Aspects of deflection basin parameters used in a mechanistic rehabilitation design procedure for flexible pavements in South Africa

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 Engineeringunrestricte

Practical guideline for trench reinstatements in the road reserve

Paper presented at the 33rd Annual Southern African Transport Conference 7-10 July 2014 "Leading Transport into the Future", CSIR International Convention Centre, Pretoria, South Africa.Trenches are regularly opened and reinstated in the road reserve by various utility companies. However, the knowledge of such utility companies regarding pavement materials and trench reinstatements can be inadequate. This paper has been written to assist the trench contractor and utility company in doing proper trench reinstatement in the road reserve. It is not suited to trench reinstatement in the road pavement. It synthesises road materials and construction knowledge and testing procedures to ensure trench reinstatement will meet end use and outcome requirements. Aspects such as soil and material knowledge, soil moisture estimation, compaction technique and measurement of bearing capacity have been re-packaged in plain English language to guide a non-road engineering person towards an acceptable and easily measurable outcome. Material description and moisture estimation are done using reliable visual description guidelines. Densification and bearing capacity achievement are guided without measuring actual density, but using instead the Dynamic Cone Penetrometer (DCP) or purpose developed Rapid Compaction Control Device (RCCD). A process and evaluation sheet is presented for quality control which is presented in a simplified format yet backed up by complex technical background information.This paper was transferred from the original CD ROM created for this conference. The material was published using Adobe Acrobat 10.1.0 Technology. The original CD ROM was produced by CE Projects cc. Postal Address: PO Box 560 Irene 0062 South Africa. Tel.: +27 12 667 2074 Fax: +27 12 667 2766 E-mail: [email protected]

A probabilistic approach to detect structural problems in flexible pavement sections at network level assessment

Presently, most of the road agencies use Non-Destructive (NDT) tools to help them prioritise pavement maintenance and rehabilitation (M&R) activities at the network level, thus optimising the limited budgetary resources. One of the most widely used NDT techniques for pavement structural evaluations, at the network level assessment, is the Falling Weight Deflectometer (FWD). Using a database comprising of a wide array of typical layer moduli and thicknesses of traditional flexible pavements, that were generated based on multiple Monte Carlo numerical simulations, as a reference datum, this study successfully developed probabilistic models that allow for analysing the condition of a flexible pavement, at the network level, from FWD surface deflection data, namely the Deflection Bowl Parameters (DBPs), to identify which layers of the pavement structure present a probability of structural failure or damage

Determination of pavement number for flexible pavements using FWD deflection bowl information

Structural Number (SN) is a well-known pavement index methodology derived from the product of structural layer coefficients, layer thicknesses and environmental (and drainage) factors. Subsequently, the Adjusted Structural Number (SNP) included the influence of the subgrade on pavement strength. The Pavement Number (PN) was recently developed in South Africa as an index similar to the SNP. However, in the PN calculation Equivalent Long Term Stiffness (ELTS) values are derived from material class inputs in a knowledge-based system. An approach to calculate the Effective Pavement Number (PNeff), is proposed which utilises the full deflection bowl more effectively in the calculation. It uses the Shape Factor (F1) to determine equivalent layer thickness (He) and FWD deflections at offset of 300mm from the centre of loading to derive Surface Modulus (SM) inputs for calculating an ELTS value representing the total pavement structure, SMpav. The product of the He and SMpav thus provides a derived PNeff value. A large database of flexible pavements was used to successfully validate this approach. It is demonstrated that PNeff, thus derived from the utilisation of the full deflection bowl and without detailed information of pavement layer thicknesses can be used to complement initial or preliminary structural evaluation. It is illustrated how PNeff is used in a benchmark methodology with FWD surveys. The well established FWD deflection bowl structural benchmark analysis method can then further enhance this preliminary structural analysis with PNeff by assisting in a preliminary analysis and helping to determine origin of distress. Hereafter detailed structural analyses can follow with detailed material type and pavement layer information in a much more focussed fashion.Paper presented at the 34th Annual Southern African Transport Conference 6-9 July 2015 "Working Together to Deliver - Sakha Sonke", CSIR International Convention Centre, Pretoria, South Africa.The Minister of Transport, South AfricaTransportation Research Board of the US

Relationship between bailey and dominant aggregate size range methods for optimum aggregate packing and permeability limitation

The Bailey method and the Dominant Aggregate Size Range (DASR) method were developed to optimize aggregate skeleton packing for enhancement of structural strength designs of Hot/Warm Mix Asphalt (HMA/WMA). These design support methods are not always properly correlated with each other. They aroften perceived as giving conflicting or confusing descriptions of the same aspects of the HMA/WMA. To help clarify and improve the correlation, the aggregate skeleton is broken into macro, midi and micro level aggregate subset skeletons to evaluate the contributions of various aggregate fraction ranges to structural strength of the mix. Rut resistance and fatigue cracking limitation are traditional design objectives of any HMA mix design. Permeability of HMA is linked with durability effects such as stripping. Permeability is however not directly controlled via the aggregate skeleton packing efficiency methods. The Bailey method, and more so the DASR method, show promise to understand this link or help to control permeability. The Bailey method is discussed as a reference by looking at new ratios and attempting to verify the aggregate skeleton packing in a logical fashion. The DASR principles of porosity are used to explain the impact of the numerator and denominator, particularly the new or rational Bailey ratios, in terms of porosity as separate and combined contiguous aggregate fraction ranges. The logical filling of voids of the macro, midi and micro aggregate skeleton subsets can thus be traced as well. These aggregate skeleton subsets combined or infilled, constitute the overall matrix of the aggregate mix. Data sets of published papers on this subject were reworked / re-analysed to help illustrate the concepts and trends observable for improved aggregate packing as well as limiting permeability. New improved criteria for permeability control are also presented in DASR and rational Bailey ratio terms to help optimize the design outcome.Papers presented at the 36th Southern African Transport Conference, CSIR International Convention Centre, Pretoria, South Africa on 10-13 July 2017.Transportation research board of the national academie

Benchmarking the structural condition of flexible pavements with deflection bowl parameters

The falling weight deflectometer (FWD) is used worldwide as an established, valuable, nondestructive road testing device for pavement structural analyses. The FWD is used mostly for rehabilitation project level design investigations and for pavement management system (PMS) monitoring on a network basis. In project level investigations, design charts based on both empirical relations and mechanistic or theoretically based approaches are often used to provide structural evaluations and rehabilitation options. The full mechanistic approach normally uses multi-layer linear elastic theory and back-calculation procedures that have come under scrutiny owing to the inaccuracy of results. A semi-mechanistic, semi-empirical analysis technique has been developed in South Africa in terms of which deflection bowl parameters, measured with the FWD, are used in a relative benchmarking methodology in conjunction with standardised visual survey methodology to give guidance on individual layer strengths and pinpoint rehabilitation needs. This benchmark methodology enables the determination of the relative structural condition of the pavement over length and in depth without the requirement for detailed as-built data. A further correlation study with calculated surface moduli and deflection bowl parameters is presented here for granular base pavements, which can enhance benchmarking methodology

Surface moduli determined with the falling weight deflectometer used as benchmarking tool

A semi-mechanistic semi-empirical analysis technique has been developed in South Africa whereby deflection bowl parameters, measured with the falling weight Deflectometer (FWD), are used in a relative benchmarking methodology in conjunction with standardised visual survey methodology to give guidance on individual layer strengths and pinpoint rehabilitation needs. This benchmarking methodology can be enhanced by the use of calculated surface moduli based on the use of Boussinesq's equations. The calculation of such surface moduli can be enhanced by determining the gradient of the surface moduli an correlated with the subgrade layer and the elastic response characteristics. Such benchmark calculations are done without complicated and detailed multi-layered linear elastic modelling and software and enables the determination of the relative structural condition of pavement without detailed as-built data being required

The appropriateness of accelerated pavement testing to assess the Rut prediction capability of laboratory Asphalt tests

Paper presented at the 24th Annual Southern African Transport Conference 11 - 13 July 2005 "Transport challenges for 2010", CSIR International Convention Centre, Pretoria, South Africa.This paper was transferred from the original CD ROM created for this conference. The material on the CD ROM was published using Adobe Acrobat technology. The original CD ROM was produced by Document Transformation Technologies Postal Address: PO Box 560 Irene 0062 South Africa. Tel.: +27 12 667 2074 Fax: +27 12 667 2766 E-mail: [email protected] URL: http://www.doctech.co.z

Possible method of determining structural number for flexible pavements with the falling weight deflectometer

Paper presented at the 31st Annual Southern African Transport Conference 9-12 July 2012 "Getting Southern Africa to Work", CSIR International Convention Centre, Pretoria, South Africa.The paper describes a procedure where the condition of flexible pavements is investigated with the help of non-destructive tests such as the Falling Weight Deflectometer (FWD). The condition or indication of structural strength is expressed in terms of the Structural Number (SN). An existing method of determining the Structural Number was used as benchmark with data from a recent detailed pavement investigation. The benchmark SN determination also makes use of the Dynamic Cone Penetrometer (DCP) method. Previously only limited aspects of the measured deflection bowl were used to determine SN non-destructively. In this improved procedure additional deflection bowl parameters were investigated for their possible improvement in the determination of the SN or PN. The proposed method was therefore benchmarked against existing methods to deterThis paper was transferred from the original CD ROM created for this conference. The material was published using Adobe Acrobat 10.1.0 Technology. The original CD ROM was produced by Document Transformation Technologies Postal Address: PO Box 560 Irene 0062 South Africa. Tel.: +27 12 667 2074 Fax: +27 12 667 2766 E-mail: nigel@doctech URL: http://www.doctech.co.zadm201

Erosion of compacted wearing course gravels-relating material grading, plasticity and compaction to erosion potential

Paper presented at the 24th Annual Southern African Transport Conference 11 - 13 July 2005 "Transport challenges for 2010", CSIR International Convention Centre, Pretoria, South Africa.This paper was transferred from the original CD ROM created for this conference. The material on the CD ROM was published using Adobe Acrobat technology. The original CD ROM was produced by Document Transformation Technologies Postal Address: PO Box 560 Irene 0062 South Africa. Tel.: +27 12 667 2074 Fax: +27 12 667 2766 E-mail: [email protected] URL: http://www.doctech.co.z