Deep Ripping and Rehabilitation 1

From Gil Fletcher LRS Environmental Townsville gil@lrsenvironmental.com 

Deep Ripping and Rehabilitation: Why rip?

Over the last 30 years of practical rehabilitation experience in the coal mining industry in the Bowen Basin and as a hay mulching contractor on civil projects I offer the following discussion on ripping. 

Recent observation of rehabilitation that has not employed deep ripping but has relied on an erosion control using hay crimping or mulching techniques have  had limited erosion control and infiltration into the topsoil/subsoil profile leading to early drying off of pasture grasses from poor water storage.

Below is my history of ripping and having been a contractor with hay mulching equipment I feel that recent development by civil engineering erosion control contractors to minimise ripping in favour of hydro mulching, dry hay mulching and crimping is not recognising the important aspect of preparing the reshaped spoil and soil profile to collect and store adequate soil moisture. This is achieved by deep ripping. Most dozer reshaping of spoil results in an upper slope of cut material and a lower slope of fill material with the upper slope compacted by dozer traffic as well as pressure glazing of the final surface. The lower slope is probably less compacted but probably of a sufficient compaction to hinder water infiltration.

I fully endorse the techniques of hay mulching and hydro mulching after deep ripping to provide further erosion control and protection of the seed bed from raindrop impaction and to extend the effective germination period for each rainfall event by reducing evaporation and drying.

In the early 1980s I used ripping with three standard dozer tynes to provide initial erosion control. The rip lines were approximately on the contour using surveyed form lines at intervals down the slope. A technique worth continuing with into the future. Successful except with intense early summer storms. The standard dozer rip lines tended to seal over quickly in intense rainfall events. 

The criticism of standard dozer tyne ripping was that the rip lines could become erosion gullies if not placed accurately on the contour. To counter this a techniques of discontinuous rip lines was proposed which relied on ripping for a short distance, say 20m, and then lifting the ripper tynes out of the ground for, say 2m,  then re- commencing the rip line.  I don’t know who proposed the idea. It did seem reasonable but when I tried this technique it proved worse than the standard technique as the water collected in the 20m length was sufficient to overflow one end of the rip line and flow into the lower rip line and so on down the slope producing a pattern of zig-zag erosion gullies. I read that this technique was recommended for one of the proposed coal projects in the Galilee basin, which has the same erosion prone spoil as the Bowen Basin.

To increase the capacity of the rip lines I developed as set of moldboards mounted on the upper section of the ripper tyne which had the effect of producing a wide V shaped section on the upper half of the rip line. Water storage capacity increased and thus larger storm events could be stored before runoff occurred. The moleboards were hinged so that they would pivot by approximately 900 to allow large rocks to pass without damage to the moleboards.

The inherent problem with both these forms of ripping was the friction sealing of the sides of the rip lines resulting in reduced infiltration into the undisturbed ground between the rip lines. The development of a wing keel ripper tyne, which I first encountered at the Ensham coal mine, was the next logical step. This tyne, I think, originated in Western Australia, but Terry Short, the then enviro at Ensham would have the details. The wing keel has stubby wings approximately 300mm long and angled up at the rear to push the spoil layer upwards during forward travel resulting in fracturing of the spoil layer and dramatically increasing the storage capacity of the ripped spoil layer. The fracturing is evident in adjacent areas not immediately above the passage of the wing keel boot. Personal observation of storm events can attest to the greatly increased water storage capacity and thus initial erosion control.

The wing keel boot is fitted to a single standard tyne of a D10 or similar dozer with the power to penetrate and to a depth of at least 900mm. I have supervised jobs where two tynes were fitted to the outer tyne bosses on a larger HD41 (D11) type dozer and the same deep ripping pattern was obtained. 

The ripping pattern involves ripping out a contour form line and then turning to one side of the line for the return rip and placing the dozer track closest to the previous rip line to run along and on the closest dozer track print of previous rip line. This results in a uniform distance between the rip lines and double cultivation of the dozer tracks. From experience the double cultivation actually provide a very good germination bed and results in very little erosion although the dozer grouser plate marks are down hill. The effect of the single pass deep ripping minimises the upheaval of spoil above or into the topsoil, while minimising the catching and dragging of large rock that can occur with three standard tynes. 

The single rip line per dozer pass allows for hay mulching and planting equipment traffic onto the ripped site with limited disturbance to the ripping pattern, provided the equipment does not travel across the rip line.

Ensham Ripper Tyne 1.jpg

Ensham Ripper Tyne

 

The stubby wings lift up the soil and fracture the spoil/topsoil profile. See next photo

Ensham Ripper Tyne 2.jpg 
Ensham Ripper Tyne 3.jpg

Ripping pattern.

 

The ripping pattern minimised the amount of rock brought to the surface and the double cultivation of the dozer tracks provides an ideal germination seed bed. The rip pattern stored more water than any other previous ripping technique.  The dozer tracks allow access for planting and hay mulching equipment.

    
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