The construction challenges of... Lydgate Tunnel

The construction challenges of… Lydgate Tunnel

Lydgate Tunnel was constructed under the superintendence of Mr J G Fraser, acting for Messrs Locke & Errington, the engineers to the railway. It was driven through the coal measures. Faults are common in this formation, and several were met with in the course of the work. One of these presented itself in a singular manner, one-half of the tunnel being in strong shale and rock in veins, whilst the other half was in a mass of wet and loose shale.

The tunnel is 25 feet wide, with parallel sides, up to 3 feet above the level of the rails; the height to the soffit is 20 feet, and the castings average 3 feet 6 inches below the rails. The total length of the tunnel is 1,332 yards, or three-quarters of a mile, of which about 1,000 yards is on a straight line, and the remainder on a curve of 74 chains radius. The following are the lengths of the different strata cut through:

The work was commenced in August 1854, and completed in March 1856, over a period of seventeen months.

Five shafts, 9 feet diameter in the clear, were sunk in the usual manner, excavating through soft material, and drilling and blasting through rock. After attaining the average depth of 60 feet, the material was raised by steam power. Four shafts, about 230 yards apart, were permanent for ventilation.

No.1A had formerly been a colliery shaft, and had not been used for many years. It was reopened by the contractor, and a cross heading was driven from it into the tunnel, the centre of which was 40 feet distant. The permanent shafts were lined with 9-inch brickwork, or 12 inches of masonry, except where in rock; they were finished at the soffit of the tunnel with ashlar curbs 2 feet 3 inches deep. Where water penetrated, iron shields, with a gutter round the edge, were suspended, and the water conveyed by a pipe down the side of the tunnel, into the regular channels. The shafts were carried 12 feet above the surface of the ground, and were completed with an ashlar coping. A 9-horse power steam engine was fixed at shaft No.1a, a locomotive engine between shafts Nos. 1 and 2, to work them both, and another locomotive between shafts Nos. 3 and 4.

The shafts were all commenced in August 1854, and completed to the respective depths measured to the formation-level hereunder stated:

Much inconvenience arising from foul air was checked by the proximity of the shafts. Foul air was driven away by means of fans fixed on the surface, which forced down a volume of air through pipes, which were fastened along the tunnel. In the neighbourhood of the old coal-workings, which ran across the tunnel, much choke-damp was met with, which was counteracted by a current of fresh air forced down through a bore-hole from the surface, lined with an iron pipe.

Great care had to be exercised in fixing the centres througl the portion of the tunnel lined from the heading of No.1A shaft, 245 lineal yards in extent, as part was on a curve and part on a straight line.

The faces walled from the cuttings at the ends, for 141 yards in length, were mined with a bottom heading, and at a distance of 30 or 40 yards from each end a break-up was made, from which lengths were driven both ways, towards the open cutting, and towards the next shaft. The remainder of the tunnel, worked from the shafts, was mined by a top heading 6½ feet high by 4½ feet wide. The shafts furnished ten faces; and 1,191 lineal yards out of the total length were worked from them, each face averaging 17·26 lineal yards per month. The open ends gave four faces in the break-ups, each making 9 lineal yards per month. The lengths mined from the different shafts are given in the following table:

The excavation was conducted in the usual manner – the rock and strong shale being blasted out, and the clay and loose shale axed out. As each length was headed it was widened out, and the roof and sides supported by larch bars and poling boards, from 9 to 10 feet above the formation level. The material was removed in iron skips, capable of holding half a cubic yard each, which were placed on light trolleys, and these pushed along tramways laid between the work and the shafts, raised to the surface by engine power, and tipped on the spoil bank. The lengths mined averaged: in loose shale, 12 feet; strong shale, 15 feet; rock, 24 feet, in some instances 30 feet.

The centres consisted of skeleton ribs placed about 4 feet apart; at the leading end, two centres were placed close together, for greater security.

The sidewalls were built of coursed rubble, the beds of the stones being punched with a hammer. The footings were not less than 18 inches below the formation level, and the walls were carried 7 feet 3 inches above the level of the rails. The arch, for 632 lineal yards, was turned with fitted rubble; and from the scarcity of good bedded stone, 700 yards were of brickwork. The mortar was composed of barrow-stone lime mixed with coal ashes, in the proportion of 2 to 1, ground by heavy iron rollers, and used fresh. Its setting power was most satisfactory.

Where the crown bars sagged much, they were built in, the intermediate spaces being filled with brickwork. Where water was met with over the crown of the arch, the tunnel was covered with zinc, terminating in a gutter to convey the water where a pipe was built through the masonry, to be discharged into the drains.

There was considerable variation in the thickness of the masonry. It was:

The following table gives the lengths of each thickness built:

The contract price for excavation, without distinction, was 4s 6d per cubic yard, including all the timbering. The prices paid to the miners varied from 8l to 18l per lineal yard, according to the material; nearly half the total length of the tunnel amounting to 12l per lineal yard, or less.

The price for setting the centres was 8s per rib.

The time the masons and labourers were allowed for building, with the cost, was as follows:

The contract price for the tunnel through rock was 26l per lineal yard and through shale 35l 16s per lineal yard; the average price was 30l per lineal yard.

The construction challenges of... Lydgate Tunnel

Wellington A Purdon recounts the construction of… Woodhead’s first tunnel

Situation and character of the work/geology of the ridge/general design and structure/plan of construction/preliminary operations

The range and levels

Ventilation of works/drainage

Sinking of the shafts

Driving the headings/excavation & lining

About the author

The situation and character of the work

The tract of country lying between Manchester and Sheffield is traversed by a well-known ridge of mountains called the Pennine chain, and sometimes the backbone of England, in which the rivers Don and Mersey take their source, and flow in opposite directions to the eastern and western shores.

When the plan of a railway for connecting the towns in question was required, it was early seen that a tunnel through this ridge was unavoidable; and it was also perceived that the best place for getting it through was near the head waters of the rivers that have been named, as their gorges penetrated further up, presented the narrowest limit of the ridge, and their courses downwards through the flanks of the mountain afforded the most desirable route for the railway. This position was found to be nearly midway and not much out of the nearest direction between the two towns. The railway between Manchester and Sheffield merits some notice, not only on account of the work I am describing but for its general design and bold works. The tunnel is situated at the summit level of the railway which falls both to Manchester and Sheffield, with inclinations equal to about forty feet per mile on either side for 18 miles. Such gradients had, at the time, a degree of novel severity; but they afforded the best way by which the great elevation could be reached at which it was practicable to commence the tunnel.

It has been stated that the route of the railway followed the courses of the rivers Don and Mersey. This description is entirely true with regard to the river Don. Its approach to Sheffield enabled the railway on its banks to abut upon the town. It was not so upon the Manchester side. The river Mersey passes wide of that town which involved another tunnel of difficult construction through the ridge at Hattersley, which separates the waters falling into the Mersey from those into the valley of the Tame, as the line approached Manchester. There were also the Dinting and Etherow viaducts, two structures of unusual dimensions, designed by Alfred S Jee Esq, and considerable viaducts over the lateral brooks of the valleys traversed, together with heavy embankments and culverts on sidelong ground, and deep excavations; so that the line may be said to have been one of heavy and difficult works which have been happily overcome.

Geology of the ridge

Having described the situation of the tunnel, it is desirable to explain the character of the formations through which it had to be carried, as this is often of more consequence in regard to the construction of such a work than its physical magnitude. The measures passed through were beds of grit, various sandstones and different qualities of shale. The order in which these strata occur is well known – resting upon the limestone, the coal series, passing up through its various beds of grit and sandstone, alternated with argillaceous shales, reaches the lowest seam of workable coal known in Yorkshire, immediately below which lay the whole of the measures that had to be operated upon in driving the tunnel. The disposition of the strata showed a moderate dip to the eastward; but it is not to be inferred that the sheets of rock around and overlying the tunnel were in one continuous plane. They lay in the usual masses of irregular form and area, with various inclinations and insulated by faults (see diagram below). There were no organic remains or mineral ingredients discovered, but those well known in the coal measures; and the only observation worthy of remark with regard to this lower portion of the series (which is not so familiar) is that there was no absence of the usual developments which occur in the upper measures of this class of rocks.

Click here for a detailed PDF diagram showing the section of the summit rock at Woodhead.

General design and structure

It has been stated that the tunnel is situated at the summit of the line. The height of the rails at this point is 966 feet above the sea and marks the eastern entrance. At the western end, the rails are but 887 feet above the same datum, which shows a difference of level, between one end and the other, of 79 feet. The distance between these limits is 3 miles and 22 yards, the total length of the tunnel.

The stratification has been described as dipping eastward. The gradient of the tunnel rises in the same direction, with a uniform inclination from end to end of 1 in 200.

From the first, it was laid out to have two parallel tunnels of smaller dimensions, instead of one larger and calculated for a double trackway. This was determined in order to save immediate outlay, with a view of constructing but one of the tunnels in the first instance and leaving the second one in abeyance until increased traffic should require its construction. This practice deserves commendation, with respect to tunnels of such magnitude as that I am describing, not only from the lesser difficulty of raising the smaller capital but in consequence of the lesser quantity of excavation requisite to be drawn from the limited number of faces of operation used; and it does not appear to me that the ultimate cost of the two tunnels should generally exceed that of the larger size, if the ground be at all of a friable nature. The thickness of the space between the two tunnels, was designed at 17 feet and that lying the more southerly was the one executed and to which the observations in this paper refer.

The clear height of the tunnel is 18 feet and its width is 15 feet. The form of the arch is a semi-ellipse sprung from the ends of its conjugate axis, resting upon vertical sidewalls. The course of the railway is straight through the summit ridge and the centre line naturally falls between the two tunnels before described. It was upon this line that the shafts were sunk, so that they were situated on a parallel line, 16 feet off the centre of the tunnel under discussion. The highest point of ground shown on the longitudinal section of the summit ridge (see diagram above) is 1,552 feet over the sea, and 620 feet above the tunnel formation. The two entrances were fixed at an extreme depth of 65 feet of open cutting, which was heavier at the eastern face owing to the ground rising less precipitately.

In consequence of the great depth from the surface to the level of the tunnel, it was calculated that but little time, in proportion to the expense, would be gained by sinking many shafts in addition to opening each entrance face. Accordingly it was determined that there should be but five shafts sunk. The position of each shaft was fixed so as to bring all the various headings of the tunnel to a termination at the same time, or as nearly so as rational pre-judgement could determine. The manner in which they were disposed is as follows (see diagram above).

Total: 5295 lineal yards

The depths of the shafts are as under, expressed from the original surface to the level of the rails.

Total: 857 lineal yards

From which it appears that the average depth may be taken at 172 yards.

Plan of construction

It was resolved to drive two driftways, one at the top, the other at the formation level of the tunnel, through the entire length, before commencing the general excavation. The size of these headings was – for the top one, 4 feet, and the bottom one, 6 feet square (see diagram below). The object of this mode of proceeding was to meet some points of difficulty that were presented. (The mode of ventilation will be subsequently explained.) It served as a means to carry air to the workings through the long stretches that lay between the various shafts and open ends, as is usual in coal works, by horizontal and parallel galleries; so by placing one of the drifts vertically over the other, the same effect was obtained. The upper one ranged the crown of the tunnel and laid open the work for final excavation, while the bottom one served for the drainage and drawing away the material; both together lessened the quantity of excavation to be afterwards raised and took off the water from the heavier work of the enlargement.

Further, there was pecuniary reason. It was not thought wise to go too headlong into so great and novel a work when, by merely driving driftways, a lesser sum of money was expended in the first instance and when the headings were gotten through the problem was solved, so far as regards the amount of water and knowing the nature of the ground: confidence in the undertaking was established, which enabled the work of greater size to be pushed more vigorously afterwards; and for these reasons it was preferred to drive a double driftway throughout before carrying the full excavation forward or following close after the headings.

The number of shafts, and the manner in which they were disposed, have been already stated. They were 10 feet in diameter and a 25 horse engine was applied at the top of each to wind out the material and work the pumps. It was assumed that the sinking would occupy about 15 months and that in the mean time the headings from the entrance faces would be advanced by as much as the greater lengths of those stretches exceed the distance between any two of the shafts; so that after the horizontal work should commence from the bottom of the shafts, the entire number of faces of operation would have equal spaces to drive before meeting the headings from the opposite direction and thus leave the mountain thrilled at one period of time. It was then proposed to follow up with the widening process and general formation of the tunnel at each face. The plan of ventilation will be detailed; but it may be observed that there was no want of air felt after the communication was opened by the drifts in the way described, between the respective shafts and the open ends of the tunnel. It was only until the headings should be gotten through that any artificial means were requisite.

Preliminary operations

A company was formed in 1836 and the act for the construction of the railway, embracing this important work, was obtained in May 1837. It was 12 months afterwards before any steps were taken for proceeding, owing to the formidable nature of the undertaking. The promoters were not assured and had to contend against the opposing views of timid and dissenting shareholders.

The engineer who laid out and entered upon the construction of this work was Charles Vignoles Esq. He was superseded by Joseph Locke Esq under whose direction it was executed.

The ground was broken on the 1st October 1838 but nothing of a determined nature was done until towards the end of the following year.

The preliminary works that were necessary for commencing the tunnel were not so trifling or such as might be done at once. It was necessary to make cart roads in different directions to convey coal for the engines from the adjacent public roads and also to connect the various points of operation, the united length of which exceeded four miles. It was requisite to build cottages for the workmen, stables, a gunpowder magazine and workshops; besides erecting the engines and constructing the reservoirs, observations etc.

It may not be wrong, at this place, to state a few particulars of the notions that prevailed at the time in question, with respect to a work of this nature.

It was generally said that it would never be made or that, if it were, it must be at an absurdly extravagant cost after many years. The opinions of those most interested were very vague and but few had any idea of how long it would take to construct or how much it would cost. It was thought however by those best able to form a judgement that the strata were generally favourable from the appearance of the bassettings and dip along and in the vicinity of the line; and that passing boldly, as it did, under the centre of the ridge, there should be no ground of a highly broken and contorted character, or (as in sidelong ground) that might occasion a creeping weight and require expensive timbering and lining for its support. The circumjacent valleys lay in such a manner, both in point of position and levels, in respect to the drainage of water from the workings, and the fact of the tunnel being situated 900 feet above the sea led to the belief that the quantity of water from the natural drainage of the surrounding district would not be excessive.

It was also seen that the time of completion must be governed by the mode of construction that might be employed and that, owing to the great depth of the shafts, the number of faces of work most likely would be but few, which shadowed forth in some degree the period for its completion.

Situation and character of the work/geology of the ridge/general design and structure/plan of construction/preliminary operations

The range and levels

Ventilation of works/drainage

Sinking of the shafts

Driving the headings/excavation & lining

About the author

A walk over Queensbury Tunnel

Stephen Prior takes a look at the Victorian art of… Tunnel construction

There are still over 600 operational tunnels in Britain and more than 500 disused ones. Most were built in the mid-to-late 1800s. Even today visible clues are there to be found showing how they were constructed and what problems, if any, were encountered. Although not officially condoned, next time you explore a disused tunnel remember to take the one item usually never thought of – the humble tape measure. You may discover more than you might think. To understand why, some knowledge of construction methods is required.

The earliest way to build a tunnel was to start digging from each end and meet somewhere in the middle. Although fine for short tunnels, this method was far too slow for any decent length so another technique involved the use of construction shafts and headings.

This method worked thus: shafts were sunk reasonable distances apart along the alignment of the tunnel. These were usually lined as far as the tunnel’s roof level, then continued downwards to below floor level, supported in timber. By digging down deeper than the floor, it meant that a sump could be formed to collect groundwater.

Once all the required shafts had been constructed, a small tunnel or ‘heading’ – usually in the region of 1.5m high by 1m wide – was driven between the shafts. These were created with timber supports and used to ensure that alignment and levels were correct through the tunnel. In straight bores, candle-pots were often lit at the base of each shaft as a quick way of revealing any discrepancies.

When this stage was completed, excavation of the full bore could be started. So a tunnel with four construction shafts could have a maximum of ten gangs of navvies working simultaneously at ten faces – two gangs per shaft working both ways, and another at each end of the tunnel.

From the base of each shaft, the tunnel was excavated and supported until a ‘side length’ of around 4.5m was formed in each direction. This was built with a lining much thicker than the rest of the tunnel as it had to support the weight of the shaft as well as itself.

Watford Tunnel is one example which highlights the problem with this method. The side lengths were being built when a collapse occurred. This did not only result in the section of tunnel being lost – the shaft was also brought down as it would only have been supported by timbers until this important part of the lining had been completed. Several men lost their lives. What’s not known is whether they were killed outright. Might some have survived the collapse only to die due to asphyxiation? Of course, no-one could attempt any form of rapid rescue as there was no shaft down which they could gain access.

Although navvies were seen as expendable, collapses like this obviously caused a delay in a railway being opened which, in turn, cost the company money. A solution had to be found and a method involving ‘break-ups’ was then employed. This involved more navvies but, being better paid than other manual labourers, they were easy to recruit.

When using this technique, the shafts and headings were constructed in the normal way but work then began on constructing a section of full-sized tunnel anything up to 45m away from the shaft. This was done by the navvies crawling along the heading to a point where this section was to be mined and then opening it up – hence the name ‘break-up’. This may have only been 3m long but had to be solid and very strong as the construction of adjacent sections depended on its ability to support the roof along its entire length. It was now possible for one gang to work towards the next shaft while another worked back to the original one, in the knowledge that they had a safe section of tunnel behind them if anything went wrong.

This method soon became the norm and the introduction of several break-ups between shafts significantly increased production, thus improving the chances of the company making money at an earlier stage. The tunnel at Chipping Sodbury is known to have had 40 gangs working from only seven shafts which would have been impossible had this technique not been adopted.

Tunnelling ‘advances’ – or lengths between break-ups – were normally set at about 4.5m. This was governed by the length and thickness of the timbers put in to support the roof as well as the ability of the miners to move the enormous weight of the timbers forward as they excavated the next length. These main supports spanned from the last length of completed brickwork to supporting timbers at the excavation face. If soft ground was encountered or penetrating water caused material above to become loose, the main support timbers started to take the weight and would bow under the load.

Sometimes, despite making an allowance for this, there was too much bow in the timbers and the brickwork could not be placed to the correct thickness in the roof. This meant that the timbers had to be reset, wasting time and effort. Usually the foreman bricklayer or carpenter paid the men on piecework – so much per yard; it was therefore in no-ones interest to be delayed by having to reset timbers.

At the slightest hint of poor conditions, the foreman bricklayer or carpenter would say how far the next advance had to be in order to be certain of getting the brickwork clearance in the crown of the tunnel. In these circumstances the advance could by reduced to 2m or less so that the timbers did not span so far and were therefore much stiffer, producing less sag under load. That said, advance rates were paramount when paid on piecework and maximum lengths would be resumed as soon as possible.

When two gangs met, a junction length of tunnel was created. It sometimes became a race between gangs to see who could claim the maximum yardage. So if, for example, 7m of tunnelling remained between two sections then one gang may opt to excavate the standard 4.5m thus leaving only 2.5m for the other gang to complete.

Shaft lengths were created when a construction shaft was not required for ventilation and could be bricked across and sealed. Officially it was backfilled to the surface and the ground above it restored, however abandoned construction shafts have sometimes been found to have been left unfilled, with only a cover at the surface!

Tunnel lengths were always built with ‘dog toothing’ at the ends of the brickwork to form a shear key between lengths. This meant that should a collapse occur then only the section to the next shear key would go, rather than a domino effect causing the total loss of a tunnel. This toothing was not always successful in forming a good joint, resulting in them sometimes being associated with flattened crowns and water ingress. They are very rarely tight and can almost always be seen.

This is where joint mapping can help to reveal things. If it is found that a tunnel generally has the normal 4.5m lengths but they suddenly become shorter, this points towards bad ground, a bricked-up shaft, a junction length or a break-up length. With practice, it should become fairly obvious which has been encountered. Bulging of failed brickwork in a tunnel can be joint mapped either side of the problem which may be found to have been caused by bad ground, a buried shaft or, potentially, a junction length with failed supports. But this method does not work in structures built using the ‘cut and cover’ method or ‘inverted arches’.

Stephen Prior takes a look at the Victorian art of... Tunnel construction

To accompany his construction film, Graeme Bickerdike offers more… Tunnel Vision

Something extraordinary is happening under London. Six mechanical navvies, bewildering in their efficiency, steer Crossrail’s tunnels through tangled subterranean history towards an end-point later this year. Forever hungry, Ada, Phyllis, Victoria, Elizabeth, Mary and Sophia each mine and line over 20 metres daily to tolerances measured in millimetres; verified by inertial navigation systems, scrutinised from comfy chairs. As enterprises go, this one is exceptional and yet that reality rarely impinges on our consciousness. Why don’t we awe anymore?

When something extraordinary happened two centuries ago – and it very often did – inquisitive crowds gathered, cheering and waving flags. Great engineers became celebrities of the day, without ever taking their kit off or eating worms in a jungle. Men of vision and tenacity – Locke, Vignoles, Stephenson, Brunel – forged national transformation. Our leaders today seem content to tinker, deciding what colour to make fag packets.

Trawl through the newspaper archives and it’s clear that tunnels were sources of intrigue and wonder to the Victorians: portals into a new age. But how were tunnels constructed in a Time Before Machinery (TBM)? Keen for answers, I spent much of last summer producing a short film about it, targeted at those amongst the public with an underlying curiosity, but perhaps also of interest to the engineering fraternity.

Written insight is not scarce on this subject, but generally accepted as the definitive work is Practical Tunnelling, a tome authored by Frederick Simms who secured the role of resident engineer on the South Eastern Railway in 1836, thereafter recording the tribulations encountered with Bletchingley and Saltwood tunnels. Contractor Charles Gripper published another book, Railway Tunnelling in Heavy Ground, in 1879, apparently unhappy that Simms had “rather hurried over his explanations of mining operations”. Noteworthy amongst the many papers is one exploring the seven-year construction of the first bore at Woodhead – extending for three miles between Sheffield and Manchester – which had been committed to the charge of Wellington Purdon, a surveyor from Killucan, County Westmeath, who was just 23 when he took on the project in 1838.

There’s little point cluttering up this space by repeating the film’s content. If you fancy investing 20 minutes of your life on the basics of Victorian tunnelling, a link to the film is provided below. Remember, the script considers a generic tunnel – it is not applicable to every one in existence. In these pages we’ll reflect in more detail on some of the challenges that had to be overcome.

Line of sight

Progress with lengthy tunnels was usually expedited by sinking construction shafts, allowing them to be driven from intermediate points as well as their ends. Sighting towers, known as observatories, were erected as fixed reference points for setting out purposes; the tunnel line, and hence the shaft centres, could then be established at any point over the hill. Although substantially built, very few still stand as their valuable fabric was mostly recycled when work had advanced sufficiently. But survivors can be found at Merstham in Surrey and Bramhope on the Leeds-Harrogate line, in brick and stone respectively.

Often 30 or 40 feet high, the towers housed a staircase spiralling around a central pier, the latter being entirely freestanding so as not to be influenced by any movement of the building. On top of it was a stone table supporting a transit instrument, typically incorporating a 30-inch focal length telescope which looked out through openings at the top of the tower. Provision of a basic telegraph system enabled the engineer to direct his assistant with the ranging pole.

Few disciplines have benefited more from the technological revolution than surveying. It’s a very digital business these days. Simms however helps us understand just how far it has come, describing the means by which the tunnel line was transferred down a shaft. Two fishing lines with 25lb plumb-bobs, secured to a triangular timber frame erected over the shaft, were dropped down either side of it and suspended in water vessels at the bottom to hold them steady. The lines were then ranged from the observatory, with notches cut into the timberwork for each one to rest in when the correct position had been set.

Such was the potential for disturbance by the wind that this was an activity restricted to calm weather. Imagine then the difficulties facing Wellington Purdon high on the Pennines with shafts almost 600 feet deep. He was an advocate of copper wire and oil barrels. However Heath Robinson this might all sound, the results speak for themselves. Purdon claimed a divergence of no more than three inches in line or level between Woodhead’s shafts, around 750 yards apart, whilst Simms asserted that “in not one of the junctions could any deviation from accuracy be detected.”

That sinking feeling

It’s hard to conceive what life must have been like at the bottom of a shaft, without the benefit of today’s foul weather gear. Progress downwards was made at a rate of perhaps six feet per week, with two 12-hour shifts worked daily, except Sundays. Shafts acted as sumps, collecting ground water from the locality, prompting navvies to use straw in an effort to stem the flow. This often proved futile and work had to be suspended whilst better pumps were brought. The need to power them was one factor in the early development of steam engines. To give you an idea of volumes, 2.4 million tons of water were pumped from Woodhead’s five shafts whilst they were being sunk.

Water was inconvenient; running sands killed. These loosely-packed layers within the rock can become fluidised, removing support for anything overlying them. Excavation work in such conditions was therefore attended by considerable danger. On 16th July 1835, a collapse at the base of one of Watford Tunnel’s shafts resulted in a vast crater opening at ground level, swallowing all around. Below, ten men were buried; their bodies took more than a month to extricate, after another shaft had been sunk alongside the original. This still offers momentary relief from the darkness when passing through the tunnel on the West Coast Main Line.

That so many construction shafts were sealed and backfilled – rather than being retained for ventilation – has left an unwelcome legacy, with records of their location often lost and the land above developed. Typically, the fill material is supported on a timber frame above the arch; if the fill becomes saturated, rotting and crushing of the timbers can follow, leading ultimately to their failure and the load’s transfer onto the lining. Of the five hidden shafts in a North Yorkshire tunnel, closed in 1958, three have given way since the Seventies. Investigations to locate such shafts continue today, their significance in liability terms not lost on duty holders.

Really boring

Pilot tunnels, known as headings and pushed outwards in both directions from the bottom of shafts, performed a number of roles when eventually joined together: to help drain and ventilate the workings, to provide a means of communication between the shafts and, most importantly, to confirm the correct line and level before the tunnel was excavated to full size. At Bletchingley and Saltwood, the headings were claustrophobic – less than 3 feet wide and just 4 feet 8 inches high: a real pain in the neck for the labourers pushing skip-loads of spoil to the shaft for disposal. It’s clear from Gripper’s book, supported by newspaper accounts and photographs, that more generous headings – between seven and ten feet square – had become the norm before the 19th century was out.

Using mining techniques, 6-8 feet of progress was generally made with a heading in 24 hours, depending on ground conditions. But by the 1870s, an assortment of productivity-boosting devices had emerged, driven by steam or compressed air. Noteworthy was a rock drilling machine, patented by Major Frederick Beaumont of the Royal Engineers and operated by the Diamond Rock Boring Company, of which he was chairman. The machine was set to work in Cymmer Tunnel, as well as Queensbury, Well Heads and Lees Moor on the Great Northern’s Halifax-Keighley line. Powered by an 8hp portable engine, it comprised an array of diamond-tipped steel tubes rotating at 250rpm – cooled by water and delivering a daily advance of about 20 feet.

The first genuine tunnel boring machine was developed in America in 1851, working to a similar principle as modern TBMs, but it proved less productive than the established drill and blast method. Two other machines, built to Captain Thomas English’s patent, operated successfully as part of an early Channel Tunnel scheme until politics and security fears brought its abandonment in 1882. Through chalk, the 2.13m cutting head drove more than 3,500m of tunnel at a highly creditable 25m per day.

Home safe every day?

Read the Daily Mail and you’d probably conclude that health and safety is now a national scandal. For different reasons, that charge could certainly be levelled at the safety record of Victorian railway companies. The sustained loss of life prompts many to infer that companies had a disregard for the navvies’ welfare, but such an assessment would be over-simplistic.

Time after time, inquests heard evidence of habitual rule breaking, albeit – as now – theoretical compliance did not always sit comfortably alongside practical needs. On 21st April 1876, miner Richard Parsons – part of the gang driving the Cymmer Tunnel – was making up charges immediately above his explosives, “in defiance of orders and in disregard of warnings and reprimands”. Inches away, in the cabinet behind him, were 150lb of dynamite. A single candle illuminated the scene; when it fell over there was only one possible outcome. Parsons and a 13-year-old boy, John Clements, were “reduced to atoms”; 11 others were also lost.

The workforce proved managerially problematic. Recklessness was endemic, though rarely did it have such devastating consequences as at Cymmer. Long and arduous shifts brought with them a culture of playing hard afterwards. Navvies fought in lumps and drank themselves into oblivion, going missing for days afterwards. Why then, according to Gripper, was five shillings worth of beer paid as a bonus for every length of tunnel completed? Combine that with the impossibly-high risks involved in the work – excavating ground above your head with a pick, for example – and a perfect storm brews.

Against all odds

What I personally find most inspiring was the Victorians’ apparent fearlessness. No matter how daunting the difficulty, they never seemed fazed by it, even if financial ruin loomed.

Most of our tunnels were accomplished without any mechanical aids beyond those worked by muscle. Consider a typical two-track tunnel, advancing forward in sections – known as ‘lengths’ – of 15 feet. For each length, a gang – comprising a ganger, three miners and nine labourers – would excavate perhaps 180 cubic yards of material, supporting the ground with 20-foot long timbers propped off transverse beams. Four bricklayers and six labourers would then take over to form the lining, consuming huge quantities of mortar and possibly 30,000 bricks. Remember, these had to be manufactured and transported, not just laid. And all this took place at height, in choking bad air and constrained by darkness. Each length took two weeks. The final act involved a boy creeping into the space above the brickwork to pack the voids. Then the process would start again.

The logistics were mind-boggling, most of the strain being taken by horse power. At Saltwood on 16th September 1842, horses hauled 4,916 water barrels (each 1,310lbs) and 464 spoil skips (1,050lbs) – collectively weighing 3,092 tons – up nine working shafts, a total lift of 555,192 feet (105 miles) for a cost of about £37.

Toil and trouble

You will have gathered by now that I am a tunnel junky and have an anorak to prove it. But there can be no denying that the stories they tell are compelling, if only we could bring ourselves to listen. Yes, let’s celebrate Crossrail and the first-class cutting-edge engineering it represents. We should though not lose sight of how it all started. Without the immense sacrifices made in the pursuit of progress – burrowing through hills – and the resolve shown during construction, we would have no railway network. To see how they did it, click the image below.

Story published February 2014

(Many thanks to The Last Main Line, Picture the Past and the Science & Society Picture Library for use of their fabulous archive photos.)

To accompany his construction film, Graeme Bickerdike offers more... Tunnel Vision

Tunnel Vision

The only thought most passengers have about railway tunnels is how they spoil the view. Beyond our imagination is what it took to build them, even if we could bring ourselves to care.

This video offers some insight into the techniques employed by Victorian engineers to drive the many hundreds of tunnels which form part of our past and present railway network. It tells a tale of ingenuity, adaptability, determination and tragedy.

Click here to read more about the challenges of tunnel construction.

Tunnel Vision

Civil Engineer G F Adams examines… The construction of Cymmer Tunnel

Although the subject of this paper has been attended by much that is interesting, it would perhaps not have been considered of sufficient importance for a communication to the Institute, from a Civil Engineering point of view only, but coupled with its mining and stratigraphical features it may possess some amount of interest. The tunnel is the principal work in connection with the Llynvi and Ogmore Railway Company’s Northern Extensions, the Act for which was obtained in 1873; the writer’s firm being engineers for the Bill and for the works. It will be observed from the plan that the new lines will form an outlet for new and very important coal fields, and this outlet becomes the more valuable by the amalgamation of the Llynvi with the Great Western system, and by the conversion of the South Wales Railway into narrow gauge.

The extensions commence with Railway No.6, which forms a junction with the existing Llynvi Valley Railway near the termination of that railway at Maesteg.

Railway No. 6, immediately after passing through the tunnel, crosses the Avon river by means of a high viaduct, with masonry piers and wrought-iron superstructure. There are four spans of 82 feet 6 inches each, and the main girders are of the “double Warren” type, 10 feet deep, with 10 feet bays. There are cross girders, 10 feet apart, carrying the wooden decking. The height from the bed of the river to rails is 107 feet. The viaduct is built on a curve of 30 chains radius, the rails being level. It was originally intended to build the viaduct with nine masonry arches of 40 feet span, but it was considered that there would be a difficulty in procuring a sufficient number of masons in so isolated a locality.

Near the village of Cymmer a junction with the South Wales Mineral Railway has been effected, and sidings are being prepared for the interchange of traffic.

Railway No.7 commences by a junction with Railway No.6 near the northern end of the tunnel, and runs up the Avon Valley to Blaenavon.

The longitudinal section of the tunnel is compiled from the progress section, supplemented by some detailed sections of the seams taken and supplied by Mr Barrow, and it may throw some little light upon a district which has been the subject of several papers read before this Institute.

The seam of coal passed through at the north entrance of the tunnel would appear to be identical with the seam proved by the Glyncorrwg Company, near Cymmer village, and supposed to be the “Wernddu Seam”, and probably identical with the “Glyncorrwg” or “No. 2 Rhondda” Seam.

The black band passed through near the south end is supposed to be the “Middle Black Band.”

The several faults passed through make it difficult to connect the sections. Very much turns upon the position of the large fault proved in the Llynvi Company’s workings at Cwmdu and Tygwinbach. One would be led to identify it with the disturbance passed through about the middle of the tunnel, by the very broken nature of the ground on the mountain above it, but the rock on each side of this disturbance would appear to indicate that it is not a very large fault in this immediate locality. It may be that the large fault is the one near the south end, in which case the black band ought to have come in again. These are merely suggestions, and it is probable that the ground can only be reconciled by those members who know the district best, and have carried on operations in it, putting their working plans and sections together.

The works were let in two contracts. No.1 contract included Railway No.6 from the north end of the tunnel to the junction with the South Wales Mineral Railway, and the whole of Railway No.7. No.2 contract included the tunnel and Railway No.6 from its commencement to the south end of the tunnel.

The Diamond Rock Boring Company have been the contractors for the section which includes the tunnel.

The tunnel is 1,594 yards in length, and quite straight, with a rising gradient throughout the whole length towards Maesteg of 1 in 226. This gradient is against the load, but it is slight, and could not be obviated, having regard to the levels which had to be adopted near the southern entrance.

Shown are the contract sections of the tunnel for different kinds of ground. Section No.1 is for soft ground, section No.2 for harder ground, and section No.3 for hard rock. The contracts were for fixed sums, with the exception of the tunnel lining, but it was considered that a contractor, in tendering, would assume, in order to keep himself on the right side, that the most expensive section of lining would be required throughout.

It was therefore decided to get this portion of the work done by schedule of prices, and to change the section as the ground varied, and by so doing a considerable saving has been effected. The following are the contract prices for the different descriptions of work in the tunnel:

Owing to the inclination and the frequent bedding of the strata, the ground has nowhere been considered quite secure enough to adopt section No.3, although a considerable amount of very hard rock has been driven through, but in order to make the underpinning at the south end easier, the contractors have been allowed to build the side walling vertical over considerable lengths, instead of curving it inwards towards formation level as shown on sections, and this gives a greater width at rail level.

The mountain rising very rapidly at each end, no assistance could be obtained from shafts, and the tunnel has been entirely driven from the two ends.

The south end has been driven entirely by hand labour, and the north end chiefly by machine drills.

The north end was commenced in April 1875, and the south end in August 1875, and a junction perfect to lines and levels was effected on 29th May 1877, 957 yards having been driven from the north end, and 637 yards from the south end.

The following is a description of the machinery which was established for driving the drills at the north end:

The motive power consisted of a pair of portable engines, one 25, and the other 20 horse power, coupled.

The air compressors were a pair of vertical single-acting cylinders, working at a reduced speed from the engine, 30 inches diameter by 2 feet stroke, and going at 35 revolutions per minute; the valves were of the butterfly pattern, self-acting, and 3 inches in diameter; the inlet valves, 19 in number, being placed in the piston, and the outlet valves, 12 in number, being placed in a disc under the top cylinder cover.

Main air-pipes 4 inches in diameter, and made of cast iron. Water pipes 2 inches diameter. Water pressure 90 lbs per square inch; the reservoir being placed sufficiently high to feed the boilers, 10 to 15lbs are sufficient for the purpose of the drills.

In the newer compressors used by the contractors, the piston is solid and the small vacant space at the end of each stroke between the piston and the top cylinder cover is taken up by a little water, which rises and falls with the piston. In this case the whole of the valves are in the top cover, the inlet valves on the outside, and the outlet valves inside the main air channel.

The comparatively slow speed of the compressors enables the heat due to compression to be partially got rid of to the atmosphere, resulting in a proportionate economy of power.

The valves are open to inspection, and, with their seats, can be easily and quickly attended to, but they rarely get out of order.

By having the cylinders single acting, their size is of course doubled, but against this is to be set the absence of slide blocks and guides together with bottom cylinder cover and stuffing box; at the same time the inside of the cylinder and piston is always kept cool by the outside air, and is open to inspection.

The compressors have water jackets, the water entering at bottom, and discharging at top.

The Beaumont percussive drill has, in common with most drills, three motions, viz – one for giving the blow; one for turning the drill; and one for feeding it forward.

The drill is worked by compressed air at a pressure of from 40 lbs to 50 lbs on the square inch. The apparatus consists of a cylinder carrying a piston and piston rod, which is supported on a frame on which it slides longitudinally, being moved by a feed screw, the feed depending on the speed at which the hole is being deepened.

The drill may look cumbersome, but it is no stronger or heavier than is necessary to do the amount of work which is involved in piercing a 2¼ inch hole in hard rock, at from 2 to 6 inches per minute; in fact, it is work which needs a small steam hammer to do it.

In designing the drill it has been arranged so that all the working parts, which are those only liable to get out of order, are on the outside of the drill.

It is true that they are exposed to the dirt of a tunnel, but that is more than counterbalanced by the great advantage of the miner being able to see, while the drill is at work, that all parts are in proper order.

Inside there are literally only two moving parts, both of which are solid, namely the piston and valve.

One of the chief specialties of the drill consists in the method of driving the valve, which is set in motion by the air in place of, as is usually the case, by some mechanical connection with the piston, or other moving part of the drill. This enables a dead blow to be given in place of a cushioned one.

Where the valve is driven by the piston, it follows that it must be reversed before the drill strikes the rock, otherwise there would be no motion left to shift the valve to the proper position for the return stroke.

By inspecting the drawings it will be seen that each side of the swell in the centre of the valve forming its piston is alternately put in connection with the pressure at either end of the main cylinder, the exhaust being effected through the open space between the two ends of the divided piston of the drill, which is permanently in connection with the outside air, by a hole drilled through the front part of the piston rod.

Suitable buffers are provided for the valve to strike against, and the same arrangement is carried out with the main piston, so that should the piston accidentally overrun its parts no harm will result.

The twist motion is given by two straight and two inclined grooves cut on the front part of the piston rod. They are made both broad and deep so as to afford a proper rubbing surface. When the drill sticks in the hole, as it often does, an excessive strain is thrown on the twist motions of the drill.

The feathers sliding in the latter are in connection with two ratchet wheels, one taking the straight, and the other the twist grooves.

The object of the two descriptions is to prevent the possibility of the drill ever turning back.

The feed is given by putting the brass nut on the feed screw in connection with a pawl driven by a roller which is pressed against the piston rod, prolonged through the top cylinder cover.

The rod is tapered at the end, and as long as the roller keeps clear of the inclined part no feed is given, but so soon as the deepening of the hole enables the piston to move further towards the front end of its stroke the roller descends the incline, and enables the pawl to take a fresh tooth of the ratchet wheel in connection with it.

The drill can be fed, if required, by hand by simply disconnecting the automatic feed arrangement. But hand feeding is discountenanced where speed is an object; indeed, without an automatic feed in hard and variable rocks bad progress would inevitably be made.

The bed on which the drill slides is of malleable cast iron, allowing a 3 feet length of traverse.

The carriage, or camel as it is called, consists of two arms supported midway by a vertical iron column carried by a low truck running on four flanged wheels. These arms carry two drills each, the top ones being above the arms supporting them, and the lower ones in boxes which hang from the bottom arms.

The object of this arrangement is to keep all the drills relatively in the same position, so that they can be changed one for the other, and so obtain a full command of holding power.

Holes can be put in in any direction, and, as a matter of fact, hand holes are never needed.

It will be seen that the central column is capable of turning; and the arms, again, can turn on it.

The clamps carried by the arms can slide horizontally, and turn upon them, while the drills have similar motions.

When the drilling is completed, the arms carrying the drills are turned longitudinally with the tunnel, and the camel is run back into a siding to allow of the muck wagons being readily passed by it.

For rapid and economical tunnel driving by machinery, it is absolutely essential that a powerful drill should be used, and that the liability to breakage should be reduced to a minimum.

A set of four of the Beaumont drills are capable of putting in 16 to 20 holes 3 feet 6 inches deep in hard rock in three hours, and of keeping this average up.

The advanced heading in which the drills have worked has been driven about formation level in the centre of the tunnel, and 8 feet wide by 8 feet high.

As a general rule 16 to 18 holes are bored into the face, their average length being 3½ feet to 4 feet in hard rock, and 5 feet to 5½ feet in soft ground.

These holes commence with 2⅝ inches drills, and finish at 1½ inches, four to five different drills being ordinarily used in the length in rock, and three inches softer ground. Considerable judgment is required to drill the holes at the angle most effective for the particular ground; as a general rule, the top holes rake upwards, and lower holes downwards.

The boring of all the holes takes about four hours as a general rule.

The four centre holes, converging inwards, are first blasted, then the top and side holes, and after the rubbish has been cleared away in front of them the bottom holes are blasted.

The blasting and clearing of the rubbish takes about four hours.

About 20 lbs of dynamite are used for the above number of holes in rock, and from 10 to 12 lbs in softer ground.

At the above rate a yard is advanced each eight hours, making 3 yards a day, or 18 yards a week.

The average for seven consecutive weeks was 18½ yards per week.

The full complement of men for driving the heading by machinery during one complete operation is, viz – 1 foreman, 1 timekeeper, 1 engine driver, 1 fireman, 1 fitter (outside), 1 fitter’s labourer ditto, 2 blacksmiths, 2 strikers, 2 labourers carrying tools and attending to air pipes, 5 (or sometimes 6) men working machines at face, 5 men blasting and clearing rubbish away, 1 horse driver, 1 miner road-laying after machine and doing any timbering that may be necessary, 1 man attending to explosives/candles etc, 1 boy messenger

26 total

The progress of the work has afforded opportunities for comparing results by machine drills with hand labour, and at one time in particular two headings were driven simultaneously in the same hard rock for some distance at the north end, the one by machinery, and the other by hand labour. Over several consecutive weeks the hand labour averaged 3⅓ yards per week, and the machine drilling 18½ yards per week, or five-and-a-half times the speed of hand labour.

Without going into the actual cost – a matter belonging exclusively to the contractors – the writer may be permitted to state, for the information of the Institute, that the actual working cost per yard in hard rock is about the same with machine drills as with hand labour, without taking into account the interest on capital and the depreciation of machinery; in addition to the increased speed, more ground is taken out by the machine drills per yard forward, as headings by hand labour are ordinarily only driven 5 feet by 6 feet; and if the hand heading in hard rock were taken out the same size as the machine headings, the progress in the latter case, instead of being 5½ times greater, would be about 8 times greater. In softer ground the advantage of machine drilling of course decreases; the speed of machine drilling as compared with hand labour would be about as 3 to 1.

The above highly favourable results were not obtained all at once, and are due to the skill and perseverance with which the patentee, Colonel Beaumont, and his agents have displayed in perfecting the mechanical details, and the practical working out of the drill machinery; and before arriving at this successful issue a large expenditure of money had necessarily to be made by the contracting company, in experiments and improvements in the drill, and the appliances attending it from time to time.

For a short time at the early stage of the contract the diamond drill was used, but the cost of the diamonds was found to be too great for this description of work, although the machine remains unequalled for the deep bore holes required in prospecting.

The plant required for driving an advance heading similar to the one at the north end of the Maesteg Tunnel may be assumed to cost about £2,000.

Where only moderate progress is required, and it is wished to incur a smaller outlay, as is frequently the case in mining, a smaller pattern of drill is sold by the Diamond Rock Boring Company with a 3¼-inch cylinder, and 2 feet length of travel; this drill has no automatic feed, and can be worked on an altogether lighter frame than the camel used for large tunnelling operations.

Where the nature of the ground admits of intermediate shafts, and the simultaneous advancement of the different faces thereby gained enables a tunnel to be driven on rapidly, the full-sized tunnel can be more economically driven by keeping the advanced heading on the top, but this system of working affords only one face for the opening out to full size; and where the ground is weak and the face has to be squared down for every length of lining that is put in, the mining during that operation has to come to a full stop. It is therefore necessary, unless time be of no importance, to keep the advanced heading at the bottom, so as to secure several different points for breaking up to full size of tunnel; and it may be stated here that the operation of breaking up was found to be easier going south with the strata rising than in the opposite direction.

At the south end the advanced heading, together with the opening out to full width at the several points, was driven for the most part only to water level. The contractors’ agent who started the work, considering that it would be more economical to go on in this way until the junction afforded free drainage to the north end, and afterwards to underpin the side walls, and bottom up, rather than take the full depth of tunnel down with the gradient, by means of pumps, but time so pressed that pumps had to be applied to assist in these operations before the junction was effected, and inclined roads were driven from the water line to formation level, and from this point the tunnel was excavated to full section forwards for some considerable distance, to the junction with the north end, and the bottoming up and underpinning of masonry, which was done in short lengths, was worked backwards on the rising gradient to the south end. The ground in some places was rather heavy, requiring 14 bars of 15 inches diameter, which is rather heavy timbering for a single tunnel, and in such cases lengths of only 12 feet lining could be put in, the general lengths being 18 feet, four or five centres or ribs being used.

Top headings had, of course, to be driven sufficiently in advance to draw the bars. In some instances where the ground was good several lengths were opened out and turned at a time.

The engineers, having regard to the difference in cost and to the greater durability of stone, elected to adopt masonry rather than brick lining, but the contractors finding the stone, although abundant, costly to dress, and that it took four to five days to turn a length in masonry, whilst it could be done in 24 hours in bricks – an important consideration when the advance heading was at the top, and the ground loose – and having a considerable amount of trouble with the Union masons, applied for permission to adopt brickwork at the same price as masonry. This was granted, and the Pencoed brick adopted.

In turning a length of 18 feet in brickwork, three bricklayers would be engaged, changing from side to side, but in masonry there would be three masons on each side. In brick lining the time in turning a length is taken up as follows – side walls, 10 hours; setting centres, 6 hours; arching, 8 hours

24 hours total.

In masonry lining, two days are taken in building the side walls and two days in setting the centres and arching.

On the 21st April 1876, a very lamentable accident occurred at the north end, in which 13 lives were lost by an explosion of dynamite, in a manhole 176 yards from the tunnel mouth, and where the charges were being prepared. Most of the men were killed in a break-up about 37 yards inside the manhole. The concussion was hardly felt at all in the face of the advanced heading, about 202 yards distant; and some men in a break-up 133 yards from the manhole were also uninjured, but the blast came out towards the entrance with terrific force. The men who were killed were not mutilated, but it is difficult to say whether death was caused by the concussion, or by the very overpowering fumes of exploded dynamite. Probably both causes operated.

The tunnel, which is nearly completed, will cost the Railway Company about £29 15s per yard forward, or about £47,422 for the whole length.

The drills have only been used in the advanced heading, but the writer ventures to think that the time is not far distant when the whole of mining work in driving tunnels through hard ground will be accomplished by machine drilling, especially in cases where the tunnel is taken out full size in one face, although improvements are probably more to be looked for at present in the appliances attending the drills, and in the detailed management of the work, rather than in the drills themselves.

The writer is informed that the same percussive drills are driving a heading in Cornwall 7 feet by 8 feet in the hardest Tin Capel at the rate of 10 yards per week; the progress with hand labour having been only 1 yard per week, the advantages here being ten times in favour of machine drilling, whilst much more ground is taken out – a very important consideration when the heading is driven in the mineral lode.

The Diamond Boring Company have just completed with these drills the junction lengths of bottom heading of the Queensbury Tunnel for the Great Northern Railway Company, near Bradford, and for which Mr Fraser is engineer; the ground was rocky shale and good for progress; an actual rate of 28 yards per week was reached, and during the last month, previous to the heading being holed, a total of 105⅓ yards was driven.

Speed with the advanced heading means actual economy of construction, because an increase in the cost of driving the heading must be set against the cost of the shafts, with all their pumps and gear for working them, which are unnecessary where the bottom heading can be driven sufficiently rapidly.

Take the case of a long tunnel like that at Queensbury, where seven shafts were commenced, five having been put down, and two abandoned owing to the great difficulty of dealing with the quantity of water which was met with. In such a case as this no cost which the use of machinery could put on the advanced heading would nearly come up to the saving effected by the shafts and the pumping being dispensed with. The writer is informed that this tunnel is 2,500 yards long, that the aggregate depth of shafting amounted to 546 yards, and that the quantity of water raised was about 1,000 gallons per minute.

The successful results achieved by machine drilling are likely to give a great impetus to tunnel driving in the future, affording new outlets for our coal and manufactured products; for without machine drilling, or some process of excavating by machinery, the Severn Tunnel, an undertaking of vast importance to South Wales, would probably never have been started, and the Channel Tunnel between France and England, although in softer ground, never seriously contemplated.