Social Resources Development Institute - Assignment Example

1 a) cut and cover tunneling method In cut and cover tunneling, the structure is built in an excavation and later on covered with some backfill material once the structure is completely built. This technique is mostly used when there is a shallow tunnel profile and at the time when the surface excavation is feasible. This technique is mostly used in underpasses, mined tunnels and in flat terrains or in places where it is feasible to construct a shallow tunnel. In the construction of these tunnels, there are two approaches that are applied; top down and bottom up. In bottom up, the excavation walls do not necessarily have to support the final structure. In top down, the excavation walls support the tunnel’s ceiling and the roof. For depths of about 10 to 12 meters, this technique gets to be more economical than mined tunneling (Pan et al., 2006). The low grounds in Hong Kong are a major reason these technique is used in the area (Meng, 2009). 1.1 b) TBM This kind of tunneling is applied in making of long tunnels in rock masses in different surroundings. In order to have a proper job done, the method requires the right TBM machines and the right equipments. In this technique, the rocks give the upper hand of providing natural support for the tunnels. There are likelihoods, however, that the hard rocks might be disadvantageous to the tunnels. In this technique, major shield methods are “earth pressure balanced (EPB)” and slurry machines. In order to select the right machine for the right jobs, some of the most important things to take care of are the condition of the ground, the condition of the surface, tunnel section dimensions, distance being bored, alignment of the tunnel and the period to be taken for construction (Bilger, 2008). Both shield methods operate in a closed face machines where the head part of the machine is closed and the rear part is in a different compartment. EPB turns the soil that is excavated into mud pressure than for the stability of the cutting face, holds it in that form. Due to this reason, it cannot be used in hard rock as it is necessary to turn this rock to slurry. The slurry machine uses the slurry that gets pressure externally for stability of the cutting face. This slurry uses fluid conveyance to transport the soil that is excavated. The slurry is pressurized using the slurry feed. The slurry properties are adjusted using the equipment for processing slurry. 1.1 c) drilling and blasting Drilling and blasting method is mostly used in areas where shorter tunnels are required and the use of TBM can be overly expensive. In this method, a drilling jumbo is made use of to drill a certain pattern of holes in the surface of the rock at the path of the tunnel. These holes are then packed with explosives. On detonation of the explosives, the rocks are broken apart. The debris then realized is hauled away. These tunnels are mainly used for underground utility, railroads, highways, and mining. They vary in length from as small as 5 meters to 60 meters. The most used explosive is dynamite. The debris is hauled away from the tunnel using a mechanical shovel which is then removed from the tunnel using conveyor belts, diesel engines or locomotives. It is a method that is however dangerous to the workers. 1.1 d) Pipe Jacking This is a method of tunneling that uses hydraulic jacks that are very powerful to push pipes that are designed in a special manner into the ground. This takes place behind a shield that also excavates the land. The pipes range from 0.5m to 2m whilst the jacks can be up to 1km in length. This method of tunneling is mainly used in the construction of sewer, gas and water lines, and subways. This method of tunneling, also known as micro tunneling is mainly about installing ducts, culverts or underground lines without having to dig open trenches. With the use of this technique, the end result is a very firm and watertight. This method has been used to install drives that are very long, straight or curved at a radius. There are various benefits that come up with this method of tunneling such as; the surface is less disrupted, little diversion of utilities in urban areas, smooth finish, less joints, free of maintenance, strength in the pipes, less disturbance to the environment, no secondary linings are required, and more other advantages (Loveridge, 2001). 1.1 f) Vertical shafts These are vertical openings like shafts and raises. Shafts are those that are used to supply personnel, equipment, and support to tunnels that are horizontal. Raisings are driven in the upper direction and gravity is mainly essential in mucking as well as drilling. This makes this process cheap and fast. Shafts are downward driven. Their dimensions are dependent on their purpose. The most stable and most common shafts are circular (ley, 2009). 1.2 construction methods in terms of construction sequence and required temporary works 1.2 a) cover and cut In cut and cover, construction can follow various forms and sequences; conventional, bottom up, top down and cast in place. In the conventional method, a trench is first dug, the tunnel constructed, and then backfilling occurs to restore the original form of the land. In the bottom up method, caisson walls are first installed to the bedrock using a drilling rig. The tunnel is then excavated between these walls to the floor. The tunnel is then constructed starting from the floor, then walls and lastly the floor. The ground is then backfilled. According to Storry et al. (2005), in top down approach, a trench is first cut out then walls are built out of concrete. The walls act as temporary structures after which permanent concrete walls are built. This is followed by the roof and restoration of the ground. Excavation then takes place and the last thing is the floor. Cast in place starts with trench excavation and installation of forms into the tunnel. They are then filled with concrete and the forms removed. After drying, ground is restored. 1.2b) TBM TBMs are mainly composed of the cutter, the main bearing, a system that provides thrust and for supporting the trailing functionalities. The choice of the machine to be used is largely dependent on the area’s geological layout, and factors like underground water. There are open and shielded TBMs. These can be used to excavate grounds with hard rock. Open TBMs have cutters that are mounted on the head. The muck gets into opening s on the head of the cutter to a system of belts that eventually ensures removal from the tunnel. Shielded TBMs make use of grippers which hold on to the tunnel walls providing thrust. The best machines to use in rocks with fractures are the shielded TBMs. In the event of instability in the tunnel walls, concrete supports are erected. The thrust in these machines, realized from the back of the machine, protects the walls that might be having fractures, thus being the best (CIRIA, 2003). In softer grounds, slurry machines and earth pressure balance machines are mostly used. These use thrust and the cutter head has additional bits, carbide discs and hard rock cutters. They have a balancing effect on the rate of cutting to the pressure being impacted on the ground. They also inject chemicals/compounds that result to additional firmness to the ground. Slurry machines are used when there is a lot of underground water. Excavated soils are mixed with bentonite and passed through tubes for exit. They have plants that separate bentonite slurry from dirt and re-use it in the tunneling process (Tatiya, 2005). Open face TBMs are made use of only if the ground has some minimum pressure necessary to support it without caving until the tunnel is erected. The ground is supported using precast concrete. 1.2c) Drilling and blasting This is a method that has proven to be more productive over time. Currently, the drilling jumbos are computerized. The levels of automation are diversified and faster drills and more durable steel has been introduced. The types of detonators have been improved to ones that cause less pollution to the environment. These explosives are dormant until they are placed in respective holes for detonation. Ventilation systems are intelligent with an additional increase in loading capabilities as well as hauling capabilities. High performance rock support equipment is also in use (Girmscheid and Schexnayder, 2002). 1.2d) Pipe Jacking Pipe jacking involves the insertion of a string of pipes using thrust, through the ground from a jacking end to a receiving pit. In this method, a launch shaft is set a distance from the target shaft. The distance is dependent on pipe’s diameters, conditions of the ground geology, the jacking stations and the material used to make the pipes. The jacking pipe is put into the launch shaft and driven using hydraulic jacks from the pipe string’s tip. This process is followed up until the target shaft is reached, after which the machine is recovered. This method rarely affects the ground as it requires no trenches (Haslem, 1996). 1.2f) vertical shafts In this method, there is no access to the bottom of the tunnel and thus the shaft is sinking from above the ground downwards. Raises are those shafts excavated from down in case of an access to the bottom. Shaft lining is a feature that improves the safety of the shaft and also helps to bolt the shaft belts. Shaft lining helps in ensuring that loose rock does not fall into the shaft. The choice depends on the rock’s geology. In case the rock is hard, there is no requirement for shaft lining but in other cases, concrete is pumped to the walls as the shaft goes down (Haslem, 1996). Question 2 2.1 A hydraulic structure is a submerged or partly submerged body that is built in rivers, seas or any body of water, with the aim of disrupting the natural flow of water either by diverting, disrupting or completely stopping flow of water. A dam is a good example of such a structure as it slows down the rate of water flow to power up turbines which are then used to produce electricity. These structures are sometimes classified as specially shaped, static devices where water is directed in such a way that a specified point, the flow of water can be used measured. A dam is a structure that pound water with the main purpose of retaining water either for storage in order to distribute evenly to other locations or to be used together with hydropower to generate electricity. a) Earth Dams Earth-fill dams are also referred to as earthen or rolled-earth dams are well compacted earth structures. Construction of earth dams can be done from practically any soils available in the construction region. Investigation methods and instruments that exist for the soil permit a useful and accurate determination of the physical and mechanical properties of soils, and the calculation methods being used permit a reliable substantiation of the dam designs being used. The technological methods available for constructing dams are constantly being modified. Construction by directed blasting is a promising technique together with the widely used methods of layer-by-layer construction of dams by means of methods such as hydraulic construction, and placing soil in water among others. The use of directed blasting has been applied during the construction of the Medeo, Baipaza, Akh-Su dams and dam on the Burly kiya River. b) Rock-fill Dams These are structures of compressed free-draining granular earth which have an impervious zone that could be made out of masonry, concrete, plastic membrane, timber, steel sheet pipes or other materials. The name is derived from the construction of the structure since a large percentage of the earth utilized is composed of large particles. In cases where clay is used as the impervious material, a filter made of specially graded soil is used to prevent internal erosion of clay into the rock due to seepage forces. To prevent disasters such as the liquefaction of the rock-fill during an earthquake, adequate quality control is applied to ensure sufficient compaction of the susceptible material during construction. The use of asphalt concrete as the core is increasing in popularity due to its excellent performance record with the main fill material being rock and gravel. Viscoelastic-plastic material is the type of asphalt that is used in these dams due to its ability to adjust to deformations as well as movements that are imposed on the structure as a whole. c) Concrete Dams These are structures that are rock-filled with concrete slabs on the upstream face, a design which offers an impervious wall that prevents leakage and provides resistance to uplift pressure. The design provides a flexible structure for the topography at the site, and is advantageous as it is easy to construct and are less costly as compared to earth-fill dams. The river training works at the Upper River Indus is a 4.6 kilometer project which included the re-provision of 5 footbridges and 4 vehicular bridges. The river channels of the Upper River Indus are meandering and they lack sufficient width and depth to give allocation for effective discharge of floodwaters into the Shenzhen River. The training project included works Widening, realigning the Upper River Indus and its tributaries. The construction of maintenance ways with related drainage works Re-planning of four existing vehicular and five existing pedestrian river crossing Question 4 4.1) flexible vs. Rigid carriageways A flexible carriageway is made up of gravel layers bound with bitumen on a gravel sub base (rolled). The term flexible comes from the elastic nature of bitumen that allows either expanding or contracting depending on the temperature or the traffic loading. Layers that make this type of a carriageway are as follows; Surface course; asphalt with aggregate and high resistance to skidding (30mm to 50mm). The layer protects against tyre wear and skidding. Binder course; made of asphalt (50mm to 80mm) Base; The layer is made of bitumen and other material. This is mainly for structural integrity and resistance of wearing out due to heavy loads (100mm to 300mm). Sub base – this layer consists of granular material for road foundation (150mm) A rigid carriageway has some rigid slab formations as a result of cement materials. There are regular joints that allow movements in times of contraction and expansion. There are jointed and continuous reinforce concrete pavements. Pictorial representations of both kinds are indicated below Both flexible and rigid carriageways differ in a number of ways; in the principles of design, the flexible carriageway uses the empirical method. Here, design is based on the component’s characteristics for load distribution. In rigid, design and analysis is through the elastic theory. Flexible carriageways use granular materials whilst the rigid ones use cement concrete Flexible carriageways have low flexible strength. The flexural strength in rigid carriageways is associated with slab action thus distributing the load over a wide region. On normal loading a flexible way undergoes elastic deformation whilst the other acts as a cantilever In excess loading the flexible has local depression against the cracks in rigid ways A flexible carriageway transmits comprehensive stress and vertical stress to lower layers whilst the rigid carriageway assumes tensile stress and an increase in temperature. There is less frictional force in flexible carriageways and deformation is not transmitted to upper layers whilst friction force is high in rigid carriage ways. A flexible carriage way can be used for traffic in 24 hrs whilst the other cannot be used until 14 days pass after curing. It is important to roll surfaces in flexible carriageways whilst it is not needed in the other. 4.2a) Railway sleeper vs. ballastless tracks in railway projects A railway sleeper or a railway tie is the rectangular support in the rail track. They are laid perpendicular to the tracks. The main function of the sleepers is to transfer the load to the ballast, hold the rails in an upright position and to the correct gauge (Taylor, 1993). The design of a ballastless, just like the name suggests, requires no ballast. Some of the alternatives applied in order to avoid the use of ties is the fastening of the track to the rocks (long ago), fastening to concrete slabs or using concrete ties with concrete around them. 4.2b) Advantages of ballastless tracks Ballastless tracks have been used as the standard mode of building railway tracks in railway upgrades and high speed railways owing to their various advantages; the tracks are almost free of deformation and have very low costs of maintenance. Owing to the lack of ballast in the tracks, there is no damage incurred by flying ballast during high speeds. In the railroad tunnels, the constructions are shallower as compared to the other kind of tracks (Flint and Richards, 1992). 4.2c) disadvantages of ballastless tracks Ballastless tracks are very expensive to build. The curing time for concrete does not allow for easy conversion of ballasted lines to ballastless. It is always hard to modify these tracks. The slab tracks are so noisy as compared to their predecessors due to greater vibrations from the tracks. In order to reduce this noise, the technology used is very expensive as it requires more dimensions. Question 5 5.1a) manpower resource plan This plan involves having the right people in the right numbers at a particular phase of the project in order to work towards achieving right and timely goals of the project. In order to come up with a proper plan in the project, the following steps will be followed; Manpower inventory analysis; this involves essential manpower for building a bridge, departments in the project, people required in those departments. In case of units, the people required in the units are quantified. Future forecasting; in case there will be future manpower needs, this is taken into consideration here. This is done through forecasts from experts, past trends, analysis of the current workforce, and methods like mathematical modeling. Development of employment programmes; this will include recruitments, selections and placements. Training programmes; this will depend on improvements in technology and any other required developments. 5.2d) contingency plan References Bilger, B. (2008) "The Long Dig: Getting through the Swiss Alps the hard way", The New Yorker, Retrieved September 15, 2008. CIRIA Report C580 (2003). “Embedded retaining walls - guidance for economical design”, CIRIA. United Kingdom Flint, E. and Richards, J. (1992). "Contrasting patterns of Shorea exploitation in India and Malaysia in the nineteenth and twentieth centuries". In Dargavel, John and Tucker, Richard. Changing Pacific Forests: Historical Perspectives on the Forest Economy of the Pacific Basin. Duke University Press. Foley, A. (2009) "Life on the Cutting Edge: Dick Robbins", "Tunnels & Tunnelling International", Retrieved May 2009, www.tunnelsonline.info Girmscheid, G. and Schexnayder, C. (2002). ”Drill and Blast Tunneling Practices.” Pract. Period. Struct. Des. Constr., 7(3), 125–133. Haslem, R. (1996). “Structural interaction at joints in pipe jacked tunnels”. The structural Engineer 74 (10): 165-171. Loveridge, F., (2001) “Evaluation of Prop Loads at Channel Tunnel Rail Link Contract 430 – Ashford Tunnels”, Ground Engineering, August 2001 Issue, pp38. Meng, W. K. (2009). “Challenges on Cut and Cover tunnels construction in busy urban areas” HKIE Transactions 16 (4): 72-78. Pan, J. et al. (2006), “Back Analysis of Cut and Cover Tunnels in Close Proximity an Operating Railway in Hong Kong”, Proceedings of the World Tunnel Congress and 32nd ITA Assembly, Seoul, Korea, 22–27. Storry, R. et al. (2005). “Challenges of Constructing a Cut-and-cover Tunnel Adjacent to a Live Railway in the Northern New Territories of Hong Kong SAR”, Tunnelling for a Sustainable Europe (AFTES) Chambery, France. Tatiya, R. (2005). Civil excavations and tunnelling: a practical guide, Thomas Telford; London, Reston, VA. Taylor, H. (1993). "The railway sleeper: 50 years of pretensions, pre-stressed concrete". The Structural Engineer  71 (16): 281–288. Read More