Road Construction Roadway Excavation

Earthmoving Operations-Ripping

The  rippability  of  any  rock  is  materially  affected  by  the  nature  and  composition  of  the  rock. Sedimentary rocks generally offer the best opportunity to rip, whilst metamorphic rocks present
the least opportunity. However decomposed and weathered igneous and metamorphic rocks can often be ripped economically.

Rock with frequent bedding planes and cracks can usually also be ripped economically whereas massive (thickly bedded) rock formations generally must be drilled and blasted.

Some physical characteristics which favor ripping are :-

•    Fractures, faults and planes of weakness of any kind.

•    Weathering resulting from temperature and moisture changes.

•    Brittleness and crystalline nature.

•    Frequent cracks and bedding planes.

•    Large grain size.

•    Moisture permeated clay, shale and rock formations.

•    Low compressive strength.

Ripping will be difficult if the rock formation is :-

•    Massive and homogenous (i.e. lacks bedding planes and cracks).

•    Non crystalline and therefore not brittle.

•    Without planes of weakness.

•    Fine-grained with a solid cementing agent.

•    Of clay origin where moisture may impede ripping because it makes the material plastic.

The following are some further practical matters to be considered when  ripping  –

(1)     When working a cutting always keep the outside deeper than the center. If the center is kept low, all plant tends to work away from the toe of the batter and it is expensive and difficult  to then  excavate the  toe.  In  hard  material,  perimeter  blasting  or  pre-splitting  of batters even when the rest of the cutting is not blasted helps to position the batter toe and tends to stabilize the batter face.

(2)     Rip in straight lines, never turn with the ripper buried as this can result in damage to the tyne tracks and frame.

(3)     Do not leave  blasting until all rippable  material  is removed unless there  is over 3  m of material  still  to  be  excavated.  Shallow  holes  require  an  excessive  footage  of  drilling compared to the volume loosened and as such are uneconomical.

(4)     To obtain penetration the tractor should not be jerked or tracks spun as this causes damage to the unit. Raising the tyne with the hydraulic cylinder will sometimes break out the rock.

(5)     When  working  on  side  drains and  in  the  vicinity  of  batter  toes  the  “radical  arc”  or “adjustable  parallelogram”  rippers  are  preferred  as  the  angle  of  penetration  is  variable, thus enabling material to be both ripped and lifted out.