THE DARK LINE
CREATION OF AN ECO-HISTORICAL ROUTE BETWEEN MUDAN AND SANDAOLING - TAIWAN THROUGH THE SANDIAOLING TUNNEL AND A NEW FOOTBRIDGE CORBELLED TO THE CLIFFS OF THE KEELUNG RIVER GORGE
THE SITE, a tropical mountainous region, a post-industrial heritage
We are in the north-east of Taiwan, in a tropical mountainous region, subject to large-scale landslides and floods.
At the beginning of the 20th century, the Japanese colonial administration undertook a colossal railway project to transport the abundant coal produced in the surrounding mines to the major ports of Keelung and Taipei.
When these mines closed, tourism became the main economic asset of the region.
The municipality of New Taipei initiated a program to network the old trails and abandoned industrial sites.
THE QUESTION, a discovery trail
Some twenty years later, the municipality of New Taipei initiated a program of cultural hiking routes, linking old historical paths and abandoned industrial sites, tunnels, galleries, industrial and railway installations. In 2018, was launched a competition to build the section of the route between Mudan and Sandiaoling, which includes two historic railway tunnels and a connection to be invented to replace a bridge that had been washed away.
OUR POSITION, to preserve the post-industrial landscape in its historical and ecological depth
In response to the competition, we take a clear option:
To preserve the post-industrial landscape in all its historical AND ecological depth.
The fact that a structure that required such considerable investment is left to vegetation and bats, with its mouth full of silt and rocks, expresses the power of the changes in History.
The passage of time has produced ecological, atmospheric, acoustic, chromatic and luminous variations along this route, which are the core of our proposal.
THE INTERVENTION, set back from the heritage and the landscape
Despite this attitude of withdrawal in favor of the environments encountered, heavy interventions were necessary to open this route to the public: how to cross a tunnel subject to possible crumbling? How to create a gently sloping floor without "touching" it? How to reinforce a vertical, slippery and fragile rock face and attach to it?
The challenge was to conceal the project's efforts to let the old structure and the landscape speak for themselves.
A SINGLE MATERIAL, iron, in order to lie low
The choice was made to use a single material capable of making forget its presence, but also of evoking the two major phenomena that have impacted the site over the last 100 years:
- steel is building a new "railway",
- the gaps left between the steel bars allow the powerful action of tropical nature to be seen and continued Some 500,000 corrugated steel bars, repeated ad infinitum, follow one another, all parallel, to create a floor that is more openwork than solid, allowing the rocks and silt in the tunnels and the luxuriant vegetation in the gorges to be seen through under our feet. They bend to create railings, benches, bicycle racks, small amphitheaters, kilometer markers... They bend to create protective vaults in the most fragile places, to protect against possible crumbling of the tunnel wall left untouched. A CONSTRUCTION SYSTEM adapted to the difficult geographical context and production conditions in Taiwan To adapt to the complex configuration of the site, the project takes advantage of the specific production conditions of the construction industry in Taiwan. SMEs, midway between industry and crafts, are capable of both efficient mass production in the workshop and "haute couture" adaptation on site. For the tunnels A design of the route based on the geometry of the railway line The track layout is based on the geometrical properties of a railway track, always with tangential junctions. This allows the use of a modular decking system produced in the workshop and then assembled on site. An implementation designed not to touch the existing ground The difficulty was to install the decking without "touching" the existing rock and silt soil and water currents:
- We enter the tunnel as if on tiptoe, on isolated foundation blocks
- metal beams build new rails above the existing ground left untouched. They allow the circulation of a custom-built transport and lifting shuttle. They also serve as a support for the panels of the twisted decking, prepared in the workshop. Once the elevated path has been created, the manual installations can be carried out easily. For the corbelled footbridge A geometric design of the route based on the irregularities of the cliff We geometrically interpreted the irregularities of the face to design a single curved module. The assembly of modules with a very large radius of curvature makes it possible to create almost straight lines as well as sharper curves by reversing the direction of installation. This principle allows the course to follow the uneven and random profile of the topography as closely as possible, without departing from a regulated route. An implementation that does not touch the vertical wall and its vegetation
- a series of concrete blocks, resting at intervals on the cliff. Their rhythm is that of the religiously preserved trees
- the metal brackets are craned from the upper road
- the planking frames, all equal, prefabricated in the workshop according to a rigorous geometry, are laid in one direction and then in the other, to create the curves. A SUCCESSION OF CONTRASTING ATMOSPHERES The eastern entrance At the start of the route, the decking raises to leave the old ground intact, which runs unbroken from upstream to downstream. It lets trees and grasses emerge through it, as well as by the fauna that inhabits them. The atmosphere here is one of undergrowth, of birdsong, chirping insects, rustling leaves, as the water flows below. The Sandiaoling tunnel We now enter the cavernous darkness of the tunnel. Artificial lighting is minimal and bathes the foot of the vault and the floor. It guides the visitors' steps and reveals under the planking, the variations of the original ground: rocks, meanders of water infiltration, colored silts, ballast. The invisible light source spares the intrados, where colonies of bats cling, in a semi-darkness. The darkness of the walls, covered with smoke residues, sometimes gives way to the wet, glittering and multicolored surfaces of limestone concretions in formation. Between the 2 tunnels At the end of this long underground gallery, we arrive at the bottom of a high vertical shaft of natural light, a gap towards the sky left by the bed of an ancient torrent. The sun's rays filter through the layers of foliage of the cliffs and produce, in contact with the vapors exhaling from the tunnel, an unreal atmosphere of a fantastic tale. The Sanzhuazi tunnel After this stop, we enter the second tunnel, which after a wide curve, opens onto the void of the gorge. There, a water mirror lets the luminosity of the opposite bank penetrate under the vault and tells us about the void left by the old bridge that has disappeared. Fed by natural run-off, this basin-haha extends over the cliff in a triangular overhang, pouring water into a waterfall. From the inside, the visitor's silhouette remains suspended between its reflection and the vegetal background of the opposite bank. The footbridge corbelled on the vertical wall of the gorge Deviating to the side, the footbridge corbelled to the vertical wall of the gorge continues the journey like a long balcony, following as close as possible to the sinuosities of the cliff. We now discover, in full light, the distant landscape. In winter, a misty sky reveals a succession of uncertain reliefs. In summer, on the other hand, the violent luminosity highlights everything. As in the tunnels, we explore the depth of the ground and its half-light, here we walk on the canopy of the luxuriant vegetation, between the highest trees, emerging under our steps.
