26 Geological setting
that stress is a tensor quantity and six independent components are
required to characterize the stress state. As an example, if the maximum
stress component is horizontal, a simple and early design step in weak
rock is to orientate tunnels so that they are parallel to this maximum
stress component. This reduces the stress concentrations, a concept
which has been used to great advantage in coal mining in the USA and
China 9.
2.3 Additional points
It is useful to read through engineering geology and structural geology
textbooks and to become aware of the techniques used in these sub-
jects. A good book in this context is Price and Cosgrove (1990) lo which
presents a ”unified approach to the mechanistic analysis of geological
structures”. In the Preface to their book, the authors state that ”... em-
phasis is placed on mechanical principles and the way in which they
can be used to interpret and understand how and why a wide variety of
geological structures develop.”
Thus, rock mechanics and structural geology are inextricably linked.
Whether the rock mass is disturbed by nature or by man, the rock
mechanics mechanisms are similar in geology and engineering; they just
differ in their emphases because of the different volume and time scales.
Our emphasis in the engineering context is on the advantages of under-
standing the geometrical and mechanical features of rock masses which
is further emphasized if one imagines slopes and tunnels constructed in
the many rock masses illustrated in the Price and Cosgrove book.
8Su D. W. H. and Hasenfus G. J. (1995) Regional Horizontal Stress and Its Effect
on Longwall Mining in the Northern Appalachian Coal Field. Proceedings of the 14th
International Conference on Ground Control in Mining (S. S. Peng, ed.) West Virginia
University, Morgantown, pp. 39-43.
Wang Tongliang and Fan Qiuyan (1999) Optimization of Soft Rock Engineering with
Particular Reference to Coal Mining. Inf. I. Rock Mech., Min. Sci., Rock Mechanics in China
Special Issue.
loPrice N. J. and Cosgrove J. W. (1990) Analysis 4 GeologicaZ Structures. Cambridge
University Press, Cambridge, 502pp.