Technology Services for the Asphalt, Bitumen and Aggregate Industries
Pavement Engineering & Field Testing
DAPS™ Software (Deflection Analysis of Pavement Structure)
Pavement structures provide a vital part of our transportation system. Efficient maintenance is necessary in order to achieve maximum cost benefit from the huge investment made by transportation agencies over the years. As part of maintenance planning and analysis, agencies have been making use of deflection testing equipment such as the Falling Weight Deflectometer. This type of equipment yields information regarding the structural performance in terms of deflections that are used to calculate layer stiffness moduli. DAPS – Deflection Analysis of Pavement Structures – is a rapid, accurate and reliable method for performing back-calculation of deflection results. DAPS enables the design of pavements incorporating advanced structural design models. For airport pavements the software follows standard methods such as computation of the PCN & PCR values.
Elastic Analysis Module
The Elastic Analysis module enables the determination of stresses, strains and displacements in a pavement structure under circular uniformly distributed loads (road, port and airport loads). It is possible to consider a maximum of seven layers plus the subgrade, and full or partial bond (slippage) between layers.
The Elastic Analysis module also offers the possibility of generating 2D & 3D graphics that portray the displacements, stress and strain states for a pavement under the action of the considered load. Each point will then be depicted using a color spectrum that relates the magnitude of the selected parameter in each particular coordinate to the maximum and minimum values calculated for the entire pavement section. On the right side of the graphic there will be a color scale, and the corresponding numerical values. Higher magnitude values are represented by the red color, while lower magnitude values will be represented by the blue color.
DAPS will allow to back-calculate FWD tests performed on pavement structures that consist of the subgrade and up to four additional layers. It will also admit an optional bedrock representative layer or to subdivide the subgrade layer. Several soil models can be selected in order to adjust the calculations to each specific test site soil properties.
To initiate the back-analysis procedure of the data obtained in a Falling Weight Deflectometer test campaign, it will be necessary to load the corresponding raw data file or files; DAPS will open any number of raw data files desired by the user simultaneously. DAPS is prepared to read the following test data formats:
DYNATEST (.fwd, .f20, .f25)
The capacity to load more than one file simultaneously means that it will possible to for example, back-calculate all of the tests alignments performed side by side over the length of an airport runway in one single take.
When the back-calculation process is complete, the main window will switch automatically to the results summary table view. This information will include not only the calculated layer moduli, but also the final rms (root mean square) and the amd (absolute mean deviation) obtained for each station solution.
DAPS offers the possibility of determining temperature corrected asphalt modulus, using the BELLS methodology. The batch analysis back-calulation results can be saved to “.xlsx” format files.
The software enables users to conduct airport and airfield strength classification using the methods and procedures officially considered by the ICAO, namely the ACN/PCN and ACR/PCR methods.
The software allows seamless migration of data for pavement designs with the typical mix of aircraft normally considered for the preparation of airport PCN/PCR determination.
Finite Elements Analysis
The DAPS 3D FEM analysis builds upon the 20 node hexahedral isoparametric element, and intends to model all possible types of pavements structures and loads, including the complex main landing gear arrangements of the aircraft listed in the PCN/PCR module. Among others, the FEM model boasts the following features:
Generates the 3D mesh automatically, factoring in the selected pavement structure and load seamlessly.
Allows to consider the subgrade soil as being an isotropic or transversely isotropic material; for the latter option, it is possible to select the ratio between the modulus to be considered for the horizontal and vertical directions (Eh and Ev).
Emulates the horizontal displacement retrrictions imposed by adjacent slabs
Enables the selection of the load imprint geometry (rectangular or square formats)
Obtains a 3D visualization of the strains, stresses and displacements of the pavement structure at the coordinates located closer to the points at the pavements surface where the loads are applied, thus completely depicting the critical stresses & strains.
The FEM is a complex and computationally demanding algorithm; as the model undergoes its development process, care is being taken in order to optimize it as much as possible, and to maintain an adequate balance between speed and accuracy. Therefore, whenever the possible symmetry of the considered load and pavement structure allows it, only a fraction of the pavement structure is indeed modeled, thus greatly reducing the time required for obtaining the final solution.
It is possible to convert your FWD tests (sensor deflections + calculated layer moduli) to a map representation obtained by implementing a Delaunay triangulation to the geo-referenced data.
The resulting surface mesh is painted by comparing the value of the represented parameter in each map position to the absolute maximum and minimum possible values listed in the data set. The value/color scale can be defined in either the absolute magnitude or percentile formats.
The scale can also be inverted in order to better accommodate parameters in which lower magnitude values correspond to better performance (such as measured deflection), or those in which the opposite is true, such as soil moduli.
Although this feature is primarily aimed at the representation of FWD/HWD data and its corresponding analysis parameters, it can be easily used with any other set of geo-referenced data, or even other X Y Z sets of values in which X and Y do not necessarily have to correspond to longitude and latitude coordinates.