Design of Flexible Granular Pavements

Presenter: Bill Hutton

Pavement Types

Flexible Pavements:• Consist of Unbound Granular Materials, typically with a thin

bituminous surface.• Also Includes pavements consisting of

substantial thickness of bitumen bound materials and even cement stabilised materials

Pavement Types

Rigid Pavements:• Those consisting of Portland Cement concrete

Pavement Types

Types of Flexible Pavements:

1.  Conventional2.  Asphalt Surfaced3.  Deep Strength4.  Full Depth5.  Modified Full Depth

Conventional and Asphalt most commonly used and most relevant to Zone Substations or Depot Roads.

Structural Analysis

Pavement design is essentially a Structural Analysis problem!

Structural Adequacy determined by one of two methods

Road Classification Pavement Material

Standard Modified

Local Urban Roads & Rural Roads

Empirical Mechanistic

State Highways & Urban Arterials

Empirical Mechanistic

Freeways, Motorways & Major Arterial Roads

Not Applicable Mechanistic

Structural Analysis

To design a pavement we need to know:• Subgrade Strength or bearing capacity

     Measured by the CBR test.  Typically CBR 2-3 for clays and       15% or greater for sandy soils.  Used directly in the empirical       design procedure

• Pavement Material Characteristics; and     Need to know what materials are available.  Generally used Type 2.1 for top 150mm       with Type 2.3 below.  For deep pavements, may also have a deep layer of CBR15       material

• Design Traffic Loading No. of equipvalent standard axles that traverse the design lane over the pavement

design life

Design Traffic Loading

 The Standard Axle loading is defined as an axle with dual tyres loaded to 80kN (8.2 tonne).

 Design Traffic Loading

 Loads on other axle configurations that cause equivalent damage to the standard axle

Axle Configuration Designation Load, P (kN) Mass (tonnes)

Single Axle, Single Tyre

SS 53 5.4

Tandem Axle, Dual Tyre

TAD 135 13.6

Triaxle, Dual Tyre TRD 181 18.5

To determine the damaging effect of loads other than the standard load for an axle type, the following equation is used:

Doubling the axle load causes 16 TIMES the damage

This equation applied to each axle/axle group on a vehicle can be used to calculate the ESA for that vehicle

 Design Traffic Loading

 

 

 Design Traffic Loading

 

 

 Design Traffic Loading

 Design Traffic Loading

 Design Traffic Loading

 Design Traffic Loading

 Design Traffic Loading

150mm

 Design Traffic Loading

Geometric Design Considerations

Earthworks – 1:200 Residential – 1:400 Industrial

Concrete – 0.5% Longitudinal (0.3% if required) – 1% Cross Fall

Asphalt – 2% Cross Fall Minimum

Chip Seal – 3% Cross Fall Minimum

Kerb & Channel – 0.3% Longitudinal

Table Drains with Grass Invert – 0.75% (0.5% min).

Table Drains with Conc. Invert – 0.35% (0.3% min).

Case Study 1 – Granite Vale Road

Case Study 1 – Granite Vale Road

Case Study 1 – Granite Vale Road

250mm -75 material with Geo-fabric

150mm Type 2.3 CTB with 3% Cement

Additional Reading & Questions

Austroads Design Guides

Mainroads Technical Specifications

Townsville City Council Ausspec Guidelines

Questions???