Construction Methods Used in Tunneling Projects - Assignment Example

Critical Event Analysis Name Course Date Course Task 1: a. Construction methods used in tunneling projects Drill and blast method This method uses explosives. Blast holes are first bored on the tunnel surface to a predetermined depth using drilling rigs. Timed detonators and explosives are thereafter placed into the blast holes. After blasting, soils and waste rocks are transported to damping sites before starting the next blast. This method however requires adequate structural support measures since tunneling constructions may be done in grounds somewhere between extreme conditions of soft ground and hard rock. Compared with other methods like the tunneling by the Tunnel Boring Machine, blasting is associated with higher vibration levels but with lesser durations (Mott MacDonald, 2013). Cut and cover method This technique has been effectively used in shallow tunnels. It can easily accommodate variations in tunnel width and other irregular shapes and will usually find use when constructing stations. The method involves several overlapping works like excavation, soil covering and tunnel constructions. The works are similar to those of road construction with the exception that in tunneling, excavation levels are deeper. Sequential Excavation Method In this method, the location for the tunnel is first divided into several segments. These segments are afterwards mined sequentially with supports. During tunnel excavation, mining equipments like roadheaders and backholes may be used. Before applying this method, the ground for excavation must first be dry. Ground dewatering is therefore an essential process before employing this method. Other methods for ground modifications like ground freezing and grouting are commonly used by this method so as to stabilize the soil. Despite the fact that the method is slow, it has found become useful in those areas with subways or sewers that cannot be relocated (Mott MacDonald, 2013). Bored tunneling This method uses the Tunnel Boring Machine and is often used when excavating long tunnels. The method becomes effective when appropriate equipment is selected for the different rocks and geological conditions. It may be suitable for grounds that have competent rocks which will provide the needed geological stability and enable boring of a long section of the tunnel without structural support. Extremely hard rock will however not be ideal due to the wear of the rock cutter and may significantly slow down the process to the point where this method becomes uneconomical and inefficient and may take much longer than the drill and blast method. The proposed project could employ the cut and cover method. This is an easy and fast method compared with the other tunneling method and is most suitable for this project. It results to minimum vibrations that may have devastating effects considering the buildings already erected near the area and will save surrounding people from noise disturbances which would be the case for drill and blast method. b. Illustrations Cut and cover method (MTR, 2013) Drill and blast method (MTR, 2013) Bored tunnel method (MTR, 2013) Task 2 The construction of hydraulic structures is a complex process and it requires proper design. This is because of the effects that it may have if the structure fails. The construction of the hydraulic structures requires the design that will ensure that the force of water can be handled by the structure. During the construction process, the river may be diverted so as to allow the construction work to proceed. On the other hand, the water must be retained as the construction takes place. The materials used for the construction process also require proper selection. Water proof cement is required during the construction of the hydraulic structures. Insitu concrete is usually required during the construction of the hydraulic structures. On the other hand, it is also important to note that the precast units may also be used during the construction process. This is for the purposes of ensuring that time is not wasted during the construction process. The use of reinforcements is also a consideration during the construction of the hydraulic structures. The use of concrete or earth is the common methods that are usually applied during the construction of the hydraulic structures. The use of concrete is considered expensive although it may be the only method of construction in some of the instances. The use of earth or clay is mainly for the purposes of retaining the water. This method is cheap and also effective (Nalluri, 2007). A turbomachine on the other hand is for the purposes of extracting energy when dealing with the fluids. The rotor is one of the most important parts of the turbomachine. This part usually rotates for the purposes of changing the energy level for the continuous flowing fluid. The rate of rotation usually varies from one machine to the other. This is because of the different needs for the machines. The turbine is also an important part of the turbomachine. Its main role is to transfer power from the fluid to the rotor. A shaft is also a part of the turbomachine and it is mainly used for the purposes of connecting the machine to the power motor. The power consumption of the turbomachine is also dependant on the capacity of the machine. On the other hand, the compressors are also components of the turbomachine and it works alongside the turbines. The use of the turbomachine is based on the concepts of Euler energy equation and the Newton’s second law of motion. These concepts play an important role in the operations of the machine. The size of the turbomachine is however varied depending on the amount of fluids that needs to be transferred. This is also related to the horsepower of the turbo machine. The efficiency of the machine can be calculated based on the horsepower and the head losses. This is however done during the design off the machine. The efficiency rate is thus a requirement before purchasing the machine in order to determine its performance (Majewski, 2012). Task 3: a. Construction Methods for Marine Structures One important marine construction is the rubble mound breakwater. These are structures almost entirely built of quarried rock. Usually, artificial concrete armour units or armourstone are used for construction of the outer armour layer and this protects the structure against strong sea wave attack. The concrete armour units and stones in the outer layer must be placed carefully so as to achieve interlocking for better stability. The cross-section of this structure will have a simple geometry that will usually be of a trapezoidal cross-section, the side slopes typically 1:1.33 to 1:2. Sometimes a berm will be incorporated in the design further increase the wave energy dissipation and permit use of armourstone of smaller grading. This concept is known as a berm breakwater. This design will allow for a considerable amount of initial movement of the stones before reaching an equilibrium profile. Rubble mound breakwaters will often be preferred by designers since their outer slopes are a great way to break storm waves and dissipate this wave energy resulting only in partial wave reflection. The choice of equipment will usually influence the design of marine structures. For the rubble bound breakwater, the choice between waterborne and land based equipment or whether the construction will combine both equipment will usually influence the design. When constructing with land based equipment, the major requirement will be that the crest width at or above 1m, the maximum sea level becomes sufficient to allow for the appropriate traffic. The crane type used also establishes a boundary for the dimensioning of the breakwater crest since the crane needs a wide track in order to operate. For the rubble mound breakwater, the crane type and size will depend on the armour stone size or concrete units that will be placed at the crest and toe of the structure (Kennisbank, 2011). Waterborne equipment is however useful for dumping materials. The materials will not be damped continuously though if water level under the damping place is no more than 3 m below the low water. Floating cranes are generally not put to use due to limited workability as well as their poor accuracy in placing. The proposed project would require construction of a rubble mound breakwater across the river to protect the tunnel from strong waves from the side toward the river source. This construction could use land based equipment since these are easier to use and manipulate and the river width is within land based crane’s reach (Kennisbank, 2011). b. Illustration Detached breakwaters at Happisburgh, Norfolk, UK (Halcrow, 2011) Task 4 The use of asphalt paving method is common in the construction of highways. Through this method, the road base has to be firm. This is achieved by compaction of the road surface. A coat of hot asphalt is usually sprayed o the road surface. It is then distributed evenly on the road surface through the use of specialized machinery. Cement concrete paving is also a method of road construction that is common in the highway construction. Cement and water is an important binding agent that is used during the construction process. Thick base layers of concrete have to be made for the purposes of paving the road. This is an important procedure that also increases the durability of the road. Grooving of the surface has to be carried out through the use of a machine. Tar and macadam is one of the most popular methods of highway construction (Creedy, 2012). This is achieved by paving the road surface with tar. The use of machinery is necessary for the realization of better results. This technique is also suitable for the project as it will provide quality road. Linking the construction with the existing work will require the construction of bypass and flyovers for the purposes of enabling the safety of the pedestrians. Diversions will also be required so as to link he road with the other existing roads. This will require structural details that are conclusive. Bridges may also be required during the construction process to link the road with the other existing works. Heavy machinery will also be required during the highway construction process. This will require highly trained personnel to operate the machinery. (Nalluri, 2007) The railway construction methods differ depending on the tracks that are used. This is also dependant on the climatic conditions in the area. The concepts of expansion as well as contraction have to be considered during the construction process. The use of slab tracks is one of the methods that are used during the railway construction. This method of construction is suitable for roads, bridges and tunnels where the railway line is being constructed (Shuping, 2010). This makes the method suitable for the project as the railway line has to pass through roads and tunnels before being connected to the existing line. This method is also efficient although it requires high level of expertise. The use of ballast is also a construction technique for the railway line. This is however suitable for a conventional railway line. During the construction, ballast has to be placed on the surface before the installation of the railway line. This is construction method is easy to implement. However, it cannot be used on the tunnels and the bridges as the ballast cannot be placed. This method is therefore not suitable for the project. The use of tunnels will be applicable for the purposes of connecting the railway line with the existing line. On the other hand, it is important to put in place special considerations during the construction process when using any technique. The railway station has to be eco friendly for the purposes of protecting the environment. The use of natural energy as well as greening the rooftops is highly advised. These considerations should be put in place during the project. The transportation of the materials should also be planned in advance as the construction process requires a lot of materials. List of References Creedy, G 2010, Evaluation of risk factors leading to cost overrun in delivery of highway construction projects, Journal of Construction Engineering and Management, 136(5), 528-537. Nalluri, C, 2007, Hydraulic structures, Taylor & Francis, London. Majewski, P, 2012, U.S. Patent No. 8,125,215, Washington, DC: U.S. Patent and Trademark Office. Mott MacDonald, 2013, Appendix 2.2 Tunnel Construction Methods, retrieved on 19th Setember 2013 from MTR, 2013, Shatin to Central Link, retrieved on 19th September 2013 from < http://www.mtr-shatincentrallink.hk/en/construction/construction-methods.html> MTR, 2013, Construction Methods, retrieved on 19th September 2013 from Halcrow, 2011, Coastal and marine structures, retrieved on 19th September 2013 from Kennisbank, 2011, Design of marine structures, retrieved on 19th September 2013 from Shuping, W, 2010, Study on Construction Method Taken by Railway Tunnels and Its Applicability, Modern Tunnelling Technology, 3, 2002. Read More