Trenching in basalt

[Matty G]

Hi
I'm developing a methodology for trenching in a basalt area in preparation for drain laying. Once the final design drops out I'm expecting several kilometers of basalt will have to be removed. My initial investigations have eliminated explosives due to residents and other existing services. Rotary grinders have been discounted as they do not have enough grunt to break up the basalt. So I'm currently looking at breakers on numerous machines.
Does anybody have any experience with getting through basalt or can recommend an attachment or plant that can break up basalt.

 

[EireChch]

1 - Your best bet would be to talk to a local contractor who has experience in trenching through basalt.

2 - Tell us more about the project, how deep is the excavation , what is the rock parameters (RQD, UCS etc.)

3 - The below Peffifer and Fookes 1994 chart can be used as an initial guide. However, I have seen this bee both very conservative and un-conservative so highlight that the contractor should choose their plant appropriate.

The chart provides recommendations for bulldozers with tail rippers. These will work fine if you have a nice and wide excavation, if you have a very thin excavation and are limited with space you may have to cut and chisel.

 

[Mad Mike]

Basalt like any rock comes in at least a half dozen forms, depending on its hardness, weathering and jointing.

If I needed to trench through several kilometres of the material I would want trial pits excavated every couple hundred meters and, if hard rock is identified as a problem in those pits, a few seismic traverses to use as the basis for a rippability assessment.

In my area, South Africa, the basalt is usually very well-jointed and even the hard rock material can be ripped with a powerful excavator to a fair depth. Every now and then we hit enormous core-stones (kernels) which have to be blasted. In other areas, the basalt is massive hard rock which requires blasting from the onset.

Better to obtain some rock mass parameters before speculating on this...

All the best,
Mike

 

[amlinerrichard]

Have you looked at "microtunneling"? What is the project? Pipelines?

 

[Matty G]

Thanks all - Ive done a little bit more investigation on the project and your comments make sense.

Seems my basalt is not uniform
My trenches are a network of drainage trenches up to 4m deep
Through a existing residential area so blasting is not favorable due to the potential damage to the other services in the area.
Micro tunneling could be an option but not sure how to accommodate the lateral connections.

Have you got any examples of plant that can be used to rip the basalt or other new attachments that are currently being used in the industry

Cheers

 

[cvg]

this can probably do the job

 

[fel3]

In the mid-1980s, I worked on the design for a 2.5-million-gallon (9,500 m^3) reclaimed water storage tank in western Los Angeles County. The Phase 1 project consisted primarily of excavating about 25,000 CY (19,100 m^3) of unfractured basalt along a ridge line to make the tank pad. We had set up the plans and specs for blasting, but the low bidder told us he planned to rip the basalt, which we had not considered. He explained that ripping would be quicker and cheaper and would avoid [1] the complications of blasting near the edge of a residential neighborhood and [2] the political wranglings between the water district (our client) and the small city we were working within. His bid was something like 25% lower than the #2 bidder and when the project was done, he said he had made a nice profit.

The contractor's equipment consisted of two Caterpillar bulldozers:
-- For ripping the basalt: a D-10 with a single 6-inch-wide (150 mm) ripper tooth mounted to a hydraulic ram that was in turn mounted to the back of the D-10 with a large steel plate about 1.25" (32 mm) thick. A D-10 weighs in at about 180,000 lb (82,000 kg).
-- For moving the ripped basalt from the excavation to the fill pad, located in a small adjacent canyon: a D-9 with no special attachments.

To rip a furrow, the D-10 operator used the hydraulic ram to lower the ripper tooth to the surface then continued pushing to lift up the back end of the D-10. Once the ram had done its job, the weight of the D-10 forced the ripper tooth down into the basalt (IIRC, at least 12" or 300 mm). The operator then mashed the throttle and 750-ish diesel horsepower forced the D-10 and the now-embedded ripper tooth forward, ripping a line in the basalt. At the end of the furrow, he turned around and moved over a bit and did it again and again until he had mostly broken up the layer of rock. Then the D-9 and D-10 bulldozed the standing rows between the furrows and the D-9 moved the broken pieces to the fill pad.

During this operation, the contractor lost a few hours due to fatigue failure of the steel plate that mounted the hydraulic ram. It had ripped like a phone book. However, that was the only equipment failure he had to deal with.

==========
"Is it the only lesson of history that mankind is unteachable?"
--Winston S. Churchill

 

[cvg]

unlikely that a ripper tooth on a bulldozer can excavate a 13 foot deep trench for utilities. on the other hand, the vermeer rock saw trencher pictured above is designed for trenching in rock. it will take plenty of teeth as they wear out quickly in hard rock.

 

[EireChch]

Agree Cvg, as I indicated, nice wide trenches a ripper is fine but if your in a residential area where you want to keep your trenches as narrow as possible, then cutting and chiseling is an option but a slow one. A rock saw as cvg shown would be quicker but probably a lot more expensive.

Youll have to see how both work out with your construction cost and time schedule.

 

[cvg]

another option might be to drill and inject chemicals to split the rock, but again expensive to mobilize a drill and still requires a lot of work

 

[Matty G]

Thanks everybody, that will give a few options to investigate.