Techniques for Roadway Tunnelling - Coursework Example

Review of Techniques for roadway tunnelling AMEL ALostad Griffith School of Engineering, Griffith Gold Coast, QLD4222, Australia This essay seeks to dissect a review of a number of techniques for roadway tunnelling. A brief introduction and background information on roadway tunnelling is given. A review of various roadway tunnelling construction technologies which includes both modern and traditional are presented. In addition, the essay seek to offer a detailed insight of the benefits and drawbacks of some of the roadway tunnelling techniques in order to show methods that are suitable and economical for construction of tunnels for given ground conditions. Keywords: Tunnelling, Roadway, Construction Technologies 1 Introduction Due to increased population and massive migration to urban areas, infrastructural facilities have either to be constructed high above ground or deep into the substrata where conditions are uncertain. This essay seeks to dissect a review of a number of techniques for roadway tunnelling in various conditions and the attributed advantages and disadvantages shall be discussed. Tunnels, both artificial and natural, exist in various shapes, and can be constructed by various techniques. Tunnels are sorted as underground and underwater passageways, transporting and carrying passengers, freights, water and sewage through pipes. For example, Gerrards Cross Tunnel in England and The Natural Tunnel State Park in Virginia, USA are being used as a train tunnel and railroad tunnel respectively. 2 Discussion 1.1 Background and origin Tunnelling has been in existence for a long time as evidenced since the 1700s as evidenced by the historic Fritchley Tunnel, in Crich, Derbyshire, which can be traced back to 1793(Daily mail UK., 2013). Tunnels are structures that require special design considerations that may include lighting, ventilation, fire protection systems, and emergency egress capacity based on the owner’s determination” (Thompson et al., 2011). Conventional tunnelling can be referred to the construction of underground openings of any shape with a cyclic construction process composed of excavation, by using the drill and blast methods (explosives) or very basic mechanical excavators, mucking as demonstrated in Figure 1 and Figure 1: Tunne mucking cranes ((ElectroMech Material Handling Systems (India) Pvt. Ltd., 2014) Placement of the primary support elements such as: steel ribs or lattice girders, soil or rock bolts and sprayed or cast in situ concrete. In certain instances grouting is used to reinforce the soil or face of the tunnel to avoid collapse or failure. The most commonly used grouting material is cement. Today, tunnels are an increasingly necessary part of our road and rail networks and continue to be employed to support our water, sewer and utilities systems. 1. 1.1. 1.1.1 Traditional process i. Cut and cover This is a common and efficient technique of building shallow tunnels and can accommodate various tunnel width variations which may be adopted by construction stations from time to time. The application of this method requires that numerous overlapping are done to ensure that tunnels meet the required standards (Dailymail UK, 2013). The technique involves three primary parts which includes the trench digging, tunnel building and soil covering. The works involving the three parts resembles the process of road construction with the exception of the extent of deepness. Drill and blast Application of explosives is the primary approach in this method. The blast holes are first drilled on the surface tunnels which are proposed. In most cases, the designated depth fro blasting should be reached by use of the drilling rigs. After the drilling process is over, specific explosives are strategically put in the holes and allowed to undergo blasting. Since this technique happens in hard rocks and some time a soft ground, there is need for adoption of enough structural measures (Thompson et al, 2011). This is to minimize the period of vibrations. At this stage of completion of blasting, a temporary site is of immense necessity for storage of the explosives ii. Hand mining Original tunnels were involved excavation by hand. Manual labour was used for exploratory activities like gold mining. This still happens on a small scale in some countries. 1.2 Advancement in methodology 1.2.1 Tunnel boring machines (TBMs) Long tunnels can be easily excavated by using this method. This approach involves cutting of the designated surface in form of a circular shape in turns. It is imperative to note that, this method works well after a rigorous research on the geological conditions that surround the designated place (Thompson et al, 2011). 1.2.2 Sequential Excavation Method Application of this technique requires that the designated place be segmented and then mining occurs in series. This technique is a blast method and equipment including backhoes and road headers are used. Some of the conditions requisite for this method includes dryness to ensure easy excavation. The only disadvantage attributed to this method is the slowness in completing a work began. However, it is advantageous in areas where sewers exist (Thompson et al, 2011). 1.3 Modern approaches 1.2. 1.3. 1.4. 1.3.1 Cut and cover The “Cover and Cut” method was originally developed for construction of shallow underground structures in congested urban areas, where open excavation techniques would cause significant disruption to traffic (Mouratidis, 2008). The first stage involves constructing the “cover”, an earth retaining concrete shell, followed by the second stage, the “cutting” operation, representing the main excavating activities under the previously constructed “cover”. These retaining effects in road tunnel engineering are established by concrete vaults, providing safe cover to excavating activities underneath. 1.3.2 Immersed tunnels Immersed tunnels have been greatly used in countries prone to earthquakes like Japan and New Zealand. This is emphasized by (Kiyomiya, 1995). He investigates immersed tunnels constructed in soft ground at port areas during earthquakes. 1.3.3 Micro-tunnelling These technique is used to construct small tunnels only and find their applications in utility projects. Examples include tunnelling across a road for a water supply pipeline or fiber optic cable. 2 Benefits 2.1 Drill and blast iBenefits The Potential environmental impacts in terms of noise, dust and visual on sensitive receives are significantly reduced and are restricted to those located near the tunnel portal. In addition, when Comparing with the cut-and-cover approach, quantity of C&D materials generated would be much reduced. Further, compared with the cut-and-cover approach, disturbance to local traffic and associated environmental impacts would be much reduced; 2.2 Bored tunnelling benefits: Potential environmental impacts in terms of noise, dust and visual on sensitive receives are significantly reduced and are restricted to those located near the launching and retrieval shafts. In addition, when comparing with the cut-and-cover approach, disturbance to local traffic and associated environmental impacts would be much reduced. Further, when compared with the cut-and-cover approach, quantity of C&D materials generated would be much reduced; 2.3 Sequential Excavation Method benefits: Similar to the drill-and-blast and bored tunnelling methods, only localised potential environmental impacts would be generated; 3 Drawbacks 3.1 Cut and cover tunnelling More dust and noise impact may arise, though these can be mitigated through implementation of sufficient control measures. In addition, the temporary decks are often installed before bulk excavation to minimise the associated environment impacts. Further, larger quantity of C&D materials would be generated from the excavation works, requiring proper handling and disposal. 3.2 Drill and blast Potential hazard associated with establishment of a temporary magazine site for overnight storage of explosives shall be addressed through avoiding populated areas in the site selection process. 3.3 Sequential Excavation Method As the method is relatively slow, duration of potential environmental impacts would be longer than that of the other methods. 4 Future Directions Tunnelling has a bright future for use in transport planning. Some of the areas of research in roadway tunnelling include use of driverless trains, electric vehicles and longer tunnels will be built with the existing knowledge. 5 Conclusion The paper has shown developments for use in transport planning and the potential for future research that exists. In the case of the construction of shallow tunnels, both traditional and modern cut and cover approaches are convenient in congested urban areas, where open excavation techniques would cause significant disruption to traffic. In the case of the long tunnels, advanced methodologies such as use of the Tunnel Boring machines are convenient in areas where a rigours research on the geological conditions has been done. On the other hand, the study on the future directions of tunnelling is critical to the complex situations of tunnelling. This implies that more focus on directions such as use of driverless train and electric vehicles will offer solutions. References Read More