The rippability of rock

Since ripper tynes were attached to bulldozers, over thirty years ago, there have been problems determining whether the rock on a particular excavation site could be ripped or would require blasting. Several methods have been developed for determining the rippability of rock but, in general, they have been based on very limited data and experience has shown them to be inaccurate. An extensive database of ripping and geological data has been obtained from observing excavation of 19 rock types on 15 sites by a range of bulldozers. This database has been statistically analysed to determine which factors have the greatest influence on the rippability of an area. Analysis has produced a new method for estimating the likely productivity of a site when certain geological parameters are known. Detailed seismic refraction arrays were performed on excavation sites in an attempt to determine whether seismic investigation techniques could be improved. Numerical modelling of the ripping process was attempted but had limited success although it was useful in assessing the influence of different defect orientations and boot angles on the ripping. Laboratory scale modelling of a ripper tyne penetrating and ripping artificial sandstone was performed. The results were compared to full scale bulldozer trials where the ripping forces were monitored by strain gauges attached to the tyne. The laboratory modelling showed that there was a parabolic relationship between ripping force and depth, and also between ripping force and unconfined compressive strength. The relationship between force and depth was confirmed by the bulldozer trials. It is shown that existing methods of prediction are inaccurate and that the new method is superior, but that there are still uncertainties possibly due to local variability of geological conditions and the influence of the operator