Maximilian SCHMITTER

Numerical and (semi)-analytical modeling of deep vibratory compaction (in German)

This doctoral thesis deals with numerical modeling of Deep Vibratory Compaction, used to compact non-cohesive granular soils in deep regions. Inside the vibrator an unbalanced mass excentric with respect to the (vertical) axis of symmetry is mounted, which applies by rotation the centrifugal force into the soil. The vibrator is connected via extension tubes to a crane. During application, at first the vibrator is embedded in the soil at the desired depth into the soil. Subsequently, supported by water jetting, the centrifugal force compacts the soil progressively from the bottom to the free surface. As state of the art, online compaction control is based on the electric current consumption of the imbalance engine. Up to now, however, the relationship between electricity and soil compaction has not been verified. In fact, the efficiency of soil compaction depends on the machine operator. The aim of this work is to model Deep Vibratory Compaction numerically, in an effort to select the relevant physical properties of soil compaction and subsequently to develop a simplified mechanical model.

Numerical modelling of Deep Vibratory Compaction considering all nonlinear properties of the soil and vibrator-soil-interaction is complex. In this doctoral thesis some physical properties of this problem are investigated. These numerical studies are based on different numerical discretization strategies and variations of the excitation frequency of the unbalanced mass rotation. The contact condition between vibrator and soil and the influence of the compaction degree on the system response are studied. The soil is assumed to be linear elastic with adapted material parameters in the sense of a current state simulation. Based on the outcomes of these numerical studies it can be conduced that the contact behaviour of the soil is a non-sensitive property. Assuming rigid bound between vibrator and soil, methods of linear algebra can be used to describe the vibrator-soil-interaction system. For vibro excitation the most relevant mode shapes were computed, which mainly describe shear deformations of the soil. In addition, modal analysis can reduce the number of degrees of freedom without significant loss of accuracy of the results. Progressive soil compaction is described by a priori defined compacted sections to show their influence on the vibrator amplitudes. In order to provide a measure of soil compaction, the equations of motion of a simplified mechanical model of the vibrator-soil-interaction system are solved for the soil parameters. These parameters are determined using numerically generated data of a more complex numerical model. With this method, the value of the Young´s modulus, specified in the numerical simulations, could be identified up to a constant offset from inverting of the simplified mechanical model.

back

Nach oben scrollen