Boring Log, Discontinuities, question...
Boring Log, Discontinuities, question...
(OP)
So, I'm going over a bunch of data for a project, and some of it is 30 or so boring logs. 2 of the borings, go about 70 feet into granite. I'm not sure how to interpret a few comments, and some suggestions would be great.
The note says this:
"
GRANITE
Weathering: Generally fresh with some stained joints
Discontinuities: Shallow or low angle joints observed, 6.38', 7.05', 15.05', 16.78', 19.1', 26.57', 31.28', 39.54', 40.06', 42.81', 43.94', 54.52', 58.3', and 59.23'
Color: Pink, gray and black specked to about 20', then black and gray to about 25.6' then gray, pink and black specked to about 39.5' then black and gray to about 42.7' then gray and black specked to 50.5' then gray, pink and black specked to 60'.
Hardness: Very hard
"
What I don't really know how to interpret is the Discontinuities, there are 2 rock boring samples, and all the numbers are different, and there are about twice as many on the second boring.
The note says this:
"
GRANITE
Weathering: Generally fresh with some stained joints
Discontinuities: Shallow or low angle joints observed, 6.38', 7.05', 15.05', 16.78', 19.1', 26.57', 31.28', 39.54', 40.06', 42.81', 43.94', 54.52', 58.3', and 59.23'
Color: Pink, gray and black specked to about 20', then black and gray to about 25.6' then gray, pink and black specked to about 39.5' then black and gray to about 42.7' then gray and black specked to 50.5' then gray, pink and black specked to 60'.
Hardness: Very hard
"
What I don't really know how to interpret is the Discontinuities, there are 2 rock boring samples, and all the numbers are different, and there are about twice as many on the second boring.





RE: Boring Log, Discontinuities, question...
RE: Boring Log, Discontinuities, question...
RE: Boring Log, Discontinuities, question...
RE: Boring Log, Discontinuities, question...
www.PeirceEngineering.com
RE: Boring Log, Discontinuities, question...
RE: Boring Log, Discontinuities, question...
www.PeirceEngineering.com
RE: Boring Log, Discontinuities, question...
The implication of fractures are that there is limited weathering along the joints. Low angle can be a good thing as it's less likely a fracture trend will daylight on a cut face and facilitate sliding. High-angle fractures can be a problem, but you don't have orientation to know the strike of the fractures anyhow.
Where is this site?
f-d
¡papá gordo ain't no madre flaca!
RE: Boring Log, Discontinuities, question...
I just graduated from University and this is one of the first things I have been tasked with. I'm going all over rock mechanics books, and geo-technical books, to get the best understanding I can. But there is really no one who can give me a hand here. As PEinc said for free that is...
RE: Boring Log, Discontinuities, question...
f-d
¡papá gordo ain't no madre flaca!
RE: Boring Log, Discontinuities, question...
Regards.
RE: Boring Log, Discontinuities, question...
http://www
RE: Boring Log, Discontinuities, question...
So far the only thing I have found that could possible lead to that is these fractures mentioned, but I don't know if they tell me that or not.
RE: Boring Log, Discontinuities, question...
RE: Boring Log, Discontinuities, question...
This is a great place to seek knowledge but don't overlook resources at your fingertips. It's entirely possible folks in your company have worked on projects in this area and may be familiar with the characteristics of the rock.
RE: Boring Log, Discontinuities, question...
1.) An engineering geoligist should be able to provide the insite you are looking for
2.) Presplitting can give you nice edges, but if you are blasting a hole you will need to plan for a relief face.
3.) The joints ar 7 feet apart more or less and the rock is higly cometent based on RQD's. I am assuming the breaks are not drilling breaks. The logs do not mention anything such as soft material on the seams that would give the impression that theses seams are large and would relieve pressure.
4)My big question is what happens after the material is blasted and possibly excavated. Fractures are frequently orientated. A fracture at a critical angle with 70 ft of overburden could slide. The owners cookie cutter edges could be the least of your worries. If you have jointing with a 70 ft exposed face, someone needs to consider stability proir to begining work.
RE: Boring Log, Discontinuities, question...
I can answer you number 4, since the hole is 1/2 done, blasted out and excavated, with a ramp. The blasters decided to do it in 2 lifts, so its at about half depth. It is awful, major failures, there is only 1 location that the outcome looks nice. There are parts where instead of a nice clean 90 degree edge it slopes from 10 ft back all the way to the bottom.
One of the blast locations was really strange. They loaded a set of pre-splits, and do to all the fracturing and problems, they reduced the loads in the holes, hopping to have a softer hit and still get the breaking. One of the owners engineers was worried that they would not get any breaking with the reduced load. Instead they got way more. The 20 ft area that was to be pre-split had almost no breaking, instead the wall was failing on ether side as far as 30ft away.
The company has blasted in this area over the last 50 years, and worked in locations near to this one. Never have the blasters had so many troubles. Going into it from the borings they expected the rock to be like other rock in the area. Now that it turns out it was not, I was tasked with going back and seeing if we should have expected this.
All blasting has stopped for the time being, as new plan is being evaluated to go forward and address the stability. I'm not part of that, as my task is to go look back words. I do know we had 3 new borings done (at this 1/2 way point), to compare with the original ones, and they are much much worse. RQD averaging around 75%, where the original ones average at 90%.
My bass says this is the job from hell... Good start for an EIT eh...
RE: Boring Log, Discontinuities, question...