Bearing Capacity - Fractured Bedrock
Bearing Capacity - Fractured Bedrock
(OP)
My question pertains to the bearing capacity of fractured bedrock. I'm dealing with spread footings placed on some pretty well fractured rock. I'm working in a new area and we don't have this problem back home. I've been giving it lots of thought, talking it over with my boss and experienced contractors onsite, so I am slowly gaining a better perspective of the issues, but I still feel as if I'm missing something.
If anyone could suggest some good references for reading material on the subject and/or simply provide some tips regarding the key issues to watch for when dealing with fractured bedrock in compression, I would really appreciate it. I imagine my question will grow from there.
Thanks
If anyone could suggest some good references for reading material on the subject and/or simply provide some tips regarding the key issues to watch for when dealing with fractured bedrock in compression, I would really appreciate it. I imagine my question will grow from there.
Thanks





RE: Bearing Capacity - Fractured Bedrock
RE: Bearing Capacity - Fractured Bedrock
I guess my question is this; is the lower bearing capacity of fractured bedrock based only on the fact that once loaded from above, these fractured pieces may be pushed out along the fracture planes? If so, then are there any concerns if the excavated area is supported on all sides by undisturbed bedrock and backfill material?
RE: Bearing Capacity - Fractured Bedrock
RE: Bearing Capacity - Fractured Bedrock
For the USACE Manual Site: http://www
For the Rock Foundations Manual:http:
RE: Bearing Capacity - Fractured Bedrock
Based on those findings, other issues besides bearing capacity may govern. For example, if the fracture line is neutral, it may still affect the FS against sliding. Once you converse with the engineering geologist, then I would look at the book by leggett "Geology and Engineering" to help gap the link to geotechnical design. If the ground water is shallow, I would also do scour study.
RE: Bearing Capacity - Fractured Bedrock
if the excavated area is supported on all sides by undisturbed bedrock why aren't the foundation elements suuported likewise?
RE: Bearing Capacity - Fractured Bedrock
A basic issue in dealing with "pretty well fractured" rocks (where I am it's inevitably fractured) is that you have isotropic conditions, so failure planes are approximatively equal to failure planes in soils.
This makes things a lot simpler.
what I usually do is to start the Roclab freeware (www.rockscience.com, Hoeck's website), enter my input parameters, get my output phi and c', and use 'em in bearing capacity formulas.
The roclab freeware in the opinion of the (very qualified) authors yields more realistic values of resistance parameters than the conservative RMR method, in weak and fractured rocks.
I usually get bearing capacity values in the region of a few megapascals, depending on the input parameters. Again, in isotropic or quasi-isotropic condition (well fractured rocks) Roclab is darn good.
I would experiment with various input conditions to get a reasonable range and a reasonable lower bound for bearing capacity.
Yet, I would try to detect potential weaker sliding surfaces, clay fillings, weak areas and so on, just to sleep well at night.