The basis of the patented MDD system is a series of Linear Variable Differential Transducer (LVDT) modules that are mounted on a rod in a 1.5in (39mm) diameter hole in the test section.
Up to six LVDT modules can be mounted at various depths in the hole.

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The modules are anchored to the soil by way of small steel balls that are forced against the walls of the hole.
The reference rod is anchored into the subgrade at approximately 10ft (3m) below the pavement surface.

The LVDT module measures the displacement of the soil relative to the rod to an accuracy of 10 microns.

The top of the hole is sealed with a cap that contains the connector to the data acquisition system.

The reference rod is connected to the anchor rod using a snap head connector so that the MDD modules can be removed for re-use.

Two or three MDDs, with modules at each layer interface, are normally placed in each HVS section. During a test the permanent deformation at each module is recorded, as are the elastic deformation basins under standard test wheel loads.

The plastic deformation data have been used to develop transfer functions relating load repetition to plastic strain in the road building materials.

The deflection data can be used to determine the effective elastic moduli for each pavement layer.

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Dynatest International A/S
Rev. 040101-10