A465 Expansion of the Way among Gilwern and Brynmawr - Case Study Example

NAME OF THE STUDENT ADMISSION NO NAME OF THE INSTITUTION Executive summary With reference to the regional traffic study carried out, 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, public agreed with its expansion and the construction work began. The existing single three lane carriageway was constructed in the 1960s. In many areas the alignment of the existing road results in reduced forward visibility, presenting an increased safety risk for road users. The three lanes section on the hill through Clydach Gorge is marked as two lanes in the uphill direction with downhill traffic confined to one lane by double white lines. This paper explains the main aim of expansion of A465 and the retaining wall requirement and recommended materials to be used. Table of Contents Executive summary 2 Table of Contents 3 1.0 Introduction 4 2.0 Existing condition 4 3.0 Environmental Issues 6 4.0 Recommended structure for Retaining wall 6 5.0 A456 Heads of Valley Road Retaining structures 7 Geogrid Reinforced Retaining Walls 8 5.1 Geogrid Reinforced Retaining Walls 8 5.2 Gravity wall 9 6.0 Factors to be considered in choosing the types of the wall 10 7.0 Earth Lateral Pressure 11 7.1 Active earth pressure 13 7.2 Passive earth pressure 14 7.3 Earth pressure while at rest 15 8.0 Conclusion and summary 15 Bibliography 17 A465 HEADS OF THE VALLEYS ROAD BETWEEN GILWERN AND BRYNMAWR FROM A SINGLE 3-LANE CARRIAGEWAY TO DUAL LANE CARRIAGEWAY 1.0 Introduction The existing A465 was built in the 1960’s as a single three-lane carriageway generally with two lanes in the uphill direction and one in the downhill direction.  In 1990 a regional traffic study identified the need for improvement of the A465. In 1994 alternatives for improvement of the 40km length between Abergavenny and Hirwaun were presented for Public Consultation, and in July 1995 the then Secretary of State for Wales announced the Preferred Route (Le Nevez & Whitfield 2012). The design was developed and a draft Line Order was published in 1997. With reference to the regional traffic study carried out, 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, public agreed with its expansion and the construction work began (Le Nevez & Whitfield 2012). 2.0 Existing condition The existing single three lane carriageway was constructed in the 1960s. In many areas the alignment of the existing road results in reduced forward visibility, presenting an increased safety risk for road users. The three lanes section on the hill through Clydach Gorge is marked as two lanes in the uphill direction with downhill traffic confined to one lane by double white lines (CILFREW & SANDSTONE 2012). The section between Glanbaiden Junction and Saleyard Junction, at the bottom of the gorge, is marked as two lanes with the centre lane being hatched out except at junctions with side roads where it forms a right turn lane. The lanes are also known as undivided highways due to the fact that there are no central reservations along the road stretch (CILFREW & SANDSTONE 2012). 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. Traffic flow and speed are restricted by the road width, road markings, at grade nature of the junction at Brynmawr and close spacing of the four minor side road junctions. This explains the need for expansion of this dual carriage highway. As recorded 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 (CILFREW & SANDSTONE 2012). The project was planned to commence in Dec 2014 and run all the way up to June 2018 having been successfully completed. Preferably, 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 construction phase. 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 (Le Nevez & Whitfield 2012). 3.0 Environmental Issues In accordance with the notice of determination, an environmental statement was prepared and was published with other draft orders. It is very large and technical set of other documents including non-technical summary which is available as separate document (Le Nevez & Whitfield 2012). The National Transport plan contains specific objectives that have influenced by the environmental design. They include; Work to the requirements under European and UK legislation for noise, air quality, water pollution and soils. Continue work to protect, conserve and enhance the historic environment, soils and geology, landscape/townscape, as well as provision for habitats and species. As well as lying within Brecon Beacons National Park and being a designated area of Historic Landscape, the road is flanked within the gorge by three Special Areas of Conservation (SAC) that require an increased level of protection from adverse effects (Le Nevez & Whitfield 2012). The proposed scheme has been designed to minimize the anticipated adverse environmental factors from its construction and operation, whilst still considering other factors such as road safety, engineering design and cost. 4.0 Recommended structure for Retaining wall 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 (Landva, Valsangkar & Pelkey 2008). These 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. Research findings and the public opinion several issues were 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 (Landva, Valsangkar & Pelkey 2008). 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. It’s therefore advisable that adequate resources including financial or labour must be sought in advance so as to manage the construction phase to the end. 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 (Le Nevez & Whitfield 2012). 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 while maintaining the quality of construction (Landva, Valsangkar & Pelkey 2008). 5.0 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 (Landva, Valsangkar & Pelkey 2008). 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:- Geogrid Reinforced Retaining Walls Gravity wall 5.1 Geogrid Reinforced Retaining Walls Just like the gravity wall, the Geogrid reinforced retaining wall is also a very important structure that can be very useful in this project especially at the Brynmawr junction. They are often known as internally stabilized mechanical walls (Rees 2011). As the name suggest, 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. In other words, the blocks, reinforced soil mass and georgic work together to make one large, heavy retaining structure, alternatively, materials such as soil nails, no files or earth anchors may be used in place of grid which tend to create some spaces when mixed with others (Rees 2011). 5.2 Gravity wall Gravity retaining walls depend on their own weight and any soil resting on the concrete in resisting lateral earth forces. They are generally economical up to 10 feet in height fore cast concrete structures. The walls are often having a short height as compared to other retaining walls such as cantilever retaining wall (Rees 2011). Walls of stone or plains or the reinforced concrete having a base with and without a heel, ledge, or buttress, the weight of the wall itself ... plays a significant role in the support of the retained material e.g. concrete gravity walls; spread footing r.c. walls; buttress 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 (Whitfield Le Nevez & Parker 2012). Figure 1:A465 Section 2 Gilwern to Brynmawr 6.0 Factors to be considered in choosing the types of the wall 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. 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. 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 tends 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 continued. Construction Considerations: - Based on the fact that 12 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. 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. Durability and maintenance costs of the retaining structures: - As agreed by the Welsh 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 7.0 Earth Lateral Pressure After having considered all factors, 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. The 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 (Whitfield Le Nevez & Parker 2012). 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. 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 (Seed & Whitman 2010). Lateral earth pressure as analyzed based on the movement of the wall include; 7.1 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. 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) 7.2 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 (Seed & Whitman 2010). This type of pressure is known as passive earth pressure (KP). 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 (Seed & Whitman 2010). 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. 7.3 Earth pressure while at rest 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) 8.0 Conclusion and summary Environmental and safety issues should be in the top list of factors to be considered in expanding the road. The contracted company, 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 maintained expenses anticipated as well as the ground water level of the region. 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 (Seed & Whitman 2010). 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 Bibliography CILFREW, N., & SANDSTONE, P. (2012). PLANNING AND DEVELOPMENT CONTROL COMMITTEE. ENVIRONMENT, 21, 02 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. Le Nevez, C., & Whitfield, P. (2012). The Rough Guide to Wales. Rough Guides UK Rees, J. (2011). Bred of Heaven: One man's quest to reclaim his Welsh roots. Profile Books. 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 Whitfield, P., Le Nevez, C., & Parker, M. (2012). The Rough Guide to Wales. Rough Guides UK Read More