Brithish Virgin Islands Limestone/Drilled Shaft Experience Question?

[grabens]

I am looking at a drilled shaft project in the British Virgin Islands. Rumor has it that the limestone there is very hard and difficult to drill. This is a design/build project and the contractor is concerned about difficult installation of drilled shaft foundations that could result in cost overruns and project delays. I am trying to confirm this rumor. Does anyone have any experience with drilled shafts in this part of the world? I had to look where in the Caribbean these islands are (map attached)…LOL. Any information you can provide would be greatly appreciated.

Thanks,

Guy

 

[Ron]

What does the geotechnical report tell you? RQD? Unconfined compressive strength? Point load?

 

[grabens]

Hi Ron,

This project is in the research stage. No field or laboratory work has been performed yet. This project is going to be an airport runway extension off the island and out into the Carribean Sea to allow for larger planes to come to the island. Project is estimated to be about $200 Million USD. I am just asking around to see if anyone has any prior knowledge. Thanks for the reply.

 

[miningman]

Never heard of a limestone that can be regarded as tough drilling. Talk to any contractor with experience in the Canadian pre Cambrian, use their estimates and you will come in way under budget.

Had some limited experience with a large water well driller from Michigan who came up North to drill a couple of 26 inch diameter holes 1000 feet long. Lets just say he went back South with his tail between his legs.

 

[BigHarvey]

Limestone can show a UCS between 5 and 180 MPa. 180 Mpa will not be a problem for small diameter drilling ( water well or mining exploration ) but will certainly be one for a pile driller. As Ron pointed it out unless you get an idea of the strength of this limestone. Technically it will be possible to drill the piles even with 180MPa UCS but progress will be slow and this will show in the price. If the limestone is real strong try to limit the diameter of your piles to 1 meter maximum, this will allow several methods of drilling and the price will be better.