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NOTES AND EXTRACTS

ON THE HISTORY OF THE

LONDON & BIRMINGHAM RAILWAY


CHAPTER 5

EASING THE GRADIENT
 


THE RULING GRADIENT


There is scarcely a portion of this line, from one end to other, which is not either carried by embankment above the general surface of the country, or sunk below it by means of excavation.  It has, indeed, in point of execution, been one of the most difficult works of the kind in the kingdom.  London clay, disrupted chalk, and running sands, sadly impeded the progress of the works; yet such is the perseverance of man, when he sets about a work in earnest, that all the formidable difficulties which sprang up in quick succession, and for awhile seemed to arrest the progress of the works, have been very creditably surmounted, and now is in full enjoyment of the benefits of this vast undertaking.”

The Railways of Great Britain and Ireland, Francis Whishaw (1842).


In the age in which the London and Birmingham Railway was built, civil engineers went to some lengths to level the natural gradient of the land ― or reduce it to a gently sloping surface ― on which to lay their track.  Their aim was to minimise the reduction imposed by gravity on the limited tractive ability of the locomotives then available, for the steeper the incline the greater is the amount of effort wasted by a locomotive in overcoming gravity.  George Stephenson had devoted much research to the subject:


“He had long before ascertained, by careful experiments at Killingworth, that the engine expends half its power in overcoming a rising gradient of 1 in 260, which is about 20 feet in the mile; and that when the gradient is so steep as 1 in 100, not less than three fourths of its power is sacrificed in ascending the acclivity.  He never forgot the valuable practical lessons taught him by these early trials, which he had made and registered long before the advantages of railways had become recognized.  He saw clearly that the longer flat line must eventually prove superior to the shorter line of steep gradients as respected its paying qualities.  He urged that, after all, the power of the locomotive was but limited; and, although he and his son had done more than any other men to increase its working capacity, it provoked him to find that every improvement made in it was neutralized by the steep gradients which the new school of engineers were setting it to overcome.”

The Life of George Stephenson and of his Son, Samuel Smiles (1862).


A firm believer in his father’s dictum, when Robert Stephenson surveyed the route for the London and Birmingham Railway he set himself a ruling gradient [1] of 1:330, or approximately 16 feet in the mile.  This he considered to be the maximum that a locomotive could manage while hauling a useful load at speed.  To the extent that his belief was correct, engineering advances soon resulted in locomotives capable of handling steeper gradients, but by then the deed was done.  The London and Birmingham Railway was thus built on easy gradients conducive to high speed running, but at the expense of considerable civil engineering work in the form of cuttings, embankments, bridges, viaducts and tunnels. [2]

Reducing the gradient.
Cut and fill ― the spoil from excavations is used to form nearby embankments.


――――♦――――

 

CUT AND FILL


Most of the civil engineering necessary to achieve Stephenson’s ruling gradient involved forming embankments and excavating cuttings ― embankments to raise the level of the line above that of the surrounding land, cuttings to lower it.  Where possible, the approach taken to the construction of both was that of ‘cut and fill’, which involved transferring the spoil excavated from a cutting to a nearby location where it was required to form an embankment.  This avoided the need to buy extra land from which to obtain the material to form an embankment, [3] and the builder was not left with the task of having to dispose of the spoil from a cutting by spreading it over the adjacent land in what were known as ‘spoil banks’.

To create a spoil bank, the Company first needed to agree compensation terms with the landowner.  The topsoil was then removed from a tract of land adjacent to the work and the spoil spread over it.  When this operation was complete, the topsoil was replaced over the spoil to restore the land’s fertility.  In his guide to the Railway, Freeling describes one such operation, which took place about a mile and a half to the south of the Colne Embankment near Watford:


“Pinner Park House just to the left of the line . . . . About 150 yards before this post, [13¼ miles] there is a large spoil bank to the left; this is formed from the ballast taken from the excavations.  Before this is placed on the land, the soil is carefully removed; the ballast is then laid down over the space, and the soil placed thereon, which will produce crops the same year.”

The Railway Companion, from London to Birmingham, Arthur Feeling (1838).


The excavation referred to was of Oxhey cutting, most of the spoil from which was used to form the southern section of the Colne Embankment (that used to form the northern section being taken from the deep approach cutting to the south of Watford Tunnel):


“It took nearly one million cubic yards of earth to make this embankment, which is in some places above forty feet in height, and is the largest throughout the whole line.  Soon after entering upon it the Railway goes over the London road, by a brick viaduct of five arches, of forty three feet span each; they are composed of ellipses, having voussoirs at the intrados; the centre arch is of an oblique form, [skewed] in order that the course of the road should be preserved as heretofore . . . . The next bridge conveys the Railway over the river Colne.  It consists of five semicircular brick arches of thirty feet span each, with side walls, and having a stone cornice its whole length, ― the total length of the parapet walls being 312 feet.  It has a light appearance; and viewed from the meadows appears very lofty, being fifty feet high.”

The London and Birmingham Railway, Roscoe and Lecount (1839).


Thus, the valley of the Colne was crossed by a combination of viaducts and embankment, the latter being formed from spoil obtained from nearby cuttings ― the principle of cut and fill.


――――♦――――

 
FORMING EMBANKMENTS

Note the inward-sloping layers.


The two approaches to forming an embankment were essentially bottom-up and top-down.

The bottom-up approach involved forming the full width of the embankment in shallow layers, a few feet thick, each layer being laid slightly inward-sloping [4] and compacted before the next layer was put down.  According to a respected civil engineering manual of the period, this produced a firm formation:


“The most expensive course is that of forming the bank in shallow layers, running out each of them to the full length of the work, and following with the upper layers after each lower one is completed.  By allowing each layer to settle . . . . before the next is formed, and, moreover, using beetles in ramming the earth down, an embankment will be formed of the greatest possible density and stability . . . . Both in embankments and excavations, the slopes should be dressed to the intended face, as shortly as possible after the formation is completed, and covered with turf, if possible, or at least with soil sown with grass-seed.”

The Practical Railway Engineer, G. D. Dempsey (1847).


The turf or grass-seed helped to consolidate the slopes.

 

Forming the Boxmoor Embankment bottom-up.
View of the Boxmoor embankment, when in progress, shewing the method of forming it, from a side cutting, with horse-runs.  John Cooke Bourne, June, 1837.


The Boxmoor embankment (above) near Hemel Hempstead was formed in this way, the spoil being lifted up the side of the embankment in a hazardous procedure involving ‘horse-runs’:


“Over Boxmoor the railway is continued on an embankment, formed with materials conveyed from adjacent cuttings.  The ballasting, &c., was raised from the surface on each side of the line by horse-runs, as shown in the drawing, No. XVII.
[above]  The horse, in moving along the top of the embankment, draws the rope attached to a wheelbarrow round two pulleys, and thereby raises the barrow of earth up the sloping board, together with the labourer who holds and guides it.  This is a dangerous occupation, for the man rather hangs to, than supports the barrow, which is rendered unmanageable by the least irregularity in the horse’s motion.  If he finds himself unable to govern it, he endeavours, by a sudden jerk, to raise himself erect; then, throwing the barrow over one side of the board, or ‘run’, he swings himself round and runs down the other.  Should both fall on the same side, his best speed is necessary to escape the barrow, which, with its contents, comes bounding down after him.”

Introduction to Drawings of the London & Birmingham Railway, John Britton (1839).


The top-down method of forming an embankment was generally preferred because it was quicker.  It involved extending the formation gradually, at its full height, from both ends.  The spoil from a nearby excavation was conveyed to the workings along a light railway in what today might be referred to as tipper trucks, but were then called ’earth wagons’.  Each wagon was then run up against a buffer placed at the end of the workings, the momentum causing the wagon’s tray, which was pivoted, to swivel upright, tipping its contents over the edge.


Earth wagon.


However, before the formation of an embankment could commence, the earth wagons had first to be assembled, a task that Francis Conder described in his memoirs:


“In a country town [Watford] where almost everyone knows as much, or more, about his neighbours business as about his own, the arrival and establishment of two civil engineers was accepted as an outward and visible sign that, for good or for evil ,the great railway experiment was about actually to be made.  Before long, one or two keen-visaged, weather beaten Yorkshire and Northumberland men, neither graziers nor farmers, nor mechanics, but seeming to possess some resemblance to each of these active classes, found means of establishing themselves in roomy farm-houses, where the rick-yard soon began to assume the appearance of a carpenter’s yard.  Then men set to work in a field very near the mail coach road, where the hill dropped rapidly to the valley, in constructing waggons of a form utterly inconceivable either to a farmer or to a carrier.  Cast iron wheels, formed with the flange which is now so familiar to every loiterer at a railway station, but which was then an unexplained puzzle to most folk, were firmly keyed on to solid axles; a ponderous oak framework was fixed on the axles, and a special provision was introduced, for tilting up the large shallow tray which rested on that framework.  A stout, hale, well-humoured Yorshireman stood or sat in this field from early morning till sunset, and inspected the progress of the waggon with a never-flagging interest.  People came to stare at him as much as at his labourers.”

Personal Recollections of English Engineers, F. R. Conder (1868).


The Yorkshireman with the never-flagging interest was possibly James Copeland, contractor for the Watford to Kings Langley section, which included the long Watford tunnel (and its deep cuttings at both approaches) and the Hunton Bridge embankment.  However, writing in the Biographical Dictionary of Civil Engineers, Mike Chrimes suggests John Willans Nowell, contractor for the Harrow section.

When the earth wagons had been assembled, work on the embankment could begin.  By this date horses were being replaced by contractors’ locomotives, especially where there was a considerable distance ― ‘the lead’ ― between the excavations where the spoil was to be obtained, and the embankment where it was to be deposited.  At some point along the embankment workings, the track on which the earth wagons ran would be fanned out through a system of points, to four or even six lines, to enable tipping to take place across the full width of the embankment.  Robert Rawlinson, assistant engineer for the Blisworth section (and later a sub-contractor), described tipping spoil over the end of a forming embankment, a dangerous practice known as ‘teeming’:
 

The tip.

“The ‘tip’ is the place where the material is teemed over to form the embankment; the tip is a removable point in a long embankment; the extreme end of the embankment; and in a heavy embankment, such as the Blisworth, at least 40 or 50 feet in height, it was a most difficult operation, with the material they had to work, to keep these tips at their ordinary level.  To do so they were constantly obliged to raise the levels, and run up hill a portion of the line; but supposing they had got the ‘tip’ 10 feet high in the morning, perhaps tomorrow morning they would find it 15 feet below the proper level . . . . Subsided or slurred out at the sides.  To do this work, the rails are laid in long shunts; there are five or six lines of railway at the tip-head, branching out of the two lines leading to it.  To run the waggons onto these shunts (sometimes the engine would be on a road that was partially formed), the train of waggons attached by a long chain 30 yards behind the engine; a velocity was given to the engine and communicated to the waggons, and the engine was then suddenly stopped, and a pair of points turned behind it, and the waggons were then run in forward, that they might be tipped into the embankment.  Horses were employed to run the separate waggons down to the tip-head, and when the end of the embankment was raised above its level, they would take a short run for the horse to get the waggon into motion and give it momentum, so as to carry it on to the tip-head; and sometimes waggon, horse, men and all would go over . . . .”

Robert Rawlinson ― Select Committee on Railway Labour (1846).


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EXCAVATING CUTTINGS

Contractor’s locomotive hauling a train of earth wagons in a cutting near Berkhamsted.
View of a cutting and bridge near Berkhamstead (sic.), looking N.W.: shewing part of the town. John Cooke Bourne, June 1837.


Building the London and Birmingham Railway involved upwards of 12 million cubic yards of excavation, or over 100,000 cubic yards of earthwork per mile.  The heaviest cutting on the line is at Tring ― 2½ miles long, averaging 40 feet deep, the greatest depth being 60 ― from which something over 1,400,000 cubic yards (approx 1.1 cubic metres) of spoil were removed.

In some respects the approaches to excavating a cutting were similar to those for forming an embankment.  One was to barrow the spoil out of the workings with the use of horse-runs (described above), as is depicted in J. C. Bourne’s famous drawing of the Tring Cutting excavation (below).  The advantage of using horse-runs was that many teams of labourers could be put to work simultaneously along the full length of the cutting, rather than being restricted to working inwards from the two extremities:


“Although there were thirty to forty horse-runs in the Tring cutting constantly working, during many months, and each labourer was precipitated down the slope several times; such, from continual practice, was their sure-footedness, that only one fatal accident occurred.  A moving platform was invented by the engineer to supersede the necessity of thus risking life and limb, but the workmen, who considered it was designed to lessen their labour and wages, broke it.”

Introduction to Drawings of the London & Birmingham Railway, John Britton (1839).


This method was most useful in circumstances where the spoil was not to be carried away, but consigned to adjacent spoil pits, although at Tring, part of the spoil excavated probably went into forming the 6-mile long embankment to the north of the cutting.


Excavating the Tring Cutting.
View of the deep cutting near Tring, with horse-runs, &c. John Cooks Bourne, June 1837.

 
The alternative approach was to excavate from a cutting’s extremities and convey the spoil away in trains of earth wagons.  This involved first creating a working faces at each end of the section of rising ground through which the cutting was to be driven.  A trench or ‘gullet’ was then cut into the face of sufficient breadth to accommodate a railway and train of earth wagons.  Excavation then took place at each side of the gullet, the spoil being tipped into the waiting earth wagons below:


“In starting an excavation through a hill of considerable height, it is desirable to get a fair face to the work, that is, one at right angles with the direction of the cutting; and from this face to start a system of gulleting or notching, by which labour is much economised . . . . As the work proceeds into the hill, and the width is increased to provide for the slopes, it becomes desirable to run a ‘gullet’ along the centre of the cutting, in order to bring the greatest number of
[earth] waggons into use.  Thus the temporary rails being laid in the gullet, a train of waggons is sent forward these receive all the produce of the harrowing on either side, which is advantageously prosecuted in advance and alongside of the waggon-filling, for the purpose of keeping the work level for starting the next stage or layer of excavation.”

The Practical Railway Engineer, G. D. Dempsey (1855).

 


Above: excavating a cutting.  A face is formed, then one or more gullets are driven into it of sufficient width to accommodate a train of earth wagons.  The gullets are driven forward as the work proceeds.

Below: this scheme in section and in plan as the gullets are driven forward, showing the trains of earth wagons.  Spoil was shovelled or barrowed down into the wagons from both sides of the cutting, which is gradually widened out:


“By the aid of the gullet the wagons can be brought close alongside the material to be moved, and a couple of men being set at work on each, the soil is deposited in them with an ease and celerity far surpassing that which would be required had each spadeful to be conveyed even for the distance of a few yards.  Meanwhile, as the stuff is removed by the workmen on either hand, the gullet is continued into the hill by those a-head, while lumps are showered into the wagons on all sides.”

Our Iron Roads, Frederick Smeeton Williams (1852).

Excavating at two levels: excavation was performed in layers.  As one layer was completed, another was started at a lower level until the required depth was reached.


Excavating a railway cutting.
Excavation at Park Village, showing the works in progress. John Cooke Bourne, September 1836.


――――♦――――

 

INSTABILITY IN CUTTINGS AND EMBANKMENTS


In the sense in which it is used here, instability refers to the failure of earthworks resulting in slip:


“SLIP, or LAND-SLIP ― a slipping of the earth of a cutting, or embankment, which most frequently occurs in the case of deep cuttings and high embankments; they generally arise from the want of stability of the soil, and general badness of foundation, also from the side-slopes being formed too steep; but clayey soil will slip at almost any slope, good drainage is, therefore, important in earthwork.”

A Glossary of Civil Engineering, S. C. Brees (1841)


Slip was a problem that occurred at a number of points along the Railway, sometimes several years after the earthwork in question had been completed, this being referred to as ‘delayed slip’.

One cause of slip resulted from building the slopes of embankments and cuttings at a steeper angle than that at which the material in question would lie naturally at rest without slipping, its ‘angle of repose’.  But the steepness of a slope is not a straightforward question to decide, for the angle of repose not only varies for different materials, but can also be affected by the amount of moisture they contain.  For instance, a wall of damp sand can be built almost vertical (as those who have seen the work of seaside sand artists will appreciate); a pile of sand, when wet, will lie at 45º to the horizontal; when dry, at 34º; but when saturated, the angle of repose reduces to as little as 15º.  Sir Henry Parnell’s much respected treatise on roads (based on the work of Thomas Telford) offered this advice on the slope of cuttings and embankments, and on the need for consolidation:


“When it is necessary to make a deep cutting through a hill, the slopes of the banks should never be less, except in passing through stone, than two feet horizontal to one foot perpendicular; for though several kinds of earth will stand at steeper inclinations, a slope of two to one is necessary for admitting the sun and wind to reach the road.  The whole of the green sod and fertile soil on the surface of the land cut through should be carefully collected and reserved, in order to be laid on the slopes immediately after they are formed.  If a sufficient quantity of sods cannot be procured in the space required for the road, the slopes should be covered with three or four inches of the surface mould, and hay seeds should be sown on it; by this plan the slopes will soon be covered with grass, which will be a great means of preventing them from slipping.”

A Treatise on Roads, Sir Henry Parnell (1833).


Before the first London and Birmingham Railway Bill was placed before Parliament in 1832, the Company commissioned two experienced civil engineers to review Stephenson’s plans for the line; they were Henry Palmer (1795-1844) and John Urpeth Rastick (1780-1856).  At the committee stage in the House of Lords, both engineers gave evidence, in the course of which they expressed their opinions on the angles that Stephenson planned for his slopes.  Of the two, Rastick’s views are the more enlightening; while generally content with Stephenson’s plans, as was Palmer, he felt that shallower slopes were advisable, especially were banks were to be formed in London clay.  But shallower slopes meant wider structures, which in turn meant that more land had to be bought and more material had to be excavated:


“Regarding the slopes, generally speaking, I agree with Mr. Stephenson; perhaps there are instances in which it may be prudent to increase them.  I made a calculation of them at 3 to 1, instead of what they are stated at by Mr. Stephenson, which made an addition of £17,303; but I should not be inclined to make them as much as 3 to 1, (I have not had experience in London clay).  Where the cuttings are shallow 2 to 1, or less, is quite sufficient, and there are few cuttings of great importance along the line.  Mr. Stephenson makes his deep cuttings 2 to 1, and his shallow cuttings 1½ to 1.  One of the principal cuttings is at Primrose Hill, there is another, rather deep, where he crosses the London Road to Harrow, perhaps it may be necessary to increase these slopes to 2½ to 1, the expense of which would be under £5,000.  In works of this nature slips will occur, even in the best material.”

John Rastrick, from Railway Practice, S. C. Brees (1839).


Speaking some years later about the construction of the Colne Valley embankment, the Resident Engineer, G. W. Buck, informed a parliamentary committee [5] that this embankment had been made shallower than the angle of repose for the spoil from which it was formed:


“The Watford Embankment is at present about 32 feet high; the Permanent Angle of the Slopes is 2 to 1; but the Natural Angle at which the Soil will stand immediately after teaming (the Angle of Repose) is about 1½ to 1, which enables us to make the Embankment temporarily wider at the head (as it is called by the workmen) and get in 6 Teaming Lines of Road: after the Line has passed that particular point, the work is trimmed down to 2 to 1, as it is no longer required.”

G. W. Buck, from Railway Practice, S. C. Brees (1839).


On the face of it, using the spoil from a cutting to form an embankment seems the sensible thing to do, but the material can sometimes be unsuitable for the purpose.  The great Wolverton Embankment is an example.  It was formed on the cut and fill principle using, in part, Oxford clay excavated from a nearby cutting, with serious consequences:


“In the formation of the embankment at Wolverton, great difficulties were encountered . . . . The length of the embankment being one mile and twenty eight chains (deducting the viaduct), and the height of a great part of it forty eight feet, some accidents were to be expected, especially in bad weather; but no one could have imagined what would take place on the south side of the viaduct.  Here the material, at the commencement, was composed of sand, gravel, and blue clay: this stood very well; but when the workmen went deeper into the cutting, they excavated some black, soapy clay; this was tipped on to a turf bottom, and the weather being also very unfavourable, although every care was taken to mix dry stuff with the wet material, yet there occurred one of the worst, if not the worst slip, along the whole line.  Earth was tipped in for day and days, and not the slightest progress was made; as fast, in fact, as it was tipped in at the top it kept bulging out at the bottom, till it had run out from 160 to 170 feet from the top of the embankment; and at last a temporary wooden bridge was formed, and, by wagoning the earth over this, the embankment between the slip and the viaduct was formed, by first digging a trench, five feet deep, and nearly the whole width of the embankment, and forming a mound on each side to prevent it from giving way.”

The London and Birmingham Railway, Roscoe and Lecount (1839).


Forming the Wolverton Embankment.
View of the embankment near Wolverton, during its progress: shewing the manner of forming embankments, and an accidental slip of earth. John Cooke Bourne, June 1837.


Likewise, the banks of cuttings driven through some types of strata also have a tendency to instability.  Much difficulty was experienced excavating the Blisworth cutting:


“In the case of the great Blisworth cutting the strata were unequal in consistency.  About halfway up the face of the cutting a stratum of limestone rock, 25 feet in thickness, was found, with loose strata below and above it, and it was necessary to prevent the lower stratum, consisting of wet clay, from being forced out under superincumbent mass by undersetting.  A rubble wall, averaging 20 feet in height, was built on each side underneath the rock, strengthened by buttresses at intervals of 20 feet, resting on inverted arches carried across underneath the line.  A puddle-drain was formed behind each wall, with a small drain through the wall to let off the water from behind.



Fig. 13 is an elevation of the west end of the cutting where it is about 40 feet deep, showing clearly the method of undersetting, and fig. 14 is a cross section of the side walls at the same place, where the left-hand shows a section of the wall in the water, and the right-hand side shows the section through a buttress, together with the invert and drains.  One of the walls is shown in front elevation in fig. 15.”

Encyclopedia Britannica 9th Edition (1902).


During the construction of the line, formations in clay gained a notorious reputation, particularly when the material was poorly compacted.  In some clays, the particles from which they are formed are loosely packed, allowing water to enter the body of the structure, which then softens and weakens it.  Furthermore, when clay dries out, fissures form within it that also allow the ingress of water, a problem that civil engineers of an earlier generation discovered when dealing with leakage in canals.  A further complication ― if one were needed ― is that this softening process in clay embankments and cuttings does not necessarily happen quickly; the ingress of water into a structure is sometimes slow, but progressive, taking several years before it is sufficiently weakened for failure to occur.  Such a delayed slip occurred in the Bugbrooke cutting (Upper Lias clay) in 1842, several years after its completion:

 
“ACCIDENT ON THE LONDON AND BIRMINGHAM RAILWAY. ― The following official report has been addressed to the Board of Trade, on the subject of a slip at the Bugbrooke excavation on Saturday last, by Mr. Creed, the indefatigable Secretary to the Railway: ―


‘Sir, ― I am instructed to report to you for the information of the Lords of the Committee of Privy Council for Trade, that in consequence of a slip, about 50 yards in length, which occurred on the down side of the Bugbrooke excavation of this railway half-way between the Blisworth and Weedon stations, about four o-clock in the afternoon of Saturday the 24th inst., several thousand cubic yards of earth covered both lines of rails, and obstructed for a time the regular passage of the trains.

By extraordinary exertions, however, the up line was cleared before eight o’clock the same evening; and the up as well as down trains have since continued to pass uninterruptedly over it.  Both lines will, it is expected, be clear in the course of this week.

The only practical inconvenience which resulted from this occurrence (for it was happily unmarked by casualty), was the exchange of passengers between the carriages of the York up train and the 1h 30min. p.m. down train on the opposite ends of the slip, and the delay of rather less than two hours in the arrival of the two other trains.

The surface of the ground, both above and on the face of the excavation, had presented no previous appearance to indicate a slip; but the attention of the overlooker of the road and engine-man of the 9h. 45min. a.m. down train having been called to this point by a slight deflection of the rails of the down line inwards, it was carefully watched.  The company’s engineer is desired to examine the slip, and to report as to the immediate cause.

I have the pleasure to add, that the directors have every reason to be satisfied with the strict observance of regulations, and the zealous exertions which were manifested on this occasions by every person in their employ.
                                                          I have the honour to be, Sir,
                                                                       Your most obedient servant,
                                                                                            R. Creed, Secretary.’”

The Northampton Mercury, 1st October, 1842.


Extra precautions ― in the form of shallow slopes, counterforts [6] and retaining walls ― had therefore to be taken when excavating and repairing cuttings in clay soils, and good drainage was essential.

Another cause of instability lies in the nature of the ground, which might be too soft to support an embankment’s weight.  Following its completion, the long embankment across the Colne Valley suffered slippage due to its foundation sinking:


“The whole of the land near this spot is most precarious in stability; and the effects are clearly visible in the amazing ‘slips’ which have taken place in the embankment across the valley.  Oftentimes, in a very few hours, the level of the newly-formed ground has sunk several feet, while the base of the embankment has widened out to an enormous extent, causing infinite labour to bring the level of the Railway back again to its original state, and to make it solid enough for the passage of the trains; this has caused many a sleepless night to the workmen and engineers.  The length of this embankment is about a mile and a half, and is composed entirely of the finest materials for such a purpose ― chalk and gravel.”

The London and Birmingham Railway, Roscoe and Lecount (1839).


――――♦――――

 
VIADUCTS

Wolverton Viaduct crossing the valley of the Great Ouse.


The following extract is from Stephenson’s specification for the Lawley Street viaduct.  Its construction formed contract 1G, dated August 1834, the contractor being James Nowell & Sons . . . .


“This Bridge or Viaduct, is for the purpose of carrying the Railway on a perfectly level plane over Lawley Street, and the two branches of the River Rea.  It will consist of ten arches, each 50 feet span; the soffits of all the arches being brought to the same horizontal line, at the height of 23 feet 6 inches, above the level of the present surface of Lawley Street at its intersection with the centre line of the Railway.

The Arch passing over Lawley Street will be built askew to suit the angle of intersection of the street with the Railway, the remaining nine to be built square.

The Direction of the bridge must be curved at a radius of one mile and a quarter, so that the parapet walls shall be parallel with the lines of Railway.

The Bridge must be built of brick with stone arch quoins springing-course, string-course, plinth, and coping.  Each front will have two projecting pilasters, and the ends of the piers will project from the face line of the arch in the manner shewn in the Drawings No 1 and II.

All the Arches will be segments of circles and of similar form on each front of the bridge . . . .”


From this it can be seen that a viaduct is a type of bridge composed of multiple spans.  In the case of the Lawley Street Viaduct it was ten, the central span being skewed (skewed bridges are described below).

In the context of a railway, viaducts were built to convey a line over an obstruction, on the level (viz. para. 1 of the extract above).  This might be a depression in the surrounding land, such as a river valley; buildings in a built-up area of a town; or a major road, especially where there was a considerable height difference between road and rail.  Some very considerable viaducts were built on British railways, that at Ribblehead on the Settle and Carlisle line being well known to railway enthusiasts . . . .


The former Midland Railway viaduct spanning the valley of the River Ribble, North Yorkshire. Photo: chantrybee.


Viaducts often fulfil the same purpose as embankments, which had the general advantage in construction cost from being able to utilise the spoil from nearby excavations.  However . . . .


“. . . . as elevations are increased, embankments lose their superiority over, and are soon superseded by, viaducts.  This is chiefly owing to the rapidity with which their sectional area is increased as they become elevated, and the consequent large quantity of land they require.  These increasing effects are not experienced in a viaduct.”

A Practical Treatise on the Construction and Formation of Railways, James Day (1848).


But as the century progressed, the economic balance between embankment and viaduct appears to have altered, to the extent that viaducts became generally the cheaper option:


“During the development of the railway system in Britain, the economy of bridge building has necessarily received much attention, and has been illustrated by a multitude of structures, exhibiting many varieties of design and of material.  That this vast experience has led to substantial improvements, and to saving in cost, may be inferred from the fact, that in many cases bridges and viaducts of great extent are now adopted in preference to mere earthworks, ― a long viaduct being now available at less cost, original and current, than an embankment of similar extent; whereas, in the early experience of railway making, it is well remembered that the most expensive earth-work was almost invariably adopted, both for economy and ultimate sufficiency, in preference to any description, then approved, of bridge work.”

The Practical Railway Engineer, G. D. Dempsey (1855).


Viaducts were not necessary for bridging streams and minor roads, which were crossed using a short bridge built into an embankment, or taken under an embankment through a culvert or tunnel.  However, where a crossing of significant breadth was encountered, such as the Colne Valley (Watford) and the valley of the Great Ouse (Wolverton), the practice on the London and Birmingham Railway was to combine a viaduct with an embankment:


“Immediately after resuming our journey, we cross the Grand Junction Canal by a handsome stone and iron bridge, and enter upon the colossal embankment, which carries the [rail] road across the Vale of Wolverton.  At a short distance from the canal we cross the rivers Ouse and Tow, by a handsome brick viaduct, whose magnificent stupendousness will be better understood by reciting its various proportions.



It consists of six elliptical arches, each sixty feet span, springing, at a height of twenty one-feet from the ground, from piers ten feet in thickness; the height, from the crown of the arches to the basement of the piers, is about sixty feet.  The whole length of this viaduct, including the brick facing on each side of the arches, is about one-eighth of a mile.  In forming this viaduct, it was found necessary to divert the original courses of the Ouse and Tow.  They now flow on together beneath this viaduct, in one spacious channel paved with brick.”

The London and Birmingham Railway Guide, J. W. Wyld (1838).


Civil engineering advice of the times warned of the importance of erecting piers on firm foundations, especially in the case of a high viaduct, where a considerable weight bore down on a comparatively small area of foundation:


“For structures of this magnitude, the sufficiency of foundation is of the first importance: the greater altitude not only imposes greater weight of materials to be supported, but also evidently requires that the cohesion of the foundations, and indeed of the whole structure, be more perfect, as any defect or dislocation is more likely to occasion extensive mischief in proportion as the height is increased.  If gravel or chalk can be reached, with a good bed of concrete nothing need be apprehended; but if loam, sand, or bog occurs, piling is found the better expedient.”

The Practical Railway Engineer, G. D. Dempsey (1855).


Occasionally, excavating the foundations for viaduct piers unearthed the unexpected:


“Now for another curious ‘find’.  On the line of the London & Birmingham Railway I had to build a viaduct over the River Avon between Wolston & Brandon Villages.  On examination as to the foundations to be expected I discovered that below the bed of the river there were 25 feet in depth of peat lying on a bed of firm gravel.  This I found out by pushing down a long bar of iron.  To reach the gravel it therefore became necessary at each of the abutments and piers of the viaduct to construct what are called coffer dams, formed of planks driven down through the peat and into the gravel to enable us to build up the foundations.

When the coffer dam was complete, we course had to excavate the black peat.  On arriving within about 5 feet of the gravel we found complete trees lying, of course, on their sides with all their branches crushed down quite flat: you may imagine our surprise to find quantities of hazel nuts in the peat amongst the branches.  Of course they were very black and soft.  I took out a large quantity of them hoping to dry and keep them as a curiosity ― but as they became dry they crumbled to dust.  We went on sinking in the same character of black stuff formed of coarse peat till the gravel bottom was reached, but here our surprise was doubled for, lying on the surface of the gravel we found skulls of the short horned breed of oxen, quite complete with teeth, horns and all, with a great number of bones not only of oxen but of sheep, hares & foxes, and most wonderful of all, the leg bone of an elephant!”

The Dairy of John Brunton (ca. 1890).


The viaduct to which Brunton refers is the London and Birmingham viaduct, one of two railway viaducts that cross the River Avon near Rugby.  The other, Rugby Viaduct, is a now abandoned structure on the former Midland Counties Railway between Rugby and Leicester. [7]




West side of the viaduct over the River Avon, near Wolston. John Cooke Bourne.


The London and Birmingham Railway viaduct is now Grade II listed, the English Heritage description of it reading:


“Railway viaduct. c.1835.  Brick faced with rusticated sandstone ashlar with strongly projecting moulded string course, and coped parapet.  9 elliptical arches and 6 narrower subsidiary round arches have rusticated voussoirs.  Canted piers between each arch.  Larger piers between main and subsidiary arches and to ends have octagonal caps.  2 subsidiary arches to west are bricked up and largely hidden by the embankment.  Built for the London and Birmingham Railway.”



Elevation of the River Avon Viaduct, London & Birmingham Railway.


“This viaduct, of which the total length is about 350 feet, consists of nine semi-elliptical arches, 24 feet span, and 7ft. 6in. rise, and three semicircular arches at each end, of 10 feet span, faced entirely with stone.  Each of the six end arches has a brick inverted arch between the piers above the foundations, which are carried along uniformly in a solid bed beneath these arches, with such steps and at such levels as the nature of the substratum required.  The three middle arches have an inverted arch of brick-work [visible in the drawing], which forms an artificial channel for the river.  This invert is faced at each end with a row of sheet piling, driven through the loam into a bed of strong gravel beneath. All the foundations which do not reach this gravel are built upon thick beds of concrete, and a layer of the same material covers the whole of the arches, forming a level bed for the gravel in which the sleepers of the railway are laid.”

The Practical Railway Engineer, G. D. Dempsey (1855).


――――♦――――

 
TUNNELS

A levelling party at work, Primrose Hill Tunnel.


TUNNEL: a subterraneous gallery or passage excavated or dug through the earth for the passage of a canal, road, or railway.

A Glossary of Civil Engineering, S. C. Brees (1844).


TUNNELS: The principal tunnels on this [London and Birmingham] line are those of Primrose Hill, which is 1120 yards in length; Kensal Green (curved), 320 yards; Watford, 1830 yards; Leighton (curved) 272 yards; Weedon, 418 yards; Kilsby, 2398 yards; and Berkswell, 300.  The Kilsby tunnel, which is by far the chief work of the kind on this railway . . . .”

The Railways of Great Britain and Ireland, Francis Wishaw (1842).


Tunnelling is a further means of reducing gradient, although whether that approach was to be preferred to excavating a cutting depended on circumstances:


The choice between the two methods will depend on the nature of the soil at the dividing ridge, and the comparative expense of the two methods: in general, it is said, that tunnelling is to be preferred to deep cutting when the depth to be excavated is above sixty feet; and, also, when the cost of a running yard of each is the same, it is said that deep cutting is generally to be preferred, from the greater facility and despatch with which it can be done.

An Elementary Course of Civil Engineering, Dennis Hart Mahan (1838).


Other factors for the civil engineer to consider were whether a short tunnel with long approach cuttings was preferable to a longer tunnel with shorter approaches; similarly, whether a short tunnel under a high point of the ridge was preferable to a longer tunnel under a lower point.  In each case the cost of sinking shafts needed to be considered, while the nature of the ground and its tendency to slip was a factor to consider in deciding the length of the approach cuttings; and while cuttings posed the risk of slip, tunnelers had to face that of the roof collapsing before ― and possibly after ― a lining had been put in place:


“In soils which required to be arched, it is seldom safe to sink the working shafts directly over the crown, as they would weaken the earth and might occasion cavings-in.  It is therefore recommended, in such cases, to mark out the lines of the piers of the arch, and to sink the working shafts ten or fifteen feet on the outside of these lines. ”

An Elementary Course of Civil Engineering, Dennis Hart Mahan (1838).


This advice appears not to have been taken by the contractor excavating the Watford Tunnel, when one of the working shaft collapsed above the tunnel arch:


“In tunnels bored through chalk, it is often necessary to act with great caution, as it sometimes contains large holes filled with gravel, which, on being opened during the execution of the works, pours in on the unsuspecting miner like water.  Thus in the Watford tunnel, which passes through the upper chalk formation, where it is covered with a thick irregular bed of gravel, such breakings-in occasioned great inconvenience and delay.  The chalk fissures, sometimes a hundred feet in depth, filled with gravel, which when worked into, ‘rushed down with such violence, as to plough the sides of the tunnel as if bullets had been shot against it.’  Such an accident, occurring at the foot of one of the working shafts, overwhelmed ten men who were there at work . . . .”

Our Iron Roads, F. S. Williams (1852).

 
The approach to tunnelling was developed by the canal engineers.  This was further refined at Blisworth, on the Grand Junction Canal, where James Barnes drove a small pilot heading (or ‘driftway’) in advance of the main excavation, mainly to assist drainage, but it also provided a more complete examination of the strata while providing a further check on the tunnel’s correct alignment.

The alignment of the tunnel having been decided, the first task was to mark this out with pegs on the ground above.  In setting the direction, when one end of the tunnel was not visible from the other, ranging towers were built to assist with alignment, although by the time the London and Birmingham Railway was built reliable Ordnance Survey maps were available.  It was then necessary to test for the presence of any potential hazards in the underlying strata ― subterranean watercourses, quicksand, gravel and unstable formations ― that might make necessary a change in the tunnel’s alignment, by making trial borings to collect samples:


A careful preliminary examination is made of the geological strata, so far as these can he discerned from the external features of the country; and levels or soundings are taken, from which a profile of the surface of the ground to be passed under may be formed.  To test the character of the underground strata, before letting the works to contractors, vertical borings are made through the site of the proposed tunnel, or trial shafts are sunk with the same object.  No matter how thorough this preliminary examination may be, the nature of the strata throughout cannot be ascertained with perfect accuracy; and it may so happen, as in the case of the Kilsby Tunnel, that the most dangerous part of the ground may not be disclosed.

‘Difficulties of Railway Engineering’, The London Quarterly Review, Issue 205 (1858).





Section through Telford’s Harecastle Tunnel showing a ranging tower and exploratory shafts.


Excavation was commenced from each end of the tunnel, and from the bottom of working shafts sunk at intervals along the tunnel’s length.  A small heading was first driven between the shafts, and carried on through the length of the tunnel; this served to verify its alignment and level.  Francis Conder, a pupil of Charles Fox, left an account of the completion of this stage of excavating the Watford Tunnel:


“The line through the tunnel was straight, and had been set out and pegged over the surface, as in other portions of the route.  At every furlong in length a shaft had been sunk, with the intention of opening a drift way (a small heading) from end to end, and thus running both line and level through under ground, before commencing the main excavation and lining of the tunnel, which it was intended to carry on through three of these shafts, properly enlarged, using the others for ventilation . . . . a week after the completion of the headway, ― which week had been spent in knocking off elbows here, raising the roof there, and lowering the floor in another place, with occasional loss of time and of temper, as some intruder came blundering through the long narrow cavern, ― the pupil of the sub engineer, [Conder] the only one of the staff left on his legs, had the extreme satisfaction of viewing the red signal lamp, fixed at the north end of the head-way, from the southern extremity, over a regular and exact line of candles, one close to each shaft.  The question of the direction of the tunnel was thus solved . . .”

Personal Recollections of English Engineers, F. R. Conder (1868).

 


Above: longitudinal section through a tunnel under construction,
showing a shaft, worked by a horse gin, and two working faces.
Below: a horse gin.



――――♦――――

 
BRIDGES


A bridge provides a means of crossing a waterway or highway.  In common with a viaduct, a bridge is not a structure for regulating a railway’s gradient.  However, this chapter is the most appropriate place in which to describe some of the bridges on the line that were constructed under Stephenson’s direction.

Generally speaking, the situations in which the need for a bridge arises are where a railway and highway or waterway intersect either on the level, or at different levels.  Each requires a different bridging solution, depending on whether the intersection is at a right angle, or an oblique angle ― the latter introduces complications when the bridge is to be built from bricks and/or masonry.

Where a railway and highway intersected on the level, the cheapest solution was to build a level-crossing.  While this required minimal civil engineering, it introduced safety implications, especially on a mainline carrying high-speed traffic. [8]  The alternative was to raise or lower the road to provide sufficient clearance, it being impractical to alter the level of the railway. [9]  In considering where the balance of advantage lay in the two approaches, the following advice was offered:


“In economy of brickwork, the bridge in cutting has the advantage, as the footings require to be sunk only 18 inches or 2 feet below the slope; while the bridge in bank . . . . will require the abutments so much below the original surface.  The latter will also require fences on the approaches, which the former will not.  On the other hand, the bridge in cutting will involve more expense in drainage than the bridge in bank; and this consideration must be entertained with full regard to the comparative levels of the surrounding districts, and will frequently be found to outweigh all the other advantages of the sunk bridge.”

The Practical Railway Engineer, G. D. Dempsey (1855).

 

Raised bridge

Sunk bridge

 

Dempsey then goes on to advise on the situation where a road crossing needs to be made with a railway on a shallow (approximately 16 feet) embankment, or in a shallow cutting:


“In either instance, the best structure will be obtained by adopting a bridge with parapets parallel throughout, or very slightly diverging from each other at each end; by making it sufficiently long to allow easy slopes for the banks, an ample width of road, and for the abutments to cut well into the slopes on each side; thus dispensing altogether with wing or retaining walls which are always expensive and seldom secure.”

The Practical Railway Engineer, G. D. Dempsey (1855).

 

Railway in cutting

Railway on embankment


An elegant bridge built into the Blisworth Embankment.
The road leading from Towcester to Northampton.


Where there is a considerable difference in height between road and rail, a viaduct then becomes necessary:


“. . . . where the difference of levels is very considerable, and an extended structure or viaduct is required, economy of construction becomes additionally important.  A reduced width of viaduct, so as to provide for one line of rails only, has been sometimes recommended; but this is a kind of economy which can be justified only under peculiar circumstances, and which may be productive not only of much inconvenience and hindrance, but of greater ultimate expense than the double width would at first involve.”

The Practical Railway Engineer, G. D. Dempsey (1855).


And where viaducts are concerned, Dempsey joins other commentators in stressing the importance of the “sufficiency of foundations” if “extensive mischief” is to be avoided.

 

Railway in cutting

Railway on embankment

 

Where a highway and waterway intersect at right angles, the abutments of a bridge built to negotiate the crossing are parallel and stand opposite each other, and the courses of brickwork or stonework are can be built up horizontally.  But a complication arises where the intersection is not a right angle.  Sir Charles Fox summed up the problem:


“Wherever a canal is thus crossed at an angle, we must either divert the canal, so as to bring it at right angles to the railway [Fig. 1 below]; or we must build a common square bridge of sufficient span to allow the canal, its course being unaltered, to pass uninterruptedly under it [engraving below]; or we must erect a proper skew bridge [Fig. 2 below].  The first of these is often impracticable, as provisions are generally inserted in the Acts of Parliament, for preserving the canal from any alteration in its course; and even if this were not the case, the diversion of a canal causes great expense, and is attended with much inconvenience to its traffic: the second is a most unscientific mode of overcoming the difficulty, and would also involve very serious expense arising from the necessity of making use of an arch of much larger dimensions than would be required were the proper oblique arch erected in its stead . . . . It is for the above reasons that oblique arches are now so frequently erected; and a good method of building them, is therefore, of considerable importance.”

On the Construction of Skew Arches, Charles Fox (1836).




A common square bridge of extra span, built at an angle ― odd-looking and ugly.
A contemporary engraving showing the London & Birmingham Railway crossing Watling Street, near to the site of the temporary station at Denbigh Hall.


The ‘skew arch’ enables a bridge to span an obstacle at other than a right angle, but when built of bricks and/or masonry ― the structure then being built up in courses of brickwork and/or stonework ― the construction is not straightforward.  Although the bridge abutments remain equal and parallel, they are no longer directly opposite each other:


“In skew bridges, in order to keep the thrust in the proper direction, it is necessary to place the courses of stones at an angle with the abutment, whereby each stone loses its parallelism with the surface of the road, and is therefore laid on an inclining bed.”

On the Construction of Skew Arches, Charles Fox (1836).


The eminent canal engineer James Brindley never succeeding in working out a solution to the problem of constructing a strong skew arch, and in consequence all his overbridges were built at right angles to the waterway, with double bends in the roadway, where necessary (as in fig. 1 above).  To this day, many of them cause inconvenience to their users:


“Down to that time [late 18th century] such bridges had always been built in the same way as common square arches, the voussoirs being laid in courses parallel with the abutments.  How very defective such an arch would he may be seen by reference to Fig. 3, in which lines are drawn to indicate the direction of the courses.  It is evident that here the portion cdfe is the only part of the arch supported by the abutments; the triangular portions cdg and efh being sustained merely by the mortar, aided by being bonded with the rest of the masonry.  This plan could therefore only be adopted for bridges of very slight obliquity, and even then with considerable risk.”

The Penny Cyclopaedia, Vol. 22 (1842).

 

 

“About the time mentioned above, Mr. Chapman [10] was employed as engineer to the Kildare canal, a branch from the Grand Canal of Ireland to the town of Naas, on which it was desired to avoid diverting certain roads which had to be crossed.  He was therefore led to think for some method of constructing oblique arches upon a sound principle, of which he considered that the leading feature must be that the joints of the voussoirs, whether of brick or stone, should he rectangular with the face of the arch, instead of being parallel with the abutment.  Thus the courses instead of taking the direction shown in Fig. 3, were laid in the manner indicated in Fig. 4 . . . . Mr. Chapman observes that the lines on which the beds of the voussoirs lie are obviously spiral lines, and to this circumstance may be attributed much of the singular appearance of oblique arches.”

The Penny Cyclopaedia, Vol. 22 (1842).

 

Masonry and brick skew arch bridges.


Various methods were later described for designing skew arches, three that were put forward being developed by engineers who worked on the London and Birmingham Railway ― Charles Fox, John Hart and George Watson Buck.  Each wrote a treatise on the subject, [11] that by Buck becoming a standard text for many years.  The bridge carrying the London and Birmingham Railway over the London Road at Boxmoor in Hertfordshire, adjacent to what is now Hemel Hempstead station on the West Coast Main Line, is an example of a ‘segmental’ arch.  It is constructed in masonry, with a brick barrel, stone quoins and a 58° angle of skew.  Designed by Buck, it was completed in 1837.

 

Boxmoor Skew Bridge.
West side of an oblique arch, in the embankment at Boxmoor, to carry the Railway over the Turnpike. John Cooke Bourne, 1838.


Where bricks or masonry is replaced with iron beams, such as in Nash Mills Bridge (shown below), the problem of obliquity mostly disappears:


“The construction of skew bridges of iron or timber is comparatively simple, the ribs or girders of which such bridges arc composed being of the usual construction, laid parallel with each other, but the end of each being in advance of that next preceding it.  Fig. 5 represents the ground plan of such a bridge, the dotted lines indicating the situation of the ribs upon which the platform is supported.



The extraordinary iron bridge by which the Manchester and Birmingham railway is conducted over Fair field street, Manchester, at an angle of only 24½º, is a fine example of this kind of skew-bridge.  It consists of six ribs, of rather more than 128 feet span, although the width of the street is only 48 feet, resting upon very massive abutments of masonry.  The total weight of iron in this bridge, which is considered to be one of the finest iron arches ever built, is 540 tons.  It was erected from the design of Mr. Buck, who has constructed several other oblique bridges of great size and very acute angles.”

The Penny Cyclopaedia, Vol. 22 (1842).

 

Iron skew segmental arch bridge (about 65ft in span and 82ft deep with 6 iron ribs) at Nash Mills, Kings Langley,
now sadly defaced by concrete reinforcement.
East side of Nash Mill Iron Bridge, near King’s Langley, over the Grand Junction Canal. John Cooke Bourne, 1838.
Sadly, the fine ironwork seen here was replaced by British Rail with concrete during track modernisation.

 

Among the other interesting bridges designed for the line was the iron bowstring bridge [12] that crossed the Regent’s Canal towards the upper end of the Euston Extension.  The problem for Charles Fox ― to whom the bridge is usually credited ― was to cross, almost on the level, the 50ft width of the canal and towing path while allowing sufficient clearance for canal traffic.  The bridge approaches had therefore to be raised.  This was achieved using the large quantities of spoil excavated from both the approach cutting to the nearby Primrose Hill Tunnel and from the Camden Incline.  All predominantly blue London Clay, it was used to fill in the area subsequently occupied by the Camden Depot. [13]  The spoil bank so created raised the former ground level by some 15ft, thereby creating (among other things) the necessary clearance required by the Regent’s Canal Company for waterway traffic to pass beneath the bridge.

The use of cast iron girders in a span of that width was considered risky, and considerable testing was carried out to prove the robustness of the design:


“Opposite this post, on the right or eastward, is the Stanhope Arms, Camden Town; and about 18 yards past is the beautiful iron bridge which carries the railway across the Regent’s Canal.  This bridge is divided in the centre by one of the main girders to which the railway is suspended.  The bridge deserves a much more elaborate description than our space permits, and is a fine specimen of the combination of lightness and strength which science can effect.  Instances of the care with which the works on this line have been completed, were furnished in the erection of this and the Park street bridge, in forming which, upwards of 100 tons of iron were broken by the severe tests to which the girders, &c. &c. were exposed; the directors, in the person of their indefatigable engineer, thus evincing a most laudable anxiety to secure the public from accident or even alarm.  It may be here remarked, that all the iron work in the bridges has been proved to three times the weight it will have to sustain.”

The Railway Companion, from London to Birmingham, Arthur Freeling (1838).




Above: half elevation for the bowstring bridge over the Regent’s Canal, London and Birmingham Railway.

Below: the same bridge as depicted by John Cooke Bourne, May 1837.

 

 

“This is one of the boldest specimens of construction on the whole line, the Railway being entirely suspended by attached rods, as shown upon the several plates.  We believe it is the first application of the suspension principle to carry locomotive engines and trains as used upon a Railway.

The railway platform contains four lines of rails, and is hung on wrought iron suspension rods, which are supported by massive cast iron main beams, of which there are three pair, well braced together, and spanning the canal by a length of 50 feet, and at an elevation of 12 or 13 feet above the level of the water.  These beams are cast with a flat arch rising in their depth, and strong horizontal tension rods, well coupled, are fixed to counteract any inclination of the ribs to spread at the abutments.  The Railway platform consists of a number of fish bellied girders, each 28 feet long, and which are supported by the suspension rods and laid athwart the bridge.  These rods are securely keyed to the main beams.  Oak beams are fixed across the girders upon which the railway chairs are secured, and cast iron gratings are filled in between the spaces, which complete the bridge.”

Railway Practice: A Collection of Working Plans and Practical Details of Construction, S. C. Brees (1859).


The following is a section from the contract specification:


“This Bridge will consist of three Main Ribs of cast iron, properly secured.  Each main rib will consist of two ribs, properly connected, and each of these will be cast in one piece.  The Cross Girders will be secured to these ribs, and the thrust of the arch sustained by tie bolts.  The open Ornamental work of the face will be bolted to the main ribs, (vide Plates 11 and 12).  The Roadway Plates to be fixed as drawing (vide Plates 11, 12, and 13), and they will be perforated for drainage.  No ballasting will be laid on the bridge.  The Chairs will be fixed on oak blocks, firmly secured to the girders.

Coffer Dams will have to be sunk by the Contractor at his own expense, and included in the amount of his tender, in order to get in the foundations of the abutments.  Concrete will be employed in these foundations, as shown on the drawings.  The Abutments will principally consist of brickwork, set in mortar, (except so much as is included between the foundations and the level of 1 foot above top water level, for 18 inches from the face of the work, which must be set in Roman cement.)  The abutments will be faced with stone, and stones will have to be built and bonded in various parts, as shown on the drawings.”

Railway Practice: A Collection of Working Plans and Practical Details of Construction, S. C. Brees (1859).


CHAPTER 6

――――♦――――

 

FOOTNOTES

1.

‘Ruling grade’ on a railway is usually synonymous with ‘maximum gradient’.  Although the ruling gradient on the London and Birmingham Railway was 1 in 330 (16 feet to the mile), the short incline between Euston Station and Camden (the ‘Camden Incline’, initially cable worked) was far steeper, ascending . . . .

“. . . . from the terminus at Euston Square for 12 chains, at 1 in 156, is then level for 13 chains, and the succeeding 59 chains are divided into four gradients ascending to Camden Town at 1 in 66, 1 in 110, 1 in 132, and 1 in 75 respectively.”

The Practical Railway Engineer, G. D. Dempsey (1855)

2.

Averaged out over the entire length of the London and Birmingham Railway, the volume of earthworks (cuttings and embankments) is estimated to have amounted to 142,000 cu yards per mile (Page 102, The Practical Railway Engineer, G. D. Dempsey (1855))

3.

Where the material to form an embankment could not be obtained from nearby cutting or tunnel workings, it had to be excavated from the adjacent land on either side of the line.  The locations from where it was dug became known as ‘borrow pits’.

4.

Because the outside walls sloped slightly inwards, they were better able to resist the internal outwards thrust from the centre of the formation.  The top of the embankment was profiled at the end of construction.

5.

Abstract of Evidence on the Great Western Railway, given before a Committee of the House of Lords, June, 1835.

6.

COUNTERFORT, a pier or buttress, generally applied at the back of retaining walls in modern civil engineering, for the support of the same, and likewise for the purpose of forming a tie to the material at the back of the wall.  Counterforts are also sometimes carried up on the face of a wall.”

A Glossary of Civil Engineering, S. C. Brees (1841).

7.

Rugby Viaduct (Grade II listed).  This structure, comprising 11 elliptical arches, is around 700 feet long and spans both Leicester Road and the River Avon.  Opened in 1840 by the Midland Counties Railway, it is one of the country’s oldest disused viaducts, forming part of the first rail route between London and York.  Engineered by Charles Vignoles, it is built in red brick with a facing of Staffordshire blue brindles and sandstone dressings.

8.

The Highway (Railway Crossings) Act, 1839, required railways companies to build and maintain gates at level crossings over roads, and provide a person to open and shut them.

9.

The situation of having to cross a waterway on the level, or tunnel beneath it, did not arise on the London and Birmingham Railway.

10.

William Chapman (1749–1832), English civil engineer, developed the first methodical technique for the design of skew arches, his ‘spiral method’ being described in Rees’s Cyclopædia.  Chapman considered the arch to be a series of arch slices, parallel to the arch faces and at an angle to the abutments.  The arch soffit (the curved underside) is drawn out into a flat plane, a parallelogram grid drawn on this, and then these diagonal lines (each one representing an arch slice) transferred to the centring of the constructed arch.

11.

On the Construction of Skew Arches, Charles Fox (1836); A Practical Treatise on the Construction of Oblique Arches, John Hart (1839); A Practical and Theoretical Essay on Oblique Bridges, G. W. Buck (1839).

12.

In a thrust arch bridge, the vertical and horizontal forces are transmitted along the arches, requiring substantial abutments and foundations to prevent the arch from flattening.  In a bowstring bridge, the deck carries the horizontal forces in tension, thus the abutments need only support the vertical load.  This allows bowstring bridges to be constructed with less robust foundations.

13.

This lay between the Regent’s Canal, Gloucester Road (now Gloucester Avenue), the western edge of Stables Yard and Chalk Farm Lane (now Regent’s Park Road).

 



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