World Record Making Kawasaki’s Tunnel Boring Machines

The moment on May 22, 1991 when one of two rail tunnels part of the Channel Tunnel, an undersea tunnel linking the European continent and the British Isles, was bored through.


The “Steel Moles” That Reconnected
the European Continent

The Channel Tunnel is a rail tunnel beneath the English Channel that connects the France and United Kingdom. Through this tunnel symbolizing the creation of the EU (European Union), runs a high-speed passenger train developed jointly by France, the U.K. and Belgium called the Eurostar that links Paris and London in a minimum of two hours and fifteen minutes and transports more than 10 million persons annually. Also, Le Shuttle, a two-story road vehicle service, and freight trains operate regularly in the tunnel. The construction of the tunnel and the large-scale high-speed transport network it helped create are important for sustaining the politics and economy of Europe. After being separated during the Ice Age, the European continent and British Isles, which had been divided by water for some 40 million years, were reconnected in May 1991. Finally realizing a grand plan Napoleon had more than 200 years ago, this feat was made possible by two Kawasaki TBM commonly known as “steel moles.”

Channel Tunnel entrance on the French side

0th Plan


The 27th Tunnel Construction Plan, 200 Years After Napoleon’s First Plan

Twenty-six previous plans to construct a tunnel had all ended in failure. Ever since Napoleon Bonaparte’s first plan, ambitious persons in both the France and the U.K. had dreams of constructing a tunnel across the channel. Attempts were made on countless occasions, but as history recounts they were never realized. However, the capsizing of large ferries crossing the Strait of Dover and many other maritime disasters resulted in people changing their dreams for a tunnel linking the channel into wishes. Those dreams were finally answered on the 27th attempt. After the French and British governments agreed to the tunnel’s construction in 1984, they signed an agreement in 1986 to initiate the project. Despite apprehension due to the history of repeated failures, the project moved forward smoothly. One reason for this was sentiment that hindering the smooth movement of people and goods was to be avoided at all costs to insure the operations of a unified market when the European Commission (predecessor to the European Union) was established a year later. In order to increase economic prowess after consolidation of the European Commission, a high-speed network that transported goods in bulk across the channel was essential to each member state, and the rail tunnel connecting France and the U.K. was a key point in the creation of such a network.

A tunnel Napoleon hoped to build is marked with a vertical shaft dug 200 years ago that remains on a hill overlooking the Strait of Dover.


Difficult Specifications Requiring One Machine to Bore an Average of 530 Meters Per Month Continuously for 16 Kilometers

To ease the burden of interest rates, a major technical issue facing this construction project that relied solely on private funding was how quickly the tunnel could be bored and then opened for business. The two TBM ordered from Kawasaki by Transmansche Construction (TMC), the joint venture contractor, were for boring the main railway tunnels underneath the sea from a vertical shaft in Sangatte, France towards the U.K. However, the strata on the French side were complicated and were the most difficult section of the tunnel to bore. On top of that, TMC’s performance specifications were even more challenging. According to the construction plan, boring for the 38-kilometer long portion of the undersea tunnel would be done in two sections – 16 kilometers from France and 22 kilometers from the U.K. – and completed in 30 months. In order to meet these specifications, the machines had to bore at a high speed of 530 meters per month. However, until then, the fastest boring speed in Japan was at most 150 to 200 meters a month. Furthermore, the machines must have been capable of boring 100 meters below sea level in soft layers 40 meters below the sea floor at an average hydraulic pressure of 10 atmospheres. Until then, Kawasaki machines had only worked under three or four atmospheres at most. Under these strict conditions, each machine was required to bore continuously for 16 kilometers.


As a Top Manufacturer, Kawasaki’s Zeal Gave Rise to Unprecedented Tunnel Boring Machinery That Performed at a Maximum Speed of 1,200 Meters Per Month

In addition to strict soil conditions and construction deadlines, Kawasaki was given an extremely tight schedule of only thirteen months to design and manufacture the TBMs in addition to planning and completing the excavation. It took on these rigid conditions since it prides itself on being the top manufacturer in the field, having produced numerous TBM in the past. Hence, it delivered on time two sturdy, intricate TBMs each containing more than 100,000 parts. One machine was assembled at the Kawasaki HarimaWorks, and the other in France. In December 1988, the TBM delivered from the Harima Works commenced boring from the French side. But before workers could get adjusted to operating it, they had to pass through a difficult layer of soil, troubled by high water pressure almost daily, and did things through repeated trial and error during the first, trying six months. But after the machine passed through this layer, it progressed with incredible ease. It easily surpassed the initially projected speed of 500 meters per month, recording an amazing 1,200 meters in its best month. It also reached its initial target point of 16 kilometers eight months ahead of schedule, a feat never achieved before by any TBM. Because of this achievement, Kawasaki was asked to extend its contract to bore an additional four kilometers, pushing the point of breakthrough into British territory a total of twenty kilometers from the starting point.

TBM en route

Newly assembled TBM after trial runs at Harima Works


An Excited Applause 100 Meters Below Sea Level at 11:30 am on May 22, 1991 as the Tunnel Integrated Europe

On 11:20 am on May 22, 1991, an excited applause resounded through the tunnel 100 meters below the Strait of Dover. At this moment, one of the main underwater rail tunnels linking France and the U.K., or better yet, the European continent and the British Isles had broken through. This breakthrough was achieved not only earlier than projected, but also at a point four kilometers farther than planned from the starting point in Sangatte, France where boring had begun in December 1988. The French official in charge of onsite operations praised the TBM, which had set highest monthly speed, continuous boring distance and other records, as being as historically revolutionary as the first jet powered airplane that appeared during the propeller age. The second main rail tunnel was completed on June 28, marking an end to the construction of tunnels that totaled some 150 kilometers in length. This breakthrough, an historical moment when a single rail line undoubtedly linked all of Europe, was welcomed by a feverous applause from personnel in the tunnel.

Breakthrough of the first main rail tunnel. The continuous 30-month long tunnel boring project under the Strait of Dover ends in a resounding success

Workers in hand-powered cars heading for the breakthrough point 20 kilometers away

The First Page in a Newly Opened History of Europe

Ever since Napoleon’s initial plan and 26 failed projects over 200 years, an undersea rail tunnel between the France and the U.K. had finally come into existence. The tunnel’s completion and the passage of a railway has ushered in the beginning of a new era. Taking into consideration the historical fact that France and England had fought each other in the 100 Year War from the 14th into the 15th century, the inauguration of this tunnel has had a major impact on Europe as a whole as it advanced towards actual unification in areas including economy and politics. Kawasaki’s TBM have accomplished a great achievement in the history and future of not just tunnel boring, but Europe, too.

A monument made of cutter heads presented to Eurotunnel by the Kawasaki, which supplied two of the main railway TBM, commemorating the opening of the Channel Tunnel

The Structure of a Tunnel Boring Machine (TBM)

A TBM is divided into a number of sections before it is delivered to a construction site. At the site, the sections are assembled after they have been lowered into a vertical shaft, which is dug in the ground. A cutter head found at the tip of the machine is rotated (three revolutions per minute for the Eurotunnel project) to excavate the tunnel. The excavated soil is removed with a screw conveyor. The excavated tunnel walls are built by connecting ferroconcrete segments. The attached segments are then pushed into place by thrust jacks. After this, the TBM moves forward. While preventing soil collapse, it excavates and reinforces the tunnel walls. This boring process for excavating tunnels is also called the mole method.
Cutter head
Thrust jack
Screw conveyor
8.78 meters
Length:13.75 meters
A vacuum suction device enables the smooth installation of segments