Riversleigh Field Trip 2014

Fracturing Rocks, New Technology And Bok’s Cordless Triumph

One of the big hurdles in the Riversleigh excavations is the hardness of the limestone rocks. These rocks need to be broken down to examine the contents, and for transportation to UNSW. Aside from sledge hammering the rocks into manageable chunks, we drill holes in the rock and fracture it mechanically or by using light explosives. For smaller jobs, we use a set of metal wedges and shims called “plug and feathers”.

Figure 17: Lizard Cannell filling the drilled holes with light explosives. Photo by Karen Black.

Figure 17: Lizard Cannell filling the drilled holes with light explosives. Photo by Karen Black.

For larger jobs, Chris Larkin and Lizard wire up the drilled holes with light explosives called “red cord” (Figure 17). These are normally used as fuses to detonate explosives but have proven quite suitable for the fracturing of the limestone rocks in Riversleigh. After detonation of the light explosives (Figure 18), the pieces of rock are collected. Adjoining pieces are marked so the pieces can be glued together in the laboratory before being dissolved in a dilute acetic acid bath. As the fossils are tightly bound within the limestone rock, dissolving the glued sections results in intact fossils.

Figure 18: Detonation of the light explosive results in the fracturing of the rock. Photo by Karen Black.

Figure 18: Detonation of the light explosive results in the fracturing of the rock. Photo by Karen Black.

I won the $500 Phil Creaser CREATE prize for presenting the Best Paleosciences talk at the UNSW Postgraduate Research Forum on my Masters of Philosophy project this year (thanks Phil). As the UNSW Vertebrate Palaeontology Laboratory has been providing me with a lot of support, I decided to plough this prize money back to the laboratory by purchasing a cordless 18 volt Lithium-Ion powered rotary hammer drill and accessories. We tested this equipment during our field trip.

Figure 19: Sledge hammers resulting in spherical boulders.

Figure 19: Sledge hammers resulting in spherical boulders.

Our first test was at the JDM site. There was this one stubborn boulder that started off rectangular in shape. Each blow of the sledgehammer chipped off the edges, finally resulting in a spherical boulder. Like an egg, the spherical boulder was mechanically in the best shape to withstand the hammer blows and we spent over an hour trying to fracture it (Figure 19).

Figure 20: Drilling three holes in the spherical boulder.

Figure 20: Drilling three holes in the spherical boulder.

With Lizard’s guidance, I drilled three 22mm diameter holes in the spherical boulder about 10 cm deep (Figure 20). This exercise drained almost three of our four Lithium-Ion battery packs.

Figure 21: Plug and feathers.

Figure 21: Plug and feathers.

We inserted two shims (feathers) into each hole, and then drove in the wedges (plug) with light hammer taps in sequence (Figure 21).

Figure 22: The cleanly split boulder.

Figure 22: The cleanly split boulder.

Success! The boulder fractured along the line of drilled holes (Figure 22).

Lizard later used the cordless rotary hammer drill at a site that Mike discovered last year. He drilled a series of three 16mm diameter holes about 400 mm deep draining just two of the Lithium-Ion battery packs. This cordless rotary hammer drill proved a success and they named this new site Bok’s Cordless Triumph (Figure 23).

We hope to use this portable drill for smaller jobs in the future as it provides the excavation team with the ability to split large boulders in remote areas and in difficult terrain (such as steep slopes) without having to transport the large generator required by the corded drill. We may need more Lithium-Ion battery packs which we can charge at Adels Grove, or charge the batteries using a smaller generator on site.

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