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INTROUDUCTION
In the development of fundamental methods of pavement evaluation by means of deflection measurements it is imperative that an accurate description of the deflection basin be given. In the majority of analysis procedures only the maximum surface deflection (<o5) is measured (Epps and Hicks, 1982). Owing to the empirical nature of analysis techniques in the past, a more detailed description of the deflection basin has been neglected. In Figure 1.1 it can be seen that the same maximum deflection value, <5o , can be measured on two pavements with totally different deflection basins and structural response characteristics. Whitcomb (1982) even concludes from various examples of this phenomenon that « ….resilient moduli for layers in a pavement system cannot be back calculated using maximum surface deflection alone ». In their analysis of Alascan highways during the spring thaw period Stubstad et al. (1983) show that the same maximum deflection value could lead to wrong assumptions of thaw depth and resulting damage potential. It is only by looking at the whole deflection basin that preventative predictions of thaw depth can be made. Although South Africa does not have pavement distress due to thaw as in North America, it is significant that the whole deflection basin can be used to indicate a change of state.
Paterson et al. (1974) states that when a pavement deflects under a load, the influence of the load extends over a certain area. In one dimension and for one depth this can be regarded as a deflection profile or influence line of, say, the surface. In two dimensions the deflection at any depth is given by an influence surface. The shape of the influence surface reflects the structure of the pavement. In Figure 1.2 the typical deflection profiles for a uniform circular load and the more complex shapes of aual wheel single axle loads and how front and back axles influence each other ,are shown. The depth profile of the deflection closely reflects the stiffness depth profile of the pavement in relation to the relevant stress levels.
This is best swnmarised by the Technical Committee Report of the XVII World Road Congress (Permanent International Association ofRoad Congresses ,1983). « There are obvious attractions in making maximum use of the information that can, in principle, be obtained by detailed evaluation of the deflected shape as it obviates or reduces the need for assumptions about, or measurement of, properties of pavement materials. »
This introductory discussion clearly indicate that there is a need for the measurement and interpretation of the full deflection basin. As will be discussed in later chapters, in South Africa the full deflection basin is measured, but the analysis historically focussed on the small area surrounding maximum deflection. In order to make better use of the full deflection basin , a literature survey was conducted. This literature survey covers the work done overseas with other measuring equipment description methods of the full deflection basin , evaluation of various deflection basin parameters and devices. In order to bring it in line with the South African scene , all these discussions are related to the practice here .
Recommendations are made by this author to enhance the current practice and use of South African devices and deflection basin description.
CHAPITRE 1 MEASUREMENT AND DATA PROCESSING OF DEFLECTION BASINS IN SOUTH AFRICA
CHAPITRE 2 ANALYSIS OF DEFLECTION BASINS MEASURED DURING ACCELERATED TESTING
CHAPITRE 3 LITERATURE SURVEY ON MATERIAL CHARACTERIZATION AND STRUCTURAL ANALYSIS USING DEFLECTION BASINS
CHAPITRE 4 EFFECTIVE ELASTIC MODULI DETERMINED FROM ROAD SURFACE DEFLECTOMETER MEASUREMENTS
CHAPITRE 5 RELATIONSHIPS BETWEEN DISTRESS DETERMINANTS AND DEFLECTION BASIN P~lETERS: A LITERATURE SURVEY
CHAPITRE 6 RELATIONSHIPS BETWEEN DEFLECTION BASIN PARAMETERS AND DISTRESS DETERMINANTS FOR TYPICAL SOUTH AFRICAN PAVEMENTS
CHAPITRE 7 PROPOSED USE OF DEFLECTION BASIN MEASUREMENTS IN THE MECIDl~ISTIC REHABILITATION DESIGN OF FLEXIBLE PAVEMENTS
