|MadSci Network: Earth Sciences|
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 (Master's). 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): 136 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
Try the links in the MadSci Library for more information on Earth Sciences.