PERMANENT DEFORMATIONS OF UNBOUND BASE COURSE

SITOMATTOMAN KANTAVAN KERROKSEN PYSYVAT MUODONMUUTOKSET

The aim of this study is to clarify on the base of simulation tests performed with a pavement test facility (PTF) the effects of the base course material, loading, structure and external conditions on permanent deformations in the structure of thinly paved roads. The facility is a laboratory-scale test track by means of which a road structure can be subjected to a wheel load corresponding to actual traffic loading. The present experiments covered a range of 16 test structures. The relative permanent deformations in the base course are substantial and increase in a regular manner, although the rate of increase attenuates with growing number of loads. The trend in these deformations conforms to expectations under simulated summer conditions, i.e. the greater the load the more quickly these permanent deformations develop. Spring conditions were simulated with test structures of thickness 200 mm, in an attempt to reproduce conditions under which the upper part of the road structure has thawed. In such a case permanent deformations increase considerably with fine content and moisture content, doubling in incidence with an increase in fines (0,063 mm fraction) from 4.5 % to 6.4 %. Similarly, this increase of 2 percentage points in the fines content rose moisture content from 4.5 % to 6.0 % and degree of saturation from about 50 % to 70-75 %. At moisture content of over 3 % the permanent deformations in an unbound base course of crushed rock of poor mineralogical composition were very much greater than when a better quality of crushed rock aggregate was used. Some of the permanent deformations in the poorer aggregate were attributable to the "hanging" nature of the grain-size distribution curve and the high flakiness of the grains. The PTIF results indicate that permanent deformations in the base course develop in a regular manner and can be modelled in terms of elastic deformations and the degree of saturation, representing moisture conditions. The results create a good basis for developing a dimensioning procedure that takes account of these deformations. In the context of road improvement schemes, relative elastic deformations can be defined by means of back-calculated or estimated moduli, while the degree of saturation can be calculated in a simple manner from the dry density as determined in a Proctor test, the specific gravity and the estimated moisture content. The main problems encountered when developing a dimensioning procedure are likely to concern how allowance can be made for the deficient edge support found in the case of narrow roads and for the quality of the subgrade.

• Availability:
  • Find a library where document is available. Order URL: http://worldcat.org/isbn/951726710X
• Corporate Authors:

  TIELAITOS (FINNISH NATIONAL ROAD ADMINISTRATION)

  OPASTINSILTA 12 A
  HELSINKI,   Finland  FIN-00520
• Authors:
  • BELT, E
  • LAMSA, V-P
  • EHROLA, E
• Publication Date: 2000

Language

• Finnish

Media Info

• Features: References;
• Pagination: 44p+14a p.
• Serial:
  • TIELAITOKSEN SELVITYKSIA
  • Volume: TIEL 3200646
  • Issue Number: 60
  • Publisher: TIELAITOS (FINNISH NATIONAL ROAD ADMINISTRATION)
  • ISSN: 0788-3722

Subject/Index Terms

• TRT Terms: Deformation; Pavement design; Ruts (Pavements)
• Uncontrolled Terms: Road structure; Rut
• Geographic Terms: Finland
• ITRD Terms: 5595: Deformation; 8035: Finland; 2955: Pavement; 3055: Pavement design; 3081: Rutting (wheel)
• Subject Areas: Highways; Pavements;

Filing Info

• Accession Number: 00926914
• Record Type: Publication
• Source Agency: VTT Technical Research Centre of Finland
• ISBN: 951-726-710-X
• Files: ITRD
• Created Date: Jul 8 2002 12:00AM