The effects of dilatancy on the load carrying capacity predicted by the South African Mechanistic-Empirical Design Method

The South African Mechanistic Empirical Design Method (SAMDM) is widely accepted in South Africa over other pavement design methods. Despite shortcomings such as sensitivity to input parameters, as a design tool the SAMDM provides the pavement designer with a reasonable level of confidence in the pavement structure and the estimated pavement life. This paper presents the results of a study on the effect which the modelling of dilatancy of granular materials has on the predicted load carrying capacity of a pavement designed using the SAMDM. Two Finite Element Analysis (FEA) packages, SIGMA/W and PLAXIS, were used to calculate the stresses and strains required for the SAMDM. Linear elastic and elastic plastic constitutive models were used. The effects which dilation has on (i) the stresses and strains calculated with the FEA package, (ii) the predicted Factor of Safety (FoS) and (iii) the load carrying capacity for a typical pavement were evaluated. The results indicate that the effect of small variations (up to 20 %) in the angle of dilatancy input term , on the predicted principal stresses and strains 1) depends on the FEA package used to calculate the stresses and strains; 2) depends on the formulation of the constitutive model which is selected for the analysis; and 3) is in general small and possibly negligible. The results also demonstrate that the SAMDM is not overly sensitive to small variations in the dilatancy input parameter. Comparison of the calculated FoS and load repetitions to failure using the stresses computed in the elastic plastic model formulation of the SIGMA/W and PLAXIS FEA packages, illustrates that the formulation of the constitutive model used in the selected FEA package has a large effect on the FoS and predicted load repetitions to failure. Incorporating a tension cut-off formulation in the FEA model as with the PLAXIS FEA package, had a significant effect on the calculated stresses and strains since it overcame the computation of inadmissible stress and strain conditions which lead to FoS values that are less than one and thus predict almost immediate failure of the pavement layer.

Language

  • English

Media Info

  • Pagination: 8p
  • Monograph Title: 11th Conference on Asphalt Pavements for Southern Africa: CAPSA15, 16-19 August 2015, Sun City, South Africa

Subject/Index Terms

Filing Info

  • Accession Number: 01597160
  • Record Type: Publication
  • Source Agency: ARRB
  • Files: ATRI
  • Created Date: Apr 22 2016 11:18AM