Retaining Wall Advancement of Valleys Road: Entail Widening of the Road - Assignment Example

Abstract Retaining structures are structures used to hold back soil mass in areas with steep slopes. The focus of this project is to design retaining wall for A465 Heads of the Valleys Road between Gilwern and Brynmawr. As part of the major project, Valleys Road will be extended from a single 3-lane carriageway to dual 2-lane carriageway. The road passes through areas with steeps slopes and harsh terrains which require extensive use of retaining structures to hold soil mass and to prevent the walls formed on the sides of the road from falling. Thus, this project will focus on the designing of retaining walls for Valleys Road section which will extend for 11.5km. Retaining walls are used to restrain soil mass from moving down the slope in areas with steep slopes. They are mainly used in places where the landscape is to be shaped for specific use like building a roadway or for farming purposes. Table of Contents Abstract 1 Table of Contents 2 Introduction 3 Objectives of the Project 3 Types of retaining structures 3 Design constraints 5 The ground conditions 6 Soil Analysis 6 Bearing Capacity 6 Factors that Affects Bearing Capacity 7 Factor of safety 8 Locations of retaining walls 8 Cost Estimates 9 Conclusion 10 References 11 Introduction Soil mass has tendency to exert a lateral pressure like that of liquid on the structures in contact with. Lateral pressure is a force exerted by the soil on the side of a structure such as a retaining wall. Soil mass can be stable if it lies at a slope which is flatter than the safe slope. But sometimes due to limited space in some locations, the soil mass has to be retained at a slope that is steeper than the safe slope. These circumstances require the construction of retaining structures to provide a lateral support to the soil. They assist in maintaining ground surface at required elevation (Ranjan, 2007). Retaining structures are rigid walls which are used to provide lateral support to soil mass such that the ground surface is retained at different levels on either sides of it. The soil mass are usually maintained in a vertical position behind the retaining wall. Therefore, the soil mass is maintained at different levels on either sides of the structure. If the retaining wall is absent, the soil mass tends to slide down the slope and may not remain stable (Hearn, 2011). The objective of this project is to design a retaining wall for Valleys Road between Gilwern and Brynmawr. The existing road is a 3-lane carriageway of varied width and alignment. But the new road will be extended to a dual 2-lane carriageway to allow more traffic. The road passes through steep valleys are rugged terrain like Clydach Gorge making it necessary to construct retaining walls at the edges of the road that covers a distance of 11.5 km. Objectives of the Project The main objective of this part of the project is to construct a retaining wall on the Valleys Road between Gilwern and Brynmawr. The road will be widened to allow more traffic as part of the section 2 of the overall project. The other objectives are to do all the consideration for preserving the environment and to deliver the scheme that will require less maintenance or cause disruption to the network in future. Types of retaining structures Due to environmental constraints and the topography of the land, there will be extensive use of retaining walls to reduce the impact and landtake on the areas. The nature of the retaining structures would vary depending on other factors such as topography, nature of the soil, among others. The main types of retaining walls that will be used include concrete facing panels or reinforced earth with masonry, traditional reinforced concrete, soil embankments strengthened with geotextiles and treated natural slopes. Most of the near vertical walls will be faced with masonry panels and textured concrete to imitate the natural geological strata in the area (Hearn, 2011). a) Gravity walls Gravity retaining wall is constructed from bricks, stones and concrete. They have thick walls which help them to remain stable. Due to its large amount of weight and stability, the material behind the wall is retained. They are less than 3 m in height. Gravity retaining wall (Adeyeri, 2015) b) Reinforced concrete walls In these types of structures, the walls are basically faced with concrete blocks or concrete panels. The embankment stability is provided by geotextile grid reinforcement in the fill behind the concrete face panels. These retaining walls are normally used to support approach ramp fill for interchanges. They are suitable to be used in moderate height of between 6 to 10m high (Hearn, 2011). Mechanically Stabilized Earth Retaining Wall is shown below. c) Soil nailing and facings This technique is used to stabilize the existing embankments by use of steel bars. The facing may be applied to produce the necessary aesthetics such as hard facings or grass. d) Soil reinforcement will be used in sections of fill in order to support elevated levels. The walls may be vertical with stone finish or block walls with elevation of about 700C. e) Concrete facing panels or reinforced earth with masonry ensures that the most stringent plan and the environment issues are taken into account. The slopes can be enhanced by planting of trees. Design constraints The earthworks would be carried out with minimum intrusion on the natural environment. It is expected that there may be some impact on the local environment, but the construction is design to be safe by ensuring that it is well adapted to the surface features like steep terrains and underground conditions such as underground caves. Design standards The scheme has been designed while taking into consideration the relevant standards such as highways agency procedure for roads, Eurocodes and all the local and national policies. The design speed for the overall scheme is 85 km/h, but there may be departures in geometry with the aim of reducing the impact on the environment. The ground conditions The ground conditions were investigated to find out about the information that can be used for the design and can assist in optimizing the amount of rocks and soil that that can be reused. The conditions vary considerably along the route, specifically as the road moves towards Clydacg Gorge. Different layers of the soil starting from the top are: Top soil Alluvium soil Glacial till The bed rock which consist of the sandstone, limestone and millstone grit. Soil Analysis The soil samples are collected from different parts along the routes to be analyzed. Some of the factors that will be analyzed are the soil properties, bearing capacity, shear and compressive strength, and dry density. They are analyzed using different tests such as standard compaction test, compression test and direct shear test (Clayton et al., 2014; Laloui & Ferrari, 2013). Bearing Capacity Bearing capacity is the capacity of the soil mass or the ground to hold a structure in the position without failure. The foundation provides stability to the structure by transferring the forces and moments from the structure to the ground. The stability of the structure is dependent on the stresses in the soil. These stresses should be within the recommended values. Tests are carried out of the soil to find out about the safety of the structure and to reduce settlement. The figure below shows the main components of a structure. Components of a structure Factors that Affects Bearing Capacity There are several factors that affect the bearing capacity of the soil. They include the soil type, unit weight of soil, the load, ground inclination, inclination of footing, load foundation depth, mode of failure, depth of water table, size of footing and the shape of footing such as circular footing, square footing and rectangular footing. Calculation of the bearing shear capacity, qu Assuming the footing is in square shape, Where Nc, Nγ and Nq are bearing factors. Where c = the cohesion D = foundation Depth γ= soil unit weight q = the ground level Surcharge B = Width of foundation (Clayton et al., 2014) Factor of safety Factor of safety is dependent on factors such as the type of soil, the uncertainty of soil strength, method of exploration, and the significance and impact of failure. Locations of retaining walls There various types of walls that will be constructed along the road depending on the conditions of different locations. The recommended types of retaining walls in this project and their locations are shown below. The types of structures are described below. Type 1 - Vertical precast paneled anchored/nailed wall Type 2 - Vertical precast paneled wall anchored at top only Type 3 - Vertical reinforced earth retaining wall clad in precast panels Type 4 (a) - Reinforced earth slope (Less than 45 degrees) Type 4 (b) - Reinforced earth slope (Greater than 45 degrees) Type 5 - Vertical reinforced concrete retaining wall Type 6 - Back to back vertical reinforced earth retaining walls Type 7 - Soil nailed slope Type 8 - Mechanically stabilized vertical reinforced earth Type 9 (a) - Near vertical fully faced rock cut (Greater than700) Type 9 (b) Steep natural rock cut (Greater than 450) stabilized using dentition and bolts Cost Estimates The costs provide here are assumed to be for preliminary estimates, and does not include the other parts of the project. The concrete block wall is estimated to cost approximately $40/foot2. The soil nailing will be used on about 75% of the wall with approximate cost of $75/ foot2. The construction (labour) is assumed to cost $ 40/ foot2 and the average height for the walls is assumed to be 10 feet, running for 11.5 km. Conclusion The improvement of Valleys Road will involve widening of the road, and this will affect the slopes on both sides of the road. This project focuses on designing of retaining wall between Gilwern and Brynmawr. The project has been laid out on the project plan. These include the location and the types of the retaining walls. Geotechnical investigation can be carried out to confirm all assumptions made in the report. Widening of the road will allow more traffic flow. We investigated various techniques used to design the retaining structures such as standard compaction test, unconfined compression test among others. These techniques are use in the estimation of the required dimensions of the retaining structures and the economical designs are approved. References Clayton C.R.I., Woods R. I., Bond A. J., & Milititsky J., (2014). Earth Pressure and Earth-Retaining Structures, Third Edition, CRC Press Hearn, G. J. (2011). Slope engineering for mountain roads. London: Geological Society. Laloui, L., & Ferrari, A. (2013). Multiphysical testing of soils and shales. Berlin: Springer. Ranjan, G. (2007). Basic and applied soil mechanics. New Age International. Adeyeri, J. (2015). Technology and practice in geotechnical engineering Read More

In these types of structures, the walls are basically faced with concrete blocks or concrete panels. The embankment stability is provided by geotextile grid reinforcement in the fill behind the concrete face panels. These retaining walls are normally used to support approach ramp fill for interchanges. They are suitable to be used in moderate height of between 6 to 10m high (Hearn, 2011). Mechanically Stabilized Earth Retaining Wall is shown below.

The earthworks would be carried out with minimum intrusion on the natural environment. It is expected that there may be some impact on the local environment, but the construction is design to be safe by ensuring that it is well adapted to the surface features like steep terrains and underground conditions such as underground caves.

The scheme has been designed while taking into consideration the relevant standards such as highway agency procedure for roads, Eurocodes, and all the local and national policies. The design speed for the overall scheme is 85 km/h, but there may be departures in geometry to reduce the impact on the environment.

The ground conditions were investigated to find out the information that can be used for the design and can assist in optimizing the number of rocks and soil that can be reused. The conditions vary considerably along the route, specifically as the road moves towards Clydach Gorge.

The soil samples are collected from different parts along the routes to be analyzed. Some of the factors that will be analyzed are the soil properties, bearing capacity, shear and compressive strength, and dry density. They are analyzed using different tests such as standard compaction test, compression test, and direct shear test (Clayton et al., 2014; Laloui & Ferrari, 2013).

Bearing capacity is the capacity of the soil mass or the ground to hold a structure in the position without failure. The foundation provides stability to the structure by transferring the forces and moments from the structure to the ground. The stability of the structure is dependent on the stresses in the soil. These stresses should be within the recommended values. Tests are carried out of the soil to find out about the safety of the structure and to reduce settlement. The figure below shows the main components of a structure.

Several factors affect the bearing capacity of the soil. They include the soil type, unit weight of soil, the load, ground inclination, inclination of footing, load foundation depth, mode of failure, depth of water table, size of footing, and the shape of footings such as circular footing, square footing, and rectangular footing.

The costs provide here are assumed to be for preliminary estimates, and do not include the other parts of the project. The concrete block wall is estimated to cost approximately $40/foot2. The soil nailing will be used on about 75% of the wall with an approximate cost of $75/ foot2. The construction (labor) is assumed to cost $ 40/ foot2 and the average height for the walls is assumed to be 10 feet, running for 11.5 km.

The improvement of Valleys Road will involve widening of the road, and this will affect the slopes on both sides of the road. This project focuses on designing of retaining wall between Gilwern and Brynmawr. The project has been laid out on the project plan. These include the location and the types of retaining walls. A geotechnical investigation can be carried out to confirm all assumptions made in the report. Widening of the road will allow more traffic flow. We investigated various techniques used to design the retaining structures such as the standard compaction test, unconfined compression test among others. These techniques are used in the estimation of the required dimensions of the retaining structures and the economical designs are approved. 

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