A465 Retaining Wall - Case Study Example

NAME OF THE STUDENT: ADMISSION NO: NAME OF THE INSTITUTION: ASSIGNMENT TITLE: Table of Contents Table of Contents 1 1.0 Introduction 3 1.1 Overview 3 1.2 Single Three Lane Carriageway 3 1.3 Dual Lane Carriageway 3 2.0 The A456 Heads of Valleys Road Project 4 2.1 Retaining Structures to be utilized in the project 4 2.1.1 The Earth Retaining Structure 5 2.1.2 The Classification of the Earth Retaining Structures to be undertaken in this Project 5 2.1.3 External stabilization of the structure 6 2.1.4 Internal Stabilization of the structure 7 2.1.5 Type of Earth Retaining wall to considered in this project 7 2.2 The Contractor should consider the following aspects before deciding on the right wall between the two to consider:- 8 2.3 Lateral Earth Pressure 9 2.3.1 Earth pressure while at rest 11 2.3.2 Active earth pressure 11 2.3.2 Passive earth pressure 12 2.4 Designing of the Retaining Walls 13 3.1 Conclusion 14 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 Introduction 1.1 Overview The current A465 Heads of Valleys road between Gilwern and Brynmawr was constructed in the early 1960’s as a single three lane carriageway which ideally had two lanes, that is, one in uphill direction and the other one in the downhill direction. Therefore, with reference to the regional traffic study carried out in the 1990, there was recommendation for the improvement of the A465, hence the initiation of the section 2 of the project despite the environmental constraints such as the idea of the road passing through the Clydach Gorge within the Brecon Beacons National Park. 1.2 Single Three Lane Carriageway A Single three lane carriageway is a road with three lanes structured in such a way that all the lanes are within a single roadway and at the same time, there is no interval provision for division that may hinder the flow of traffic. They are also known as undivided highways due to the fact that there are no central reservations along the road stretch. In most cases, these roads are marked by colors so as to clear indicate the direction to which a traffic flow should be observed. These colors can either by solid or broken stretch marks or to some extend combination of the two parameters but with specific styles so as to show motorists when to join or leave another lane for the other one within the same carriageway, for instance Europe, they tend to reserve the central part of the road as an overtaking avenue (Sze & Wong 2007). 1.3 Dual Lane Carriageway This is a type of two structured highway with two roads for motorists travelling in opposite directions. These two road stretches are often separated in the middle with a central parameter. They are known as divided highway due to the fact that they have a separating stretch in between the two roads. Most countries prefer having these types of roads in their urban set up since they are believed to be improve road safety in comparison to the single lane highways. As a result, a number of countries through their respective National Highway Authority bodies have resorted to imposing high speed limits for dual lane highways unlike the single lane carriageway (Hunt & Lyons 2010). Normally, the lane that is closer to the central parameter separating the two lanes is often preferred to be the reversed lane for overtaking other motorists along the highway. 2.0 The A456 Heads of Valleys Road Project When the Weish Government out rolled the project to improve the road between the two locations, the Government’s main agenda was to improve the traffic flow in this region so as to facilitate easier clearance of the site and enable the land surveyors to carry out their surveillance successfully. As stated by Mark Young, the leading construction manager of the company given the tender to spearhead the project, as a result of the many environmental constraints that were in existence, the company had to temporarily close down part of the road especially over the weekend so as to get adequate time to carry out thorough work in fixing the retaining structures 2.1 Retaining Structures to be utilized in the project According Seed & Whitman (2010), the retaining structures are parameters properly premeditated to hold up the pressure exerted by the retained ground as well as other externally initiated loads during processes such as road construction and therefore transmitting these pressures to a particular base. Ideally in road construction for instance in this particular case of improving the A465 Heads Valley Road between Gilwern and Brynmawr from a single three lane carriageway to a dual lane carriageway, an earth retaining structure should be considered since it will be the appropriate parameter to be used to hold back the earth while retaining an adequate difference with the ground level, this should be constructed in the 502 Brynmawr Junction Over bridge, that is, the Gateway bridge to minimize chances of motorists or pedestrians falling off the bridge in the event off accident. 2.1.1 The Earth Retaining Structure As stated by Simpson (2012), the total cost incurred in putting up a strong retaining wall often tends to be very high as compared to the total cost of designing a new slope during a road diversion process. For this reason the Costain Construction Company through its top construction management lead by Mark Young should have a thorough and careful preliminary examination of the retaining wall they aspire to put up in the project. In the course of the construction process, they should try to maintain the height of the retaining wall as low as possible so as to reduce on the cost of putting up the structure as well as the subsequent maintenance costs that will be incurred from time to time especially in the structure put up at the Brynmawr Junction that has an over bridge as well. 2.1.2 The Classification of the Earth Retaining Structures to be undertaken in this Project The construction mechanisms should entail filling up the retaining walls and maintaining them at a desirable height. In some places, for instance in the existing brynmawr roundabout stretching towards the factory as well as the brynmawr bridge, the retaining wall should be fixed such that it is slightly higher in order to act as barrier that may restrain motorists from rolling over and instead bounce back to the road incase of accident (Underwood, Bowden, & Crundall 2002). The system that should be considered in this particular project should be as firm as possible to maintain the wall since this road is used by so many motorists and passengers and in the event that the system considered in the construction process is weak, then the probability of the road lasting is will be minimal (Underwood, Bowden, & Crundall 2002). The Load support apparatus especially on the Gateway Bridge should be of high stability so as to hold on to the pressure that will be on timely basis exerted by the motorists as well as passengers taking the route The ideal earth retaining structure design in this particular project should be as shown below Earth Retaining Structure Externally stabilized internally stabilized In situ walls Gravity walls Stabilized mechanically in situ reinforced Structural Chemical Cast in place concrete Modular gravity 2.1.3 External stabilization of the structure As indicated in the above, the externally stabilized parameter consists of the In situ walls as well as the gravity walls. The in situ walls can either be structural or chemical. The structural walls are composts of the cut walls, bored piles that are often contiguous and con contiguous with tangent piles therein. The chemical composition which is often cut wall on the other hand has got the mix of the deep soil and the jet grout. Thereafter, the structural and the chemical composition are normally braced with cross lot kakers and anchored based on the injected pressure and belled as well forming the in situ wall of the structure under construction (Griffiths & Fenton 2013). Meanwhile, 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. The modular gravity on the contrary, is the filled wall that is compost of the bin, crib, concrete module and the masonry elements as well (Zeng & Steedman 2010). 2.1.4 Internal Stabilization of the structure As stated by Pellegrini & Salençon (2009), unlike the external stabilization, the internal stabilization of the retaining wall as compost of two apparatus, that is, stabilized mechanically and in situ reinforcement of the wall. The mechanical stabilization tends to be the fill walls consisting of the metallic and polymeric strips for reinforcement and the sheets plus the grids. There are also the reinforced soil slopes and the anchored earths to be incorporated in making up the fill walls. At the same time, the in situ reinforcements are the cut walls which ideally are compost of the mini and micro piles that are often reticulated as well as soil nailing. 2.1.5 Type of Earth Retaining wall to considered in this project In improvement of the A465 Head of Valley Road between Gilwern and Brynmawr from single three lane carriageway to dual carriageway, The Costain Construction Company should opt for gravity walls or reinforced earth walls since at some point along the track they will need to put up some strong structures especially next to the brynmawr junction where there is an over bridge. The gravity wall are often strong based on the fact that they are made from cast in place concrete that make them stronger hence able to withstand in any kind of load that may be imposed on it and likewise the reinforced earth walls are made from micro piles and soil nailed together (Richardson & Lee 2011). 2.2 The Contractor should consider the following aspects before deciding on the right wall between the two to consider:- The speed of Construction: - The time frame that they have anticipated to complete the construction process 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). 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 Considerations:- Based on the fact that 11.5 kms of the retaining structures is required in improving this road stretch, 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). Ground type:- 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 maintenance costs of the retaining structures:- As agreed by the Weish Government while accepting the tender, then contractor should instead focus on adhering to the terms and conditions as specified by the Government. In most cases, the Government would desire to have a permanent road with low maintenance costs (Landva& Pelkey 2008). Ground water in the road track under construction:- 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). 2.3 Lateral Earth Pressure After having considered the factors stated above, the contractor of this section 2 of A456 Heads valley road should also take into consideration the three different types of lateral earth pressure that are normally witnessed in the course of putting up the retaining structures during road construction. Lateral pressure is the force that the soil tends to exert in the horizontal direction, that is , the relationship of the pressure on the wall whenever the wall changes its position, for instance moving towards the backfill as shown above, moving outwards or remain in its position at the time as well. The study and analysis of the lateral pressure is an important aspect since it affects the consolidated behavior and strength of the soil hence must always be considered during the designing of the engineering structures such as retaining walls as in the case of the A465 Heads Valley Roads’ improvement. The coefficient of the lateral earth pressure, K, can be described as the ration of the horizontal effective stress, denoted as he to the vertical effective stress , vs. .The effective stress is normally calculated by subtracting the pole pressure from the total pressure as indicated in the soil mechanics. The Coefficient of the lateral pressure for a given soil deposit is often considered as the function of the soil properties and the related stress history witnessed therein(Richardson & Lee 2011). When the retaining structure, that is, the wall is at rest and the material is in its natural state, the pressure that will be exerted therein by the material will be known as the earth pressure while at rest. It is normally denoted by Po. There are three types of lateral earth pressure as analyzed based on the movement of the wall. These includes:- 2.3.1 Earth pressure while at rest According to Richardson & Lee (2011), whenever the constructed retaining wall is at rest, and the material be it a motorists or a passenger 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.’ 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 In circumstances when 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 Sometimes, there are situations 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 and is often denoted as KP. Hence considered as the maximum value of the coefficient of the lateral earth pressure(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 Designing of the Retaining Walls As stated by Zeng & Steedman (2010), once the analysis of the factors above has been completed, the contractor should therefore go ahead with the designing process of the retaining wall. The following steps should be followed:- Selection of the suitable type of 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. Determination of the dimension of the retaining wall (empirical); the contractor should take appropriate measurement and decide on the correct dimension prior to the construction process Estimate Earth Pressure; 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. Estimation of the uplift forces; just like the lateral earth pressures, the contractor should be note down the uplifting forces to expect upon completion of the wall Estimation of the gravity forces; the construction should be initiated having in mind the weights of the road users Determination of the external forces to be expected should also be factored in Checking aspects to be considered while addressing chances of the wall sliding or overturning eventually 3.1 Conclusion Therefore, the whole project becomes a successful once all the measures pertaining to the construction of the retaining walls are practically addressed as clearly stated above. Hence completion of the improvement of A456 Heads of Valleys Road as desired by the Weish Government through its regional traffic department. 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

1 Retaining Structures to be utilized in the project According Seed & Whitman (2010), the retaining structures are parameters properly premeditated to hold up the pressure exerted by the retained ground as well as other externally initiated loads during processes such as road construction and therefore transmitting these pressures to a particular base. Ideally in road construction for instance in this particular case of improving the A465 Heads Valley Road between Gilwern and Brynmawr from a single three lane carriageway to a dual lane carriageway, an earth retaining structure should be considered since it will be the appropriate parameter to be used to hold back the earth while retaining an adequate difference with the ground level, this should be constructed in the 502 Brynmawr Junction Over bridge, that is, the Gateway bridge to minimize chances of motorists or pedestrians falling off the bridge in the event off accident. 2.1.

1 The Earth Retaining Structure As stated by Simpson (2012), the total cost incurred in putting up a strong retaining wall often tends to be very high as compared to the total cost of designing a new slope during a road diversion process. For this reason the Costain Construction Company through its top construction management lead by Mark Young should have a thorough and careful preliminary examination of the retaining wall they aspire to put up in the project. In the course of the construction process, they should try to maintain the height of the retaining wall as low as possible so as to reduce on the cost of putting up the structure as well as the subsequent maintenance costs that will be incurred from time to time especially in the structure put up at the Brynmawr Junction that has an over bridge as well. 2.1.

2 The Classification of the Earth Retaining Structures to be undertaken in this Project The construction mechanisms should entail filling up the retaining walls and maintaining them at a desirable height. In some places, for instance in the existing brynmawr roundabout stretching towards the factory as well as the brynmawr bridge, the retaining wall should be fixed such that it is slightly higher in order to act as barrier that may restrain motorists from rolling over and instead bounce back to the road incase of accident (Underwood, Bowden, & Crundall 2002).

The system that should be considered in this particular project should be as firm as possible to maintain the wall since this road is used by so many motorists and passengers and in the event that the system considered in the construction process is weak, then the probability of the road lasting is will be minimal (Underwood, Bowden, & Crundall 2002). The Load support apparatus especially on the Gateway Bridge should be of high stability so as to hold on to the pressure that will be on timely basis exerted by the motorists as well as passengers taking the route The ideal earth retaining structure design in this particular project should be as shown below Earth Retaining Structure Externally stabilized internally stabilized In situ walls Gravity walls Stabilized mechanically in situ reinforced Structural Chemical Cast in place concrete Modular gravity 2.1.3 External stabilization of the structure As indicated in the above, the externally stabilized parameter consists of the In situ walls as well as the gravity walls.

The in situ walls can either be structural or chemical. The structural walls are composts of the cut walls, bored piles that are often contiguous and con contiguous with tangent piles therein. The chemical composition which is often cut wall on the other hand has got the mix of the deep soil and the jet grout. Thereafter, the structural and the chemical composition are normally braced with cross lot kakers and anchored based on the injected pressure and belled as well forming the in situ wall of the structure under construction (Griffiths & Fenton 2013).

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