[Back]

C. Müller:
"The Light Falling Weight Device";
Supervisor: D. Adam, F. Kopf; 221 Grundbau und Bodenmechanik, 2003.

In this research project the dynamic load plate test in the form of the Light Drop Weight Tester is investigated both theoretically and practically. Moreover, several commercial devices are tested with regard to their reliability and practicability.
The Light Drop Weight Tester provides the dynamic deformation modulus, which is used to evaluate the stiffness of the tested subsoil. The required loading is produced by a falling mass, which transfers a defined impact via a spring-dashpot-element to a circular, rigid load plate being in full contact with the ground. The dynamically measured maximum deflection of the plate is used to determine the deformation modulus taking a constant soil contact pressure into consideration.
In the first section of the research report history and development of dynamic load plate tests are presented; furthermore, standards and regulations dealing with the Light Drop Weight Tester are discussed.
In the scope of theoretical investigations a mechanical modelling is set up for the dynamic interaction system. In a first step the device and several different soil models are treated separately, in a second step the systems are coupled by means of the compatibility requirements using the substructure technique. Calculations and parametric studies are carried out using these models simulating the complex motion behaviour of the Light Drop Weight Tester. Parameters influencing the dynamic deformation modulus can be detected and the essential phenomena occurring in practice can be understood and explained.
Measurement results of large scale tests under exactly defined soil conditions are analysed on the basis of the theoretical mechanical models and, furthermore, the measured data is compared with the results of the theoretical calculations.
The results of in-situ dynamic load plate tests are compared with measurement data of traditional and innovative compaction control methods (static load plate tests, determination of density with the nuclear gauge test, continuous compaction control).
Finally, technical prerequisites and demands are made on the device and, moreover, recommendations for regulating the standardised application of the Light Drop Weight Tester are specified.