THICKNESS DESIGN FOR UNBOUND ROAD CONSTRUCTION

A simple rational method is proposed for the thickness design of roads in which the main structural component consists of unbound granular material. Using a modification of elastic layer theory and certain empirical results from the literature, a relationship is derived between the number of standard axles to be carried and the thickness of unbound material required. The basic mechanical input is the elastic modulus of the subgrade, estimated at stresses similar to those under a standard axle. Techniques for measuring this quantity or for estimating it from CBR values are discussed. The predictions of the method are compared with those of empirical CBR methods, with the aid of asphalt institute ratios to calculate equivalent thicknesses. Such comparisons are of necessity confined to low CBR values (up to 7 per cent) and suffer from uncertainty as to the validity of the use of substitution ratios. However, though the picture is complex, the predictions are in good agreement at least up to 2.5 million standard axles. Above this value the comparison was inconclusive. However, agreement even to this extent, together with the rational nature of the approach, suggests that pilot applications of the technique in a wider context are justified. Nevertheless, the method requires further testing for longer design lives and higher values of subgrade modulus (or CBR). A technique for overlay design, where the overlay also consists of unbound material, is proposed. (TRRL)

• Corporate Authors:

  An Foras Forbartha

  St Martin's House, Waterloo Road
  Dublin 4,   Ireland 
• Authors:
  • Golden, S J
• Publication Date: 1980-11

Media Info

• Features: Figures; References; Tables;
• Pagination: 34 p.
• Serial:
  • Road Construction
  • Publisher: An Foras Forbartha

Subject/Index Terms

• TRT Terms: Axle load force; California bearing ratio; Coefficient of subgrade reaction; Design methods; Modulus of elasticity; Pavement layers; Thickness
• Old TRIS Terms: Thickness design; Unbound pavement courses
• ITRD Terms: 1322: Axle; 3067: Axle load; 4173: Crushed stone; 9011: Design (overall design); 4107: Granular; 2952: Layer; 5919: Modulus of elasticity; 4511: Particle; 2961: Roadbase; 3096: Strengthening (pavement); 9078: Theory; 5933: Thickness
• Subject Areas: Design; Highways; Pavements;

Filing Info

• Accession Number: 00349510
• Record Type: Publication
• Source Agency: An Foras Forbartha Teoranta
• Report/Paper Numbers: NRC218 Monograph
• Files: ITRD, TRIS
• Created Date: Jun 30 1982 12:00AM