Seikan Tunnel

In 1954, a typhoon sank five ferry boats in Japan’s Tsugaru Strait and killed 1,430 people. In response to public outrage, the Japanese government searched for a safer way to cross the dangerous strait. With such unpredictable weather conditions, engineers agreed that a bridge would be too risky to build. A tunnel seemed a perfect solution. Ten years later, work began on what would be the longest and hardest underwater dig ever attempted.

Engineers couldn’t use a tunnel boring machine to carve the Seikan Tunnel because the rock and soil beneath the Tsugaru Strait was random and unpredictable. Instead, tunnel workers painstakingly drilled and blasted 33 miles through a major earthquake zone to link the main Japanese island of Honshu with the northern island of Hokkaido. Today, the Seikan Tunnel is the longest railroad tunnel in the world at 33.4 miles in length, 14.3 miles of which lie under the Tsugaru Strait.

Three stories high and 800 feet below the sea, the main tunnel was designed to serve the Shinkansen, Japan’s high-speed bullet train. Unfortunately, the cost of extending the Shinkansen service through the new tunnel proved to be too expensive. In fact, air travel today between Honshu and Hokkaido is quicker and almost as cheap as rail travel through the tunnel. Despite its limited use, the Seikan Tunnel remains one of the greatest engineering feats of the 20th century.

Unit five. Underground

1. Reading Comprehension

The Construction of London Underground

Location: London, England

Completion Date: 1863 (first line)

Length: 19,800 feet (3.75 miles)

Purpose: Subway

Setting: Soft ground

Materials: Cast iron, brick

Engineer(s): Sir John Fowler

The London Underground is a public transport network, composed of electrified railways that run underground in tunnels in central London and above ground in the city’s suburbs. The oldest metropolitan underground network in the world, first operating in 1863, the London Underground is usually referred to as either simply ‘the Underground’ by Londoners, or (more familiarly) as ‘the Tube’.

Shortly after the opening of the Thames Tunnel, Parliament authorized construction of the first subway system in the world, the London Underground. Work began in 1860 on the first stretch of the underground subway, the Metropolitan Railway. By all accounts, it was a royal mess. Tunnel diggers used the cut and cover method: they carved huge trenches in the streets, lined the trenches with brick, covered the trenches with arch roofs, and then restored the street above. This sloppy method paralyzed traffic and made canyons out of city avenues. Cut-and-cover construction on the District line necessitated the demolition of a number of houses over the site of the line between Paddington and Bayswater, but it was a huge success. The new subway carried more than nine million people in its first year!

Soon, Londoners were craving more, and they got it. This time, with the help of James Henry Greathead’s tunnel shield, London engineers could tunnel under the city without completely destroying the streets above. Greathead’s round iron shield supported the soft soil as it moved forward and carved a perfectly round hole hundreds of feet below London’s bustling city streets. Inside the shield, tunnel workers laid cast-iron segments end to end. These segments eventually formed a stiff, waterproof tube, perfect for subways.

Lines on the Underground can be classified into two types: sub-surface and deep level. The sub-surface lines were dug by the cut-and-cover method, with the tracks running about 5 metres below the surface. Trains on the sub-surface lines have the same loading gauge as British mainline trains.

The deep-level or ‘tube’ lines, bored using a tunnelling shield, run about 20 metres below the surface (although this varies considerably), with each track running in a separate tunnel lined with cast-iron rings. These tunnels can have a diameter as small as 3.56m and the loading gauge is thus considerably smaller than on the sub-surface lines, though standard gauge track is used.

The first trains were steam-hauled, which required effective ventilation to the surface. Ventilation shafts at various points on the route allowed the engines to expel steam and bring fresh air into the tunnels. One such vent is at Leinster Gardens, W2. In order to preserve the visual characteristics in what is still a well-to-do street, a five-foot-thick (1.5 m) concrete façade was constructed to resemble a genuine house frontage.

Following advances in the use of tunnelling shields, electric traction and deep-level tunnel designs, later railways were built even further underground. This caused far less disruption at ground level than the cut-and-cover construction method did. It was therefore cheaper and preferable. The City & South London Railway (now part of the Northern line) opened in 1890. It was the first ‘deep-level’, electrically operated, route.