DYNAMIC DEFLECTION MEASUREMENTS UNDER MOVING WHEEL LOADS

The Institute for Roads, Railways and Rock Engineering (ISETH) has in the neighbourhood of Zurich a circular test track for road pavements: "the rundlauf". The five test fields (one with gravelly sand base, four with cement stabilized base) are built in a concrete casing of 32 meters diameter. The loading machine is constructed with three turning arms, each supplied with one dual truck wheel (wheel load: 5-8 tons/max speed: 80-60 km/h). Not only are routine measurements done on the test pavement but the test track is also an ideal site for trials of new measurement techniques or new equipment. In the framework of the research it is necessary to detect at the same moment the deflection and strain values in a single point in order to verify the structures in an analytical model (program BISAR). The static deflection measurements made till now (Benkelman beam) have not allowed to consider the influence of speed. In order to obtain deflections under the moving wheels (speed 7-80 km/h) the following equipment has been tested: optical-electronical system: a light spot is emitted by a laser or an infra-red diode and modulated by the moving point; a special camera transduces the optical signal into an electrical one corresponding to the amplitude of the movement; inductive deformation transducer; geophone: the deflection is obtained by integration of an acceleration. The equipment, the practical experience and the limits of application for each system are described in the following paper. (Author/TRRL)