The embankment to the north of the Tring Cutting is, with the inclusion of short cuttings, some six miles long and 30 feet high in places, much of the 1.4 million cubic yards of chalk used to form it having being excavated from Tring Cutting.  At Pitstone (Cook’s Wharf), the Grand Junction Canal is bridged by one of the line’s formerly attractive iron segmental arch skew bridges, depicted below by Bourne in its original condition.

Built to carry two tracks, the original bridge was widened on its eastern side, first (ca. 1859) by the addition of a third track and again (ca. 1876) with a fourth.  During this widening, the bridge’s brick abutments were rebuilt and then, in the British Rail modernisation era, its cast iron arches were replaced with reinforced concrete ― the outcome, shown above, is, as one might expect, unappealing.  The land on the right of Cooke Bourne’s illustration now houses Cook’s Wharf Marina.

“. . . . the Aylesbury railway is on the left; it is seven miles in length; has only one line of rails; is nearly level from end to end; and has no curve, except at its junction with the main line.  An Act was passed in 1836 to incorporate the Company, and to make this branch line; which was planned and directed by Robert Stephenson, Esq.; and was opened on the 10th June, 1839.  It is rented by the London and Birmingham Railway Company, for five years, at £2,500 per annum.  The Vale of Aylesbury, which surrounds the town, has long been noted for its extensive and fertile grazing farms, its prolific arable fields, and for other agricultural distinctions.”

Historical and Descriptive Accounts of the the London and Birmingham Railway, John Britton (1839).

Some 2-miles north of the Cook’s Wharf canal bridge is the site of the former junction with the Aylesbury Railway.  This branch line, the U.K.’s first, left the main line in a southerly direction before veering to the south-west to follow a straight course across the Vale to Aylesbury.  Construction began in May 1838 and the line opened in June of the following year.  It had one intermediate station at Marston Gate (one mile north of Long Marston and 2½-miles from Cheddington). [1]  Its proprietors’ ambition was to extend the line to Oxford, and with that in mind they bought sufficient land to accommodate double tracks, but nothing came of their plan and the line remained single.

The Aylesbury Railway closed to passengers in 1953 and to freight in 1964.  Oddly, its erstwhile competitor, the Aylesbury Canal ― whose trade was much damaged by the railway ― somehow managed to struggle on into the canal preservation era.  Its basin now forms the hub of a major property development just off Aylesbury town centre and a marina has opened nearby.

A short distance to the north of Cheddington, another of the line’s bridges, No. 127 near Ledburn (a.k.a. as Bridego Railway Bridge), gained notoriety when, in 1963, it became the scene of the robbery of a Glasgow to London mail train, which was brought to a halt through the robbers tampering with the line’s colour light signals.  The bulk of the £2.6 million stolen in what became known as the ‘Great Train Robbery’ was never recovered ― neither did Jack Mills, the train’s driver, ever recover from the head injuries he sustained during the hold-up.

――――♦――――

 
LINSLADE

The long embankment continues to Linslade where, just north of Leighton Buzzard station (actually within Linslade), the line enters a cutting and the short Linslade Tunnel.  Greensand Ridge, under which the tunnel passes, is part of a range that extends across Bedfordshire by the Brickhills, to Woburn, &c.  It consists of a deep stratum of indurated red sand, with bands of iron stone and occasional beds of fuller’s earth:

“Immediately after leaving the Leighton Station the train enters the Linslade Tunnel, which is cut through the blue clay and iron sand: it is 284 yards in length, and curves rather to the left, and is ventilated by one shaft: at the end there is a deep cutting through the iron sand rock, which stands in steep yellow walls, forty feet high at each side of the line.  Just afterwards a bridge crosses the line, over which is the road from Leighton to Stoke Hammond; and then we may obtain, on the right a momentary glimpse of a scene the most striking of any on the line; it consists of a valley bordered by hills and cliffs of the yellow sand rock, round the side of which winds the canal; at the bottom is a streamlet bordered by willows; the whole well wooded, and the distant hill tops crowned by a dark heath.  The bright appearance of the sand rock has a peculiar effect, and gives the whole scene a panoramic appearance that cannot but attract attention.”

Osborne’s London & Birmingham Railway Guide, E.C. and W. Osborne (1840).

None of the colours described in Osborne are evident today.

The Grade II listing describes the northern entrance to Linslade Tunnel thus:

“Red brick castellated retaining wall with 3 horseshoe arches in moulded surrounds, central arch taller, 3 semi-octagonal embattled turrets.  An interesting example of early railway architecture.”

English Heritage (list entry number: 1114529).

The Tunnel’s southern entrance (also Grade II-listed) is a less elaborate affair.

Linslade Tunnel, southern portal of the original bore.

――――♦――――

 
THE WOLVERTON EMBANKMENT

From Linslade the Railway, the Grand Junction Canal and the River Ouzel keep close company as they make their way northwards until, at Bletchley, they diverge.  The Railway then heads directly for Wolverton while the canal and river follow the contour around the eastern side of Milton Keynes until, at Newport Pagnell, the Ouzel flows into the Great Ouse.  The Canal then veers westwards towards Wolverton where, just north of the station, it passes underneath the Railway.  At this point Barnes and Stephenson were both faced with the challenge of taking their respective highways across the valley of the Great Ouse.  Barnes crossed upstream of the Railway, near the village of Cosgrove, on a massive earth embankment, the Canal being carried over the Great Ouse in Benjamin Bevan’s iron trough aqueduct (1812).  Stephenson also employed a massive earth embankment ― much longer than its neighbour ― crossing the Great Ouse on a substantial brick viaduct.

“At this Station [Wolverton] the railway crosses the Grand Junction Canal, for the fourth time, by an iron bridge with horizontal main ribs, and then enters the great Wolverton Embankment, which extends across the valley of the [Great] Ouse to an extent of one mile and a half, being the longest on the line: it averages 48 feet in height, and is composed chiefly of clay, gravel, sand and lias limestone.  In its course is a viaduct consisting of six principal arches, of an elliptical form, having a span of 60 feet each, and rising 46 feet from the ground to the crown.  In the abutment of each of the viaduct, are two bold pilasters, and four subordinate arches: a stone cornice runs through the whole, which is 660 feet in length, and 57 feet high on top of the parapet.  Beneath one of the main arches is an artificial channel, formed by the Company, for the united waters of the River Ouse and a smaller stream called the Tow, which formerly flowed separately through the valley.”

Historical and Descriptive Accounts of the the London and Birmingham Railway, John Britton (1839).

Whereas the Primrose Hill Tunnel was the first of Stephenson’s major civil engineering headaches, the Wolverton Embankment became the second:

“The Wolverton embankment, another of the contracts which came back to the Company for completion, gave the engineer much anxiety.  In an embankment a mile and a half long, exclusive of the Wolverton viaduct, some difficulty was anticipated; but human foresight could not have provided for all the disasters attending its construction.  The embankment on the north side of the viaduct gave comparatively little trouble.  Composed of blue clay, lias, limestone, gravel, and sand, it stood well, except at one place where it slipped, not from its own weakness, but because the ground gave way beneath its enormous weight.  On the south side of the viaduct, however, a grievous mishap occurred, in the form of ‘a slip’ that was not overcome for months.”

The Life of Robert Stephenson, F.R.S., John Cordy Jeaffreson (1866).

Initially, stable material not dissimilar to that used for the northern section of the embankment was brought up from a cutting being formed at Denbigh Hall, some three miles to the south.  It stood well, but as work on the cutting progressed, Oxford clay was encountered.  When this was added to the embankment, it was found that it would not support the load and, as tipping progressed, the embankment began to spread.  To compensate, more material was added, but the spreading continued:

“The length of the embankment being one mile and twenty-eight chains, (deducting the viaduct) [80 chains in a mile] 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 . . . . stood very well; but when we got deeper into the [Denbigh Hall] cutting, we worked out some black, soapy clay, very wet; this was tipped onto a turf bottom, and the weather also being 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 days 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 . . . . ”

The History of the Railway Connecting London and Birmingham, Lieut. Peter Lecount R.N. (1839).

At this point Lecount describes a temporary bridge being built to enable tipping to continue on the far side of the slip, which is the state of play depicted by Cooke Bourne above.  A five feet deep trench was then dug across the width of the embankment and mounds of earth formed on each side to prevent the new formation from slipping.  However, the slip continued to give trouble:

“In fine summer weather the bridge was removed, and that part of the embankment, where the slip had been, was filled up; but away it went again, just as it did before, and the yawning gulf appeared to be insatiable.  It was months before it was conquered, and this was done at last by barrowing as much earth to the outer part of the slip, as would balance the weight on top.”

The History of the Railway Connecting London and Birmingham, Lieut. Peter Lecount R.N. (1839).

Slippage was not the only problem encountered at the Wolverton Embankment; spontaneous combustion was another, the outcome being the unusual sight of a railway embankment on fire, the railway sleepers adding to the blaze:

“No sooner was the way seen how to fill up the slip, than Robert Stephenson was informed that the troublesome embankment had caught fire.  In its composition was a portion of alum shale, containing sulphuret of iron [iron sulphate].  This material decomposing afforded a striking instance of spontaneous combustion.  Great was the consternation of the peasants at beholding a railway on fire.  Roguery was, they were convinced, at the bottom of the catastrophe.”

The Life of Robert Stephenson, F.R.S., John Cordy Jeaffreson (1866).

Work at Wolverton was finally completed in April, 1838.

――――♦――――

 
THE BLISWORTH CUTTING

About 10-miles to the north of Wolverton, the Railway passes through the Blisworth Cutting: [2]

“Immediately after entering Northamptonshire the line of the Railway is obstructed by the Blisworth ridge, which forms the division between the valley through which we have come, and the valley of the Nene, a stream which rises in the high lands near Daventry and runs east to Northampton.  The Grand Junction Canal is carried through a tunnel at Blisworth 3,080 yards in length.  The Railroad avoids a tunnel but is carried through an open cutting of limestone resting on a stratum of rock.  The rock has been ‘blasted’ with great labour and expense.”

The Penny Magazine (1838).

Approximately 1½ miles long and averaging 50 feet in depth, the excavation was first estimated to contain some 800,000 cubic yards, but subsequent widening increased this to over one million.  The contract for this section was let to William Hughes, an experienced contractor whose curriculum vitae included work on the Caledonian and Gotha (Sweden) canals.  Hughes was faced with a formidable task.  At 1,400,000 cubic yards, the Tring Cutting was the largest on the line and although flooding proved to be a problem, the strata in the Chilterns is solid chalk.  At Blisworth, the excavation cut through three distinct strata; a mixed layer of clays over 20 feet deep on average, overlying limestone, under which lay yet more clay and waterlogged shale, although this mix varied along the length of the cutting.

Work commenced in March 1835, but progress was soon hampered by flooding.  According to Samuel Smiles, “for a year and a half the contractor went on fruitlessly contending with these difficulties and at length he was compelled to abandon the adventure”; Lecount is much less sympathetic, “During the first year and a half the progress was extremely slow, owing to the want of proper energy on the part of the contractor, combined with general bad management.”  Whatever the reason, Hughes suffered a stroke and died, and by December 1836 the work was back in the Company’s hands.

The contract was then taken over by one of Stephenson’s assistants, (later Sir) Robert Rawlinson, George Phipps being the Company’s resident engineer.  Rawlinson attacked the task with vigour, working his force of 700 to 800 men and boys around the clock in an effort to bring the work back on schedule.  Steam pumps were erected to deal with the influx of water, gunpowder was employed to shatter the limestone ― Lecount records that 25, 100lb barrels of gunpowder, were used each week ―  and locomotives were used at both ends of the cutting to remove the excavated material to be used in the nearby Ashton and Blisworth embankments.

“. . . . blasts of the rock continually deafening the ear.  In fact, the whole cutting seemed alive; and the busy hum of labour, resounding from the one end to the other, gave ample testimony to the zealous exertions of the engineer . . . .

The mode of blasting made use of was by drilling a hole in the stone, about one inch in diameter; the depth was determined by the thickness of the bed.  This is done by means of a round iron bar shod with steel, which is lifted up, and then struck down in the hole, water being used with it, causing the stone to cut more readily, till the hole is drilled to the requisite depth.

When the hole is sufficiently deep, it is dried out; a piece of fuse, of the requisite length, is then put in, and the gunpowder is poured all round it, in the requisite quantity, and secured by a covering of pounded brick and stone.  Several charges being thus prepared, the ends of the fuse are lighted, and the workmen retreat to a sufficient distance for security.  In a few minutes the whole explode, tearing up large masses of the rock, and sending the lighter pieces high into the air.  The least noisy of these explosions are generally the most effective, rending up the larger masses of rock.”

The History of the Railway Connecting London and Birmingham, Lieut. Peter Lecount R.N. (1839).

In the southern and central sections of the cutting, the slopes were at two gradients; 1:4 in the limestone (the lower shale in the central section being contained by retaining walls) at the top of which a 9 feet wide bench separated a shallower slope of 2:1 in the upper levels of clay:

“The object of the benching was to catch any loose portions of clay which might be detached from above; they have also been found very useful as affording foundations for walls of pebble-stone, which it has been found necessary to erect in many places, to retain the numerous slips of clay above.”

The History of the Railway Connecting London and Birmingham, Lieut. Peter Lecount R.N. (1839).

Retaining wall to be built in Blisworth Cutting.

An extract from the specification for the retaining walls in Blisworth Cutting reads:

“. . . . The whole of the Walls and Buttresses to be of masonry; the stones to be procured from the excavations.  The courses to run as thick as the material obtained from the excavation will afford when properly quarried.  The facing stones to be at least 18 inches; the beds to be square with the face of the buttress, or wall.  The stones to be hammer dressed, and brought to a rough bed, but perfectly true; special care being taken to prevent too full a bearing in the centre of them . . . . The object of this arrangement being to secure a sound support to the rock, and to effect by the dove-tailed Stones a connexion with the rock, to prevent the top of the wall being pushed out.”

From Railway Practice (1838 edition) by S. C. Brees.

At the bottom of the central section a rubble wall, averaging 20 feet in height, was built on each side underneath the limestone layer.  This was strengthened by buttresses at intervals of 20 feet, resting on inverted arches carried underneath the line.

To reduce the risks of both slip and flooding by the strata of clay and water-bearing shale, Stephenson paid the strictest attention to drainage.  A puddle-drain was to be formed behind each wall, with a small drain through the wall to let off the water from behind.  A drain was also formed beneath the track along the central section of the cutting:

“To prevent any injury to the Slopes by the springs of water issuing from the rock and other strata in this excavation, the strictest attention will be required on the part of the Contractor, and the modes of drainage adapted to the varying thickness of the shale and other strata . . . . The central Drain to be made according to the dimensions in plan.  Where it crosses the inverts, they will form its bottom; and between the inverts, the bottom to be laid to an uniform inclination.  At a depth, never falling short of 1 foot below any wet stratum that may occur, two courses of the recess wall and buttresses to be projected beyond the back of the wall; the lower course to project beyond the upper, so as to receive a stone, to rise 1 foot above the upper course, forming a Drain 12 inches deep and 6 inches wide; to be surrounded at the bottom and back with a casing of sound Puddle, and filled in at the top with Rubble stone, to allow the top water to have access to the drain . . . . This drain to have a regular fall from the centre of each buttress . . . . The water, when thus collected, shall be carried through the recess wall, and down the sunk channel in its face . . . .”

An extract from the specification for Excavations in Blisworth Cutting,
reproduced in Railway Practice (1838 edition) by S. C. Brees.

In the northern section, which was mostly soft shale, slopes were built at a shallower gradient of 2:1.

Section and details of Blisworth Cutting, Prof. A. W. Skempton.

Drifts were also driven into the sides of the cutting behind the retaining walls to drain off the water.

Some years later, in addressing the House of Commons Select Committee on Railway Labourers, Robert Rawlinson had this to say about excavating the Blisworth Cutting (his are the answers):

Q. ― “A very severe cutting?”
A. ― “The heaviest open cutting, and largest work in its character, excepting the Kilsby tunnel, on that railway.”

Q. ― “Were those works attended with a considerable loss of life?”
A. ― “There was a considerable loss of life, and very many accidents upon the work; I kept no account of the number.”

Q. ― “In what way did those accidents occur?”
A. ― “At that cutting there was a top lift of from 10 to 12 feet of gravel and clay, and marl of various consistencies; the bottom of a portion of the cutting was composed of limestone rock, but a portion of that rock at each end founded itself upon the clay again.  The top lift was taken off in the ordinary method of working excavations, by means of wagons, and a great portion run out into spoil by barrow runs.  The bottom portion was cut off with picks and wedges, and an immense quantity of gunpowder was used.  I believe as much as 100,000lbs in weight; the top portions of the excavation was brought down at each end of the cutting by inclines to the ordinary level of the railway, and those inclines were the cause of considerable accidents from the temporary waggons; the men would sometimes, through carelessness, put more waggons on the incline than the brakesman could hold, and they would overcome him, and sometimes a wheel would break, or a rail would get out of place.  I have seen as many as 20 waggons broken up at one time.  Frequently accidents would happen in this way: the men would get upon these temporary waggons to ride from their work, and I believe six or seven men had their arms and legs broken at one time, though the contractor told them to get off the waggons at the top of the incline, and they disobeyed him.”

Report from the Select Committee on Railway Labourers (1846).

After almost three years work on the cutting there remained difficulties, especially with flooding.  In his report to the directors of February, 1838, Robert Stephenson describes how he planned to expedite progress in extending the line from the temporary terminus at Denbigh Hall to Roade, by forming the embankment ― presumably that at Ashton ― using the technique known as ‘side cutting’ [3]:

“The Blisworth Contract, which consists of an extensive cutting is progressing favourably; but the character of the excavation is now more difficult than at first, and as it gets deeper, the space for employing men gradually becomes more confined.  The material is increasing in hardness, and there has also been a greater quantity of water.  In order to facilitate the completion of this part of the line, an arrangement has been made for throwing an additional quantity of earth into spoil from the centre of the excavation, and supplying the deficiency in the embankment by a corresponding quantity of side cutting at the southern extremity of the contract.  The object thus aimed at is the completion of the south portion of the contract in May, nearly at the same time with the Wolverton and Castlethorpe contracts, at which period an extended opening may be made from Denbigh-hall to the village of Roade, situate on the turnpike road leading from Stony Stratford to Northampton, and only five miles from the latter town.  This position appears highly advantageous for the next temporary terminus, which must remain the terminus for the London division until the opening of the whole railway.

In the Blisworth cutting there now remains 100,00 cubic yards of materials which will be disposed on nearly in the following manner:―

30,000 cubic yards to Ashton Embankment;
35,000 cubic yards to Blisworth Embankment
35,000 cubic yards to spoil.

The first quantity is that which relates to the opening of the line as far as Roade, and reckoning the south end of the cutting to yield at the rate of 10,000 yards per month this may be effected in three months, allowing necessary time for joining the permanent road.”

Robert Stephenson’s Report, 17th February 1838.

Blisworth Cutting was eventually completed in August 1838, shortly before the line was opened throughout, and Cooke Bourne was soon on hand to produces two romanticised drawings of it.  To the extent that the artist’s hand and eye between them produced an accurate depiction, his drawings contain several points of interest.

In the drawing above, note the top-hatted ‘policeman’ having given the all clear to the southbound train, which is double-headed, not unusual during the Edward Bury small-locomotive era.  The artist gives a good impression of what an exposed and isolated job was a railway policeman’s lot.  Note also the stone-block sleepers, the very unfinished appearance of the trackbed by today’s standards and, in both drawings, the rough and ready finish to the stonework in the upper part of the cutting, which seems to be inviting frost-induced rock fall.

View of the cutting near Blisworth, looking North.
John Cooke Bourne, October 1838.

In the view looking north, note the change in the slope of the embankment in front of the bridge.  Presumably this is where the stratum changes from limestone, which will stand vertically, to clay/soft shale that has a lesser angle of repose.

Completion of the Blisworth Cutting did not end its civil engineering problems ― clay continued to make its presence felt.  Shortly after the opening of the line, several slips occurred [4] and over a decade later slippage remained a problem:

Parliamentary Papers, House of Commons and Command, Volume 30.

In each case the solution was to build ‘counterforts’ ― in this context, 5-feet wide trenches, dug at 20 feet intervals into the slip (i.e. at right angles to the rails) and then filled with well compacted gravel or crushed stone.  The counterforts thus divided the slip area into segments, acted as drainage channels, and applied frictional force to the body of the clay to prevent it from sliding forward.

――――♦――――

 
THE BLISWORTH EMBANKMENT

About a mile to the north of the Blisworth Cutting lies the Blisworth Embankment, at the northern end of which the line crossed the Grand Junction Canal on an iron bridge, the construction of which was depicted by Samuel Brees:

“The Railway intersects the Canal at an angle of 40º and at a point where the height of the rails above the level of the water is 29 feet 8 inches, and the depth of the Embankment 25 feet.  The Railway rises in the direction of Birmingham at the rate of 1 in 330.

The Bridge will consist of six Main Ribs of cast iron, forming an arch of 66 feet span on the skew, and 11 feet 9 inches rise, and leaving a clear width of 33 feet 6 inches between the abutments, measured at right angles, to the centre line of the canal.  Each of the Ribs will consist of three pieces, upon which the open work of the spandrels will be fixed.  Beams of Oak will run along the top of the four middle ribs, and be bolted to them; to these beams will be attached the Railway Chairs.  The spaces between the ribs will be covered with cast iron Plates, upon which the ballasting of the Railway will be laid.”

An extract from the specification for the Blisworth canal bridge,
reproduced in Railway Practice (1838 edition) by S. C. Brees.

In common with the neighbouring cutting, the Blisworth Embankment also proved problematic.  As Robert Rawlinson, contractor for the work, explained in evidence to a Parliamentary select committee, the plastic nature of the material from which the embankment was formed caused frequent slippage during construction:

Q. ― “The last witness mentioned just now that there had been some accidents at the ‘tips’; can you explain the nature of the ‘tip’?”
A. ― “I will try to do so.  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 time; 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.”

Q. ― “The material would have sunk?”
A. ― “Subsided or slurred out at the sides.”

Evidence give by Robert Rawlinson to the Select Committee on Railway Labourers, 1846.

Nevertheless, it still came as a surprise when a phenomenon ― later to become known as ‘delayed embankment failure’ ― occurred two years after the Railway had opened for service:

“Saturday evening a considerable subsidence took place at the Blisworth embankment, half way between the station and the bridge over the canal.  The earth having become thoroughly saturated by the late rains, gave way at the bottom, and the surface in consequence gradually sunk, at one point several feet.  Since then it has continued to subside at the rate of about a foot an hour, and on one occasion between two and six in the morning, when the men ceased to work, it sank eight feet.  A large force of men were collected the moment the slip was discovered, and employed day and night replacing the soil that had given way with ballast, the trains in the mean time passing slowly over the spot.  The gap is always filled up by the arrival of a train, and the precautions taken are such as to do away with all idea of danger.  The ballast is brought partly from Bugbrook, but chiefly from Hillmorton about 16 miles distant.”

Northampton Mercury, 11th January 1840.

Delayed failure is yet another aspect of risk in clay formations, and one that continues to affect railway embankments:

“Cyclic shrinking and swelling of clay earthworks causes a major maintenance headache for UK asset managers.  Millions of pounds are spent each year to realign and tamp sections of track twisted by embankment movement, a problem compounded by vegetation that increases clay shrinkage in the summer.  Vegetation removal could ease the problem, however, it could also increase the risk of slope instability . . . . The type of soil and vegetation were also important in controlling the water content within embankments.  High plasticity soils such as London Clay have a greater swelling capacity and take up more water during wet periods . . . . The shrinking and swelling movement is thought to result in progressive embankment failure.  Strain softening at the toe results in deformation retrogressing back into the embankment, resulting in a deep-seated failure.”

New Civil Engineer, 4th August 2008.

――――♦――――

 
A VERY UNUSUAL RAILWAY BRIDGE

In two of the contemporary railway guides, there are descriptions of a very unusual bridge that the line once crossed in its northbound approach to Weedon Station:

“This part of the road is, perhaps, more curious than any along which we have hitherto passed.  A branch of the [Grand Junction] canal, which is carried to the storehouse of the depot, is here crossed by a strong draw bridge, over which we rattle fearlessly and merrily, and, passing by the long dead wall of the barrack grounds on our left, we arrive at the Weedon Station.”

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

“The village, however, is chiefly interesting to the stranger on account of its Royal Military Depot.  This magnificent establishment, which is supposed to be equal to any of the kind in Europe, consists of a handsome centre and two detached wings, and is capable of containing 240,000 stand of small arms, with a proportionate quantity of artillery and ammunition.  The barracks, in which troops are continually kept for the protection of the place, stand on the top of the hill, and are intended to accommodate 500 men.  A cut made from the Grand Junction Canal to the magazines, for facilitating the conveyance of stores, gave considerable trouble to the engineers of the railway, by its having to be crossed at a height very little above its own level.  This object was, however, at last effected by means of a drawbridge, of peculiar construction and extraordinary strength.”

Drake’s Road Book of the London and Birmingham Railway, James Drake (1839).

The Royal Military Depot ― now the decaying remnant of an architectural gem ― is a relic of the Napoleonic Wars.  Built during the first years of the nineteenth century, the Depot was probably sited at Weedon to be well away from potential invasion shores, but with good communications to other parts of the country via the Grand Junction Canal.  Indeed, the Depot was linked to the Canal by a short spur, which entered the (then) walled area through a portcullis, before passing between its two imposing rows of warehouses/armouries to a turning basin at the far end of the site.

The route taken by the Railway passed along the Depot’s eastern boundary, crossing the branch canal ― as Drake relates ― “at a height very little above its own level.”  Understandably, the Military did not wish their branch canal to be obstructed by the Railway, so Stephenson came up with an unusual solution, a drawbridge, not of the lifting variety but one that could be pulled back horizontally to permit canal barges to enter the Depot.  To ensure that the Railway Company delivered their end of the bargain, the details relating to the drawbridge and its operation were included in the second London and Birmingham Railway Act:

“LXXXII.  And be it further enacted, That the said Company shall, at their own Costs and Charges, construct a Drawbridge in that Portion of the said Railway which is to pass over the said Basin of the Ordnance Canal, for the Purpose of affording a free Passage for the Boats and other Craft of the Ordnance Department into and out of the said Canal; and shall and will at all Times thereafter, and at the like Costs and Charges, provide and maintain a proper Person to be always in attendance at the said Drawbridge, who shall without Delay open the same whenever he shall be so required by any Ordnance Officer, Boatman, or Servant, that the Boats and other Craft belonging to or hired by the Department may pass into and out of the said Canal.”

William IV, Cap lvi, R.A. 3rd July 1835.

A description of the bridge and its operation together with part of the drawings are reproduced at Appendix II.

――――♦――――

 
THE KILSBY TUNNEL

“We now proceed for rather more than half a mile, when we arrive at the KILSBY TUNNEL.  This astonishing memorial of the power of mind over matter, was accomplished only by the most persevering exertion combined with engineering skill, and presented constant and unexpected difficulties, which were continually demanding the promptest exertion of the engineer’s resources.”

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

The Primrose Hill Tunnel, the Tring Cutting and the Wolverton Embankment might be considered to share one level of civil engineering difficulty, with the Blisworth Cutting on the next level above.  But the crowning challenge faced by Stephenson and his team was to drive the railway tunnel through the Kilsby Ridge, a feat that must rank among the great civil engineering achievements of the railway building era:

“Another instance, in which difficulties of no ordinary magnitude were encountered, was at the Kilsby Tunnel, about six miles on the London side of Rugby station.  This tunnel is about 2,400 yards long, and was originally intended to be chiefly built [the brick lining] eighteen inches thick; but it was found necessary to increase this, in most cases, to twenty-seven inches; and the whole has been built in either Roman or metallic cement.  The works were commenced about the middle of June, 1835, by J. Nowell and Sons, contractors; but such serious difficulties were met with, at an early stage of the proceedings, that they gave up their contract on the 12th March, 1836, and nearly the whole had to be performed by the Railway Company.”

The History of the Railway Connecting London and Birmingham, Lieut. Peter Lecount R.N. (1839).

The Kilsby Tunnel lies near to the ‘Watford Gap’ in Northamptonshire.  As its name suggests, the Gap marks a low-lying point on a range of high ground, similar to the Tring Gap through which the line crosses the Chilterns further south.  In this case the high ground is a limestone ridge that runs in a south-westerly to north-easterly direction, from the Cotswolds to the Lincolnshire Wolds, and although not of particular prominence, it forms an obstacle to transport communications.  Since Roman times, civil engineers have found the Watford Gap a convenient route for connecting the Midlands with the South East ― the A5 (the Roman Watling Street), the West Coast Main Line (formerly the London and Birmingham Railway), the M1 motorway and the Leicester Line of the Grand Union Canal traverse the Gap in parallel within its width, a mere 1,300 feet.

An extract from Stephenson’s sectional drawing of the line, showing the Kilsby Tunnel.
The two marked heights above datum indicate the line’s depth below the ridge.

There is no hard and fast rule, but a point is reached at about 60 feet below surface level at which it becomes more economical to drive a tunnel than to excavate a cutting (taking into account the cost of land, labour, and the disposal of excavated material where this is necessary). [5]  In order to maintain the line’s ruling gradient (1:330), Stephenson was able to take the Railway over the ridge of the Chilterns (at Tring) in a cutting of average depth 40 feet (maximum 60 feet), but at Kilsby the line needed to traverse the summit at a much greater depth, hence a tunnel was necessary.

Previous tunnelling in the area had exposed the risk of quicksand.  During the 1790s, Barnes and Jessop had encountered a 328-yard deposit of quicksand while driving the Braunston canal tunnel through high ground to the north of Daventry (some 3½-miles south of Kilsby).   Some 20 years later, Benjamin Bevan encountered quicksand at Crick, 1½-miles east of Kilsby, while building the ‘old’ Grand Union Canal; the problem was sufficient to cause him to abandon his original line to the west of Crick Village and take a route (and a longer tunnel) on its eastern side. [6]  During a visit that Stephenson paid to Dr. Arnold, the famous head master of Rugby School, he received a salient warning, probably based on Arnold’s knowledge of the canal builders’ experiences:

“On his first visit to Rugby after the Bill for the London and Birmingham Railway had received the Royal assent, Robert Stephenson called on the great schoolmaster to offer him his respects.  The young man brought no letter of introduction, and either was, or imagined himself to be, received with coldness and hauteur.  Dr. Arnold was certainly polite, but perhaps formal, his manners being of a school with which, at that period of his life, Robert Stephenson was not familiar.  Anyhow the interview left on the mind of the engineer an unpleasant impression, which was doubtless in some part due to Arnold’s last words: ‘Well, sir,’ he said, pointing in the direction of the Kilsby ridge, ‘I understand you carry your line through those hills.  I confess I shall be much surprised if they do not give you some trouble.’  In due course the trouble came.”

The Life of Robert Stephenson, F. R. S., J. C. Jeaffreson (1864).

Building the tunnel commenced in the usual manner.  Bore holes sunk along a line to the east of the existing tunnel caused it to be abandoned when they revealed the presence of quicksand.  Bore holes were then sunk along a more westerly line; these revealed various clays, some gravel and limestone and, in some, a considerable quantity of water, but no quicksand.

Excavations were then commenced by the contractor, Joseph Nowell & Sons, whose family had also taken the Harrow contract.  A number of working shafts were sunk along the line of the tunnel, from the base of which working faces could then be opened in both directions.  However, a shaft sunk near to the tunnel’s southern end encountered what Lecount, presumably referring to its high fluid content, described as “a perfect quicksand”.  Further exploration established that one of the trial bore holes had only just missed the deposit, which further testing revealed to be considerable and extending down below rail level.  The deposit’s extent precluded tunnelling on a different alignment.

The working shafts sunk in the central and northern sections of the line were dry, and excavation was commenced from those points, but the shaft sunk some 500 yards from the southern portal encountered the quicksand.  Driftways run into the quicksand to drain it became blocked with sand, so Stephenson resorted to steam pumping, probably the first occasion that approach had been used on any scale in civil engineering work.  Initially, two steam powered pumps were erected and shafts sunk to allow pumping to take place.  This met with moderate success at first, but was suddenly reversed by renewed and serious flooding:

“Mr. Stephenson was led to suppose that the water might be pumped out, and that under the sand thus drained the tunnel might be driven with comparative facility; this proved to be the case, but the expense was of course enormous.  Engines for pumping were erected, and shafts sunk a little distance out of line of the tunnel.  These shafts were carried through the sand by means of wooden tubbing, and from them, headings were driven into the quicksand to allow the water to flow with freedom to the pumps.  The pumping was contained nearly nine months before the sand was sufficiently dry to admit to tunnelling, and during a considerable portion of that time the water pumped out was two thousand gallons per minute.”

The History of the Railway Connecting London and Birmingham, Lieut. Peter Lecount R.N. (1839).

In the meantime Joseph Nowell fell ill and died.  Although his sons continued the contract for a time, they eventually gave up and the work was returned to the Company, Stephenson placing it under the supervision of Charles Lean, a sub-assistant engineer of whom Samuel Smiles relates the following anecdote:

“The tunnel, thirty feet high by thirty feet broad, arched at the top as well as the bottom, was formed of bricks laid in cement, and the bricklayers were progressing in ‘lengths’ averaging twelve feet, when those who were nearest the quicksand, on driving into the roof, were suddenly almost overwhelmed by a deluge of water which burst in upon them. [this happened in November 1836]

As it was evident that no time was to be lost, a gang of workmen, protected by the extreme power of the engines, were, with their materials, placed on a raft; and while, with the utmost celerity, they were completing the walls of that short length, the water, in spite of every effort to keep it down, rose with such rapidity that, at the conclusion of the work, the men were so near being jammed against the roof, that the assistant engineer Mr. Charles Lean, in charge of the party, jumped overboard, and then swimming with a rope in his mouth, he towed the raft to the foot of the nearest working shaft, through which he and his men were safely lifted up into daylight, or, as it is termed by miners, ‘to grass’.  The water now rose in the shaft, and as it is called, ‘drowned out’ the works.”

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

Further steam pumps were erected to counter this renewed flooding, more pumping shafts were sunk down to trackbed level, and headings were then driven to connect them with the working shafts.  By these means, the water was gradually drained out of the workings.  And to claw back lost time, Stephenson also sank further working shafts to permit additional faces to be opened up.  At the Company’s 9th General Meeting in February 1838, he was able to report that . . . .

“The works of the Kilsby Tunnel are at present in a very satisfactory state, and the monthly progress as regular as can be expected considering the nature of the operations.  No new difficulty has recently occurred, except the capricious appearance and disappearance of water in some of the shafts both in and beyond the quicksand.  Between these shafts the junction of the respective portions of the tunnel has consequently become rather uncertain, the actual rate of progress in tunnelling through the intermediate space falling short of what was estimated.  To remove this source of contingency as much as practicable it has been found necessary to sink additional shafts for the purpose of dividing those unfinished portions which would require the longest time to execute, or in which the average rate of progress was most likely to be interrupted by water or a change in the nature of the strata.  On the 20th of January last, a careful admeasurement was made to determine accurately the distance unfinished between each pair of shafts, and the time of completion for each calculated upon an average which there are the no reasonable grounds for doubting.  From which it appears that the whole tunnel will be completed by the end of next July.  In the quicksand, especially, although effectually drained, the utmost caution in mining has been required, and an expenditure of timber unavoidably incurred, which would appear excessive and lavish to any one whose experience has been confined to ordinary tunnelling.  Several circumstances have occurred demonstrating that none of the precautions or expenses have exceeded what the magnitude of the difficulties attending this work imperatively demanded.”

Extract from Stephenson’s report to the 9th General Meeting:
Mechanics’ Magazine, p.399, Vol. XXVIII. (1838).

Work was eventually completed in June 1838 at a cost of £320,000, £221,000 above the contract price.  Charles Lean layed the final brick with a silver trowel: [7]

“By the main strength of 1250 men, 200 horses, and thirteen steam engines, not only was the work gradually completed, but during night and day, for eight months the astonishing and almost incredible quantity of 1800 gallons per minute from the quicksand alone was raised by Mr Robert Stephenson, and conducted away!”

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

. . . . to which Stephenson’s other early biographer, Jeaffreson, [8] added further information (the number of bricks referred to should, perhaps, be taken as a general indication of scale, rather than of factual accuracy):

“A few facts briefly stated, will enable the reader to form some conception of the labour expended upon it.  Thirty-six millions of bricks were used in its construction.  The two shafts by which it is ventilated and supplied with light are sixty feet in diameter, and the deeper of them contains above a million of bricks.  These two enormous shafts the walls of which are perpendicular, were built from the top downwards, small portions of the wall (from six to twelve feet long and ten feet deep) being excavated at a time, and then bricked up with three feet depth of bricks, laid with Roman cement.  At one time 1,250 labourers were employed in building the tunnel.  To lodge and cater for this army of navvies, a town of petty dealers soon sprung up; sheds of rude and unstable construction rose on the hill above the tunnel, and in them a navvy could obtain at a high rent the sixteenth part of a bed-room.  Frequently one room containing four beds was occupied by eight day and eight night workmen, who slept two in a bed, and shifted their tenancies like the heroes of a well known farce.”

The Life of Robert Stephenson, F.R.S., J. C. Jeaffreson (1864).

Kilsby Tunnel.―Interior view, under a working shaft.
John Cook Bourne, July 1837.

Kilsby Tunnel.―Interior view, under one of the great
Ventilating Shafts.
John Cook Bourne, October 1838.

“In May, 1836, one of the large ventilating shafts was commenced, and completed in about twelve months.  This shaft is sixty feet in diameter in the clear, and 132 feet deep; the walls are perpendicular, and three feet thick throughout, the bricks being laid in Roman cement.  The second ventilating shaft is not so deep by thirty feet.  These immense shafts were all built from the top downwards, by excavating for small portions of the wall at a time, from six to twelve feet in length, and ten feet deep.”

The History of the Railway Connecting London and Birmingham, Lieut. Peter Lecount R.N. (1839).

View from above Kilsby Tunnel, looking towards Rugby.
John Cook Bourne, July 1837.
The railway on which the two figures are standing was built to assist engineering work.

Above: northern portal, Kilsby Tunnel.
Below: elevation of Kilsby Tunnel
reproduced in Railway Practice by S. C. Brees (1847 edition).

 
CONSTRUCTION IN WARWICKSHIRE

A short distance to the north of the Kilsby Tunnel, the Railway enters Warwickshire and for the next dozen miles descends gently into the valley of the River Avon, which it crosses near Wolston.  From Kilsby onwards to Birmingham there were no further significant civil engineering challenges, although that is not to say that construction was devoid of difficulty . . . .

“Another troublesome and expensive part of the line was the Coventry contract.  This did not arise through any peculiar difficulty in the nature of the work, but from the supiness and incapacity of the contractor.  The work went on without spirit or energy, and the time was rapidly going by which would enable it to be completed with the other parts of the line at the end; the opening of the railway would hence be delayed, and it was difficult to foresee all the consequences.  In this dilemma the Company could do nothing but take the work into their own hands; and by great exertions, and a corresponding outlay, it was completed in time.”

The History of the Railway Connecting London and Birmingham, Lieut. Peter LeCount R.N. (1839).

. . . . nor of interest; indeed, Cook Bourne’s romantic vistas illustrate how well Stephenson’s creations once blended into ― indeed, complemented ― what was then a rural landscape.

“This viaduct, of which the total length is about 350 feet, consists of nine semi-elliptical arches, 24 feet span, and 7 ft. 6 in. 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, 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, George Drysdale Dempsey (1855).

Bourne’s view of the Avon depicts a magnificent structure striding across the river valley, its central arch mirrored in the water.  Sadly, this view of the Wolston Viaduct is now partly obscured by foliage, while some of the its secondary arches have been bricked in and the embankment extended.  The top dressing of high tension paraphernalia further detracts from what remains on view, but such is the cost of progress.

From the Avon Valley, the line commences a 10-mile ascent to traverse the final summit on its journey to Curzon Street.. The authors of contemporary railway guides generally name this the Meriden Ridge, although the deep cutting and tunnel that carry the line over the ridge is much nearer Reeves Green, a name also used on occasions:

“The valley of the river Avon forms one of the basins, or lowest points to be passed as has been before explained, and the intersection of high ground between it and Birmingham, called the Meriden ridge, one of the summits.  On the present line the rate of inclination between the Avon and Meriden ridge is sixteen feet per mile only.  Now on the direct line the Meriden ridge must have been crossed as well as in the present line, but in a less advantageous place; inasmuch as the river Avon near Warwick is very considerably lower than at Wolston, where it is now crossed, and the Meriden ridge would have been intersected at a higher point than at present, besides the circumstance of these high and low points being much nearer together.”

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

Regardless of the topography, Roscoe and Lecount neglect the commercial advantages of taking the line through the growing industrial areas of Rugby and Coventry.

It was originally planned to take the line over the Meriden Ridge in a cutting.  Perhaps the terrain, mainly sandstone, suggested tunnelling to be the more economic solution, but whatever the reason the resulting Beechwood Tunnel is the sole example of its type between Kilsby and Birmingham.

Stephenson’s judicious use of stone in the single-span bridge fronting the Beechwood tunnel, and in the tunnel entrance, caused the architectural critic Henry Noel Humphreys to wax lyrical:

“POLYCHROMY ― Across the Beechwood excavation through this solid rock, where upwards of 193,766 cubic yards of stone have been removed, is thrown one of the most beautiful structures of the whole line.  It consists of a single arch of 76ft span, springing from the natural abutment of the naked rock, to which it is cemented, as it were, by a bold but simple moulding; and the arch being of the same stone as the rock produces a beautiful mingling of art and nature, which is most agreeable to the eye.  We now enter the Beechwood tunnel, and here meet with another fine piece of architecture in the entrance.  It is in the Egyptian style, the cumbrous proportions of which seem well fitted for such a purpose, particularly in the manner of their adoption in this design, which is simple and good; though, perhaps, the boldness of the string courses have been a little exaggerated, the lower one having a projection of 2ft 9in.  But this entrance is more interesting in another point of view, I mean on account of the introduction of a polychromic effect, produced in what I conceive a more legitimate way than by the use of artificial colour; by the employment of materials of various natural colours; the string courses and copings being of a fine bluish grey stone (I should imagine from the Roade excavation), whilst the mass of the structure is of the red stone found upon the spot.  The effect produced is varied and agreeable, and the two colours contrast exceedingly well; the effect, indeed, is such, that I feel convinced that, if this method were pursued upon principles of pure taste, so as to vary the effect of a building without rendering it patchy, and to call in colour judiciously to the aid of form, we should soon come to consider a great building all of one colour as monotonous, and entirely wanting in one of the great elements of pictorial effect.”

The Architectural Magazine, Volume 5 (1838).

It seems that the excavation was not, as the previous commentator states, entirely through “solid rock”, for part of the tunnel required a brick lining, which was soon in need of major repair:

“The tunnel is built of brick, is 302 yards long and passes through strata consisting of alternate layers of rock and marle, [9] abounding in springs water; it was completed at the latter end of the year 1837; that winter being of unusual severity, many of the bricks were partially destroyed owing to their containing lime, upon which the weather acted.  Mr. Robert Stephenson first contemplated applying a coat of cement throughout the inside of the arch, but it was apprehended that it would not adhere, in consequence of the constant dripping of the water.  No positive steps were, however, taken until the effects of the winter of 1839-40 had so injured the brickwork as to render further delay dangerous; it was then resolved to line the whole length of the tunnel with an interior brick arch, 9 inches thick, so as to support and insure the stability of the old work . . . .

. . . . The whole of the work was done with blue hard burnt Staffordshire bricks, laid in cement and sand, in equal proportions, for the side walls; for the arch, up to within 15 inches of each side of the crown, two-thirds of cement, and one third of sand; the two rings for keying up the centre or crown were laid entirely in cement, without any mixture of sand.  Previous to commencing the new work, a series of chases [10] were made in the old wall, which, when closed in front by the lining arch, formed drains, 4½ inches square, terminating in the culvert beneath the centre of the railway, and conveying thither all the water, which would otherwise have separated the new from the old brickwork.  This work was finished, and the scaffolding removed, within the short space of forty days, by Messrs. Grissell and Peto, under the direction of Mr. Robert Stephenson, and the immediate superintendence of Mr. Dockray.”

The Civil Engineer and Architect’s Journal, Volume 4 (1841).

To the east of Hampton in Arden lies the next point of interest on the line, the viaduct over the River Blythe, the drawing of which by John Cooke Bourne has been particularly admired.  It . . .

“. . . . consists of two bold arches, each of fifty feet span, separated from the abutments by pilasters of ten feet in width; the whole length of the parapet being 132 feet.  Mr. Bourne’s drawing of this viaduct is, probably, the most poetical in the series; it is a scene of new-born art and picturesque decay; the fresh and substantial Railway Viaduct, contrasting forcibly as Mr. Britton observes, ‘with the old and ruined footbridge over the same stream, a few yards below.’  Here, indeed, are ‘sermons in stones:’ thousands dart along the new structure quickly as the sand of life runs out; years may roll on, and the viaduct be deserted, as the foot-bridge is now, for some new triumph of ingenuity; whilst the river flows on softly beneath both structures . . . .”

The Literary World, Volume 2 (1840).

The Railway’s Birmingham terminus at Curzon Street Station, the remains of which are pictured above, is covered in Chapter 11.

CHAPTER 9

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APPENDIX I.

IRON BRIDGES

from
The Encyclopaedia Britannica, Vol. 12 (1856).

The iron segmental skew arch bridge across the Grand Junction Canal at Nash Mill.

The requirements of railway practice have by no means been favourable for the introduction of the iron arch the height required, from the circumstance that the roadway must be over the top, the practical difficulty of meeting the thrust, and the necessity of a perfect stability in its foundations, have all been drawbacks to its use, although some of our most elegant and efficient railway bridges are cast iron arches.

The earliest examples we have of such an application of cast iron arches are in a series of three bridges for crossing the London and Birmingham Railway over the Grand Junction Canal at Blisworth, Boxmoor, and Nash mill [above].

That at Blisworth is of 50 feet clear span, and consists of six cast-iron arched ribs, having a rise of 8 feet; the four inner ones are arranged in two pairs, one under each line of rails; the two ribs composing each pair being 4 feet 11 inches from centre to centre, and a 6-feet space between each pair; the two single outer ribs are again 6 feet from those in pairs; making a total width from centre to centre of the outer ribs of 27 feet 10 inches.  The depth of the ribs is 2 feet 3 inches at the springing, diminishing to 2 feet at the crown; their thickness is 2 inches, with a projecting flange 6 inches wide at the top and bottom; making a total sectional area of 51 square inches in each rib at the crown.  They rest on cast-iron skew back plates, and these again on blocks of stone let into the brick piers.  The ribs are each made in three equal segments bolted together, and are connected by a system of trussing which we shall hereafter describe.  The haunches are filled in with three separate castings, one over each spandril, and one as a saddle over the crown.  The pattern consists of bars of a cruciform section, crossing each other diagonally, and forming diamond-shaped panels, decreasing in size towards the crown, whose upper apices are connected together by a rib or top table, and their lower ones connected to the main rib by being keyed in between projections upon it.  Upon the top tables just mentioned, and firmly bolted to them, are placed strong cast-iron plates 3 feet wide, ¾th of an inch thick, with flanges 4¾ inches deep all round, and diagonal flanges from corner to corner.  These answer the double purpose of steadying and bracing together the spandrils, and also of carrying the ballast, which, however, is not used for bedding sleepers, the rails being carried in chairs resting on longitudinal balks of timber, and bolted down through them to the top table of the spandrils.

The peculiar feature of the bridge is in the system of trussing employed to connect the main ribs.  At equal distances along the curved rib there are cast iron struts furnished with skew ends, with bevelled edges, for the purpose of keying them in between projections cast on the main ribs; these struts are 12 inches deep, 2 inches thick, and all radiate towards a line joining the centres of curvature of all the arched ribs.  The skew end of one strut is placed opposite that of the strut on the other side of the rib, so that they form a zig-zag line, the general direction of which is parallel to the abutments; between these struts are placed distance pieces of a cruciform section, with broad ends with bevelled edges, and keyed in between projections on the struts in the same manner as the latter are fixed to main ribs.  The skew-back plates before mentioned the whole length of the abutment, and are of an irregular shape, so as both to fit the springing of the arch, and to radiate in the same manner as the struts above mentioned, forming, indeed, the last of these struts on each side.

It will be observed that the whole of the bearing portion of this bridge is put together without any bolts (with the exception of those at the junctions in the main ribs, and those fastening the platform plates to the top tables of the spandrils), every junction being made with keys in the manner just described, so as to render motion in the almost impossible, and to assimilate the system, as it were, to one entire piece.

The bridge, indeed, though not perhaps remarkable for its great span, is one that justly deserves notice for the extreme care bestowed by the designer on the minutiae of all its parts, and the great rigidity given to it by the system of trussing so well adapted to the purpose.

The bridge over the canal at Boxmoor is of much the same description; the arrangement of the ribs is precisely the same as of those at Blisworth, but the span and rise are greater; the former is 66 feet, and the latter 11 feet 9 inches, the depth being 2 feet 9 inches at the springing, diminishing to 2 feet at the crown; the spandrils are similar to those at Blisworth, and also the top plates, except that they are lozenge shaped instead of square.  The trussing of the main ribs is different, the system of keying not being so entirely adhered to.  It consists of cast-iron struts of a cruciform section keyed in between the main ribs in lines perpendicular to the abutments, and of cast-iron pipe struts, through the entire length of which wrought-iron tie-rods pass, and which extend from side to side of the bridge parallel to the abutments.  These also are keyed in between the main ribs, but are not in any way connected with the struts described as being placed at right angles to the abutments.

The bridge at Nash-mill is precisely similar to the one at Boxmoor.

The outer ribs of these bridges are surmounted by light cast-iron railing which extends some distance each way past the arch to the top of the slopes on either side, and gives the bridge a neat and pleasing appearance.

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APPENDIX II.

Description of a Drawbridge on the London and Birmingham Railway,
at Weedon. By CAPTAIN JEBB, Royal Engineers.

From
PAPERS ON SUBJECTS CONNECTED WITH THE DUTIES
OF THE
CORPS OF ROYAL ENGINEERS.
Vol. III, 1839.

The London and Birmingham Railroad crosses a branch canal at Weedon, which communicates between the Grand Junction Canal and the extensive storehouses and magazines belonging to the Ordnance Department at this station.  As it was provided in the Act of Parliament that a drawbridge should be placed over this branch canal, in order that the water communication might be preserved, Mr. Stephenson, the chief engineer, designed a bridge for this purpose, which having been submitted for the approval of the Master-General and Board of Ordnance, was sanctioned by them, and has been recently completed.

Plate 26 will serve to explain the principle upon which the bridge is constructed, and the mode in which it is adjusted in its place as a portion of the line of railway, and removed, when necessary, for the passage of boats.

Fig 1, is a horizontal section through the middle of the main frame, showing a plan of the line of railway and the canal, with the bridge in its place; ABCD is a cast iron frame, which carries the chairs for the rails.  This, when in its place, is supported at the angles by four large screws, l, m, n, o, and, when a passage along the canal is required for boats, is removable upon the three wheels, E, F, G, which work on two rails, HI and JK, fixed on the solid walls, which appear below, at an angle of 45º with the line of the railroad.  Such weights as may be necessary for adjusting the centre of gravity of this mass, so that when in motion it may rest fairly on the three wheels, are placed on the broad flanges in the line CD and about the wheel G.

Part of the drawing for Stephenson’s railway drawbridge at Weedon.

The platform of the bridge is covered with cast iron plates, bolted down upon the main beams by ½-inch bolts.  These beams are placed at the same distance apart as the rails on the line of road, and chairs bolted down to them with ⅞-inch bolts serve to support the line of rails across the bridge: both the chairs and the plates have a thickness of patent felt between them and the main beams.

It will be obvious that the proposed object of removing the bridge is effected by rolling it bodily out of the way on the lateral rails, laid at an angle of 45º, until the passage of the branch canal is clear.  The force necessary for this purpose has hitherto been applied in a very simple manner, by inserting iron crow-bars into the holes shown in the circumference of the wheels: this mode, however, is tedious, and as expedition is an object under the circumstances, an apparatus, the nature of which will be understood by referring to the explanatory sketches, figs. 4 and 5, is to be placed in the vacant space PP under the bridge, by which its removal will be accomplished in about three minutes.  This apparatus consists of an endless chain, connected with the under side of the bridge by the pin S, working over the circumference of two lanterns Q and R; one of these is in connexion with a train of wheel-work having a power of 20 to 1: by working this then in one direction the bridge is withdrawn, and in the other it is replaced in its proper situation.  It has been before stated that when the bridge is in its place it is supported by four screws at the angles; these are found of the utmost advantage in adjusting the bridge to its proper level as a portion of the railway, and in supporting it in that position.  If the bridge, carrying as it does the main line of rails, was left supported on the three wheels, the passage of trains would not only cause a great wear and tear in the parts connected with these wheels, but would jar and shake the carriages very much: however accurately the work may be laid down, some play must be allowed, and if the weight of a carriage be thrown upon that part of the frame-work which forms the bridge, it would descend, while the opposite side would rise, and the rails of the fixed road and those of the bridge would no longer coincide in level.  The four large screws at the angles are intended to obviate this inconvenience.  When the bridge is run up into its position in the line of road, these screws are worked round by a lever until their points are inserted into sockets prepared for their reception, and from these points of support the bridge is then screwed up and accurately adjusted; the three wheels E, F, and G, being at the same time raised from the lower rails HI, JK, and the four screws becoming the only points on which the bridge rests.

Since it has been in operation it has been found in all respects extremely well adapted for the purposes proposed, being easily removed when required for the passage of boats, and affording as solid a bearing for the railroad as if the rails had been permanently fixed on blocks or sleepers.

J. Jebb,
Captain, Royal Engineers.

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