EDITOR'S NOTE: The following article by Ralph C. Heath which appeared in the January 1973 issue of the North Carolina Engineer is another excellent example of how ground-water geologists and hydrologists should and must speak out in their communities in support of ground-water development.

What about ground water

This paper describes the quantification of three-dimensional tyre/pavement contact stresses for vehicle tyres. The Vehicle-Road Surface Pressure Transducer Array (VRSPTA) system was developed to measure contact stresses under moving loads, i.e., Stress-In-Motion (SIM). Prediction equations for quantification of these stresses, based on tyre inflation pressure and loads for seven different tyre types, are given. Tyre inflation pressure predominantly controls the vertical contact stresses on the pavement at the tyre centre, whereas the tyre load controls those at the tyre edges. Analysis indicated that during instantaneous overloading/under-inflated conditions the maximum strain energy of distortion (SED) in the asphalt surfacing occurs close to the tyre edges, while under instantaneous uniform vertical stress conditions the SED is within the asphalt surfacing at the tyre centre. In addition to improved load/contact stress idealization for modelling, this finding may have important implications for the design of relatively thin asphalt surfacing layers for pavements.

Determination of pneumatic tyre/pavement interface contact stresses under moving loads and some effects on pavements with thin asphalt surfacing layers

Full-depth reclamation is one of the most used rehabilitation methods for subbase courses in high-traffic roads. The use of both cement and bituminous binders as binding agents for reclaimed pavement materials can lead to mixtures having high bearing capacity and resistance to permanent deformation, avoiding premature cracking due to shrinkage. This article focuses on two main topics: compactability and thermal sensitivity of cement–bitumen-treated materials (CBTMs). The dosage of liquids in CBTMs is a key parameter in order to obtain an effective compaction. The volumetric characteristics and the optimum liquid content of CBTMs were studied by means of two compaction methods: Proctor and Shear Gyratory Compactor. The temperature susceptibility of CBTMs can be a valuable factor in both design and construction quality control. The influence of temperature on the stiffness modulus of CBTMs was investigated using two testing methods: indirect tensile stiffness modulus and ultrasonic pulse velocity (UPV). Whi...

Compactability and thermal sensitivity of cement–bitumen-treated materials

Railway transitions like bridge approaches experience differential vertical movements due to variations in track stiffness, track damping characteristics, ballast settlement from fouling and/or degradation, as well as fill and subgrade settlement. Proper understanding of this phenomenon requires the integration of field instrumentation with analytical and numerical modeling. This paper introduces an integrated approach to dynamic analysis of the railway track transitions behavior using field instrumentation, analytical modeling, as well as numerical simulations using the Discrete Element Method (DEM). Several bridge approaches have been instrumented to monitor the track response on a problematic portion of the US North East Corridor (NEC), which is primarily a high-speed railway line with occasional freight traffic, carrying high-speed passenger trains operating up to a maximum speed of 241 km/h. Previous publications by the authors have focused on findings from geotechnical instrumentation of railroad track transitions, as well as the validity of a fully coupled 3-dimensional track dynamic model and image-aided discrete element models. The primary contribution of the current manuscript involves the combination of these three components to propose an integrated approach for studying the behavior of railroad track transitions. Track response data from instrumented bridge approaches were used to determine track substructure layer properties and calibrate a fully coupled 3-dimensional track dynamic model. Loading profiles generated from this model were then used as input for a discrete element based program to predict individual particle accelerations within the ballast layer. The importance of modeling the ballast layer as a particulate medium has been highlighted, and the particle to particle nature of load transfer within the ballast layer has been demonstrated.

An integrated approach to dynamic analysis of railroad track transitions behavior

The response of an instrumented flexible pavement structure in southern Sweden, subjected to seasonal freeze–thaw cycles, was investigated during the spring thaw and the recovery periods in 2010 The pavement environmental condition was continuously monitored by measuring subsurface temperature and moisture contents The mechanical behaviour of the pavement structure was investigated by conducting frequent falling weight deflectometer (FWD) measurements throughout the study period Considerable decrease in the pavement-bearing capacity was observed as thaw penetrated the pavement structure and consequently moisture content increased in all pavement unbound layers Highest annual moisture content in the subgrade upper section was registered as thaw penetrated the subgrade and pavement exhibited its weakest structural condition The analyses of the deflection basin indices and back-calculated unbound layer stiffness from the FWD measurements exhibited a clear correlation with the measured subsurface moisture content Furthermore, the dissipated energy measured from the FWD time–history data was calculated, exhibiting its highest annual value during the thawing period Using the back-calculated layer stiffness and moisture measurements in unbound layers, a degree of saturation-based moisture-stiffness model was developed for the granular layer and the subgrade This model fell on a unique curve showing promising agreement with the laboratory-based model proposed by Mechanistic-Empirical Pavement Design Guide that analytically predicts changes in modulus due to changes in moisture

Investigation of a pavement structural behaviour during spring thaw using falling weight deflectometer

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.

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Benchmarking the structural condition of flexible pavements with deflection bowl parameters

The falling weight deflectometer (FWD) is used world wide as a well established and valuable non-destructive road testing device for pavement structural analyses. The FWD is used mostly for rehabilitation design investigations and for pavement management system (PMS) monitoring on a network basis. On project level investigations, both design charts and mechanistic approaches using multi-layered linear elastic theory and back-calculation procedures are often used to provide structural evaluations and rehabilitation options. As an alternative to this a semi-mechanistic semi-empirical analysis technique has been developed in South Africa whereby new deflection bowl parameters measured with the FWD used to give guidance on individual layer strengths and pinpoint rehabilitation needs. This approach is fully suited to supplementary analysis of FWD data in the Australian design systems, and overcomes some of the limitations of the curvature parameter. This paper briefly describes the current practice and basis of this use of deflection bowl parameters, and illustrates the use with a current pavement rehabilitation project underway in South Africa.

Falling Weight Deflectometer Bowl Parameters as Analysis Tool for Pavement Structural Evaluations

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

This paper describes a nondestructive pavement testing system called the multidepth deflectometer (MDD), which is used to measure depth deflection profiles of pavements. Effective elastic moduli of multilayered pavement structures can be backcalculated from these measurements. This system was developed in South Africa during the late 1970s to enhance the extensive program of full-scale accelerated testing with the aid of the heavy vehicle simulator (HVS). The MDD consists of a series of up to six linear voltage differential transducers (LCDTs) installed vertically into the pavement at preselected depths in a relatively small-diameter hole. Normally the MDDs are anchored at a depth of approximately 2 m below the surface of the pavement. Resilient depth deflections are measured with the MDD in association with a moving load. Case studies of measured deflections are backcalculated effective elastic moduli are given the tests on an asphalt base, a granular base, a cement base, and a concrete base pavement section. The results are interpreted and discussed in terms of the behavioral characteristics and pavement responses, including permanent deformations. It was found that: (1) asphalt bases may become granular after extensive accelerated testing; (2) crushed stone bases may become stronger as a result of trafficking; (3) lightly cemented bases crush near the surface, thus weakening the layer; and (4) one cement pavement debonded from its subbase after 190 000 load repetitions.

The multidepth deflectometer (MDD) system for determining the effective elastic moduli of pavement layers

International benchmark studies confirm that school mathematics and science education in South Africa is weak and suffers from systemic problems. The Teacher Mentorship Programme (TMP) based at the Department of Civil and Biosystems Engineering of the University of Pretoria was borne out of lessons learnt from ongoing outreach and awareness creation projects and recent research findings. The most cost effective and sustainable support for maths and science learners can be achieved by mentoring their teachers in their work environment using experienced teachers as mentors. A pre-pilot implementation was launched in 2003 and a pilot project at five schools in Greater Pretoria (Tshwane) was implemented in 2004. This article describes the rationale behind the mentorship intervention programme, reports on the implementation strategies and makes recommendations based on the lessons learned during this implementation. A review of relevant literature supports the strategies employed.

Emile Horak

Papers

Benchmarking the structural condition of flexible pavements with deflection bowl parameters

Falling Weight Deflectometer Bowl Parameters as Analysis Tool for Pavement Structural Evaluations

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

The multidepth deflectometer (MDD) system for determining the effective elastic moduli of pavement layers

Lessons from a Mathematics and Science Intervention Programme in Tshwane township schools