Order from us for quality, customized work in due time of your choice.
Underground Tunneling
Underground pathways and tunnels are among the most extraordinary engineering constructions ever built by man. By definition, a tunnel is an underground pathway that is fully enclosed except for an opening for egress, commonly at each end (Tunnel Encyclopedia, n.d). According to the International Tunneling Association (ITA), Tunneling plays a significant role in society (Why Go Underground, n.d). In 2002, the ITA published a booklet that illustrated several features and reasons for the exploitation of underground space.
Nowadays, underground structures are one of the best solutions for urban problems and interurban links in a mountainous landscape. As regards cities, a wide range of underground structures has been used to improve living conditions. Tunnels for transportation (highways, metros) and public utilities (water supply, sewerage, electrical and telephone cables) are a priority in developing countries, and underground structures for city centre revitalization and public use (libraries, museums, car parking and entertainment & leisure facilities) are of considerable interest in developed countries.
This booklet aimed to convince urban designers, politicians, and decision makers to work together to realize the benefits of underground structures. The key extraordinary thing about tunnels is that they were founded in ancient times where the construction technology principle was weak. The presence of ancient tunnels is another proof that tunnelling played an essential part in human societies.
According to Harvey Parker & Associates, the ITA paper is concerned with the global effect of underground interaction with the environmental issues that have come into the existence over several years (Parker, 1998). The author emphasizes that man has exploited the underground since he first used caves for shelter, protection and simultaneously improving the environment. Long before the environment and sustainable development became household words, use of the underground has contributed to an improved environment, sustainable development, and, in general, an improved quality of life for society (Parker, 1998).
The Qanats in Iran
Despite the enormous construction work and design difficulties faced by ancient civilizations, a man successfully constructed underground structures to achieve sustainable development. As such, the lack of sophisticated machines, modern tools and information was not a hindrance to such developments. According to Boustani, the Qanats in Iran is estimated to have been built around 800 BC and is still functional today (Angelakis, n.d). This amassing engineering achievement also inspired the development of similar structures that use the same technological principles from irrigation. For instance, Henry Gubler believes that, around the same period, coal miners in Iran modified some canals to extract water from coal mines. The technology was effective, and farmers in Iran used it over several decades. By 525 BC and 500 BC, the technology had reached Saudi Arabia and Egypt respectively. In Mexico, the technology was introduced by the Spanish in 1520 AD and later taken to Los Angeles around the same time.
The extraordinary engineering work was initiated in the hot and arid climate of Iran where the need for irrigation was inevitable. As such, artificial underground water channels were developed to provide water supply for irrigation farming.
The Eupalinian Aqueduct
The Eupalinian aqueduct is another example of using an underground tunnel to supply water for irrigation purposes. Angelakis and Koutsoyiannis (2003) established that the tunnel is located in the Greek Island Samos. In the Greek civilization, there were limited natural water resources which necessitated the use of the Eupalinian aqueduct. On the contrary, civilizations such as those in Egypt and Mesopotamia were characterized by the exploitation of water from large rivers that include; Euphrates, Tigres and Nile. The aqueduct of ancient Samos, which is located, in Tigani village (Samos Island), is considered to be the greatest hydraulic achievement of ancient Greece (Angelakis & Koutsoyiannis, 2003).
The most imperative assumption of this review is that Eupalinian used a modern construction process that is used today to reduce construction time. In the modern construction process, the excavation of the tunnel is conducted from both ends starting at the same time. The goal of this excavation procedure is to meet at the central point, thus, save most of the construction time. As a result of the construction procedure, Herodotus characterized the tunnel as bi-mouthed . An obvious question is how Eupalinian managed to direct his workers to keep excavating at the correct angles towards each other without modern monitoring equipment.
The overall outcome of this review is that the need for tunneling found its place in an irrigation system for the communitys water supply. The use of underground structures has facilitated the existence of man for several centuries. However, it is easier to differentiate the general kinds of underground tunnels in order to appreciate the impact of tunneling on mans existence. The most popular applications of underground tunnels include; use for public needs, transportation and mine tunnels.
Firstly, tunneling for public needs refers to underground structures like water supply, sewerage, gas lines and electrical/telephone cables. Secondly, transportation tunneling refers to pathways for people such as railways, highways and pedestrian walkways. Lastly, mine tunnels are constructed for minerals excavation.
Although some underground facilities were found in ancient times; it is more unlikely to find them in most of the known civilizations. In modern civilization, tunneling is usually done to create space for the establishment of structures to meet public needs. Nowadays, facilities such as water supply and sewer systems tunnels are so integrated into societies that some people are ignorant of their existence.
Read (2004), asserts that life cycle management in relation to sewerage networks is of paramount importance if the maximum cost-effective life span is to be obtained. According to the author, there is a growing concern on sewer management due to the tendency of neglecting sewers. In addition to that, he points out that the tendency to neglect sewers arises from the fact that they are hidden from public view. As such, the only way that the above estimation is possible is by the use of an underground tunnel.
Characteristics of Tunneling
The design and construction of the above tunneling facilities in the earth is the most crucial part of the entire process. Although there are variations in the designs for different tunnels, the design procedure is more or less the same when the underground tunnel is constructed in soil. However, the designer can use the different functionalities and meet the requirements of each construction.
Cost and Functionality
Cost is one of the most salient aspects that will influence the design of the constructions, and whether to use a tunnel or an alternative structure. As mentioned earlier in the literature review, underground structures are usually constructed at a higher cost than their equivalent aboveground structures. However, there can be substantial savings in the cost of constructing such structures with some combinations of scale, geological environment and structure (Why Go Underground, n.d).
For instance, telephone and electrical cables are most preferably located in tunnels in order to save space at the surface for other purposes. It also helps in cable isolation and protection from corrosion, thus, cost beneficial in the long term. Furthermore, cable isolation in electricity cables provides increased levels of public safety. As mentioned earlier, other facilities such as sewerage collection and treatment points are built underground in order to guarantee public health and hygiene.
With regards to irrigation, underground systems have been utilized from ancient times due to the advantages offered by such structures. In underground irrigation systems, a preferable gradient can be created to allow water to flow towards users due to the hydraulic properties of fluids.
Finally, transportation (railways, highways) and other underground facilities such as libraries, museums, car parking, entertainment and leisure facilities are of immense importance. These constructions can easily be found on the surface and in the underground; thus, their solution in tunneling can be given as a combination of geological suitability of the existing site and environmental safety or environmental topography demands.
Safety
As much as the cost and functionality of the design are of considerable value, safety should also be considered. According to relevant sources, safety can be attained by the use of an optimization process strategy (multi-objective optimization, n.d). However, the first setback arises from the fact that the design objectives result in conflicting views. As such, it is difficult to meet the requirements of one of the objectives without the others. Therefore, a compromise must be achieved in order to move on with the process.
Bieniawskis strategy that is used by decision makers and designers in optimizing the variables in tunnel construction is discussed. The three variables that need to reach a compromise in tunnel construction include cost, safety and functionality of the structures. This strategy is based on different stages in order to allow the design to reach a compromise and still have a safe, functional and less costly solution. The following stages describe the procedure that is followed in the design of an optimized underground tunnel:
-
Stage 1: Statement of the problem experienced.
-
Stage 2: Identifying the constraints and functional requirements of the design.
-
Stage 3: Collection of information such as geologic site characterization, soil mass properties, groundwater, in situ stress field, applied loads.
-
Stage 4: Formulating the concept for use.
-
Stage 5: Using analytical, observation, and empirical methods.
-
Stage 6: Using alternative solutions (i.e., shapes and size of excavation and associated safety factors).
-
Stage 7: Evaluation.
-
Stage 8: Optimization.
-
Stage 9: Recommendation.
-
Stage 10: Implementation.
In accordance with Bieniawskis design methodology, a typical design process for underground excavation will be considered as summarized above. In the paper, it is assumed that the design objectives and variables (stage 2) can be mathematically quantified. It is believed that the process of defining the objectives and design variables is beneficial to the rationalization of the design process. As such, a set of variables defines a design solution (stage 6) in a manner that satisfies some design constraints to be considered feasible. Finally, an evaluation and optimization (stages 7 and 8) process can be carried out at this point.
Geological/topographical aspects
The geological/topographical aspects investigation is the next key stage of the design procedure to be investigated. During the initial stages of the design process, it is highly recommended to study the topography of the area. In such scenarios, topographic maps and climate situations (wind load, rainfall intensity, etc.) are investigated to establish possible solutions.
Once the alternative solution of tunneling is identified, a geological investigation must take place to illustrate the geological behavior of the strata. This is considered the fundamental tunneling investigation. There are various steps taken by a geological engineer during the geological and topographical investigation as explained in table 8.1 (Read, 2004).
Table 8.1: Parameters for Identifying the Geological and Topographical Aspects.
In a geological investigation, various steps of geological testing are conducted in different ground conditions (Read, 2004). For instance, the following tests are undertaken for clay soil; standard penetration tests, index tests, pressure meter tests, triaxial tests, undrained strength, pocket penetrometers, soil chemical tests, particle size distributions, swelling, consolidation, moisture content, liquid limit, plastic limit, and Sieving/sedimentation.
Soft clays such as alluvium require the following tests; cone penetration tests, Index tests, Shear vanes, Undrained shear, In-situ permeability strength, Particle size distributions, Soil chemical tests, Moisture content, Liquid limit, Plastic limit, Triaxial undrained drained, and Sieving/sedimentation.
Granular soils undergo the following geological tests; standard penetration tests, In-situ permeability, Soil chemical tests, Cone penetration tests, SPT tests, Friction lines for cohesion-less soils, Particle size distributions, and Sieving/sedimentation.
One of the fundamental tasks that the geological engineer must accomplish is to analyze the groundwater conditions. As a result, various tests such as Drilling observations, Piezometers, pumping tests, Tracer tests, and Water chemical tests are conducted in this field. Geological investigation and management of the soil have imposed a significant impact on tunneling procedures. As such, the risk in tunneling has been effectively put under control with help of engineers, and sophisticated plant and equipment used in the process (Read, 2004).
Although the geological characterization of the soil has an outstanding use in tunneling procedures, sometimes the relative test measurements can be misleading. In some cases, the wrong perception of ground conditions may result from factors such as; improper desk study, inappropriate fieldwork, in-situ testing or lab testing inadequacies, and poor geological interpretation (Read, 2004).
Tunnel Construction Methods
In order to construct tunnels in the soil, various construction methods are used. The most appropriate construction method to be employed is determined by conducting a geological investigation and should be safe, functional, and economical. Tunneling procedures are usually divided into two broad categories referred to as cut and cover and bored tunnels .
Cut and Cover Method
The latter method is widely known and used worldwide due to its easy concept. The main idea of the cut and cover construction procedure is to excavate a temporary trench and insert or build the tunnel circumference to replace and support the excavated soil. This procedure can be used for both shallow and deep tunneling excavations.
In this technique, it is sometimes necessary to include temporary supports to join ground faces; therefore, creating areas for an adjoined structure. The use of these supports allows for safety and makes the structure economically affordable (Read, 2004). In restricted working areas, however, there is limited space that leads to the use of timbered trenches. This is also the case in water-bearing sands where unsupported ground slumping to a flat angle of repose results.
The temporary support structure maintains the status quo between the exposed excavated faces. On the sides, the sheeting collects the earth pressure on the face and transfers it through the walling to the struts. On the other hand, the struts provide equal and opposite forces at each end to maintain the equilibrium of the system, all forces involved being horizontal (Read, 2004).
Tunnel Boring Methods
Under this method, there are several types of techniques that are used. In this method, supports for the tunnel are constructed while excavation into the soil progresses. In less than two decades ago, it was difficult to undertake any excavation in soft soils by using bored tunnel techniques. The alternative solution to this problem was to use the clay kicking tunneling technique, which became obsolete, due to its time-consuming nature.
The New Austrian Tunneling Method gave a new impulse to the construction of bored tunnels. This construction method involves three key steps in preparation for the works. First of all, a thin layer of concrete is sprayed inside the excavation to minimize soil movement and harden the circumference of the excavation (Karakus & Fowell, 2004). A supporting arch for the surface of the soil is then inserted by joining precast concrete or steel members. Lastly, the soil deformation is systematically measured to estimate the time that the excavated soil could take without supports (Karakus & Fowell, 2004).
Another tunnel boring technique is the use of machinery to construct tunnels. One of these methods is pipe jacking that involves the installation of pipes under highways, runways and railways without cutting the ground open. In this method, a pipe with steel or reinforced concrete casing is jacked into the soil strata (Sofianos, Loukas & Chantzakos, 2004). With the aid of hydraulic pressure machinery, the pipe is then jacked into the soil.
The development of the tunnel boring machine (TBM) has improved the tunneling industry as tunnels can now be created faster, safely and in a cost saving manner (Spencer, 2004). As such, tunnel boring machines have enabled the possibility of creating tunnels in areas that seemed impossible and still remain a cost-effective solution (Spencer, 2004).
The next figure shows the different parts of a tunnel boring machine with a brief description of its operation given shortly (Spencer, 2004). The machine has a cylindrical shape and consists of one or two-cylinder shields at the face of the machinery. The function of the shields is to provide temporary support as the TBM excavates through the soil. A circular cutting wheel is located inside the shields and serves as the excavating arm of the machine. Behind the cutting, wheel is a chamber for the deposit of the excavated material. A vacuum system is attached behind the chamber, and its function is to transmit the excavated material to the surface. Furthermore, a hydraulic jack pressure system (positioned beneath the cutting wheel) assists in pushing the machine forward through the ground. According to the Tunnel Boring Machines paper, there are two categories of TBM machinery used in soil excavation.
Conclusions
As established in the paper, it is inevitable to mention that significant advances in technology have facilitated tremendous growth in the tunneling industry. Unlike many centuries ago, technology has opened up new and better ways of tunneling that are fast, environment friendly and economical. As such, decision makers and designers in the United Kingdom rival to be the best tunneling providers in Europe. As a result, the construction of tunnels has become easier; hence, more tunnels are being constructed globally (Going underground, n.d). As established earlier, the following are benefits that are associated with recent tunneling activities.
-
Cost: It has been established that the cost of tunnel construction has been falling at around four percent each year. At around £50m per km, urban tunnels are considered more economical than aboveground facilities were acquiring land and moving pieces of machinery are expensive (Going underground, n.d).
-
Construction: The Channel Tunnel and other projects triggered the development of tunnel boring technologies and consequent improvement in the underground structure. Furthermore, new technologies for blasting tunnels have transformed the economics of rural tunneling where the right geology exists. Unlike the direct vehicle emissions into the air on surface streets, technologies have been developed to clean harmful tunnel emissions before they are released into the atmosphere (Going underground, n.d).
-
Safety: According to relevant sources, accident records show that rural tunnels are twice as safe as rural roads. As such, urban accidents can be reduced by using tunnels as the key enabler for integrated transportation and environmental improvement schemes. Also, high standards of emergency, equipment monitoring, and operation can be maintained in tunnels (Going underground, n.d). Furthermore, the separation of heavy vehicles from light vehicles reduces the risk of serious incidents in tunnels.
-
Environment: Where tunnels are used in rural areas, outstanding environmental benefits are achieved. In urban areas, tunneling can help to ease traffic congestion, and existing roads could be used for emergency services, walking, cycling, and general livability (Going underground, n.d).
References
Angelakis, N., and Koutsoyiannis, D. (2003). Urban water engineering and management in ancient Greece. The Encyclopedia of Water Science, pp.9991007.
Angelakis, A. N. (n.d). Water and Wastewater Technologies in Ancient Greece with Emphasis on Minoan Era. Web.
Going Underground Tunnels: What Role in Town and Country? (n.d.). Web.
Karakus, M. & Fowell, R. (2004). An Insight into the New Australian Tunneling Method (NATM). Web.
Multi-objective optimization under uncertainty in tunneling. (n.d.). Web.
Parker, H. (1998). ITA Work and Experiences on the Urban Environment. Web.
Read, F. G. (2004). Sewers: Replacement and New Construction. Great Britain: Elsevier Butterworth-Heinemann.
Sofianos, P., Loukas, & Chantzakos, Ch. (2004). Tunnelling and Underground Space Technology. Volume 19, Issue 2, Pages 193-203.
Spencer, M. (2004). Tunnel Boring Machines. Web.
Tunnel Encyclopedia. (n.d). Tunnel Information. Web.
Why go underground. (n.d). Web.
Order from us for quality, customized work in due time of your choice.