Intelligent compaction with vibratory rollers - Feedback control systems in automatic compaction and compaction control

Dynamic compactors with parameters that adjust automatically to the condition of the subgrade form the basis for intelligent compaction. Dynamic soil compactors create nonlinear vibrations, and the typical characteristics of these vibrations are taken as the basis for the feedback control system for intelligent compaction. With the model of the machine and the soil as the starting point, the periodic loss of contact between the drum and the subgrade is postulated to be the main nonlinear effect. This nonlinearity leads to near periodic and subharmonic vibration phenomena, and it can bring about unstable drum dynamics. The machine behavior can be investigated with the help of the chaos theory. Feedback control systems for rollers are based on the results from the theory of nonlinear oscillations, and they allow optimal compaction performance thanks to continuous adjustment to the compaction status. Starting with large amplitudes and low frequencies, the automatic control system ensures a good depth effect. As the compaction increases, the frequencies rise and the amplitudes are automatically reduced; those actions lead to optimal surface layer compaction at the end of the process. The soil stiffness measurement, which is performed in parallel with the automatic control, is directly correlated with the plate-bearing test to enable continuous compaction control. In conjunction with a documentation system, intelligent compaction makes it possible to prove the homogeneity and the achieved compaction degree. In the field, intelligent compaction ensures that compaction jobs are completed in a minimum number of passes and allows monitoring of results as work progresses. In addition to optimal compaction with no risk of overcompaction, laboratory costs are reduced and process reliability is maximized.