QUESTION
Has anyone used Gneiss as an aggregate for structural fill?
If so, is there any good FHWA literature on the material, which discusses its typical aggregate values like LA fragmentation, crushed and rounded particles etc. I have seen online that LA for Gneiss can range from 30-60.
The request stems from a client of ours who is looking to supply this aggregate to their client. But their client has aN LA fragmentation limit of 30, which I feel is too stringent. The Design Manual for Roads and Bridges (DMRB) allows an LA value of up to 50.
If anyone knows of any other standard which has less stringent LA values or specifically information on Gneiss I would love to hear it.
REPLIES
Mad Mike
So gneiss is effectively a granite which has undergone enormous compression under ductile conditions (deep in the earth a long time ago), such that it’s mineral constituents are now strongly aligned, or “foliated”. The foliation is usually produced by mica.
The term “gneiss” is very generic, and covers a whole family of layered, granite-like rocks.
In my area (South Africa) some of the gneiss is horrible material- there can be such enormous variation between the layers that it becomes impossible or impractical to separate and control during construction. On the other hand, I’ve seen gneiss which behaves effectively as a granite and is reasonably consistent.
Watch out for large amounts of mica in the gneiss, which makes it very friable and susceptible to flagging, among other things.
Doesn’t answer your question, but some geological context to consider.
SOURCE
https://www.eng-tips.com/viewthread.cfm?qid=459764
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