Methods of loosening materials either by scarifying , ripping or drilling and blasting. Scarifying will be suitable only for loosening thin layers of soil, usually in conjunction with a grading operation . Rippers may be used to loosen soil., decomposed rock and even hard rock provided it is sufficiently jointed and fissured to enable it to be ripped to the required size for the hauling plant and be handled by the hauling plant and where it is to be used in embankments , to meet the size limitations placed on the embankment material by the specification.
Where reasonable production rates can be maintained, ripping is cheaper than blasting.
Methods of loosening materials should be carried out with the minimum disturbance to batters and the sub grade. Where ripping is producing unstable batters, blasting may have to be used to remove the material adjacent to the batter.
Preliminary seismic reports will give some indication of the material rippability and the depth at which the various layers are likely to be encountered. Where doubt exists, monitoring of ripping costs should be undertaken. In particular the quantity of material ripped per hour will indicate when blasting should be considered.
If it becomes obvious that ripping is not economical, or that excessive strain is being placed on the ripper and tractor the rock must be blasted. Continued ripping can in fact make future drilling and blasting more difficult.
Ripping should be discontinued when fragmentation of the rock strata produces rock sizes larger than the specification limits. When this is the case properly designed blasting should produce suitable material for specification requirements.
Where both ripping and blasting is required on the job, works can be planned with sufficient flexibility for ripping teams and blasting teams to be used at appropriate times, in different locations.
It must be appreciated that a change from ripping to drilling and blasting takes time and incurs non-productive costs and delays. By implementing a large scale blasting operation cots can be reduced to be comparable with difficult ripping. Consequently on jobs where most of the rock required blasting isolated areas that may be capable of ripping might well be shot at minimal extra direct cost, offsetting otherwise additional unproductive cots involved in obtaining a ripping unit. Also, better fragmentation is normally obtained if the soil rock is overlain with a collar of rippable work. First part of the earthmoving operations can be accessed here.