Introduction
The building of tunnels dates back to the canal age. The first English canal tunnel was that of James Brindley on the Bridgewater canal directly entering Worsely coal mine (Muir 14). It was opened in 1761 and subsequently extended. This marked the beginning of tunneling, with numerous tunnels on the extending canal network. Brindley’s next achievement was the Harecastle tunnel built on the summit of the Grand Trunk Canal that was later damaged by mining activities. Since then tunneling has been an important aspect as far as infrastructure is concerned not only in the construction industry but also in art and architecture.
Tunneling techniques used in England in the nineteenth century
The English system of tunneling is one of the most unique systems in history. One of its characteristic aspects is the use of two timber crown bars as applied in the central-to-heading design of the tunnels. This allowed the rear ends to be supported by a complete length of the tunnel lining with the forward ends strongly propped within the central heading. Additional bars were erected around the tunnels perimeter an aspect that was necessitated by the central heading. The bars played a pivotal role in excluding the ground. Their positioning enhanced this-they were erected around the perimeter of the face with carefully selected boards between each pair. The system was very economical in terms of timber. It also permitted the construction of the arch of the tunnel in full-face excavation, and its tolerant of wide variety of ground conditions, but depends on relatively low ground pressures.
In the absence of other than primitive means for foreseeing the nature of the ground ahead of advancing tunnel, there were frequent surprises. Linings were in masonry or brickwork depending on the local availability of supply. Some of the early railroad tunnels in most of the regions in Europe were lined in timber, with long, shaped voussoirs supported on vertical side members.
Rock tunneling began in Germany. It was revolutionalized by the vast use of explosives for mining especially in the seventeenth century (Muir 66). The builders also used compressed air for pneumatic drills. Previously, methods had been laborious and slow, scarcely improving on principles used by the Egyptians and later the Romans who had a very clear or rather good understanding on how to use plugs and feathers, as well as the expansive effects of wetted wooden plugs driven into drill-holes. Several tunnels used these techniques such as the Frejus Tunnel (also known in Britain as the Mount Cenis Tunnel).
One of the major achievements or rather innovations by the engineers of the time was the steam-driven rock drill. It was invented by a British engineer: T. Bartlett (Muir 67). Its design was in such a manner that it was successfully adapted for compressed air in 1855. Despite is special role in the British construction industry it was not produced commercially. Several features of other instruments for the construction of tunnels were proposed including that of Joseph Fowle of the United States (Ibid). They were incorporated in the rotary-impact drills with automatic feed used by G. Sommeiller for the formidable task of driving the 12, 224 meters long Frejus Tunnel. Another major device that was used in the construction of tunnels during that period was the first compressor installation of 1861, which used falling water with entrained air, separated under a pressure of 700kPa, but the biggest challenge of the system was excessive dynamic stresses. This was generated by some unreliable mechanical operation. To solve the problem, the engineers introduced a waterwheel, like the one used by the Egyptians, to power the compressors (Bonnett 80). Another device for tunneling purposes that was invented during that time was the drilling carriage commonly referred to as the ‘jumbo’. It first application was in the construction of the Frejun Tunnel. It was used to mount four to nine drills in the construction of the tunnel. This was a major development in the development of technologies that would be used in the construction of tunnels. Frejus is also notable for the consideration given by Sommeiller for the accommodation, medical and school services provided for work place (Muir 81).
M.I Brunel, one of the renowned engineers of the time, liberated soft ground tunneling from its constricted use following the invention of the shield. Additionally, Brunel introduced other expedients, which later became widely adopted methods of face support –soil-nailing. This demonstrated a clear, although yet largely qualitative, understanding of the interaction between the ground and its support. It also provided an effective means for controlling the entry of water into the tunnel during the construction process. According to Bonnett Brunel’s contribution to tunneling was very remarkable as it solved most of the problems that were faced by the builders of previous tunnels (96).
His patent application of 1818 depicted two types of circular shield. The first type was significantly advanced in that it had some propelling rams while the second type had a rotating drum. The propelling rams were instrumental in as its effect on the reaction frame blocked against the already completed length of the tunnel lining. The techniques employed by the different engineers are essential in enhancing an in-depth understanding of the Thames tunnel.
The Thames tunnel was the first shield-driven tunnel. It was initially designed predominantly for horse-driven traffic serving the docks under construction on the south bank of the River Thames. It was rectangular. Essentially, it comprised of 11 (later 12) “vertical cast-iron frames each containing three cells, each about 2m by 0.8m wide, one above the other” (Ibid). At the head, as well as to each side of the shield, it comprised of a series of ‘staves’ which pivoted support from the frames. The frames had cutting edges at their leading end. Additionally, they had an extension of wrought iron specifically at the rear end. This played a pivotal role in permitting brickwork to be done without further protection devices or rather techniques. Another important aspect in the construction of the tunnel was the use of screw jacks. They enhanced the propulsion of not only the frames but also the staves. Muir (89) notes that the measurements of the initial and second excavation were as follows:
The elm poling boards that were strategically placed facing the screw jacks were essential in supporting the face of the tunnel. The builder’s approach for excavation was the removal of one or more of the polling boards in each of the cells. Some of the aspects that needed the expertise of well-seasoned engineers included delicate nature of the features of the specific ground and the poor lighting. The builders also needed good techniques of dealing with the irruptions from the Thames river as well as in tackling all the activities. It took the builders approximately one and a half decades to complete the construction of the tunnel i.e. from 1825 to 1841. By the time the tunneling of the Thames Tunnel was completed, the specific requirements had changed so that the tunnel was initially opened for pedestrians in 1843 and for the East London Railway, which is now part of the London Underground, in 1869.
The contributions made by Brunel played a pivotal role in the construction of the tunnel. The quality of the bricks as well as the design of the design of the roman mortar used by Brunel were tailored or rather designed to limit to a minimum flow of water. In order to drain any water seeping through the brickwork, Brunel provided a system of circumferential slots cut or otherwise formed at the intrados of the brickwork, at intervals of about 0.2 m, with the internal lining provided by the tiles and a plaster rendering. The main principle of conservation was assured at this time by causing minimal change to stress regime of the original brickwork and reinforced concrete lining, which may well itself require during the future period of expectation of life of the tunnel.
Romanesque Architecture as the core of the architectural design of the tunnel
Architecture history is an interesting subject in which we know how art has evolved over centuries from Neolithic architecture of 10000 BC to the contemporary architectural designs. The existence of this history shows the gradual evolvement of the art to what the world has today. Each of the architectural designs has its own outstanding and unique features that make them stand as original. Apart from these being history, there have specific architectural elements that are of use and can help us appreciate these pieces of art for what they are- pure architecture as used in the construction of tunnels in the nineteenth century (Tatton-brown, and John 35).
According to the oxford dictionary, the word “Romanesque” means “descended from Roman” and used to denote the roman languages. In architecture, the term first described architectural designs in west Europe from the fifth to the thirteenth centuries. The term is used to describe a style that was identifiably of medieval origin and prefigured in the Gothic, but still maintained the rounded Roman arch that made it appear to be a continuation of the traditional building style of the Romans.
Specific elements of Romanesque Architecture
Walls
The major aspects that are characteristic of the walls constructed for buildings based on Romanesque architectural designs are their small openings as well as their thickness. They are made of double shells whose main constituent is rubble. Different regions of the world have different building materials. This depends on the nature of the locally available stones as well the traditions that govern buildings’ designs in any given locality. The stone ranges from brick, limestone, and granite to flint. The style involves small irregular stones bedded in thick mortar (Fletcher 56). Smooth ashlars’ masonry is not commonly used. In the medieval period, it only occurred mainly in areas where people used easily workable limestone. The same principle was used in the construction of the walls of the tunnel-with the primary building materials being bricks and wood.
Buttresses
These are not an outstanding feature because of the massive-size walls of the architectural design. A flat square profile is one of the major characteristics of the buttresses among other aspects that are specific to the design of the wall(s). Some of the elements that architects employed in the construction of buttresses include barrel vaults, which can be either full or half depending on the design of the buttresses in question. This idea was borrowed from the construction of aisles in churches-the vaulted ones.
Arches and openings
The other feature that is outstanding in the Romanesque is the use of semi- circular arches for all openings such as doors, windows, for arcades and for vaults. Wide doorways are in most cases surmounted by a semi-circular arch, however, exceptions exist in cases where doors with lintels are set into large arched recess and surmounted by semi-circular "lunettes" with decorative carvings (Fletcher 62). The openings of tunnel employed the principles of the arches and openings as applied in the Romanesque churches.
Arcades
According to Fletcher, arcades mainly comprise of rows of arches (2001, p. 65). To enhance the stability of the arches, architects employ columns or piers. They form an integral part of the interior parts of large buildings besides occurring in cloisters and atriums. Their major role is to separate the nave from the aisle especially in church buildings. Traditionally the arcade of cloister is of a single stage, while the arcade that divides the aisles and nave is traditionally of two stages, and a third stage of windows (clerestory) rising above them. Traditionally, the purpose of arcading is to fulfill structural purpose but it is also use for decorative purpose both internally and externally.
Piers
In Romanesque architectural designs, architects employ piers to offer support to the other components of a building especially the arches. Though they are typically of rectangular shape, piers can take forms that are more complex with half-segments of large hollow-core columns on the inner surface that supports the arch, or clusters of smaller shafts that lead into the arch ‘mouldings’ (Fletcher 67). Piers occur in different shapes depending on their usage. For instance, they assume a cruciform shape when the architects use them to join two significantly large arches.
Columns
Columns form an integral part of Romanesque architectural designs in buildings. Fletcher argues that, to enhance their aesthetic value, most architects incorporate not only attached shafts but also colonnets in the structure in question (76). Other columns used in this architectural design are salvaged columns, drum columns and hollow core columns (Fletcher, 2001, p.70). Each of these columns designs gives them strength because they carry the massive weight of the upper walls. Some of them like the hollow core columns can be ornamented with incised decorations.
Vaults and roofs
Wood plays a pivotal role in the construction of roofs and vaults as far as Romanesque architecture is concerned. Vaults and roofs can take the form of a king post, simple truss or even a tie beam. The lining in such cases comprise of a wooden ceiling. Vaults of stone or brick take on different forms. There are several types of vaults, which include barrel vault, groin vault, arched vault and ribbed vault. Unlike the arched and ribbed vaults, the groin and barrel vaults are relatively easy to construct. Most architects argue that the easiest type of a vault to construct is the barrel. For the construction of such barrels, there need to be strong walls, which may or may not have small holes to enhance the support of such vaults. A groin vault is similar to the barrel that only that it requires the use of two barrels. The design of timber support was also being developed from the experience in mines.
How the tunnel would be
More generally, appreciation of the merits of light support with properties of deformability to suit the ground has long been a feature of the approach of many engineers in the contemporary society. The common objective has been to enable the ground to be self-supporting around the periphery of the tunnel to the greatest degree. This has led to the development of new techniques in tunneling.
The tunnel would have assumed the new alpine tunnel design, light support capable of tolerating high degree of inward convergence of highly stressed rock to establish equilibrium. This approach has received or rather achieved great economies by comparison with the traditional methods-the methods that were used in the construction of the tunnel. This was achieved for the Alberg and Tauern tunnels by use of yielding Touissaint-Heinzmann arches, as opposed to the Romanesque arches that were employed in the construction of the Thames Tunnel, since the degree of convergence would be excessive for load bearing Shortcrete lining. Additionally, in weaker ground, the techniques of building side by side or crown-heading directly into the full tunneled section of the alpine approach draws upon earlier traditional practices with steel arch supports, in other than squeezing the ground. The principle objective in applying these techniques would be to establish stability while limiting the extend of the loading to be transferred to the support or to any subsequent lining. It would also serve to provide support so expeditiously as to secure the ground and to limit ground movements, which may otherwise be expensive to compensate or cause damage to other structures and services. Reduced loading on the support in soft ground, as applied in this technique, is natural and adventitious as result of the deformation of the ground ahead of the installation of support.
Some of the materials that are available in the current century for the construction of tunnels include sprayed concrete, spiles, dowels and bolts. Sprayed concrete lining is of major importance especially in the construction of contemporary tunnels. Early examples sprayed concrete lining (SCL) were based on simple analysis of a tunnel in ground of uniform initial stress, considering the ground as a linear elastic material up to yield and as a material of uniform plastic strength thereafter (Muir 100). Subsequently, the effects of anisotropy and the strength reducing to a residual value have been considered. For yielding rock, the approach remains largely empirical. There have been many developments in different forms of rock-bolt, spiles and dowels to suit different circumstances. Problems of ‘shadowing’ of sprayed concrete by traditional steel arches has encouraged increasing lattice arches formed of bar and mesh. The techniques of sprayed concrete have been deployed to include robotic application and the inclusion of steel fibre reinforcement.
An alternative scheme of providing immediate ground support prior to excavation has been adopted for use in the development as well as the construction of tunnels. The technique was initially developed in France and it is referred to as the Bridge (Muir 102). It involves the creation of a slot that is later filled with sprayed concrete, which enhances the development of enough strength to support the periphery of the ground prior to the main excavation. However, this does not imply that the Thames Tunnel has a rather weak foundation since this technique had not been invented by the time of its construction. The builders as well as the architects at any given point in history use their expertise to develop structures. Therefore, all measures that were needed in enhancing maximum strength of the tunnel were taken based on the available raw materials. This also applies to the techniques that are used in building tunnels or any other building-they are tailored to meet all the standard requirements of the construction or rather building in question.
Works Cited
Bonnett, Clifford F. Practical Railway Engineering. London, GBR: Imperial College Press,
2005. Print.
Fletcher, Banister. A History of Architecture on the Comparative method. USA: Elsevier Science
& Technology, 2001. Print.
Muir, Wood A. Tunneling Management by Design. London, GBR: Spon Press, 2000. Print.
Tatton-Brown, Tim, and Crook, John. The English Cathedral. New Holland: New Holland
Publishers, 2002. Print.
