Analysis Pertaining to Improvement of the A465 Heads of the Valleys Road Between Gilwern and Brynmawr - Coursework Example

NAME OF THE STUDENT: ADMISSION NO: NAME OF THE INSTITUTION: ASSIGNMENT TITLE: Table of Contents Table of Contents 2 1.0The Background 2 2.0The Improvement of A456 Heads of Valleys Road commencement 3 2.1 The Retaining Structures Recommended 3 2.1A456 Heads of Valley Road Retaining structures 4 2.1.3 Gravity Walls 5 2.1.4 Geogrid Reinforced Retaining Walls 6 2.2Factors determining the type of wall to be used at a given time includes:- 7 2.3The Lateral Earth Pressure that Retaining walls are subjected to 9 2.3.1 At Rest Lateral Earth pressure 10 2.3.2 Active earth pressure 10 2.3.2 Passive earth pressure 11 2.4 The procedure of designing the Retaining structures 12 3.1 Summary 13 ANALYSIS PERTAINING TO IMPROVEMENT OF THE A465 HEADS OF THE VALLEYS ROAD BETWEEN GILWERN AND BRYNMAWR FROM A SINGLE 3-LANE CARRIAGEWAY TO DUAL LANE CARRIAGEWAY 1.0 The Background As reported by the Weish Government through its National Traffic Management Unit, the existing A456 Heads of Valleys Road needed renovated having been built in the early 1960 as a single three lane carriageway with two lane that were aiding motorists moving in the uphill direction and the other lane for the motorists travelling towards the downhill direction. Therefore, the country have witnessed tremendous growth in terms of population and economic, the traffic management unit did a survey in the year 1990 and came up with resolutions pertaining to the improvement of the A456 Heads of Valleys Road between Gilwern and Brynmawr regions. Among the issues cited by the Traffic Management Authority that needed to be addressed were:- The poor visibility by the motorists plying the route hence contributing to the many accident cases that were being witnessed every now and then in that road Due to the growth of the population and the road users, the road had become smaller hence restricting smooth traffic flow as well as overtaking by other motorists Therefore, the team of expert from National Traffic Management Unit recommended the improvement of the A456 Heads of Valleys Road between Gilwern and Brynmwawr promising that the will be efficiency in terms of accessing services as well as adequate growth for those doing business in areas such as Ebbw Vale Enterprise Zone. 2.0 The Improvement of A456 Heads of Valleys Road commencement As documented by the National Traffic Management Unit, the construction of this projected was to be spearheaded by the Costain Ltd at an estimated cost of £ 230m. The project was scheduled to commence in Dec 2014 and run all the way up to June 2018 having been successfully completed. Ideally, prior to commencement of this construction in the late 2014, the Traffic Management Unit sought public opinion with regard to how they desired the road to be and this eventually influenced the design of the road that Costain Ltd was to spearhead in the course of the constructionphase. All the alternative pathways that had been suggested by the public was seriously taken into consideration as was led by Phil Baker, a community manager and public liaison administrator whom the construction company decided to include in their team to oversee the implementation process. 2.1 The Retaining Structures Recommended Retaining structures are structural elements that are connected to the ground and are designed to withstand the material pressure of the earth or other loads that may be above it at a given time. They are in most cases a combination of steel, concrete, masonry stone, soil, blocks or even pierces of wood firmly fixed together. Following the surveillance findings as well as the public opinion, a number of issues as raised by the relevant bodies must be adequately taken into consideration prior to deciding on the most appropriate retaining structures to be put up during the improvement of the A456 Heads of Valleys Road connecting the Gilwern and Brynmawr. Among the issues that need to be scrutinized is the type of soil, that is, whether the soil is sandy, clay or loamy However, the constructing a standard retaining structure is very costly and thus adequate measures needs to be in place to manage the entire construction phase. Its therefore advisable that adequate resources be it financial or labour must be sought in advance so as to manage the construction phase to the end (Underwood & Crundall 2002). 2.1 A456 Heads of Valley Road Retaining structures The improvement of A456 Heads of Valleys Road between Gilwern and Brynmawr is expected to be a major project based on the fact that the single three lane carriageway is being improved to be a dual carriage way. Ideally, single three lane carriageway, also known as undivided highway, is road with three lanes mostly used by motorists moving in the same direction. They normally do not have central reservation in between the lanes that may interfere with the flow of traffic plying the route. However, when the road is improved to a dual carriage way, which is ideally a highway with two lanes for motorists moving in the opposite direction, some retaining structures will have to be constructed in the process. This is due to the fact that, dual carriageway are normally separated at some interval with a central reservation that act as barrier so as to minimize road related accidents such as vehicles rolling over and hitting other vehicles plying the opposite route in the highway. At the same time, along the A456 Heads of Valleys Road, there is an over bridge next to Brynmawr junction which ideally need to have some retaining structures that may act as barriers to minize the many accidents that had been rampant in those areas. Some of the appropriate earth retaining structures that ought to be put up in A456 Heads of Valleys Road between the two regions includes:- 2.1.3 Gravity Walls These are type of walls that entirely relies on their own weight and setbacks to withstand the lateral earth pressure. These walls are often having a short height as compared to other retaining walls such as cantilever retaining wall. Therefore, Costain Ltd should use a type of gravity wall known as Allan Block Retaining wall on the sides adjacent to the Gateway bridge next to the Brynmawr junction, this is because, these type of wall are stacked together and locked in such a way they form a block known as s setback which will prove to be vital especially when an accident occurs next to the bridge hence preventing severe damages based on the fact the wall will be able to hold the vehicle from rolling over (Griffiths & Fenton 2013). Likewise, the gravity wall is often the combination of the cast-in-place concrete and the modular gravity walls. The cast in place concrete are the filled walls of the structure consisting of the buttress, counter fort as well as the cantilever, these as well will be in handy in minimizing the accidents occurring next to the bridge (Zeng & Steedman 2010). 2.1.4 Geogrid Reinforced Retaining Walls Engineered for durability and long life, VERSA-Grid geogrid is high-performance soil reinforcement composed of high-molecular-weight, woven polyester yarns with a polymeric coating. Properly designed VERSA-LOK walls with VERSA-Grid soil reinforcement can be constructed to heights of 50 feet or more. They are often known as internally stabilized mechanical walls. These walls uses some form of reinforcement to add strength to the retaining wall structure, hence increasing its ability withhold the soil behind it. At the same time, reinforcement walls are normally the cut walls which ideally are compost of the mini and micro piles that are often placed between courses of blocks in the wall and rolled back into slope during installation process so as to create a strong and firm soil mass. Soil, Cross Section. Retaining walls hold back potentially unstable wedges of soil. Depending on soil type and other site conditions, unreinforced VERSA-LOK walls can be three to four feet tall. If the weight of the VERSA-LOK wall units alone can't resist the force of an unstable soil wedge or any load on top of it, then geogrid soil reinforcement is needed. Horizontal layers of geogrid provide tensile strength to hold the reinforced soil mass together. The geogrid-reinforced soil mass becomes part of the retaining wall system, giving the wall system more size and weight to resist pressures from behind it. This is shown below 2.2 Factors determining the type of wall to be used at a given time includes:- Local contracting practices:- The subsequent practices that the local contractors have been engaging may influence the choice to be made, that is, if the previous contractors preferred reinforced walls which in the long run never was deemed in appropriate, the Costain Construction Company should therefore go for the gravity wall so as to bring the required change in terms of minimizing the road maintenance costs (Landva& Pelkey 2008). Construction S specifications: - Due to the fact that 11.5 kms of the retaining structures is required in improving this road stretch between Gilwern and Brynmawr, the constructor should consider taking into account the availability of the raw materials for putting up a given structure before deciding on the appropriate wall structure to put up (Landva& Pelkey 2008). The type of Soil in the site:- The type of soil in a given place plays a significant role in terms of determining the retaining structures to put up, for instance, a sandy region tends to be weak hence thorough analysis ought to be carried out first before deciding on the adequate measure to take in the course of putting up the retaining wall (Landva& Pelkey 2008). Durability and Road maintenance expenses:- As stated by the traffic management unit while offering the tender to Costain Ltd in 2011, the contractor should adhere to the terms and conditions as agreed by the Weish Government. Ideally, the Government often desires to have permanent roads with lesser maintenance costs (Landva& Pelkey 2008). The Ground Water:- in some cases, the road track under construction may be having a poor water table, therefore, in the event that a weaker retaining structure is constructed in such places, the probability of the structure collapsing within a short period of time tends to be very high, therefore the contractor should consider setting up a very strong structure to withstand the water pressure in such a place (Landva& Pelkey 2008). The urgency of the project: - The time to be taken in the A456 Heads of Valleys Road project should be factored in when considering the retaining wall to construct. The gravity wall tend to take slightly longer time in comparison to reinforced wall since the concrete elements have to be given time to dry before the construction process continues (Landva& Pelkey 2008). 2.3 The Lateral Earth Pressure that Retaining walls are subjected to This is normally the horizontal pressure exterted by or subjected to the soil when it is against some external loads such as vehicles, building structures and the retaining wall. The Lateral Earth pressure at any given depth is a factor of the combined effective stress and the cohesion therein. v Lateral pressure is the force that the soil injects in the horizontal direction, that is, the relationship of the pressure on the wall when the wall changes its position, for example when moving towards the object above it or moving outwards or when in the same position. The lateral pressure is an significant parameter because it infuences the behavior and strength of the soil hence must always be considered during the construction phase as was the case during improvement of A456 Heads of Valleys Road from a single three lane carriageway to dual carriageway. The coefficient of the lateral earth pressure, K, can be states as the ratio of the horizontal effective stress (he) to the vertical effective stress (vs). .The effective stress is obtained by subtracting the pole pressure from the total pressure (Richardson & Lee 2011). There are three types of lateral earth pressure as analyzed based on the movement of the wall. These includes:- 2.3.1 At Rest Lateral Earth pressure Whenever the retaining wall is at rest, and the material above it is at its normal state, then the pressure that will be exerted by the given material will be known as at rest earth pressure and is designated as K0, During this condition, the ground level deposit is considered to be having absolutely zero lateral strain in the soil surface hence the term ‘at rest state.’ (Richardson & Lee 2011), The coefficient of the lateral earth pressure while at rest; during the situation when the retaining wall is at rest, the ratio therein between the pressure applied in the vertical direction as a result of material lying above it and the lateral earth pressure is often known as the coefficient of the earth pressure at rest KO = (Lateral Earth Pressure)/ (Vertically exerted pressure) 2.3.2 Active earth pressure Whenever the retaining walls tend to move far away from the backfill, there tend to be reduction in the pressure on the wall; this normally tends to be the trend until a minimum value is reached such that there is no more reduction in the wall pressures hence the state of the wall becoming constant. This is often denoted as Ka and is ideally the minimum value of the coefficient of lateral earth pressure (Richardson & Lee 2011). The coefficient of active lateral earth pressure; whenever the retaining wall is moving away from the material lying above it, the ratio therein between the lateral earth pressure and the pressure applied in the vertical direction due to the material placed above it is often known as coefficient of active earth pressure Ka = (Lateral Earth Pressure) / (Vertical Pressure) 2.3.2 Passive earth pressure When the retaining walls tend to move towards the backfill as had shown in the diagram above; this move eventually increases the pressure of the retaining walls. This process often goes on and on until a higher value is attained such that the pressure on the wall cannot increase any longer hence the state of the retaining wall becomes constant. This type of pressure is known as passive earth pressure (KP) (Richardson & Lee 2011). The coefficient of the passive lateral earth pressure; whenever the retaining wall is moving towards the material lying above it, then the ratio between the lateral earth pressure and the pressure exerted in the vertical direction as result of the weight of the material above it is known as the coefficient of the passive earth pressure KP = (Lateral Earth Pressure) / (Vertical Pressure) Therefore, the illustration of the lateral earth pressure implies that, whenever the retaining wall is almost slipping due to the lateral thrust imposed by the load therein, there is always a resistant force applied by the soil in the front of the retaining wall. 2.4 The procedure of designing the Retaining structures According to by Zeng & Steedman (2010), after the analysis of the conditions stated above have been finalized, Costain Ltd should roll out the designing process of the retaining wall as stated below:- Select a suitable retaining wall; Based on their analysis as discussed above, the Costain Construction Company should decide on the type of the retaining wall to construct, that is, be it gravity walls or the reinforcement earth walls. Approximate the dimension of the retaining wall; the contractor should take appropriate measurement and decide on the correct dimension prior to the construction process Approximate the Lateral Earth Pressure to expect; having analyzed the lateral earth pressures previously, the contractor will be in a pole position to preempt the expected pressures on the retaining wall s to be constructed. Approximate the uplift forces that are likely to occur; just like the lateral earth pressures, the contractor should be note down the uplifting forces to expect upon completion of the wall Approximation of the gravity forces; the construction should be initiated having in mind the weights of the road users Evaluation of the external forces to be expected in the road track Have adequate mechanisms in place for addressing cases of the wall sliding or overturning in the long run 3.1 Summary With consideration of the issues highlighted above, Costain Ltd will be able to achieve the desired output. Costain Ltd, should consider choosing between the gravity wall and reinforced earth walls depending on the outcome of their analysis regarding time of soil, urgency of the project, construction specification, durability and maintance expenses anticipated as well as the ground water level of the region. On the other hand, Costain Ltd should adequately have a proper understanding of the lateral earth pressure to expect and hence decide on the appropriate retaining wall between gravity and reinforced earth wall to put up at every given interval. BIOBLIOGRAPHY De Buhan, P., Mangiavacchi, R., Nova, R., Pellegrini, G., & Salençon, J. 2009. Yield design of reinforced earth walls by a homogenization method. Géotechnique, 39(2), 189-201. Griffiths, D. V., & Fenton, G. A. 2013. Seepage beneath water retaining structures founded on spatially random soil. Geotechnique, 43(4), 577-587. Hunt, J. G., & Lyons, G. D. 2010. Modelling dual carriageway lane changing using neural networks. Transportation Research Part C: Emerging Technologies, 2(4), 231-245. Landva, A. O., Valsangkar, A. J., & Pelkey, S. G. (2008). Lateral earth pressure at rest and compressibility of municipal solid waste. Canadian Geotechnical Journal, 37(6), 1157-1165. Richardson, G. N., & Lee, K. L. 2011. Seismic design of reinforced earth walls. Journal of the geotechnical engineering division, 101(2), 167-188. Seed, H. B., & Whitman, R. V. 2010. Design of earth retaining structures for dynamic loads. In Lateral Stresses in the Ground and Design of Earth-Retaining Structures (pp. 103-147). ASCE. Simpson, B. (2012). Retaining structures: displacement and design. Géotechnique, 42(4), 541-576. Sze, N. N., & Wong, S. C. 2007. Diagnostic analysis of the logistic model for pedestrian injury severity in traffic crashes. Accident Analysis & Prevention, 39(6), 1267-1278. Underwood, G., Chapman, P., Bowden, K., & Crundall, D. 2002. Visual search while driving: skill and awareness during inspection of the scene. Transportation Research Part F: Traffic Psychology and Behaviour, 5(2), 87-97. Zeng, X., & Steedman, R. S. 2010. Rotating block method for seismic displacement of gravity walls. Journal of Geotechnical and Geoenvironmental Engineering, 126(8), 709-717. Read More

This is due to the fact that, dual carriageway are normally separated at some interval with a central reservation that act as barrier so as to minimize road related accidents such as vehicles rolling over and hitting other vehicles plying the opposite route in the highway. At the same time, along the A456 Heads of Valleys Road, there is an over bridge next to Brynmawr junction which ideally need to have some retaining structures that may act as barriers to minize the many accidents that had been rampant in those areas.

Some of the appropriate earth retaining structures that ought to be put up in A456 Heads of Valleys Road between the two regions includes:- 2.1.3 Gravity Walls These are type of walls that entirely relies on their own weight and setbacks to withstand the lateral earth pressure. These walls are often having a short height as compared to other retaining walls such as cantilever retaining wall. Therefore, Costain Ltd should use a type of gravity wall known as Allan Block Retaining wall on the sides adjacent to the Gateway bridge next to the Brynmawr junction, this is because, these type of wall are stacked together and locked in such a way they form a block known as s setback which will prove to be vital especially when an accident occurs next to the bridge hence preventing severe damages based on the fact the wall will be able to hold the vehicle from rolling over (Griffiths & Fenton 2013).

Likewise, the gravity wall is often the combination of the cast-in-place concrete and the modular gravity walls. The cast in place concrete are the filled walls of the structure consisting of the buttress, counter fort as well as the cantilever, these as well will be in handy in minimizing the accidents occurring next to the bridge (Zeng & Steedman 2010). 2.1.4 Geogrid Reinforced Retaining Walls Engineered for durability and long life, VERSA-Grid geogrid is high-performance soil reinforcement composed of high-molecular-weight, woven polyester yarns with a polymeric coating.

Properly designed VERSA-LOK walls with VERSA-Grid soil reinforcement can be constructed to heights of 50 feet or more. They are often known as internally stabilized mechanical walls. These walls uses some form of reinforcement to add strength to the retaining wall structure, hence increasing its ability withhold the soil behind it. At the same time, reinforcement walls are normally the cut walls which ideally are compost of the mini and micro piles that are often placed between courses of blocks in the wall and rolled back into slope during installation process so as to create a strong and firm soil mass.

Soil, Cross Section. Retaining walls hold back potentially unstable wedges of soil. Depending on soil type and other site conditions, unreinforced VERSA-LOK walls can be three to four feet tall. If the weight of the VERSA-LOK wall units alone can't resist the force of an unstable soil wedge or any load on top of it, then geogrid soil reinforcement is needed. Horizontal layers of geogrid provide tensile strength to hold the reinforced soil mass together. The geogrid-reinforced soil mass becomes part of the retaining wall system, giving the wall system more size and weight to resist pressures from behind it.

This is shown below 2.2 Factors determining the type of wall to be used at a given time includes:- Local contracting practices:- The subsequent practices that the local contractors have been engaging may influence the choice to be made, that is, if the previous contractors preferred reinforced walls which in the long run never was deemed in appropriate, the Costain Construction Company should therefore go for the gravity wall so as to bring the required change in terms of minimizing the road maintenance costs (Landva& Pelkey 2008).

Construction S specifications: - Due to the fact that 11.5 kms of the retaining structures is required in improving this road stretch between Gilwern and Brynmawr, the constructor should consider taking into account the availability of the raw materials for putting up a given structure before deciding on the appropriate wall structure to put up (Landva& Pelkey 2008).

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