The hosting provider for the blog moved the blog to a new server infrastructure earlier last week. Apart from problems getting e-mail working again, everything seems to be working, however this will be the first post to be sent out via the e-mail subscription service, so I hope it is received. As well as the blog being moved, the weather last Wednesday was wonderful, so I did what seemed a good choice on a day of sunny weather, I headed to the Isle of Dogs and the Greenwich Foot Tunnel.
The Greenwich Foot Tunnel is at the southern tip of the Isle of Dogs, to the western side of Island Gardens, one of the best places to stop and take in the view across the river to Greenwich:
Island Gardens are relatively small, but a very welcome area of green, open space facing onto the river. View through the trees of the four chimneys of the old Greenwich power station across the Thames:
It would have been easy to stop and watch the river for some time, however after a walk from Poplar Station on the DLR, I wanted to cross to the other side of the river before the sun set too low on a late autumn day.
There are almost identical entrances to the Greenwich foot tunnel on both sides of the river. This is the entrance in Island Gardens, with a low sun directly behind the entrance:
On the opposite side of the river, the translucent glass roof of the Greenwich entrance can be seen alongside the Cutty Sark:
The Greenwich Foot Tunnel was one of a number of tunnels constructed under the River Thames in the late 19th and early 20th centuries. Those wanting to travel between the north and south sides of the river had long been restricted to a ferry, or long journey to the nearest bridge in central London.
A single tunnel Blackwall Tunnel had opened in 1897, the Greenwich Foot Tunnel in 1902, the Rotherhithe Tunnel in 1908 and the Woolwich Foot Tunnel in 1912.
A period of fifteen years that had opened up a range of new routes to travel between opposite sides of the River Thames, no doubt one of the benefits of having the London County Council responsible for major works across the city.
A foot tunnel for those who lived and worked on different sides of the river, or who had business that needed a crossing, had been identified as an urgent need for a number of decades in the second half of the 19th century, however it was not until the final five years of the century that the scheme would get underway.
On the 12th May 1896, newspapers were reporting that a Bill for the tunnel was to be put before Parliament:
“PROPOSED NEW THAMES TUNNEL. A LONDON COUNTY COUNCIL SCHEME – The Bridges Committee of the London County Council have prepared a report, to come before the Council today, recommending that application should be made to Parliament for power to construct a foot passenger tunnel to connect Greenwich and Millwall, at an estimated cost of £75,000, and that the Parliamentary Committee of the Council be instructed to prepare the necessary Bill, to be introduced in the Session of 1897.
The report states that, in addition to the above amount, which is the estimated cost of land and works for the proposed tunnel, a sum of not less than £25,000 as the law at present demands, would have to be paid as compensation to persons interested in a ferry which exists at the spot in question; but it is hoped that the Council will succeed in obtaining a clause by which ‘improvement of interest will be considered, thereby reducing this amount very considerably.’
The plan is to have a tunnel with a footway of eight feet, and a headway of rather more than nine feet in the centre, reduced to a minimum of seven feet and a half at the outsides. Electricity is to be used for lighting the tunnel, as also for working the ventilating and pumping machinery. The time required for the execution of the works is expected to be about twelve months, Calculations are given to show that the proposed tunnel would be a more economical provision than establishing a free ferry.”
The London County Council estimated a cost of £75,000 for the construction of the tunnel, and this was the value put forward in the Bill to Parliament, however as with almost every major civil engineering project since, the cost would turn out to be much higher.
The council invited tenders for the construction of the tunnel, and the winning tender was from Messrs. J. Cochrane with a price more than one third above the estimated cost. The Bridges Committee recommended that the council accept the bid, however the council were not happy and wanted the additional third of the estimated cost to come from “local or other sources”, however when put to the vote, the recommendation of the Bridges Committee was accepted and the work would soon commence.
The new tunnel was opened on the 4th of August 1902.
The route down to the tunnel is via several flights of stairs from the entrance in Island Gardens. The lifts are currently out of use.
Spiral stairs line the inner wall of the shaft, with the central space being used for the lift:
From the bottom of the Island Gardens shaft, the view along the tunnel towards Greenwich:
In the above photo, a cream coloured section can be seen a short distance along the tunnel.
The section is the temporary war time repairs following damage caused to the tunnel by the nearby explosion of a high explosive bomb. A closer view is seen in the photo below, and there is an information panel on the left:
The damage to the tunnel happened on the evening of the 7th September 1940, when a bomb exploded on the foreshore, over the route of the tunnel.
Within the tunnel, the blast caused the outer tiles and inner concrete lining of the tunnel to collapse over the length of the tunnel now covered by the temporary repairs. The outer iron lining appears to have held, however this was now leaking and water was entering the tunnel to such an extent that a week after the bombing, the tunnel was full of water.
The tunnel was such a key part of the local infrastructure, providing workers living on the south of the river with easy access to the docks, ship yards and factories in the Isle of Dogs and east London, that a repair of the tunnel was essential.
It took around ten days to pump out the majority of the water, enough that work could start on repairs.
Being wartime, a temporary repair was put in place, consisting of a length of iron collars bolted together to line the damaged area, and effectively form a smaller tunnel within the larger tunnel. At the time, these repairs were considered sufficient to last the war, following which, more permanent repairs could be put in place, and the tunnel restored to its original size.
As well as infrastructure projects always running well over their initial budget estimates, temporary repairs also often become permanent, and so it is with the repairs in the Greenwich Foot Tunnel, and the cream coloured iron rings, reducing the diameter of the tunnel, are still the result of the original 1940 repair work.
Walking through the temporary repairs and at the end we can see the tunnel continuing on down to the lowest point roughly under the center of the Thames.
Now we are roughly in the center of the tunnel, it is a good place to stop and consider the original construction.
I have a fascinating little booklet called “The Greenwich Footway Tunnel by William Giles Copperthwaite and Subaqueous Tunneling Through The Thames Gravel: Baker Street and Waterloo Railway by Arthur Harry Haigh”.
The booklet is an extract of the proceedings of the Institution of Civil Engineers, and was published in 1902, the year the Greenwich foot tunnel opened. It is a wonderful little booklet with details of tunneling below London and the impact of the geology through which the tunnels are constructed.
The first part of work to build the tunnel was the sinking of the shafts down to the point where the tunnel could start to be bored under the Thames.
The shafts were formed by sinking a caisson around the edge of the shaft, as the shaft was gradually excavated. A caisson is basically a hollow ring of iron or steel that forms a tube from top to bottom of the shaft and provides the strength to stop the sides of the shaft collapsing inwards, or the walls deforming.
The shafts, as with the whole of the tunnel, were constructed in an environment of compressed air. This method was used to control the ingress of ground water and to provide some support to the ground through which the tunnel is being bored. The use of compressed air did require some additional support for the workers, and faclities such as air locks to provide access to the work face.
The following diagram shows the method of sinking the caissons. The shaft was sunk through the water level which was found at a depth of 35 feet, from which point, construction continued using compressed air.
The caissons, today the walls of the shaft, are made up of two steel rings. The outer diameter of the shaft is 43 feet, and the inner diameter is 35 feet. Allowing for the width of the two steel rings (one outer, one inner), there was a four foot gap between the two rings of the shaft. This was filled with a mix of 6 to 1 Portland cement concrete. The use of concrete as a filling between the two rings meant that accurate construction and fitting of the rings was essential as once the concrete was poured, there was no way to make any further adjustments.
This method of construction created a pair of incredibly strong shafts on either side of the river, and the weight of the caisson forming the wall of the Poplar shaft was a remarkable 2,560 tons.
Compressed air was put in place from the 2nd of May, and the following table records the depth below the surface achieved each day until completion of the Poplar shaft on the 31st May, 1900.
The table also shows the accuracy of the excavation by the very small amounts that the cutting edge was out of level. The increasing weight of the caisson can be seen by the load on the shaft.
The following drawing shows the route of the tunnel between the Poplar and Greenwich shafts. Note that just above the Greenwich shaft is the Ship Tavern. This pub was badly damaged during the war, demolished, and the Cutty Sark is now on the site of the pub.
The following drawing shows a cross section of the tunnel. As will be seen in my photos of the tunnel today, the tunnel descends from both shafts with a gradient of 1 in 15 feet, down to the central part of the tunnel where it passes under the deepest part of the Thames.
The diagram also shows the type of material that was being excavated through, and was a key consideration in the tunneling method used.
The drawing is a text book example of how to present lots of information in a single drawing. As well as the key lengths, gradients of the tunnel, high and low water level of the Thames, depth of water, dimensions of the shafts etc. the Progress of Tunneling at the bottom of the drawing shows how the tunnel was making its way under the river through 1900 and 1901 as it started from the Poplar shaft and headed to the Greenwich shaft.
Newspapers reported on reaching the half-way point:
“IT IS NOW HALF-WAY TOWARDS COMPLETION – A new tunnel between Poplar and Greenwich is another step in the piercings of the river bed which the London County Council splendidly inaugurated with the making of the Blackwall Tunnel.
The new tunnel will be opened to the public in about a year’s time, and, inasmuch as it is being made wholly in the interests of working men, it might be called the ‘Working Men’s Tunnel’. From shaft to shaft it will measure 1217 feet in length, and will cost about £109,500. The depth of the tunnel at the centre of the river is about 72 feet below the ground line, while the shafts have been sunk to an average depth of 63 feet.
At no part will the top of the tunnel be less than 13 feet below the river bed. No fewer than 1600 tons of cast iron tubing will be used in building the tunnel which will be lighted by electricity. You will approach the tunnel from the Greenwich side from the north end of Church Street, in the rear of the famous Ship Tavern; and on the Millwall side at the Western end of Island Gardens. Some such easy means of communication between one shore and another has long been needed, and many thousands of people will daily find it very handy once it is opened to the public.”
The lining of the tunnel was made up of cast-iron segments, of which eight segments and one key piece formed a complete ring around the tunnel. The lining was 12 feet, 9 inches in outer diameter and 11 feet 9 inches internal diameter.
The following drawing shows a cross section of the tunnel, including the lining, and ducts for services such as electrical wiring, ventilation pipes and cable conduits.
The interior of the tunnel was lined with white glazed tiling, which is still in place today.
The booklet includes some wonderful detail of sections of the tunnel lining:
The washers where the bolts secured the sections together were made using a short section of lead pipe. When the bolt was tightened, the lead would compress forming a water tight seal around the bolt.
Lead wire and iron filings were used to fill any spaces between sections, and the method of construction was so successful, that when air pressure was removed at the end of construction, only a dozen places had a small problem with water ingress and needed repair.
The tunnel was constructed using a shield of the type known as a trap or box shield, which the booklet describes as follows:
“The trap consisting of two diaphragms, the front one filling the upper half and the back one the lower half, of the circle enclosed by the cylindrical skin of the shield.
The bottom of the front diaphragm is a few inches lower than the top of the back one. In the event of an inrush of water from a ‘blow’ occurring at the face, the water must flow over the top diaphragm to get into the tunnel, and before it rises high enough to do this, the bottom of the top diaphragm is under water, and all escape of air through the shield is stopped. the water in fact becomes a seal to hold the air.”
The above description simplifies the design, construction and use of the shield, and cross sections through the shield as used at Greenwich are shown in the following drawings.
The central box formed a water tight chamber, and the shield consisted of thirteen rams for pushing the shield forward, and together exert a pressure of 1.5 tons per square inch, and a total thrust to push the shield forward of 750 tons.
The design of the shield was changed as it progressed on its route under the Thames, as improvements were identified and as different types of strata were encountered.
This included putting doors in the upper part of the shield, as well as the lower, giving workers an additional method of exit if there were problems at the face of the tunnel. It was noticed that after these additional doors were added, workers were more inclined to stay at the face of the shield after there had been a fall of material, as they had a higher route of exit than before.
As well as the safety of workers at the shield face, another consideration was the conditions of working in an environment where compressed air was used. As well as care of their workers, there was also probably a financial motivation as the Act of Parliament authorising the tunnel included compensation to those whose health had been damaged by working in compressed air. Compensation seemed rather limited though as a total of £20 had been awarded to three workers.
Two medical officers were appointed to oversee the construction of the tunnel. Those working in the tunnel were examined at least once a week and before anyone could commence work, they had to have a certificate of health from the medical officers.
Of those who applied to work on the tunnel, 13.9% were found to be unfit to work on initial examination, and of those who passed the medical, a further 5.7% were found to be affected by the increased air pressure, and forbidden to continue work in the tunnel.
Men worked an 8 hour shift with a rest period of 45 minutes, during which time they had to exit the tunnel.
Rooms were available with washing facilities at the construction site for the workers, and hot coffee was served as they left the tunnel.
A “medical lock” was available for treating those with “caisson-sickness”, probably similar to today where a diver has to decompress in a chamber. Only three workers needed to make use of this facility during the construction of the tunnel.
A concern with tunnel construction was the potential build up of carbon dioxide, and as the construction of the tunnel progressed, an experiment was approved whereby an apparatus was made and installed to removed carbon dioxide. This consisted of a series of wooden boxes bolted together. In each wooden box there was an amount of crushed pumice stone. Air was passed through the boxes, and it was found that deposits of carbonate of soda were found on the pumice stone, and that the experiment did result in the removal of some of the carbon dioxide in the air within the tunnel.
Construction of the tunnel was relatively straight forward given the technologies of the time, and construction methods were able to adapt to the changing sand, clay and ballast through which the tunnel was being bored. For a period between the 22nd February and the 1st May 1901, an impressive 10 feet per day was being achieved in driving the tunnel forward.
The tunnel met the Greenwich shaft without any problems, and minor precautions were made to stop any fall of sand or ballast from the area around the shaft as the tunnel was completed.
The Isle of Dogs and Greenwich were finally connected by a walking route.
In the following photo, the incline up to the Greenwich shaft from the centre of the tunnel can be seen:
I am not sure whether it was my imagination, however standing in the centre of the tunnel, it seemed possible to hear the sound of the occasional passing boat on the river above.
At the start of the incline where the tunnel rises by 1 foot in every 15 feet, up to Greenwich:
Almost at the Greenwich end of the tunnel looking down the incline:
Approaching the Greenwich end of the tunnel, and it looks as if we are approaching an entrance to some secret infrastructure below London – unfortunately it is only the closed entrance to the lift which should be operating.
The tunnel today is brightly lit and there is a frequent flow of walkers through the tunnel. It has not always been this way, and as the docks and industries closed on either side of the river the numbers walking through declined and there were times during the 1980s when you needed to be cautious when using the tunnel.
A final look down the Greenwich foot tunnel:
The Greenwich shaft is slightly deeper than the Island Gardens shaft. I counted 87 steps down from Island Gardens, and was rather surprised to count a round number of exactly 100 steps up the Greenwich shaft:
Whilst walking up the shaft, a look up shows the cantilevered steps of the spiral above:
At the top of the steps, one of the current landmarks of Greenwich confirms that you have arrived on the south bank of the River Thames:
But before leaving, another look up shows the wonderful construction of the glass dome that covers the entrance to each shaft:
As well as the bomb damage to the tunnel, the entrance buildings and shafts were also damaged by bombing, with an oil filled incendiary hitting the Island Gardens shaft, causing considerable damage to the lift control equipment. The Greenwich entrance was also hit by an incendiary bomb, but did not suffer as much damage as at the northern shaft.
Plaques above both entrances to the tunnel record the opening in August 1902, along with key figures in the London County Council responsible for the tunnel:
A view of the Greenwich entrance to the tunnel, with the Island Gardens entrance across the river, just to the right:
The original lifts were added in 1904, two years after the tunnel opened, these were attendant operated until the early 21st century. New lifts were installed in 2012, however there have been periods when the lifts were not that reliable, with significant problems with the glass doors closing reliably, and they are currently closed.
A major problem with the lifts is that they are almost a custom design, having to fit inside the original lift space in the centre of the shaft, and also within such a historic structure.
Special parts for the lifts are sourced from Germany, and it is still expected that the lifts will be closed for some months.
Outside the tunnel entrance is an excellent view of the Cutty Sark:
And looking across the river is the ever expanding collection of towers that are growing across the Isle of Dogs:
View to the west, towards the City of London from close to the Greenwich entrance to the tunnel:
Looking east from the entrance to the Greenwich foot tunnel:
The Greenwich foot tunnel was certainly a success, and a major improvement on the ferry which the tunnel replaced.
A ferry had been operating between the Isle of Dogs and Greenwich for hundreds of years, and such was the level of traffic, that from 1883 the Thames Steamboat Company operated a steamboat ferry, which did have problems operating in a very crowded section of the river (hard to believe when looking at the view today just how busy the river has been).
Despite this, the steam ferry was carrying around 1,300,000 passengers a year, which seems remarkably close to the 1.2 million a year that the Royal Borough of Greenwich state on their website as using the tunnel today.
The booklet states that the foot passenger ferry rights continued to exist after the opening of the tunnel and were owned by the Great Eastern Railway Company.
It would be interesting to know if these rights still exist and whether Network Rail could today run a passenger ferry across the Thames at Greenwich.