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Modified Structural Number Determined from Falling Weight Deflectometer Deflection Bowl Parameters and Its Proposed Use in a Benchmark Methodology



Author(s)

Emile Horak¹, Arno Hefer² and James Maina³

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DOI:10.17265/2328-2142/2015.04.003

1. Kubu Consultancy Pty Ltd., Centurion 0157, South Africa
2. Arno Hefer Consultancy CC Pretoria, Pretoria 0001, South Africa
3. Department of Civil Engineering, University of Pretoria, Pretoria 0001, South Africa

The structural capacities of various flexible pavements are often determined with the SNC (modified structural number) or SNP (adjusted structural number). The need for a non-destructive measurement technique, such as the FWD (falling weight deflectometer), had previously been explored to overcome the laborious test pit material characterization and layer thickness determination which had normally been needed to determine SNC or SNP. Lately, viable correlations were established between SNP/SNC and a variety of FWD deflection bowl measuring points or parameters. However, a large portion of the inherent structural information in the rest of the deflection bowl remains unused. The paper presents and validates relationship between effective structural number (SN_eff for pavement layers contribution) and for adjusted structural number (SNP_eff) and deflection bowl parameters utilizing the whole deflection bowl. The latter is inclusive of subgrade contribution. SNP is widely used to gather information on the structural integrity of the pavement system during preliminary network or project level investigations. A range of SNP_eff values are suggested for preliminary investigations using a benchmark methodology to help guide more efficient detailed investigations. However, using SNP_eff in this benchmark fashion cannot identify origin of the distress in a pavement system. The complementary use of deflection bowl parameter benchmark analysis can greatly enhance such investigations based on SNP_eff and identify origin of distress. In this paper, the use of SNP_eff, complemented with deflection bowl parameter benchmark analysis, is demonstrated with a case study.

SNC and SNP, flexible pavements, falling weight deflectometer, deflection bowl parameters, benchmark analysis.