The non-destructive measurement of deflection basins has come a long way from measuring only maximum deflection or radius of curvature and using empirical relationships in rehabilitation design. New equipment was developed world-wide and analysis techniques moved towards utilising the full deflection basin in fundamental analysis procedures. This author addressed the problem of a proper description of the full deflection basin by doing a detailed literature survey on this subject. Various deflection basin parameters that describe the deflection basin are listed, as well as the various measuring apparatus related to them. The apparatus are all discussed in detail and related to the equipment available in South Africa. The measurement of deflection basins with the road surface deflectometer (RSD) under accelerated testing with the fleet of heavy vehicle simulators (HVSs) are described in detail. An improved data manipulation procedure is proposed which simplifies the calculation of all the deflection basin parameters found in literature. Various models to fit the measured deflection basins are also investigated in an effort to describe the deflection basin in full too. The measured deflection basin parameters of a bitumen, granular, cemented and light structured granular base pavement are discussed in detail as being tested with the fleet of HVS's. It is shown how the deflection basin parameters reflect the structural capacity of the various layers and behaviour states. A more accurate description of the behaviour states is made possible with the proposal of ranges for the various behaviour states for these deflection basins selected. A literature study was carried out to investigate the various analysis procedures that use measured deflection basins as basic input in the characterization of materials. On the basis of this study, linear elastic programmes were used to calculate effective elastic moduli for each pavement layer, using measured deflection basins as input. The possibility to relate typical distress determinants to measured deflection basins were investigated in the literature. Based on this, typical South African flexible pavement structures were analysed mechanistically and typical design curves were established for typical bitumen and. granular base pavements. The effect of overlays were investigated too, resulting in typical overlay design curves. In the final chapter the author endeavours to summarise the research by indicating how deflection basins can be measured and enhance the South African mechanistic rehabilitation design process. Only the latter rehabilitation design procedure is discussed with specific reference to the enhancement of the behaviour state identification, material characterization, analysis procedure and rehabilitation design with measured deflection basin parameters. The author ends off by giving an indication of the future research need in this field of deflection basins. / Thesis (PhD)--University of Pretoria, 2010. / Civil Engineering / unrestricted

For the past three decades, geosynthetics have been recognized as materials that can significantly improve the performance of pavements on weak subgrade. Pavements exhibit non-linear elasto-plastic behavior. The addition of geosynthetics is undoubtedly beneficial. This being said, researchers have concentrated more on lower life cycle cost and high benefit-cost ratio whereas much less attention has been given to the complex behavior of the reinforced pavement system. Comprehension of the short-term and long-term field performance of reinforced pavements under continued traffic and cyclic environmental loading has remained unexplored. There is empirical evidence indicating quantitative benefits of reinforced versus unreinforced pavement structure. However, quantification of the relative benefits of different types of reinforcement like geogrids and geotextiles lacks information. Further, evaluation of the benefits and comparison of chemical stabilization in the form of lime treatment with mechanical stabilization in the form of reinforcement for pavements on soft soils has received lack of attention. In view of this, full-scale instrumented reinforced and lime treated pavement sections with different schemes were studied. Regular Falling Weight Deflectometer (FWD) testing was conducted in a Farm-to-Market Road, in Grimes County, Texas. Three different geosynthetic products were used for base reinforcement and lime treatment was used for subbase stabilization. Deflection measurements for 9 field trips in 3.5 years were evaluated. Modified deflection basin parameters (DBPs) were defined to typically identify layer properties and were used to measure the relative damage to the base, subbase and subgrade for different sections. A modified Base Damage Index (BDI) and a modified Base Curvature Index (BCI) were defined as a part of this study to capture the benefit of reinforced base and lime stabilized subbase respectively. The variation in the DBPs over three periods of wetting and drying along with explanation of the observed trends forms a part of this research. In addition, a number of condition surveys were performed, during 3 years, to visually identify distresses in various sections. A unique distress quantification technique was developed for measuring deterioration of the pavement sections in terms of the observed distresses and FWD measurements. With this, an index of pavement performance was developed. Thus, the FWD deflection data analyses complemented by visual observation, reveals important information on performance of different geosynthetics with the same base course. Analysis of the field performance of the multiple experimental sections throws light on the relative merits of base reinforcement against lime stabilization. / text