Retaining Wall: The A465 Head of the Valley Road between Gilwern and Brynmawr - Coursework Example

Name Instructor’s name Course Name Date RETAINING WALL In the quest to improve the A465 head of the valley road between Gilwern and Brynmawr, a lot has to be done to cut down the land use and the impact that the planned dual 2-lane carriageway will have on the sensitive areas such as the area around water works and sewage works. A retaining wall structure has to be built to solve and prevent such impacts of the planned carriageway. A retaining wall can be defined simply as a structure that is specifically designed and put up for the purpose of soil or backfill retention and to maintain the different terrain of unnatural slope or ground surface (Bowles 1968). A retaining wall can be utilised effectively to bind soil or rocks together in areas that have rough terrain or steep slopes. The wall can be alternatively utilised effectively in areas that may require to be altered severely or sometimes completely replaced for a rather more unique purposes such as in our case as we set to build the dual 2-lane carriageway. A retaining wall structure is a necessity in areas around the valley road between Gilwern and Brynmawr as the area is characterised by rough terrain and steep slopes. The retaining wall will be used to resist pressures that the surround areas exert. It will also prove necessary for the wall to be built to achieve the desired ground elevation in these areas as it will present a challenge to the project engineers because of its unnatural slope (Crosbie & Watson 2005). For the construction of the retaining wall, we will have to consider that for every extra length in filling with the retaining wall, it will be more costly to construct the same by cutting through the hilly terrain, and therefore a retaining wall structure will be relatively cheaper to construct (Bowles 1968). This report will detail the most suitable design of the retaining wall structure that will be considered by the team that will undertake the task of improving the A465 head of the valley road between Gilwern and Brynmawr from the existing single 3-lane carriageway into a dual 2-lane carriageway. The retaining wall will stabilise the areas under construction and also reduce soil erosion. Since the construction of the dual 2-lane carriageway is a necessity, the steep slopes on the rugged terrain should not be an obstacle; therefore, a retaining wall will prove necessary in reducing the land take of the road and also help avoid environmental degradation that would have otherwise been unavoidable. The areas between Gilwern and Brynmawr are in use, and a further cut through it by a dual carriageway may prove a challenge. This and the factors discussed above hence will thus leave us with the option of constructing a retaining wall structure. The retaining wall structure will enable the successful construction and completion of the dual carriageway. Soil erosion and excessive surface runoff of water may also pose a challenge to the construction of the dual 2-lane carriageway and. Therefore, the construction team have to consider the essence of a retaining wall structure deeply. This is because, in such situations, the construction of the wall will be a better option than cutting through the hills and causing more harm to the environment and soil erosion. A RETAINING WALL DESIGN The most suitable design of the retaining wall structure will mainly consist of the two main parts, that is, the test and evaluation of the anticipated pressures and also loads that will affect the retaining structure either directly or indirectly and also those factors that may affect the planning and design of the retaining wall structure. This will also include plans and the design of the best possible way of how the retaining structure can withstand these loads and pressures (Ambrose 1991). Since the retaining walls structures are specifically designed and constructed to reduce the pressures exerted on the roads by several forces, they will be will very suitable for the valley road between Gilwern and Brynmawr because the road goes in several partial hill cutting and valley filling The benefits of the retaining wall structures are many, apart from protection of natural resources and prevention of contamination from sewage works, the structures also have many other benefits such as reducing congestion, avoiding road carnage, lessening land wastage and thus improving the movement of people and goods from one place to another. The wall used in this design will be a permanent retaining wall; its height will have a range of 5 ft to slightly more than 110 ft constructed to resist a wide range of pressures exerted on the valley road. In planning and designing the retaining wall, several loads and pressures will have to be considered, these includes the weight of the retaining wall itself, the weight that is expected to be exerted on it when it is finally in use, the force of gravity acting on the retaining structure, the force that is exerted by the water table on the structure and finally the forces that may be exerted on the retaining wall by earthquakes and tremors. The weight of the exerting wall and that of loads exerting pressure on it will be estimated, and high considerations will be taken. Also, the total force exerted on the wall by the force of gravity, the force exerted by the water table and that of earthquakes will be estimated for the team to make adequate arrangements on what to expect. The retaining wall will be designed in our case as a strong, impermeable wall. This will be done with the following factors taken into considerations; the factors are; the safety of the structure in overturning and the highest possible pressure on the base area of the wall. Safety to guard against possible sliding, the possibility of the retaining wall to weaken with time and the lowest pressure to be exerted on the wall, and, safeguard against possible floatation must also be considered. The safety in cases such as slipping or falling hilly terrain towards Brynmawr area, the state of earthquakes and tremors in the surrounding areas and lastly the stability of the wall when live forces and its weight. (Ambrose 1991). The design of the retaining will also aim to achieve the set minimum standards for safety of the structure and the road and, therefore, reduce possible dangers in the future. This will be done by designing the wall with a large base area and using the strongest possible foundation material that will last such as the use of concrete in building the foundation of the retaining wall (Bowles 1968). In building the retaining structure, it will be an almost impossible task to come up with a detailed designed plan of each and every wall along the valleys road between Gilwern and Brynmawr. The planned dual 2-lane carriageway will need a retaining wall of over 11.5 km of and, therefore, there is a need to adopt a unique design of retaining wall. The wall will vary in height, length and width, for instance, a wall less than 10m in height and 120m will be proposed for areas with low cases of dangers whereas high hazard areas will be required to have larger walls (Ambrose 1991). The retaining wall structures will be been placed in a low depth of approximately 40 m below the ground level or the terrace level in case of rough terrains. The walls will be placed 10 m deep in areas characterised by highly jointed rocks as they are more stable and firm to hold the foundation of the retaining wall structure (Terzaghi 1943). In case the structure is built on a rocky slope, the foundation of the wall will need to be built in a steep. This will result in a wall characterized by near vertical and a rock filled a face to give the best stability to the wall. The design of the wall will need to incorporate a dip at the base towards the hilly areas of the valley road; this will prove necessary as it is economical in areas prone to earthquakes and tremors. The dip will also be a safety measure against the possibility of sliding. (Bowles 1968). The retaining wall will be a normal masonry wall that is designed to give support to the slopes of a hilly terrain from the long-term effect of weather and soil erosion. It will provide the much-needed stability on a rather unstable ground. Building a retaining wall around RW66a and RW06b type B road of the valley road is a necessity. The wall will be designed and constructed to give the areas around Brynmawr the much-needed resistance to pressures exerted on it by vehicles, human traffic and other forces acting on the road. The use of the retaining wall will, therefore, be extensive in this area as it experiences heavy traffic. In choosing the design, the dimensions of the retaining wall will give enough considerations and thus much allowance will be given for the wall to bear the great weight exerted on it by its weight. This will be in such a way to give the base area and foundation a capacity to bear the forces acting on it. The design of the wall will ensure that the base of the structure has much thickness to enable it to support the rest of the wall structure (Bowles 1968). The width of the base will, therefore, require most of the material to build as compared to the other parts of the wall. The retaining wall will also have a V-shaped water filter on its back to drain off water and prevent water retention on one side (Ambrose 1991). The inclusion of a water filter would ensure that collected water is drained off and, therefore, reduce the pressure on the valley road. The design of the retaining wall will also incorporate water holes into the walls. Holes will be dug in the cement walls at some regular intervals. These water holes shall be placed strategically at the base of the structure for effective water drainage. The retaining walls will also include a semi-permeable layer of soil at the base of the wall. The function of the semi-permeable layer is to filter water and reduce soil erosion on the sides of the wall. The layer will prevent seepage of water and also maintain the balance between the two sides (Terzaghi 1943). The design of the wall will also include the use of natural gullies and gabions on its sides to divert the water mostly resulting from surface runoff and rain water away and, therefore, prevent soil erosion from accumulated water. Water drainage should be included to drain the water to the water works and sewage works towards Gilwern. For safety against earthquakes and earth tremors, the length, thickness and the height of the structure should be highly considered. For areas with high intensities, the walls will be much thicker but lower in height. Areas experiencing low cases and only earth tremors will on the other r hand have thinner walls and taller walls. In areas with the poor type of roads, the retaining walls will not be designed with pressures of earthquakes and earth tremors in mind. This will thus require that the walls in such areas are of good quality and design. The design will, therefore, include this consideration for the valley road to have a standard type of retaining wall structure. In the design, the pressure that the pressure has on the wall will have to be taken into full consideration for the wall to be effective. The design will, therefore, have in place a suitable method for the release of this pressure due to water. By taking this into consideration, efficiency will be achieved in the building of the retaining wall. The design of the wall will also need to take into consideration the stability of the whole retaining wall structure. The walls will have a stable base design to guard against sliding, excessive pressure exerted by several forces and also sliding. The design of the wall will be in such a way that the walls depend on their weight. This is achieved through the use of gravel, concrete or even metals. The mass of the wall should be able to resist pressure from the forces of gravity, its weight and the weight exerted on the carriageway through traffic. In areas that are more stable, a short retaining wall will be built around the valley road. The wall structure should be built using stone and concrete. These walls will not necessarily require rigid base structure as compared to areas of low stability. In areas that are unstable and more rugged, taller retaining walls will be built. The tall wall structures are built using a mixture of concrete and stones. The walls can be made stronger by the use of reinforcing steel or concrete poles (Ambrose 1991). Areas around the New Pont Harri Footbridge will require a high retaining wall that is made up of concrete and reinforced steel and designed with a wider base area to improve the stability (Bowler 1968). The design of the retaining wall will have most of the wall made up of a thin reinforced material. The best choice of material for the wall is concrete reinforced with steel that will be used extensively along its length. The type of the retaining wall structure will be the cantilever retaining wall. This type of retaining wall structure will have an inverted T-shape whereby are a vertical stem and a slightly bent foundation slab as the base. The erect vertical stem is designed in such a way that the thickness is largest at the base of the stem and reduces with every increasing height. This is due to the decrease in pressure against the wall with height (Ambrose 1991). Another design option that will be used in constructing the wall in some of the areas along the valley road is the counterfort retaining wall structures. These counterfort retaining wall structures will be specifically used in areas where tall retaining structures are required. In this type of wall design, the vertical stem is constructed of one foundation slab between several counterforts. The counter forts, in this case, will act as base supports for the wall (Bowles 1968). For the most parts of the wall, the cantilever retaining wall structure will be adopted as it is a freestanding structure and hence the extra cost that may be incurred in purchasing several counterforts will be avoided. The design and construction of retaining wall structures will result in various types of retaining wall structures as discussed below; The first resultant wall structure resulting from the different dimensions used in constructing the wall will be the curbs. The types of cantilever retaining walls are relatively shorter regarding height (Crosbie & Watson 2005). This is attributed largely to the choice of leaving out water gutters on the sides of the wall. Another type of retaining wall structure design will result in short retaining wall type. These short retaining walls will have the erect vertical stem rising to about 4 m in height. This is because the material used to construct the wall will be steel-reinforced concrete and will also have a uniform thickness. The slab, in this case, will be slightly bent to distribute the weight of the wall to a larger area (Ambrose 1991). The different dimensions used in the design may also result in tall retaining wall structures. In designing these tall retaining wall structures, a more complex construction will be adopted. This is because the structures are tall and hence needs the best design and use of a stronger building material (Bowles 1968). In designing a cantilever retaining wall the following considerations need to adopt, these are; the soil type around the wall structure and the extent to which the soil can support the wall structure. The ability of the wall to retain its weight, the structural composition of the wall itself and the possible damage that the weight of the wall has on the shape of the structure and on the structures that are adjacent to the wall structure (Ambrose 1991). The force exerted by the earth pressure on the retaining wall structure will also be taken into considerations. This is because the wall is largely dependent on the earth pressures to maintain its balance. The design also takes into account the assumption that the retaining wall structure will have enough force acting upwards for it to minimize the pressure that the structure has on the ground. Another consideration that should be taken into account in constructing the retaining wall is the total loads exerted on the valley road are equal to the pressure exerted on it by the earth forces and the pressure exerted on the wall by the hydrostatic pressure of the water table (Bowles 1968). For the purpose of stability, the design should ensure that the resultant earth forces acting on the wall structure are not less than the opposite pressure resulting from the downward forces such as loads, traffic and the pull of gravity. Another consideration that should be taken into account in the design and construction of the retaining wall structure is the possibility of a new structure such as railway lines or subways constructed in the areas around the new carriageway. This will ensure that allowance is left for possible hill cutting or ground excavation in the areas where the retaining wall is built. This will ensure that the stability of the retaining wall structure is always maintained (Bowles 1968). For the team to estimate the pressure exerted on the retaining wall structure by the earth forces, they will have to consider the whole length of the wall, that of the road and also the height of the retaining wall structure (Crosbie & Watson 2005). The design of the retaining wall must also take into consideration the general properties of the soil in the areas around the valley road that the new dual 2-lane carriageway will pass through. Taking this into account, the design for the retaining wall structure with a height of more than 4 m and build in a rugged terrain of a slope, the properties of the soil in the area should be tested first before settling on the material on the material that will be used to construct the retaining wall structure. Attention should also be paid when determining the level of the ground water or how the deep the water table is from the retaining wall (Terzaghi 1943). The general properties of the soil will, however, be a minor factor when it comes to walls that are less than 4 m in height. In constructing short retaining walls, the soil test will not be necessary since the choice of material that will be used in constructing the wall can be done by studying the material that has been used in constructing the taller retaining wall structures. Only the foundation slab will require the use of a stronger material for to support the wall and last for a longer period. The design must also take into consideration the type of backfill to be used when building the retaining wall. In the process of building a retaining wall structure, one must carefully select the material to be used as a backfill. The material chosen for this purpose should be a porous type for it to be able to drain off the water. The cost of the material to be used as a backfill for the retaining wall should also be considered as well as the availability of the backfill material (Bowles 1968). The ideal material for the purpose of backfill to be used in constructing the retaining wall should be porous, cheap and easily available at the construction site. The most suitable choice of backfill to be used in constructing the retaining wall in our case in building the dual 2-lane carriageway in Valley road is rock fill. This is large because the rock fill is easily available and apart from that it is relatively cheaper as compared to other granular materials. The rock fill is also a perfect choice because it is a porous granular material that will easily drain off water (Ambrose 1991). The design of the retaining wall structure must also take into serious consideration the effect that the surcharges have on the retaining wall. These are the pressures that are exerted on the retaining wall structure by several forces or loads acting on the sides of the wall. The surcharge pressure should be equivalent to the earth pressure for the retaining wall structure to maintain its stability and last long. Another factor that must be considered in designing and construction of the retaining wall structure is the long-term effect that the water has on the retaining wall. In areas around the carriageway, water may collect with time when it rains and exert pressure on the retaining wall. This pressure resulting from collected water should be considered as it may impact negatively on the retaining wall. The construction team will, therefore, put safety measures in place such as constructing gutters and water holes (Ambrose 1991) Stagnant water may exert pressure on the retaining wall structure, and the long-term effects of the pressure due to this may prove catastrophic in the long-term run. The construction team must hence carry out a study on the condition if the ground water and rainwater before the construction of the wall and, therefore, come up with several measures that will avoid the impacts of the water or reduce the effects of water considerably. The team constructing the retaining wall will put in place several adequate measures such as the use of water holes and water gutters to drain off the rain water and, therefore, prevent a damming effect on the sides of the retaining wall structures. Lastly, the design should also factor in the stability of the retaining wall structure. The stability of the retaining wall can be determined by studying the factors of safety such as the total moments or forces causing instability in the sides of the wall. The retaining wall should have a strong foundation to satisfy the stability criteria. The foundation can be made stronger through the use of strong reinforced concrete and use of the bent foundation slab (Ambrose 2009). The retaining wall structure will be stable as long as it satisfies these criterions. References Ambrose, J 1991 Simplified Design of Masonry Structures. John Wiley and Sons, New York. Bowles, J 1968 Foundation Analysis and Design. Mc Graw-Hill Book Company, New York. Crosbie, M & Watson, D. (Eds) 2005 Time-Saver Standards for Architectural Design. Mc Graw-Hill, New York. Ching, F et al. 2006 Building Codes Illustrated: A Guide to Understanding the 2006 International Building Code. Wiley, New York. Terzaghi, K 1943. Theoretical Soil Mechanics. John Wiley and Sons, New York. Read More

The areas between Gilwern and Brynmawr are in use, and a further cut through it by a dual carriageway may prove a challenge. This and the factors discussed above hence will thus leave us with the option of constructing a retaining wall structure. The retaining wall structure will enable the successful construction and completion of the dual carriageway. Soil erosion and excessive surface runoff of water may also pose a challenge to the construction of the dual 2-lane carriageway and. Therefore, the construction team have to consider the essence of a retaining wall structure deeply.

This is because, in such situations, the construction of the wall will be a better option than cutting through the hills and causing more harm to the environment and soil erosion. A RETAINING WALL DESIGN The most suitable design of the retaining wall structure will mainly consist of the two main parts, that is, the test and evaluation of the anticipated pressures and also loads that will affect the retaining structure either directly or indirectly and also those factors that may affect the planning and design of the retaining wall structure.

This will also include plans and the design of the best possible way of how the retaining structure can withstand these loads and pressures (Ambrose 1991). Since the retaining walls structures are specifically designed and constructed to reduce the pressures exerted on the roads by several forces, they will be will very suitable for the valley road between Gilwern and Brynmawr because the road goes in several partial hill cutting and valley filling The benefits of the retaining wall structures are many, apart from protection of natural resources and prevention of contamination from sewage works, the structures also have many other benefits such as reducing congestion, avoiding road carnage, lessening land wastage and thus improving the movement of people and goods from one place to another.

The wall used in this design will be a permanent retaining wall; its height will have a range of 5 ft to slightly more than 110 ft constructed to resist a wide range of pressures exerted on the valley road. In planning and designing the retaining wall, several loads and pressures will have to be considered, these includes the weight of the retaining wall itself, the weight that is expected to be exerted on it when it is finally in use, the force of gravity acting on the retaining structure, the force that is exerted by the water table on the structure and finally the forces that may be exerted on the retaining wall by earthquakes and tremors.

The weight of the exerting wall and that of loads exerting pressure on it will be estimated, and high considerations will be taken. Also, the total force exerted on the wall by the force of gravity, the force exerted by the water table and that of earthquakes will be estimated for the team to make adequate arrangements on what to expect. The retaining wall will be designed in our case as a strong, impermeable wall. This will be done with the following factors taken into considerations; the factors are; the safety of the structure in overturning and the highest possible pressure on the base area of the wall.

Safety to guard against possible sliding, the possibility of the retaining wall to weaken with time and the lowest pressure to be exerted on the wall, and, safeguard against possible floatation must also be considered. The safety in cases such as slipping or falling hilly terrain towards Brynmawr area, the state of earthquakes and tremors in the surrounding areas and lastly the stability of the wall when live forces and its weight. (Ambrose 1991). The design of the retaining will also aim to achieve the set minimum standards for safety of the structure and the road and, therefore, reduce possible dangers in the future.

This will be done by designing the wall with a large base area and using the strongest possible foundation material that will last such as the use of concrete in building the foundation of the retaining wall (Bowles 1968).

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