, an area of confluence of north-south and east-west trending major tectonic lineaments. This confluence results in the area being characterised by complex geology, with a series of major fold axes and compression fractures of the rock strata that run predominantly north (sub-parallel to the project alignment), but occasionally east.
The geology along the expressway generally changes in the area of Chumi Town, to the north of Tongzi and very approximately in the middle of the project. To the south of Chumi Town, the exposed rocks are mainly Cambrian dolomites, with limestones, shales, claystones (mudstones) and coal. To the north of Chumi Town, the exposed rocks are Ordovician limestones, Silurian shales, and Permian limestones with coal and sandstones etc.
The lithologies are complex. Limestone is frequently karstic throughout the region, with some significant caves and underground watercourses, some of which have been intersected by the tunnels.
Groundwater levels are often found at high elevations, and represent significant resources. Groundwater conditions presented a significant potential difficulty to construction of many of the tunnels, although major uncontrolled inrushes have been relatively few.
Seismicity in the project area is generally classified as low (Richter Class IV).
Design
The design speed for the tunnels is relatively low at either 60km/hour or 80km/hour. Lane widths are either 3.5m or 3.75m. Initial traffic usage will be predominantly by heavy goods vehicles and long distance buses.
Tunnel design follows a conventional combination of temporary support and permanent concrete lining with waterproofing membranes. The permanent linings are generally reinforced and are 600mm-800mm thick depending on rock conditions. Cross passages for pedestrian escape to the adjacent tunnel tube are provided at 250m intervals, and some of the longer tunnels have vehicle turning bays at 500m intervals. Pavements are of concrete construction, with 3mm deep grooves, sawn at 25mm centres.
Passive fire protection is to be provided to the linings of all tunnels, with a painted or pigmented finish. Where needed, ventilation will be by roof mounted jet fans.
Construction
Excavation of all tunnels has been by drill and blast methods. Almost without exception, no drilling jumbos have been used on the project and all face drilling has been done by hand. All rock bolting and shotcrete – invariably dry mix with mesh – has also been carried out by hand.
The difficulties with drilling for bolts by hand, and applying large volumes of shotcrete safely and quickly by hand, together with the difficult rock conditions, have generally resulted in a greater use of steel arch ribs (or lattice girders) than might otherwise be expected.
High investment costs, and uncertainties of local power supplies, have generally deterred contractors from using drilling jumbos and wet-mix shotcrete spray mobiles on the project
Progress and problems
Impressive progress has been made in all areas of tunnelling. The majority of the tunnels have now broken through, with concrete lining works also complete in many tunnels, and pavement construction begun. At the time of writing (April 2004), the tunnelling works overall are estimated to be approximately 65% complete.
Considering the limitations on mechanisation of excavation and support work, the rates of excavation progress in most cases should be seen as a credit to the workforce.
The rates of lining construction have been equally impressive – the low rates in some contracts generally being the result of other factors, such as waiting for excavation to proceed through adverse ground conditions.
The safety record has been good with no fatal accidents to date. However, there have been particular problems met during tunnel construction including:
weakness, occasionally resulting in squeezing ground conditions.
Conclusion
The scale of tunnel construction for the Chongzun Expressway probably has few parallels at present. Tremendous progress has been made in a relatively short period of time, despite very complex geology and numerous technical difficulties.
Achievements to date are the result of enthusiasm, determination, and sound technical ability at all levels. The technical difficulties encountered have been overcome by adopting sound engineering principles, and making the best possible use of available resources and materials.
Overall progress has been maintained at an entirely acceptable level, and the quality of finished tunnel construction is high. Driving on the finished ChongZun Expressway is a keenly awaited and exciting prospect.
Related Files
Fig 2 – Project alignment plan
Fig 1 – Map of China, showing the location of the ChongZun Expressway
Fig 3 – Project longitudinal profile
