Pavement Design AWS
Pavement Design Information Sheet IS-04 September 2017 Information Sheet Purpose This Information Sheet has been produced to provide information to assist road planners in understanding the design aspects of pavements particularly pavement types and situations most commonly occurring in local government practice. Pavements are an integral component of road construction, comprising nearly a third of construction cost. Thus, cost savings from frequent maintenance and repairs can be realized if proper pavement design methodology and processes are considered and followed thoroughly from the onset. The information presented in this information sheet gives an overview of the pavement design procedure, the types of pavements, factors that contribute to pavement choice, and the main considerations in pavement and rehabilitation design.
Issues covered
design relies on data consisting of information on layer thickness, material properties, and performance in conjunction with test results obtained from destructive and non-destructive tests. Definitions Pavement - The portion of the road, excluding shoulders, placed above the design subgrade level for the support of, and to form a running surface for, vehicular traffic. Pavement Design - A process to select the most economic pavement thickness and composition which will provide a satisfactory level of service for the anticipated traffic and environmental loading. Flexible Pavement - A pavement which obtains its load spreading properties mainly by intergranular pressure, mechanical interlock and cohesion between the particles of the pavement material. Mainly consists of unbound granular materials, usually with a thin bituminous surface. Rigid Pavement - A pavement composed of concrete or having a concrete base course.
Overview Definitions Pavement Requirements Pavement Types Design Procedure Inputs to the Design Procedure Performing the Design Brief for Pavement Design Design Report Conducting Pavement Design References
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Overview
•
One of the primary responsibilities of asset owners is to manage the network of assets as a whole with the view of achieving an agreed level of safety, serviceability, and structural capacity across the network. The main objective of pavement and rehabilitation design is the selection of the most cost-effective pavement thickness and composition that will provide a satisfactory level of service for both current and anticipated traffic needs. Pavement
Pavement Requirements Ideally, a pavement must meet the following requirements:
•
• • • • •
Sufficient thickness for easy distribution of wheel load stresses to a safe value on the sub-grade soil Smooth surface to provide comfort to road users even at maximum speed Structurally sturdy to withstand stress Adequate coefficient of friction to prevent vehicles from skidding Be able to produce the least noise from vehicles in motion Dust proof surface to prevent reduced visibility Long design life with low maintenance cost Impermeable surface to protect subgrade soil.
Pavement Types Pavements are generally classified as either flexible or rigid. The primary difference lies in how the stress from traffic loading is distributed to subgrades. The selection of pavement type is often affected by factors such as initial cost, maintenance cost, availability of suitable materials, environmental conditions, traffic intensity, cost of maintenance, etc. A rigid pavement is very stiff, often composed of pre-mixed concrete making it initially costly. It is considered to deliver a longer service life and provide a lower overall service cost. A flexible pavement is often composed of bituminous materials such as asphalt and is less stiff, therefore allowing it to flex rather than crack under heavy loads. Each pavement type achieves a different solution based on their respective design methods/procedures. Austroads Pavement Design Procedure Pavement design is essentially a structural analysis problem where structural adequacy is determined by one of two methods. 1.
Empirical Design Method – used for unbound pavements with thin bituminous surfacing. As this method is a chart-based simplified procedure, it is not recommended for high volume roads or significant freight routes of typically more than 107 equivalent standard axles (ESA).
2.
General Mechanistic Procedure (GMP) – requires the estimation of the stresses and strains in the pavement and uses the strains calculated at critical locations to determine the life expectancy of the base and subgrade. The GMP method requires detailed knowledge of traffic and of materials and calculation of stresses and strains in the pavement with a suitable linear elastic layered model such as the CIRCLY, which is the most commonly used software for the GMP method.
The design process consists of selecting a trial pavement configuration which is often selected by judgement or past experience and checking the selected design against the required lifespan.
•
Pavement materials and Surfacing Materials – It is necessary to know which materials are available. The materials most often used are: o Unbound granular materials consisting of gravel or crushed rock that has a grading making the materials mechanically stable, workable and able to be compacted. When soil or unbound granular materials do not meet the specification requirements, the material can be modified by blending or stabilising. o
Pavement design may be conducted for existing or new pavements. The former is also referred to as pavement rehabilitation which may include structural or non-structural overlays. Rehabilitation is the major surfacing action meant to bring the pavement’s structural condition back to its as-constructed condition or to exceed its as-constructed condition. It may comprise the following: • •
Non-structural overlay Structural overlay
For heavy duty applications, both flexible and rigid pavements should be designed for a 40year design period.
•
Inputs to the Design Procedure In designing pavements, it is necessary to be aware of the following: •
•
•
Future role of the road section – The designer must take into account the importance of the road and the nature and volume of traffic to be expected for current and future use. After adopting the functional classification and selection of suitable geometry, the pavement designer can commence the design process. Estimated traffic loading – This may be estimated by using the heavy vehicle access groups (HVAG) or if undetermined, the percentage of heavy vehicles from overall traffic. For rigid pavements, the HVAG method must be used. The procedure for determining total HVAG is described in detail in Austroads (2012). Subgrade Evaluation – Subgrade quality is critical to the overall pavement design as the subgrade provides the fundamental strength to pavements. Factors to be considered in determining design strength/stiffness of the subgrade include sequence of earthworks construction, the compaction moisture content and field density specified for construction, moisture changes during design life, subgrade variability, and the presence or otherwise of weak layers below the design subgrade level.
IPWEA (NSW) Roads & Transport Directorate Level 12, 447 Kent Street SYDNEY NSW 2000
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Bituminous materials are available in a varying range to satisfy the demands of road pavements under various circumstances. Bituminous materials must be selected to match their intended function. The behaviour, load bearing capacity, and safety aspects largely depend on the bitumen and aggregate properties, composition, and the quality of workmanship. All these must be considered and selected solution must be aligned with locally available technologies.
Environment – Climatic and geographic effects to pavement design relate to subgrade moisture conditions, drainage requirements, predisposition to flooding, and the selection of suitable subbase materials. Construction and Maintenance Considerations – Involve the consideration of various construction and maintenance factors such as: o Extent and type of drainage important as subsurface drainage must be considered by the designer for all pavements o Use of either boxed or full-width construction o Equipment available to the contractor o Environmental, Aesthetic, and Safety requirements o Social considerations o Construction under traffic o Ongoing and long-term maintenance costs
Design Report The design elements should be summarized in a detailed report. Table 2.2 in ROADguide 2012 provides an example of the contents of the report. It is important to note that pavement requires expertise and design experience and is best conducted by an expert and experienced pavement designer. Conducting Pavement Design The design steps for both new and rehabilitation design are summarised in Austroads (2011 and 2012) and are illustrated with worked examples. REFERENCES and FURTHER READING: The information contained in this Information sheet has been summarized from a number of resources. More detailed information may be sourced from the references below: Austroads 2011, Guide to Pavement Technology: Part 5: Pavement Evaluation and Treatment Design AGPT05-11, Austroads, Sydney NSW Austroads 2012, Guide to Pavement Technology: Part 2: Pavement Structural Design, AGPT02-12, Austroads, Sydney NSW IPWEA (NSW) Roads & Transport Directorate, 2012 ROADguide Road Design and Performance, Sydney NSW McDaniel, Rebecca 2010 Pavement Design Overview, Purdue University, USA
Performing the Design Empirical design for lightly-trafficked granular pavements with thin bituminous surfacing can be performed using the design chart shown in Figure 12.2 in Austroads 2012. This design chart is based on presumptive design values. Brief for Pavement Design Before proceeding to determine the pavement thickness, it is essential to gather all the necessary information. Table 2.1 in ROADguide, IPWEA NSW Roads & Transport Directorate 2012, provides a summary of the design process.
(02) 8267 3000 (02) 8267 3070 [email protected]
Issues covered
design relies on data consisting of information on layer thickness, material properties, and performance in conjunction with test results obtained from destructive and non-destructive tests. Definitions Pavement - The portion of the road, excluding shoulders, placed above the design subgrade level for the support of, and to form a running surface for, vehicular traffic. Pavement Design - A process to select the most economic pavement thickness and composition which will provide a satisfactory level of service for the anticipated traffic and environmental loading. Flexible Pavement - A pavement which obtains its load spreading properties mainly by intergranular pressure, mechanical interlock and cohesion between the particles of the pavement material. Mainly consists of unbound granular materials, usually with a thin bituminous surface. Rigid Pavement - A pavement composed of concrete or having a concrete base course.
Overview Definitions Pavement Requirements Pavement Types Design Procedure Inputs to the Design Procedure Performing the Design Brief for Pavement Design Design Report Conducting Pavement Design References
•
Overview
•
One of the primary responsibilities of asset owners is to manage the network of assets as a whole with the view of achieving an agreed level of safety, serviceability, and structural capacity across the network. The main objective of pavement and rehabilitation design is the selection of the most cost-effective pavement thickness and composition that will provide a satisfactory level of service for both current and anticipated traffic needs. Pavement
Pavement Requirements Ideally, a pavement must meet the following requirements:
•
• • • • •
Sufficient thickness for easy distribution of wheel load stresses to a safe value on the sub-grade soil Smooth surface to provide comfort to road users even at maximum speed Structurally sturdy to withstand stress Adequate coefficient of friction to prevent vehicles from skidding Be able to produce the least noise from vehicles in motion Dust proof surface to prevent reduced visibility Long design life with low maintenance cost Impermeable surface to protect subgrade soil.
Pavement Types Pavements are generally classified as either flexible or rigid. The primary difference lies in how the stress from traffic loading is distributed to subgrades. The selection of pavement type is often affected by factors such as initial cost, maintenance cost, availability of suitable materials, environmental conditions, traffic intensity, cost of maintenance, etc. A rigid pavement is very stiff, often composed of pre-mixed concrete making it initially costly. It is considered to deliver a longer service life and provide a lower overall service cost. A flexible pavement is often composed of bituminous materials such as asphalt and is less stiff, therefore allowing it to flex rather than crack under heavy loads. Each pavement type achieves a different solution based on their respective design methods/procedures. Austroads Pavement Design Procedure Pavement design is essentially a structural analysis problem where structural adequacy is determined by one of two methods. 1.
Empirical Design Method – used for unbound pavements with thin bituminous surfacing. As this method is a chart-based simplified procedure, it is not recommended for high volume roads or significant freight routes of typically more than 107 equivalent standard axles (ESA).
2.
General Mechanistic Procedure (GMP) – requires the estimation of the stresses and strains in the pavement and uses the strains calculated at critical locations to determine the life expectancy of the base and subgrade. The GMP method requires detailed knowledge of traffic and of materials and calculation of stresses and strains in the pavement with a suitable linear elastic layered model such as the CIRCLY, which is the most commonly used software for the GMP method.
The design process consists of selecting a trial pavement configuration which is often selected by judgement or past experience and checking the selected design against the required lifespan.
•
Pavement materials and Surfacing Materials – It is necessary to know which materials are available. The materials most often used are: o Unbound granular materials consisting of gravel or crushed rock that has a grading making the materials mechanically stable, workable and able to be compacted. When soil or unbound granular materials do not meet the specification requirements, the material can be modified by blending or stabilising. o
Pavement design may be conducted for existing or new pavements. The former is also referred to as pavement rehabilitation which may include structural or non-structural overlays. Rehabilitation is the major surfacing action meant to bring the pavement’s structural condition back to its as-constructed condition or to exceed its as-constructed condition. It may comprise the following: • •
Non-structural overlay Structural overlay
For heavy duty applications, both flexible and rigid pavements should be designed for a 40year design period.
•
Inputs to the Design Procedure In designing pavements, it is necessary to be aware of the following: •
•
•
Future role of the road section – The designer must take into account the importance of the road and the nature and volume of traffic to be expected for current and future use. After adopting the functional classification and selection of suitable geometry, the pavement designer can commence the design process. Estimated traffic loading – This may be estimated by using the heavy vehicle access groups (HVAG) or if undetermined, the percentage of heavy vehicles from overall traffic. For rigid pavements, the HVAG method must be used. The procedure for determining total HVAG is described in detail in Austroads (2012). Subgrade Evaluation – Subgrade quality is critical to the overall pavement design as the subgrade provides the fundamental strength to pavements. Factors to be considered in determining design strength/stiffness of the subgrade include sequence of earthworks construction, the compaction moisture content and field density specified for construction, moisture changes during design life, subgrade variability, and the presence or otherwise of weak layers below the design subgrade level.
IPWEA (NSW) Roads & Transport Directorate Level 12, 447 Kent Street SYDNEY NSW 2000
•
Bituminous materials are available in a varying range to satisfy the demands of road pavements under various circumstances. Bituminous materials must be selected to match their intended function. The behaviour, load bearing capacity, and safety aspects largely depend on the bitumen and aggregate properties, composition, and the quality of workmanship. All these must be considered and selected solution must be aligned with locally available technologies.
Environment – Climatic and geographic effects to pavement design relate to subgrade moisture conditions, drainage requirements, predisposition to flooding, and the selection of suitable subbase materials. Construction and Maintenance Considerations – Involve the consideration of various construction and maintenance factors such as: o Extent and type of drainage important as subsurface drainage must be considered by the designer for all pavements o Use of either boxed or full-width construction o Equipment available to the contractor o Environmental, Aesthetic, and Safety requirements o Social considerations o Construction under traffic o Ongoing and long-term maintenance costs
Design Report The design elements should be summarized in a detailed report. Table 2.2 in ROADguide 2012 provides an example of the contents of the report. It is important to note that pavement requires expertise and design experience and is best conducted by an expert and experienced pavement designer. Conducting Pavement Design The design steps for both new and rehabilitation design are summarised in Austroads (2011 and 2012) and are illustrated with worked examples. REFERENCES and FURTHER READING: The information contained in this Information sheet has been summarized from a number of resources. More detailed information may be sourced from the references below: Austroads 2011, Guide to Pavement Technology: Part 5: Pavement Evaluation and Treatment Design AGPT05-11, Austroads, Sydney NSW Austroads 2012, Guide to Pavement Technology: Part 2: Pavement Structural Design, AGPT02-12, Austroads, Sydney NSW IPWEA (NSW) Roads & Transport Directorate, 2012 ROADguide Road Design and Performance, Sydney NSW McDaniel, Rebecca 2010 Pavement Design Overview, Purdue University, USA
Performing the Design Empirical design for lightly-trafficked granular pavements with thin bituminous surfacing can be performed using the design chart shown in Figure 12.2 in Austroads 2012. This design chart is based on presumptive design values. Brief for Pavement Design Before proceeding to determine the pavement thickness, it is essential to gather all the necessary information. Table 2.1 in ROADguide, IPWEA NSW Roads & Transport Directorate 2012, provides a summary of the design process.
(02) 8267 3000 (02) 8267 3070 [email protected]
