A Retaining Wall along the Edges of Pritchard Road in Florida - Coursework Example

Design of retaining wall for Pritchard road Our project is to design a retaining wall along the edges of Pritchard road in Florida. Pritchard road is to be reconstructed and widened by creating dual left turn traffic lanes for the traffic to facilitate traffic flow. New barrier walls will be constructed along the outside edge of Pritchard road. Thus, this report will focus on designing of retaining wall for the new construction of Pritchard road. The purpose of retaining walls is to bound soils in places that possess undesirable slopes. Abstract Retaining walls are structures used to back soil mass in unnatural slope. Our project is to design a retaining wall along the edges of Pritchard road in Florida. Pritchard road is to be reconstructed and widened by creating dual left turn traffic lanes for the traffic to facilitate traffic flow. New barrier walls will be constructed along the outside edge of Pritchard road. Thus, this report will focus on designing of retaining wall for the new construction of Pritchard road. The purpose of retaining walls is to bound soils in places that possess undesirable slopes. They are also constructed in areas whose landscape needs to be engineered and shaped for more uses like building roadways or farming in a hilly place. The design of retaining walls structures requires information on earth pressure acting on the retaining wall due to soil backfill. Table of Contents Abstract 2 Introduction 5 Aims of the Project 6 Site Location 6 Soil Analysis 6 Bearing Capacity 7 Dry Density, γd 7 Moisture Content 7 Shear Strength 7 Compression Strength 7 Water and Earth Pressure 8 Retaining Wall 8 Types of Retaining Wall 8 Gravity retaining wall 8 Mechanically Stabilized Earth Retaining Walls 8 Counter-fort Retaining Wall 9 Anchored Retaining Wall 9 Cantilever Retaining Wall 10 Sheet pile Retaining wall 10 Methods of Soil Test 11 Standard Compact Test 11 Direct Shear Test 12 Unconfined Compressive Strength Test 13 Estimating Of Safe Bearing Capacity 14 Factors that Affects Bearing Capacity 15 Factor of safety 16 Design Considerations for a Retaining Wall 16 Influences on Design 16 GEOTECHNICAL CONDITIONS 16 Durability & Maintenance 17 Locations of retaining walls 17 Cost Estimates 17 Conclusion 18 References 19 Introduction Soil mass is stable on a slope that is flatter than the safe slope, but it has to be retained in slopes which are steeper than the safe slope. Such conditions require the construction of retaining structures to provide a lateral support to soil mass. Retaining structures are rigid walls that support the soil. The soil masses are vertical behind the retaining wall, and it maintains the soil in its vertical elevations. If the retaining wall is absent, the soil on the high level tends to slide and may not remain stable. A roadway in constructed without retaining walls on less sloping areas (Hearn, 2011). This report is focused on designing of retaining wall on steep areas along Pritchard Road. Pritchard Road is being reconstructed and widened to allow for dual left turn lanes for the traffic flowing from westbound of Pritchard Road to southbound I-1295 and form eastbound to northbound I-295. Therefore, new barrier walls will be constructed along edges of the roadway. New barrier walls that will be constructed along the edges of Pritchard Road will protect the existing bridge of northbound 1-295. Other barriers that will be constructed include sidewalks, gutters and curbs. The retaining structures are structures used to hold back the soil mass. They include crib walls, retaining walls, basement flow, sheet pile walls and others. A retaining wall maintains the ground surface at the required elevation ion each side of the wall. If such structures are not built on a steep area, the soil at a higher elevation will move down until it acquires stable and natural configuration (Clayton, 2014; Ranjan, G2007). As a result, the soil at the slope which cannot be supported by its shearing strength, exert a force called earth pressure on the retaining wall. The soil mass supported by the retaining wall is called backfill. Counter-fort walls and gravity retaining wall are the simplest type of retaining walls. The design of retaining wall requires knowledge on earth pressure on the back side of the wall due to soil backfill. Earth pressure is influenced by the relative movement and magnitude of the soil mass. The evaluation of the earth pressure is difficult because due to the fact that it is difficult to determine the magnitude of earth pressure on the retaining wall statistically. Retaining structures are determined based on the line of action and the magnitude of the earth pressure acting laterally. This depends on other factors such as the wall flexibility, drainage conditions, wall movement and soil properties. The design is accomplished after performing a number of tests. The site has soil strata which is rockier. This means that the soil has safe bearing capacity (Ranjan, 2007). This report provides the definition of retaining wall, types, tests and safe bearing capacity of the soil. Aims of the Project The main aim of this report is to design retaining wall for Pritchard Road. This is as a result of the widening of the road to allow more traffic. The current four ways will be extended to six to allow more traffic. Before designing, all the soil mass properties that include the moisture content, the dry mass, soil density, shear strength and cohesion are determine. The safe bearing capacity of the soil is calculated from the results obtained from the tests, which is economical. Site Location Site is located along westbound of Pritchard Road to southbound I-1295 and form eastbound to northbound I-295. Soil Analysis Soil mass consists of broken rocks that has undergone through physical, chemical or biological process. The strength of the soil an important engineering soil properties from strength at it holds back vertical face of soil that would slide or slump at a steeper area. The important properties which are considered during soil analysis include the soil properties, dry density, compressive and shear strength, and bearing capacity. Bearing Capacity This is the capacity of soil mass to support applied weight. It is the maximum pressure applied and does not result in shear failure. The ideal shearing capacity is the theoretical value, allowable bearing capacity is the theoretical value multiplied with factor of safety. Dry Density, γd Dry density is determined from the standard compaction test. This test provides the dry density of the surrounding soil which can product both economical and safe retaining wall design. The dry density of the soil affects its bearing capacity. Thus, the soil mass with sufficient dry density will carry large loads. Soil stabilization is expensive. Soil is compacted to increase its density by packing solid particles and minimizing the amount of air in the soil. Moisture Content This is the amount of moisture content at which the maximum soil density is obtained. This soil property is important in constructions. It is also obtained through standard compact test. Compaction increases the soil unit weight. The water content does not change. The maximum dry weight is obtained at optimum water content, which is which affected by the number of impacts, the weight iof the hammer, the number of passes and the weight of the roller. Shear Strength This is the magnitude of shear stress that can be sustained by the soil sample. It is determined from direct shear test method. The interlocking of the soil particles, the friction and bonding of the particles affect the shear resistance. It is the interaction between the cohesion angle and the angle of internal friction. Compression Strength This is the compressive stress at which unconfined soil specimen fails in compressive test. It is equivalent to the load per unit area. Water and Earth Pressure This is the pressure exerted by soil and water on the side of the retaining wall in horizontal direction. This pressure is important when designing the retaining wall. Retaining Wall This is a structure which holds back any material such as soil and prevents it from eroding away. It is designed to withstand the pressure exerted by the material. Types of Retaining Wall The retaining wall includes Counter-fort Retaining Wall, Anchored Retaining Wall, Cantilever Retaining Wall, Piling Retaining wall, and Gravity Retaining wall. Gravity retaining wall 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) Mechanically Stabilized Earth Retaining 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. Mechanically Stabilized Earth Retaining Wall is shown below. Counter-fort Retaining Wall Counter-fort wall are cantilever structures supported by counter forts with base and back of the wall slab. They connect the base and the wall slab to minimize shearing stress and bending moments. Counter-forts reduce the bending moments on a high vertical wall. A counter-fort retaining wall of up to 8 to 12 m can be build. Counter-fort retaining wall is shown below. (Adeyeri, 2015) Anchored Retaining Wall Anchored retaining wall derived its name from the cables used as anchors behind the wall. A robe or a cable is driven into the material by boring before expanding the anchors at the end of the cable. They are used on slender walls, especially if the high loads are expected (Adeyeri, 2015). The dsign of anchored retaining wall is shown below. Cantilever Retaining Wall This is a more popularly type of retaining wall as it is more commonly used. It consists of a wall which rest on a slab foundation. As it can hold a large amount of soil material, it must be constructed well. The foundation is loaded with back fill and this enables the wall to stabilize against sliding or overturning as is shown below. Sheet pile Retaining wall It is made of steel or wood planks that are driven to a depth of between a third to two third if its height into the ground. They are usually in tight spaces and soft soil. A tie back anchor cable can be used in taller walls, especially at a potential failure plane. The benefits of this type of wall are that it can be anchored to provide greater capacity at increased height. It is also suitable for retaining existence grounds, requires small space and can be used on grounds with poor conditions. The demerits are: it is time consuming, costly and not suitable heights greater than 7m. Sheet pile Retaining wall is shown below. (Adeyeri, 2015) Methods of Soil Test The soil can be analyzed using various tests. This include direct shear test, standard compaction test and unconfined compression test Standard Compact Test This one of the most widely used and effective method for soil stabilization. This test is performed in order to determine the relationship between the soil dry density and the moisture content of the compacted soil sample. It is used by geotechnical engineers to perform an analysis of field control test to ensure that the compacted fills meets the design specifications that include the water content and the required density. By increasing the soil density, most of the engineering properties like stiffness and strength are improved. A standard compact test is carried out to determine the optimum amount of water in the soil. If the water content is higher than the prescribed optimum water content, the soil structure will be weak, softer, susceptible to shrinking and more ductile. If it is compacted lower than the optimum water content, it results in a more flocculated soil structure. Compaction Rammer and Mould The soil that is to be compacted is placed in the standard cylindrical mould in a number of layers. The layers are compacted through a number of blows as shown below. Compacting soil sample Direct Shear Test Direct shear test is the oldest soil strength test. Consolidated-drained shear strength of a soil sample is determined through this method. Shearing strength determines the soil shearing resistance which affects the stability of the slopes. Using this technique, the bearing capacity for the foundation is determined. It is also used in the calculation of the pressure exerted by the soil on a retaining wall. The apparatus used for shearing test is shown below. Apparatus used for direct shearing test An angle of internal friction and the optimum shear stress are determined. Unconfined Compressive Strength Test The unconfined compressive strength is the compressive stress at which unconfined cylindrical soil mass fails in a compression test. It is used to calculate the unconsolidated undrained shear strength of the sample in unconfined state. The unconsolidated undrained shear strength is used to calculate the bearing capacity of the foundations. The load is applied as shown below. The soil sample specimen under a load and after a failure Estimating Of Safe Bearing Capacity The foundation transfers the forces and moments of a structure to the ground. It provides stability against overturning and sliding. The structure is stable if the stresses in the soil are within the permissible limits. The tests are carried out to ensure that soil and the foundation are safe from failure and reduce excessive settlement. The bearing capacity is the ability of the soil to hold the forces from structure without failure. The soil in contact with the foundation is exposed to stresses when the structure is constructed on the ground. 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. 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. Design Considerations for a Retaining Wall Major retaining walls and reinforced embankments are expected to be constructed along the route. The main retaining structure is expected to be constructed at Pritchard Bridge. Influences on Design The design of retaining walls requires considerations of factors such as geotechnical conditions, durability and maintenance, the cost and materials. GEOTECHNICAL CONDITIONS Geotechnical conditions of the route are taken into consideration. Specific investigation will be undertaken and a geotechnical report of the route is produced. Generally, the ground profile contain top soil layer that overlay a colluvium layer with varying depth, and is followed by greywacke bed rock. Retaining walls requires shallow soil undercut and replacing them with compacted material. The retaining walls which are not related with the bridge will generally be designed to withstand seismic occurrence. A design displacement of approximately 150mm is generally acceptable. Durability & Maintenance The type of design adopted for the locations near the bridge stabilized earth retaining walls with concrete facing panels and galvanized steel straps. Steel - Highly durable structural steel has been adopted due to its durability. The system is expected to take upto 50 years to the first maintenance. Special care will be used to minimize corrosion. Concrete – the concrete element in the retaining walls is designed in harmony with 100 years design life requirements. It is expected that there will be little or no maintenance over the structural life. Locations of retaining walls Some sections of the road will be supported by retaining wall with steep natural slope. The walls will be up to 15 m high above the ground surface. Due to its possibility of being unstable, the earth retaining wall will be used, with foundations that have the following characteristics. The outer edge of the wall will be supported with reinforced concrete bored into the bedrock such that it cannot be affected by the possible soil failures. Excavation into the bedrock and construct a stable foundation that will not be affected by any instability. An alternative way would be to replace wall sections with 450 reinforced soil embankments. Especially in locations where there is enough space. Cost Estimates The costs for the type of wall were compiled as preliminary estimates, but do not include all the costs related with the project. The costs are for 2015 dollars. The crib block wall is estimated to cost $40/foot2. It was assumed that soil nailing was used on 75% of each wall with approximate cost of $75 per square foot. The masonry was assumed to cost $ 40 per square foot. The average height for the walls was assumed to be 10 feet. Conclusion The improvement of Pritchard 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 along Pritchard Road. The project has been laid out on the project plan. These include the location of the retaining walls. Geotechnical investigation can be carried out to confirm all assumptions made in the report. Widening of the road will allow for dual left turn lanes for the traffic flowing from westbound of Pritchard Road to southbound I-1295 and form eastbound to northbound I-295. New barrier structures that will be constructed along edges of the roadway include sidewalks, gutters, curbs and retaining walls will hold back the soil mass. We explored different methods that can be used in designing of the retaining walls. This includes tests such as direct shear test, standard compaction test and unconfined compression test. The methods enable estimation of the standard dimensions of the retaining wall. The most economical designs that provide optimum strength are adopted. References Hearn, G. J. (2011). Slope engineering for mountain roads. London: Geological Society. Clayton C.R.I., Woods R. I., Bond A. J., & Milititsky J., (2014). Earth Pressure and Earth-Retaining Structures, Third Edition, CRC Press Ranjan, G. (2007). Basic and applied soil mechanics. Place of publication not identified: publisher not identified. Adeyeri, J. (2015). Technology and practice in geotechnical engineering Read More

The evaluation of the earth pressure is difficult because due to the fact that it is difficult to determine the magnitude of earth pressure on the retaining wall statistically. Retaining structures are determined based on the line of action and the magnitude of the earth pressure acting laterally. This depends on other factors such as the wall flexibility, drainage conditions, wall movement and soil properties. The design is accomplished after performing a number of tests. The site has soil strata which is rockier.

This means that the soil has safe bearing capacity (Ranjan, 2007). This report provides the definition of retaining wall, types, tests and safe bearing capacity of the soil. Aims of the Project The main aim of this report is to design retaining wall for Pritchard Road. This is as a result of the widening of the road to allow more traffic. The current four ways will be extended to six to allow more traffic. Before designing, all the soil mass properties that include the moisture content, the dry mass, soil density, shear strength and cohesion are determine.

The safe bearing capacity of the soil is calculated from the results obtained from the tests, which is economical. Site Location Site is located along westbound of Pritchard Road to southbound I-1295 and form eastbound to northbound I-295. Soil Analysis Soil mass consists of broken rocks that has undergone through physical, chemical or biological process. The strength of the soil an important engineering soil properties from strength at it holds back vertical face of soil that would slide or slump at a steeper area.

The important properties which are considered during soil analysis include the soil properties, dry density, compressive and shear strength, and bearing capacity. Bearing Capacity This is the capacity of soil mass to support applied weight. It is the maximum pressure applied and does not result in shear failure. The ideal shearing capacity is the theoretical value, allowable bearing capacity is the theoretical value multiplied with factor of safety. Dry Density, γd Dry density is determined from the standard compaction test.

This test provides the dry density of the surrounding soil which can product both economical and safe retaining wall design. The dry density of the soil affects its bearing capacity. Thus, the soil mass with sufficient dry density will carry large loads. Soil stabilization is expensive. Soil is compacted to increase its density by packing solid particles and minimizing the amount of air in the soil. Moisture Content This is the amount of moisture content at which the maximum soil density is obtained.

This soil property is important in constructions. It is also obtained through standard compact test. Compaction increases the soil unit weight. The water content does not change. The maximum dry weight is obtained at optimum water content, which is which affected by the number of impacts, the weight iof the hammer, the number of passes and the weight of the roller. Shear Strength This is the magnitude of shear stress that can be sustained by the soil sample. It is determined from direct shear test method.

The interlocking of the soil particles, the friction and bonding of the particles affect the shear resistance. It is the interaction between the cohesion angle and the angle of internal friction. Compression Strength This is the compressive stress at which unconfined soil specimen fails in compressive test. It is equivalent to the load per unit area. Water and Earth Pressure This is the pressure exerted by soil and water on the side of the retaining wall in horizontal direction. This pressure is important when designing the retaining wall.

Retaining Wall This is a structure which holds back any material such as soil and prevents it from eroding away. It is designed to withstand the pressure exerted by the material. Types of Retaining Wall The retaining wall includes Counter-fort Retaining Wall, Anchored Retaining Wall, Cantilever Retaining Wall, Piling Retaining wall, and Gravity Retaining wall.

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