28.iv.98 (Minor Rev. 12.x.98)
|Bicentenary of the Lapal Tunnel|
This article was first published in;
Dudley Canal Trust Newsletter, August 1998
and is reproduced here by kind permission of the author : J. Ian Langford
Members [of the Dudley Canal Trust] with long memories may recall a two part article on the Lapal tunnel which appeared in the Dudley Canal Trust Bulletin for January and March 1980 (Nos 99 and 100). My excuse for returning to the subject is that 1998 is the bicentenary of the opening of the tunnel. Aside from that, newer members may be interested to read the sorry tale of the fourth longest tunnel of the canal system. The precise completion date is not known, but an optimistic report in Ariss Birmingham Gazette for the 8 January 1798 stated that It is with pleasure we learn that the Netherton Canal to Selly Oak is now finished and will be navigable to Birmingham in a few weeks. In April two boats loaded with coal evidently travelled along the canal to the Worcester & Birmingham wharf in Birmingham and it was reported as being completely open in a letter dated 28 May 1798 from Thomas Brettell, the Dudley Companys clerk, to William Hooper.
The saga of Lapal tunnel starts in September 1792, a few months after the completion of Dudley tunnel, when the Dudley Company decided to extend their canal from Parkhead to Selly Oak, a distance of almost 11 miles. The route was surveyed by John Snape, who seven years earlier had carried out the original survey for Dudley tunnel. There were to be no locks, aside from a stop lock at the junction with the Worcester & Birmingham, but a high embankment was needed at the Leasowes, near Halesowen, and there was to be a short tunnel (557 yards or 509 m) at Gosty Hill in addition to the 3795 yard (3470 m) tunnel at Lapal. It is a credit to Snape that the line of the canal crosses the Severn-Trent watershed at one of its lowest points in the West Midlands, but he could not have foreseen that the ground traversed by Lapal tunnel could hardly have been less suitable. The tunnel is almost entirely within Upper Coal Measures, known nowadays as the Westphalian D Series. It passes through some sandstone beds, but much of it is surrounded by marl and clay. There are also several zones of disturbed ground where major faults cross its line. The paucity of sound rock and an abundance of water led to serious difficulties during construction of the tunnel, were a continual source of trouble during its working life, and contributed to its eventual closure in 1926.
The bill for the extension was read for the first time on 24 December 1792 and it had a turbulent passage through parliament, mainly due to opposition from the Birmingham company. The Act of Parliament for the canal eventually received the assent of George III on 17 June in the following year. On 16 July, Josiah Clowes, who had successfully completed Dudley tunnel and earlier had been responsible for Sapperton tunnel on the Thames & Severn Canal, was engaged as consultant engineer and William Underhill was employed as clerk of works, or resident engineer. Work on the tunnel started immediately; on 13 August Underhill was instructed to place a contract for half a million bricks from kilns at Moor Street, on the line of the tunnel, and on 15 November the companys committee requested that the Eastern end of Lapal Tunnel is to be started as soon as may be. It was soon apparent that excavation of the tunnel was far from straightforward, though in committee minutes there are only indirect references to the difficulties encountered. Perhaps this was deliberate, in an attempt to avoid alarming the shareholders unduly. Subterranean springs were encountered in the faulted zones and at junctions between porous and impervious beds. However, as early as 3 December 1793 the committee decided to use this abundance of water to advantage; an order was placed for three boats, each to carry 9 - 12 tons, for conveying spoil from working faces to construction shafts or out of the tunnel.
There is evidence that as many as 30 shafts were sunk, some being separated by as little as 50 yards (46 m) where particularly difficult terrain was encountered. (The average separation of shafts for Dudley tunnel, which is mainly in solid rock, was 220 yards (201 m).) Three steam pumping engines were purchased and, as excavation proceeded, it became necessary to isolate sections of the tunnel by means of stop gates. These measures added considerably to construction costs.
Shareholders normally relied on a committee to oversee the building of a canal, but on 1 September 1794 Clowes was required to present a report on construction of the tunnel at a general meeting of the Dudley proprietors. Whether this was prompted by slow progress is not recorded, but its content helps to explain the subsequent history of the tunnel; the report included dimensions of the tunnel and the measures Clowes was taking to tackle difficult sections. The overall height, from the centre of the invert to the crown of the arch, was given as 12 ft 7 in (3.84 m) and the depth of the canal was to be 5 ft 6 in (1.68 m). The width was 9 ft 7 in (2.92 m) at water level, reducing to 8 ft 4 in (2.54 m) at the invert and arch springing. The side walls rested partly on solid ground and partly on a single-brick (9 in or 0.23 m) invert. In general, the walls were to be one-and-a half bricks in thickness (1 ft 2 in or 0.36 m) to a height of 6 in (0.15 m) above water level and thereafter single brick, but he stated that in very hard good ground then one brick may well do all round, but if slippery or wet ground then the side walls to be brick and a half with brick pillars (outside the tunnel) every 5 ft (1.52 m) one brick length back. A uniform profile was maintained by means of a wooden leading frame and timbers from one of the frames were found in 1982 when a spoil heap was levelled during the building of a housing estate near Moor Street. The internal dimensions were in fact the same as those for Dudley Tunnel, aside from a slight reduction in height, but the method of construction was quite different.
Clowes died early in 1796 and from 1 March Underhill was solely responsible for the tunnel. However, the problems persisted; in a letter dated 16 June 1796 to Jervoise C. Jervoise, Brettell wrote The difficulties we have encountered in the execution of Lapal Tunnel, by reason of the great quantity of Water which was found in almost every Shaft that has been sunk, as also by the running sand (probably red marl, in the main), which has extended itself more or less for three fourths of the whole line of the Tunnel .... our Engineer has been very unequal to the undertaking in the point of Judgement and conduct, but now that he has had the advantage of experience, and is perfectly acquainted with the whole of the Works, it is thought more prudent to continue him under the direction of the Committee of Works, who have had an Augean Stable to cleanse. Aside from giving an insight into the appalling conditions prevalent in the tunnel as the navvies battled with nature, it is clear from this letter that the committee had little faith in Underhills ability, but had no choice but to let him complete the tunnel.
The unforeseen difficulties had greatly increased costs and by mid 1796 the authorized capital of £90,000 for the extension had been spent. An Act passed the following year included provision for raising a further £40,000, but in the event not all of this was needed to complete the canal. The tunnel itself was nearing completion as 1797 drew to a close; on 29 September the Committee gave instructions for the Moor Street Fire Engine and horse gin to be sold, followed by another pumping engine and other horse gins on 13 February 1798. Only one shaft was retained for the purpose of ventilating the tunnel and the rest were arched and probably infilled, in the main, the fill being supported on large baulks of timber placed across the bottom of each shaft. The greater part of the tunnel was lined with brick as work progressed. Only two sections, where the tunnel passed through sounder rock, were left unlined. Underhill continued to supervise construction until the end, but Lapal tunnel had taken its toll; on 3 July 1798 he was given leave of absence to go to Cheltenham because of ill health!
The battle with nature had been won, but it was a precarious victory. It was soon evident that all was not well and the cause of the problem was considered to be Clowess specification for the brickwork. A cross-section marked Lapal Tunnel 1800 BCN Co., but with no explanatory text, suggests that the Dudley proprietors may have sought the advice of the Birmingham company. This section has a wall thickness of 1 ft 10½ in (0.57 m) to a height of 10 ft 7 in (3.23 m) above the invert, reducing to 9 in (0.23 m) at the crown of the arch, and a reduction in the depth of the canal to 4 ft 6 in (1.37 m). Although the profile and increased wall thickness may have been better suited to withstanding pressure from the surrounding material, there is no record that the modifications were carried out. A collapse occurred during the early part of 1801, when the tunnel was closed for two months, and on 18 June 1805 the committee held a special meeting to discuss its condition after it had been closed for four months. It was then decreed that the tunnel should be inspected weekly, increased to twice a week the following year, and that a stock of bricks for repairing damaged sections should be kept at each portal.
The building and maintenance of Dudley and Lapal tunnels had been costly and shareholders saw little return on their capital until about 1820. That the company then enjoyed modest prosperity until it became part of the BCN in 1846 was due in no small measure to Thomas Brewin, who had been appointed superintendent of the canal. He carried out numerous improvements, notably the removal of severe bends between Parkhead and Windmill End, and in 1841 he introduced a novel system for reducing the time taken for boats to pass through the tunnel. This consisted of a stop gate near the Lapal portal and a second-hand steam engine coupled to a scoop wheel, which transferred water from the west side of the gate to the east, thus creating a flow of water towards Selly Oak. A paddle was raised to assist the passage of boats in the reverse direction. In order to tackle the problem of instability of the tunnel, in 1819 he consulted Samuel Hodgkinson, a civil engineer in Birmingham. In a series of letters during February and March, illustrated by plans and sections based on Clowess 1794 report, Hodgkinson made various recommendations for strengthening the weaker sections. Interestingly, it was the view of Hodgkinson that the execution of the tunnel had been an enormous waste of Money and Time, to the material loss and disgrace to the concern. Hodgkinsons proposals for strengthening the arch in fact amounted to minor adaptations of Clowess section. It is not known if they were implemented and the tenor of his letters suggests that they were not. Reports of intermittent falls continued throughout the 19th century. These were repaired, but there was little incentive for the BCN Co. to undertake any major work after the opening of Netherton tunnel in 1858, provideding an alternative route to Birmingham.
Due to the great age of the Lapal engine and the general decline in traffic, pumping was discontinued on 1 October 1914 and thereafter boats were again legged through the tunnel. On 15 June 1917 it was reported that another collapse had occurred and that boats were unable to pass the fall. Inspection revealed that about 19 ft (6 m) of the north wall at 2310 yards (2112 m) from the Lapal portal had given way and that the adjoining brickwork was damaged, the total length affected being about 20 yards (18 m). The estimated cost of repair was a mere £800, but the work was not carried out. The damaged section was shored up in an attempt to prevent further collapse and a 9 in (0.23 m) pipe was laid in the bed of the canal to maintain a flow of water. A thorough survey was carried out towards the end of 1924 with a view to making a decision on the future of the tunnel. BCN ice breakers were used, since the rounded bilges of ice boats were less likely to dislodge brickwork than the usual maintenance boats. The Antarctic entered the tunnel from Lapal, but damaged brickwork prevented it from reaching the main fall. The Baltic started from the eastern (California) portal and was able to reach the collapse. The tunnel was completely blocked by that time and there was a large void with baulks of timber above the brickwork. Several sections between the collapse and a point 2750 yards (2515 m) from the west portal were reported as being in bad condition or dangerous and on 22 September 1926 the tunnel was officially closed to traffic. However, boats continued to use the canal between the Worcester & Birmingham and the brickworks at California. The entire canal, including Lapal tunnel, was abandoned as far as Manor Lane, Halesowen, in 1953.
In 1939 the War Office expressed an interest in using the eastern end of the tunnel as an ordnance store, but this came to nothing, as did a suggestion that it could be used as an air-raid shelter during the War. A fall at 2750 yards (2515 m) was reported in the 1939 survey, but the first 1000 yards from the California portal were then in good condition. A further fall about 1954 produced a tidal wave which lifted stop planks and stranded the workboat while clearance work was being carried out near Bottetort Road, Selly Oak. A similar incident occurred near the west end of the tunnel and a partial collapse about 200 yards from the portal was encountered during a visit by canoe early in 1951. Otherwise, the western end of the tunnel was then intact at least as far as the air shaft, though subsequently the section under the M5 collapsed during construction of the motorway and is said to have beenwas evidently grouted with concrete. A total collapse, probably the one which occurred about 1954, was reached during a visit via the California portal early in 1961. The material blocking the tunnel contained a quantity of angular blocks, with squared timbers at the foot of the slide, suggesting that shaft infill may have been the cause of the fall. About 200 yards nearer the portal was a side fall, where a length of the south wall bulged inwards. A further collapse, evident as a crowing in at the surface, occurred about 1964 at a point which is now the yard of a coach depot.
Lapal tunnel was not a success; indeed, it was a liability to the Dudley Company, and later the BCN Co., throughout its working life. The basic problem seems to have been Clowess adoption of Dudley tunnel profile, which was unable to withstand the pressures exerted by groundwater and fluid marl and clay at Lapal. As was customary with early legging tunnels, the width was little wider than a narrow boat, an acceptable displacement being achieved by the depth of water. Had the tunnel been wider and with less depth, Lapal tunnel may well have survived. Available reports suggest that failure was usually due to fracture of the side walls initially, rather than collapse of the arch, though this appears to have occurred in later years under infilled shafts. Unlike Dudley and Netherton tunnels, no coal seams were worked under Lapal and mining subsidence was not a problem.
The Lapal portal of the tunnel disappeared when the approach canal was filled with spoil during construction of the Halesowen bypass and the basin at the California end was filled with refuse and rubble in the mid 1960s. The outline of the portal and adjoining abutments were marked by a hawthorn hedge when the site was subsequently landscaped, but this was swept away in 1994/5 when pipes were installed to vent methane from the buried tip. The airshaft was infilled by Birmid Industries Ltd in 1978, thus blocking the tunnel at this point, and its wrought-iron grid was taken to the Black Country Museum. Now, two hundred years after it was opened to navigation, the only visual evidence that Lapal tunnel existed are a number of spoil heaps along its line.
J. Ian Langford