brittle vs. ductile behavior in carbonates (dolomite vs. limestone)

[coreman]

Does anyone have any references which will describe the term &quot;brittleness&quot; in rock mechanics terms?&nbsp;&nbsp;I'm trying to get a handle on the relative &quot;brittleness&quot; of a dolomite versus a limestone.&nbsp;&nbsp;This is specifically in reference to the formation of fractured super K (permeability) in thin-bedded dolomites, sandwiched between limestones.&nbsp;&nbsp;The theory is that the dolomites are more brittle then the limestone, and tectonic events which deform (i.e., ductile behavior) the limestone will fracture the dolomite (i.e., brittle behavior), creating super-K intervals.&nbsp;&nbsp;I've tried a few of the available web sites for civil engineering, but haven't found any good answers yet.&nbsp;&nbsp;<br><br>Any ideas, short of actually measuring the properties?&nbsp;&nbsp;.&nbsp;&nbsp;If we did measure the properties, what would be the parameters which would define the term &quot;brittle&quot;.&nbsp;&nbsp;I know the common stuff like using the triaxial yield points versus the failure point to evaluate the ductile versus brittle failure, but are there any guide lines, general references or studies which define a given rock type as more or less “brittle”?<br><br>Do you have a reference to the experimental work with dolomite and limestone?&nbsp;&nbsp;or any other associated references I can read through?&nbsp;&nbsp;The major problem will be that there is generally no unfractured core recovery from these dolomite intervals,&nbsp;&nbsp;so I don't think we could get a decent set of plugs to look at.&nbsp;&nbsp;I can show that this has happened by looking at the core, and postulate that the differences in &quot;brittle vs. ductile&quot; behavior is the root cause, but that doesn't give the engineering gang any hard laboratory data.<br><br><br>Regards,<br><br>Jack D. Lynn<br>

 

[derubertis]

A couple of general references you might find helpful are (1) Chapter 4 (Brittle Failure of Rock) by Evert Hoek in Rock Mechanics in Engineering Practice by Stagg and Zienkiewicz and (2) Chapter 8 (Strength) by John Franklin in Rock Engineering by Franklin and Dusseault.&nbsp;&nbsp;On page 258 of (2) you'll find a clear definition of the boundary between brittle compressive shear rupture (Region III) and ductile rupture (Region IV).&nbsp;&nbsp;An interesting paper describing some aspects of brittle and ductile behavior in limestone and dolomite is &quot;Relationship of Fault Displacement to Gouge and Breccia Thickness&quot; by E. C. Robertson in the October 1983 issue of Mining Engineering.&nbsp;&nbsp;You might want to consider cross-hole shear wave velocity measurements as a way of distinguishing the differences in the mechanical properties of limestone and dolomite.<br>