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About the Author
Edmund W. Jupp (BSc (Eng), FIMech E) was born during the First World War in Sussex, England and received his early education at Brighton. After service in the 1939-45 war he worked in engineering and education, and travelled widely. He was appointed Principal of the Technical Institute in Guyana.
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By Edmund W. Jupp
Intellect LtdCopyright © 2000 Intellect Ltd
All rights reserved.
When people began to move about the country, in ancient times, it was along paths, following tracks through forests or across open spaces; and these were along the best routes, not always the shortest, with changing steepness here and there. These tracks ran over hills and valleys as convenient, for a man might move up and down hill with little difficulty. There was no problem about siting the paths. They just followed the trails long established by generations of feet trampling the ground as they went about their business.
They often had to dodge round obstacles like large trees, deep holes, dangerous areas, and marshy ground, so the ways were rarely direct or straight. They wriggled their way along from place to place. These paths became well-established in time, and in some cases were eventually made more permanent, perhaps having laid upon them some hard-wearing material.
Sometimes the swerving lines persisted long after the original obstacles had vanished, as is clear from the twisty lanes to be seen in the countryside today. In recently-developed countries, modern machinery deals easily with obstructions, sweeping them away to provide straight swathes along which roads are built. So one usually finds straighter roads in modern countries and rather less direct routes in older-established areas.
Roads follow old trails
Where development has been slow, and when buildings have been erected along the old ways new roads have had to follow the twists of the trails to minimise demolition work of earlier buildings. In some cases the havoc wrought by war has flattened large areas, so that new construction work has been able to take advantage of this to plan more direct routes.
When getting around no longer depended upon walking only, i.e., when men began to use animals, these could manage the smaller hills generally with little discomfort. However, even sturdy nimble pack animals could not cope with very steep places, and they had to find ways round; so there were inevitable kinks in the routes; and when draught animals were used, pulling carts and wagons of various kinds, even the gentler gradients or narrow passes often entailed detours. Steep gradients were formidable obstacles. So more kinks developed, and the wagons followed slow and twisty routes to get from one place to another.
Need for direct routes
For movements of people and goods there was little call for going underground. Only for providing shelter, or getting at the wealth of mineral deposits was it necessary to start digging. Tunnelling into the sides of mountains could bring rich rewards for those willing to take risks. Archaeology is revealing much of what went on in those days, and we have been able to reconstruct the methods of the early tunnellers from remains of the people and the tools they used.
When man, faced with hills and mountains, began to seek more direct routes his thoughts turned to making holes through the obstructions. There have always been problems when working beneath the earth's surface, even when it consisted of little more than scratching away at soft surfaces to make a hole and then slowly enlarging and lengthening it; and the overall challenge of drilling large holes consists of a large number of related problems, some of which require the attention of specialists.
The gradient problem
In more modern days, with the coming of canals and the spread of road and railway systems, steepness became the principal problem. Road traffic could manage fairly steep stretches; and it wasn't too hard a problem to ease the slopes for motor- driven transport. The road itself could be built with curves so as to wind about a little thus reducing the effective rate of climb. A gradient is defined by the amount of height gained or lost in unit distance traversed along the route, so that any increase in distance horizontally for a given rise decreases the gradient.
When a road skirted a particularly steep mountain side the builder was forced to tunnel through here and there, as in the Alps, and in the Rockies of North America, and this was to avoid running the road too near a precipitous edge.
A good example of a road tunnel is that through Mont Blanc. Here a great mountain blocked the direct route for a road connecting Switzerland and Italy. No road system could climb over the obstruction, and a tunnel was the only solution. A great hole was bored through the mountain, and traffic now flows freely along its length. There are many more like this. With the railways, even more limited by the inability of locomotives to drag heavy trains up steep gradients, many hills and valleys presented a daunting problem. Here was the need to begin tunnelling on a huge scale.
The short answer
Striving to connect places by the shortest and most direct route, transport engineers were compelled to tackle head on the challenge of hills and mountains, valleys and lakes. Crossing many stretches of water could generally be achieved with bridging, but hills demanded detours or tunnelling.
Crossing the Channel
In some cases, such as the rail link under the English Channel, connecting Britain with France, there was not much choice. It was either a bridge or a tunnel. To tunnel under a wide stretch of water like the English Channel was an enormous undertaking; but the alternative solution of a bridge was rejected in favour of the ambitious and adventurous boring under the sea. It had already been attempted on several occasions, but abandoned each time in face of financial and other difficulties. Eventually it was completed, and now finds favour with the travelling public, who enjoy smooth and rapid riding between Britain and France.
Any bridge would have had to allow a way through for the very busy maritime traffic, and the exposed site would have called upon much ingenuity on the part of the designers of a suitable bridge. This does not rule out forever a Channel Bridge, of course, to complement the tunnel, but this must lie some years ahead. It will be an exciting project for some future bridge engineer, and some clever financial wriggling, too!
Canal locks and gradients
Along the routes of canals a hill could be negotiated by the use of locks, chambers which could be filled and emptied as required to lift or lower the waterborne traffic. Locks were expensive to build and maintain, and slowed up the traffic as the great barges queued up to go through.
High hills called for a long series of locks, and these caused slow movement of goods. In some places, therefore, it was found more economical to take the canal underground. This was especially sound when the levels at each side of the hill did not differ very much.
Locks are not built within the tunnel itself, but on the approaches; so the canal traffic traverses a level stretch within the tunnel. Hence the bore is a level one for canals, and usually straight, too.
The problem when taking canals underground is much like that for underground viaducts or water pipes of large bore except for the matter of scale. In Roman Britain some interesting work was carried out to carry water from place to place, and much of the construction is still in evidence. Before the internal combustion engine was invented and brought into use, you could get a barge through a canal tunnel with a low roof by men lying on their backs on top of the barges and "walking" the craft through.
Pushing with their feet upon the invert or roof was a commendably cheap, effective, and efficient method. Perhaps men who ran their own canal businesses as a family concern found this a harmonious way of keeping family and friends occupied, and used up some of the spare energy of the adolescents on board.
Brickwork canal linings
Because of the sometimes soft and crumbly nature of the soil these tunnels were strengthened by linings of brick. Millions were required to cope with the spreading network of canals. So the construction of tunnels had a good effect on the numerous brickyards throughout the country. Many of the bricks were themselves taken by canal barge to the sites, a cheap and efficient way of dealing with the heavy loads.
Canals are much less in vogue nowadays, except for the increase in holiday and recreational purposes. In many ways it offers a much better way of dealing with very heavy loads, but at a much slower speed than the modern lorry. There are no new canal tunnels being built at this time. If there were, they would be much more rapidly completed than the earlier ones.
Meanwhile, thousands of people every year enjoy the peace and quiet of a canal holiday, puttering along through pleasant countryside, in a well-equipped floating home.
The mole is a charming little velvety creature that spends most of its life below ground, continuously creating tunnels. It is an efficient and tireless digger, sustained in its efforts by the need to eat an enormous amount of food each day; but it can manage only comparatively soft soil, as gardeners know to their sorrow.
Tunnel engineers encounter hard rock, as well as crumbly material, and they have to find ways of dealing with difficult routes around a curve underground, or cutting from both ends, to meet in precise alignment for the join. Cutting holes in the earth costs a lot of money, and those who settle the bills ask for quick results, at a reasonable charge.
Here then is the problem in general for, say, a railway line. Given a line drawn on a map, straight or curved, it is required to drill a hole through the ground to follow that line faithfully, and to keep within the limits of slope that a locomotive can manage when drawing a train, hauling goods and passenger rolling stock.
Shaping a tunnel
The bore, whether circular, or of some other section, must be big enough to provide good clearance all round for the outline of a locomotive and its train of wagons or carriages, and needs to have a flat floor to take the track.
When most railway traffic was hauled by steam locomotives the tunnels would fill with smoke and steam, and although the trains themselves helped to "pump" this out of the tunnel by their passage, still a ventilation problem remained, especially with many trains following one another at short intervals, perhaps with traffic in both directions. If a train were stopped inside a tunnel the air would soon be a little difficult to breathe. The old steam locomotive, much loved though it is, could be a smoky kind of beast, particularly when pulling a long and heavy train up a long steep incline.
Locomotives and gradients
Climbing any gradient within the bore calls for more work from the engine, and hence more pollution of the air. Effectively, the locomotive has to lift the whole load through the difference in level between the ends of the incline. This is why a steam engine tends to huff and puff on a steep bit of line, and why such slopes are usually avoided as far as possible in railway networks. The little white posts beside the line indicate the rates of climb and descent, and they show gradients that are nothing like as steep as those along roads.
Coal, even the best steam coal, is a fuel that has some particularly dirty residue and produces pollution that is unpopular among many people. This has changed with the coming of electrical and diesel-powered locos, but the keen tunnel- watcher can still see traces of soot on the walls of older tunnels, giving some indication of what it was like in the past.
Planning for getting rid of the polluted air is an important demand on the resources of the designers. So adequate ventilation is yet another part of the overall problem; and this must be done without in any way weakening the structure.
At one time the railways employed great numbers of linesmen to inspect the lines frequently, and to correct malalignment, shifting of ballast, slackening of fixings and so on. Little gangs of workmen were often to be seen, working on the track, with a lookout man keeping an eye on the line for approaching traffic.
With trains nearly filling the bore, provision had to be made for people working on the line to dodge out of the way of passing traffic. This was all part of the design requirements. There has to be adequate access to the hole during the excavation, for men, materials and machinery, both entering and leaving the works. This entails proper provision of approach arrangements. At any one time there might be two streams of material and personnel, one going in and one coming out.
Other problems call for attention, too. The safety of people must always be considered; means of dealing with the excavated material is needed, and precautions against collapse of the roof are essential. Straight or curved, the hole must emerge exactly where required; or if excavation is carried out from both ends at the same time the two parts of the hole must meet precisely. Again, one ought not to forget the requirement to provide suitable fare for celebrations when the junction is made.
Weather conditions or tidal action on some sites may provoke difficult decisions. Severe cold or unexpected shortage of labour, cloudbursts causing flooding at the approaches, all kinds of hardly foreseeable problems add to the overall picture.
The electricity supply may fail, a belt may jam or break, the labour force may strike, a sub-contractor may go bankrupt, the chief engineer might be taken ill, food poisoning can put the whole staff out of commission, and so on.
Cost of tunnelling
Above all, the engineers must have costs constantly in mind, for grossly exceeding the budget can produce a great deal of unhappiness for those involved. Tunnels don't come cheap, and serious overspending is not readily forgiven.
This is a formidable list of contributory possibilities, and it all adds up to a "problem". It is not a complete list, either. If you talk with an experienced tunnel man you may get a long list of additions, culled from past experience.
Well, problems do not usually lead to despair among engineers. Their training is directed towards the solution of problems. Their studies involve mathematics, and physics, as well as specialist subjects like soil mechanics, fluids, theory of machines, theory of structures and so on subjects which may be thought of as tools of the profession.
Engineers are not turned out in a few minutes. Even on completion of their formal education many years are spent in a kind of "apprenticeship" with experienced engineers, so that in time they are competent to tackle the specialised demands of ground penetration for tunnels.
Firms that undertake the construction of tunnels are usually specialised companies that have long years of experience and have acquired a staff of experts in the field, wise in the ways of ground-boring, up-to-date in the latest techniques. Because of this they can usually submit a more attractive quote for undertaking the work than less-experienced competitors, and can handle problems as they arise.
Planning an approach
The siting of the work is pretty well fixed by the approaches to the obstruction as well as the nature of the obstacle itself. It is of interest to the tunnel-watcher to look at the approach roads or railways at the ends of a tunnel seen in his or her travels. Not only the plan view, but the variation in elevation or height, should be considered, so that the way in which the approach problem was handled when the tunnel was designed can be appreciated.
Range of problems
You can see that with tunnelling there is not just one big problem, but a whole lot of smaller ones, of different kinds, all adding up to the overall difficulty. Although it is the engineer who carries the main responsibility, there is a range of specialists in other disciplines, too, each responsible for dealing with problems in their own fields.
Lawyers, accountants, clerks, typists, computer experts, financial analysts, geologists and so on are needed to raise the money, keep clear of legal disputes, deal with records and mail, oversee safety arrangements, and in general manage the whole enterprise.
Some engineers regard all these others as so much "sand in the bearings" but without them the project cannot proceed.
There are people to make the tea, or run the canteen, provide first aid, clean the huts, transport men and materials to and from the site, order the daily requisites, operate the lavatories, and so on; and all these details demand close attention. They are part of the total many-faced problem.
The assembly of all this expertise requires substantial knowledge of what is involved to deal with sub-contractors, local government officials, "men from the ministry" and other interested parties; and a great deal of work is done before the first little bit of material is dug out at the site. Large tunnels involve thousands of people at many different levels of specialisation, and part of the overall problem is managing this formidable team, so that it all slots in smoothly.
The effect upon the local population, employment, and the prosperity of the shops and suppliers in the vicinity may be significant. It is temporary, of course, but those responsible have to know about the social impact brought about by massive civil engineering undertakings like long tunnels, and any possible long-term effects.
Excerpted from Tunnel Watching by Edmund W. Jupp. Copyright © 2000 Intellect Ltd. Excerpted by permission of Intellect Ltd.
All rights reserved. No part of this excerpt may be reproduced or reprinted without permission in writing from the publisher.
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Table of Contents
The Problem, 1,
The Materials, 10,
Some Solutions, 20,