MadSci Network: Earth Sciences

Re: Do you know of any research on rock fractures caused by excavation methods?

Date: Fri Apr 27 12:16:33 2001
Posted By: David Smith, Faculty Geology, Environmental Science
Area of science: Earth Sciences
ID: 987723012.Es

Your question is a quite sophisticated engineering and rock mechanics 
question and your location leads me to wonder if you are concerned with 
the tunnelling to be done in association with the Yucca Mountain 
repository.  I do not know your level of expertise, but I hope my brief 
answer will steer you in a productive direction.  To answer your question 
in detail will require a sophisticated mathematical background on your part 
and the willingness to read a great deal of technical literature.  I would 
not try to answer your question completely without the better part of a 
year to devote myself to the study of the (enormous) body of literature on 
tunnels and rock mechanics.  A quick search of the Bibliography and Index 
for Geology (available in many University libraries in paper or on-line) 
turned up the references at the end of this message, which would make a 
good starting point.  These are only a quick sampling and your question 
demands much more detailed research.  You should read these carefully and 
then read the papers that they refer to.  For a good primer in rock 
mechanics, start with Fundamentals of Rock Mechanics, by Jaeger and Cook, 
published by Chapman and Hall, London.  If you can survibe their math, you 
will probably be able to tackle the relevant papers.

There are several potential problems in tunnels.  Rock burst, which results 
from the formation of a free, low-stress surface in an anisotropically 
stressed rock body, leads to spalling of the tunnel wall along fractures 
parallel to the wall (much like the exfoliation joints in Yosemite or other 
granite domes.  Tunnels may also cross pre-existing fractures and change 
the stress field across that fracture, leading to slip on the fracture or 
other effects.  A single blast charge will produce extension fractures 
(mode I fractures) that radiate away from the charge, however, multiple 
simultaneous or sequenced charges are normally used in excavation and can 
lead to very different fracture patterns.

Any fracture that cuts rock in the tunnel wall instead of within the rock 
body to be removed represents wasted energy and therefore wasted money 
(since you have to spend money on dynamite, drill bits, boring machine 
cutters, etc.)  A lot of time and effort has gone into minimizing the 
energy input needed to do excavations and minimizing thre disruption of 
surrounding rocks. These references should get you started.  The McKown and 
others reference is from an annual conference proceedings that looks like 
it will contain a lot of relevant papers for you.  I would try not just to 
get hold of that one reference, but to actually locate the entire 
proceedings volume for each of a number of years.  Also, check the annual 
indexes (usually in the December issue) of  journals such as Journal of 
Engineering Geology or Rock Mechanics and Rock Engineering I would start 
with the UNLV geology or engineering library.

 Gupta, I. C. ; Prem, K. S. Dynamic rock behaviour in tunnelling, in  Jain, 
O. P., ed., International symposium on soil structure interaction (1977): 
25-32.  Sarita Prakashan, Meerut, India

Bedell, Geoffrey Charles, The effect of macrofractures on fragmentation by 
blasting.  University of Utah, Salt Lake City, UT, United States 

Dershowitz, William S. ; Hermanson, Jan ; LaPointe, Paul ; Follin, Sven, 
Scale effects related to fracture intensity.  Geological Society of 
America, 28th annual meeting Abstracts with Programs v. 28, no. 7 (1996): 

McKown, Andrew F. ; Thompson, David E., Experiments with fracture control 
in tunnel blasting, in Einstein, Herbert H.; Scandariato, Diane P., eds., 
Rock mechanics from research to application.  Proceedings - Symposium on 
Rock Mechanics 22 (1981): 237-244.  A.A. Balkema, United States

Broch, E. ; Soerheim, S., Experiences from the planning, construction and 
supporting of a road tunnel subjected to heavy rockbursting.  Rock 
Mechanics and Rock Engineering v. 17, no. 1 (1984): 15-35

Kobayashi, S. ; Tamura, T. ; Nishimura, N. ; Mochida, Y. Stresses and 
deformations around tunnel face in soft rock, in Akai, Koichi; Hayashi, 
Masao; Nishimatsu,Yuichi ; eds,Weak rock; soft, fractured and weathered 
rock; Proceedings of the international symposium on weak rock; Vol. II 
(1981): 813-818.  A.A. Balkema, Rotterdam, Netherlands

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