Free Road Pavement Design Report Dissertation Example
Road Pavement Design Report
A road pavement also referred to as a road surface, is a durable surface material that is laid on a surface that is required to sustain foot traffic or vehicular traffic or both. Such surfaces include roads and walkways. Different methods are used in Australia and other parts of the world in the design of pavements, and with the current advancements in technology, the making of pavements has been significantly revolutionized. This engineering report encompasses four pavement design technologies that can be implemented to ensure sustainability and efficiency in the design of pavements. One of these pavement design technology is the design of an unbound granular, flexible pavement surfaced with a bituminous layer. In this pavement design method, thin bituminous surfacing is not adequately taken into account for the impact of traffic loads. Furthermore, the unbound granular materials are characterized regarding their California Bearing Ratio (CBR). Another pavement design technique is the flexible pavement design of flexible pavements, that is, an asphalt pavement comprising of cemented subbase material and an unbound granular layer. A flexible pavement has a characteristically less flexural strength, and it acts as a flexible sheet. This is in contrast to rigid pavements where the wheel loads can be transferred to the subgrade soil, courtesy of the flexural strength of the soil. Rigid pavement design involves the use of cement concrete. This design is based on the provision of a structural concrete slab that is of sufficient strength to resist the traffic loads. The fourth activity involved the design of light trafficked pavements. Principally, light traffic pavements are used for pedestrians or light traffic in minor towns. Regardless of the nature of the pavement design, it must be structurally sound and capable of sustaining the traffic and vehicular loads it is subjected to.
Different design methods can be applied to the design of pavements. According to Powell, Potter, Mayhew, and Nunn, any engineering pavement design should lead to the construction of a structurally sound surface, cost-effectively and sustainably (1991, 187). Therefore, road engineers should be capable of designing the pavements depending on the requirements of the client and the road standards set in the country (Taylor and Patten, 2006, 56). The geometric design of road pavements in Australia, for local roads, national roads and pedestrian walkways are regulated by the Australian Transport Council and the National Transport Commission. State governments also have their parallel road authorities to ensure the design of proper roads in Australia.
The knowledge of the design technologies for pavements is salient for the successful design of sustainable and durable pavements in Australia and other parts of the world. In Australia and New Zealand, the government agencies in charge of road projects have adopted various technologies to ensure an efficient and cost-effective design of road pavements. The pavement design process entails the design of the structural elements and partially the aesthetics, depending on the needs of the client, the class, and level of service of a pavement, among other considerations (Mayhew 199, 23).
Considering the provisions of the Austroads Design Manual, this report encompasses four elements, that are, the design of unbound granular, flexible pavement surfaced with a bituminous layer, the design of flexible pavement, the design of a rigid pavement and the design of a light trafficked sidewalk for a local town. Conventionally, the product of any engineering idea is a design, reflecting the thoughts and the opinions of an engineer towards solving a particular problem (Mayhew Supe and Gupta, 2014, 45). The road transport sector is the most critical sector in driving economies of many countries in the world. By performing the four tasks, I was able to appreciate the need for sustainable pavement design. Aside from this, I recognized the need for common reference material for the design of pavements. The Austroads design manual was the primary reference material in the four tasks. In the design of the different types of pavement, it is salient to have a good understanding of the design criteria and the necessary assumptions that need to be made to ensure the design of structurally sound highways and pedestrian walkways (Charman, 1998, 141).
The Design of an Unbound Granular, Flexible Pavement Surfaced with a Bituminous Layer
This task involved the design of an unbound granular, flexible pavement which is surface by a thin bituminous layer. The first step in this task was to determine if the nominated pavement was compliant with the design requirements using the requirements stipulated in the design manual. (Bangui, 2012, 233). After the compliance was confirmed, the pavement was redesigned using a different thickness. The objective of this change in thickness was to determine the minimum pavement thickness for compliance. After finalizing the design, a schematic outline of the pavement was drawn for the compliant design.
In this design, thin surfacing was not adequately taken into account for the impacts of traffic loads due to the following:
It was assumed that the tire loading is uniformly applied and hence the vertical stress distribution is also uniform.
There exists an entire bond between the surfacing and the pavement that underlies it.
Horizontal loads due to braking, accelerating, turning and climbing movements are omitted in this design.
Other considerations in this design were the construction variability, the neglect of environmental effects and the assumed moisture levels.
Unbound granular materials are characterized regarding their California Bearing Ratio (CBR) (McCluskey, 1979, 67). When the mechanistic-empirical design procedure is to be used, granular materials are characterized by their elastic parameters (modulus and Poisson’s ratios). Unbound granular materials are anisotropic; meaning that the modulus in the vertical direction is different from that in the horizontal direction and the vertical modulus is taken as being equal to twice the horizontal modulus.
Primary Data for the Design
EH = 0.5×Ev, and likewise for the performance of the granular fill.
CIRCLY value is 920με
A CBR of 8 (17th to 20th)
Assumed thickness is 540mm.
Design Traffic for 30-year design life: 2.3×10E7
Design of the pavement will entail having a subgrade material that behaves anisotropically.
The first step in this design was the selection of the trial pavement, with an assumed unbound granular material of thickness 540mm. The elastic parameters of the in-situ subgrade selected subgrade and lime-stabilized subgrades were determined. From the calculations, EH was found to be 55.2. The elastic parameters of the top sublayer were also established, including the modulus, Poisson’s ratio and the degree of anisotropy. Next, the elastic parameters and the thickness of other granular sublayers were determined. In this case, the total thickness of unbound granular materials was divided into five equi-thick sublayers, 540/5= 108 mm thick. The elastic parameters for cemented materials and lean mix concrete were determined, including the pre and post-fatigue cracking. Since the finishing of my design is of bituminous surfacing, there was no need to specify the elastic parameters of asphalt. Furthermore, my pavement was designed to limit the perpendicular compressive strain at the subgrade’s top to a tolerable level. The design period of the pavement was determined, and the estimated traffic flow determined. The approximate standard axle tire loading was taken as a four uniformly loaded circular are at the center to center spacing of 33mm, 1470mm and 330 mm. The vertical load was taken as 20kN, and the stress distribution was of 750kPa. The crucial locations in the pavement were determined for the purposes of calculating strains and the values were used for the calculation of maximum perpendicular compressive strain at the subgrade’s top and the maximum horizontal tensile straining at the foot of each asphalt, cemented material and lean mix concrete layer. The allowable ESAs were then calculated and compared with the design ESAs. The layer thickness was then adjusted to 380mm and then checked for design compliance.
In unbound granular materials, performance is primarily governed by the shear strength, modulus, and resistance to material breakdown under construction and traffic loading.
The preferred method of design is the empirical method. This approach requires materials to be characterized by their strength. For boundless grainy materials, modulus escalates markedly with cumulative mean normal pressure and declines with cumulative shear stress (Bagui, 2012, 300). Since the modulus of boundless granular materials is stress dependent, the utilization of finite element frameworks, which permit the stress-dependent and anisotropic actions in both the upright and plane orientations, would permit a more precise fit between the designed and assessed deflections.
Flexible Pavement Design- Asphalt Pavement containing cemented material subbase and an unbound granular layer
From the data provided, a pavement was redesigned and the possible areas for improvement identified. In this design, various assumptions were made, primarily to make the design more realistic and applicable (Appendix 2-1). Through laboratory tests, the flexural strength of the cemented material can be determined. To design a flexible pavement, it is essential to determine the properties of the sublayer (Appendix 2-3) and the properties of other granular sub-layers (Appendix 2-4). The pre-cracking of cemented materials is also another critical check in this kind of design. After the pre-cracking is examined, the elastic properties of all materials must be determined (Appendix2-5). Next, the asphalt fatigue is defined, assuming a volume of bitumen of 11%, shift factor of 6, and a reliability factor of 9. This procedure is repeated for the cemented material and asphalt. Fatigue testing is critical to the sustainability and success of any engineering project (Charamn, 1988, 43) The loading subjected to a pavement determines if it will meet the design standards or not. Therefore, in this design, the standard axle load was examined before proceeding to the final design. Testing was also done to check for the compliance of asphalt to the design manual provisions.
In this task, the allowable loading for both asphalt fatigue and permanent deformation exceeded the design loading; the candidate pavement was acceptable. The checks for cracking are essential as the cracking of a flexible pavement may lead to the entry of water which may affect the structural soundness of the pavement (Gadiya, 2015, 98). The entry of water accelerates distress through the weakening of the pavement and subgrade layers, erosion of cemented material or pumping of fines from below and between cemented layers. Often asphalt or granular material is placed over cemented elements to minimize reflection cracking (Appendix 2-31). To improve this design, there is a need to reduce the shrinking in cemented layers (Appendix 2-32). From this task, it was determined that the best surfacing type is 14 mm dense graded asphalt except where open graded asphalt or stone mastic asphalt is needed due to functional requirements
Rigid Pavement Design
Pavements distribute vehicular loads over a large area and can be classified as rigid or flexible (Chakravarthi and Chaitanya, 2015, 34). The main difference between the various types of pavements is in the distribution of the vehicular loads to the subgrade. Rigid pavements do not flex under applied loading as compared to flexible loading due to their high flexural strength (Appendix 3-3). The four main types of concrete pavements: jointed plain (unreinforced) concrete pavement (PCP), jointed reinforced concrete pavement (JRPC), continuously reinforced concrete pavement (CRCP) and steel fiber reinforced concrete pavement (SFCP). Rigid pavements have a longer lifespan as compared to flexible pavements. They can last 20-40 years before the first rehabilitation is carried out. Rigid pavements have at least twice the service life of flexible pavements (Ketema, Quezon and Kebebe, 2016).
In this task, the type of pavement selected was a plain concrete pavement (PCP). The concrete pavement is two lanes wide and has concrete shoulders. In the design of highways, one of the most critical elements is the determination of the traffic volume expected (Okutani and Stephanedes, 1984, 243). Another important aspect is the determination of the damage due to erosion, through laboratory and field experiments. The results obtained from the PCP design were acceptable. The damage due to erosion and fatigue was meager. For the selected base thickness of 250 mm, the joints were placed at a depth of around 62.5 mm depth to ensure there was efficient weakening in the vertical plane. With a 62.5mm joint depth, there will be avoidance of surface cracks on the pavement.
Conclusively, Rigid pavements were seen to be more suitable that flexible pavements, especially in heavy traffic roads. They are considered to be more economical due to the reduced fuel consumption, the lower energy levels required in lighting and higher flexural strength. Very low damages for all axle group types were realized with the 250mm thick base.
Design of Lightly-Trafficked Pavements
The design of road pavement is dependent on the desired use and the financial factors. The higher the class of the road, the higher the finances required to construct the road. In this task, a design for a flexible pavement for local government was accomplished. The sprayed seal surface was needed to drain directly into the subdivisions’ constructed curb and gutter system (Adlinge, N.d, 10). Additionally, it was to be a cost-effective design for the local government.
The design of pavements is dependent on the location where the bus pad is being made. Construction engineers approve the pavement with the proper checking of the site features. Also, engineers may add unwanted layers to the pavements to make them stable. The structurally sound design is that which is reliable and free from cracking.
The design of the slabs for the bus pads with the use of the bituminous sprayed seal focuses on high strength-weight ratio and high flexural strengths for the slabs (Appendix 4-3). To perform this design project efficiently, the CBR layer is set to have adequate flexibility and hence prevent the cracking or movement of slab materials. Other important factors are the deflection and the loads transmitted to the slab which affect the reliability and durability of the pavement (Appendix 4-3). Considering some assumptions (Appendix 4-3), the values for the calculation of the design concrete cover, bar diameter, sufficient depth, live force, dead force and design force can be done (Appendix4-4). The recommended thickness of the asphalt layer is 100mm while the granular fill layer thickness is 120mm to avoid the breakage of the pavement when the maximum load designed is applied.
Conclusively, the aim of all design process for roads should be to design roads that are both cost-effective and durable. For instance, rigid pavements are more durable compared to flexible pavements. However, the initial cost of setting up a rigid pavement is much higher compared to that of constructing a flexible pavement. Therefore, depending on the funds available and the purpose of the pavement to be constructed, the engineer has to decide on the most cost-effective method to construct the road. In local towns, pavements are designed for light traffic. This is both cost-effective, and a sustainable means as the pavements are not subjected to high vehicular loads. Despite the cost implications of constructing rigid pavements, they are still preferred in cases where the pavement is required to withstand heavy traffic. Flexible pavements are the most common types of pavements, mostly due to their less construction cost and also easeof the availability of the construction materials. However, there is a need to strike a balance between financial requirements and the safety of road infrastructure.
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