The dynamic stress applied to the formation levelto be tested is similar in intensity and frequency to that caused by the passage of an axle loaded to 13 tonnes and travelling at 60 km/h. It is generated by the fall of a weight on a shock absorber spring placed on a load plate.
The soil deflection caused by this pulse and the impact force are measured as a function of time.
The combination of these two parameters during the loading phase (force build-up) in a force-deflection diagram, such as the one shown here, allows the dynamic deformation modulus of the structure at the test point to be calculated directly. The device is mounted in a fixed position on the chassis of a light vehicle.
• the shock generator is made up of the falling weight, the maneuvering cylinder which also ensures the guidance of this weight, the damping spring block, and the triggering hooks.
• the sensors integrated in the load plate are the force sensor consisting of three highly rigid piezoelectric washers, and the non-contact displacement sensor mounted on a suspended and damped base.
• the maneuvering frame with the fork, the tilting cylinder, and the hydraulic unit.
• the distance travelled encoder for the location in the longitudinal profile.
Placed inside the cabin, the electronic system consists of:
• an interface box with the power control order for the automation and conditioning force and displacement sensors.
• a portable industrial microcomputer and an electronic box with an analogue to digital conversion card, a counting card.
• a resident software application for ordering the automation, acquisition, data processing, and display of results.