One of the main characteristics of the development of rock mechanics in some countries is a close cooperation between experts in rock mechanics and workers in related fields, including soil mechanics and engineering geology. The purpose of this chapter is to outline the contribution that engineering geology can make to rock mechanics and to present a few examples of engineering geology studies that have been used in solving some practical rock mechanics problems.
Engineering geology investigations dealing with the influence of geological factors on the physical properties of rock materials and rock masses fall into three main categories:
Systematic study and correlation of the physical properties of the main rock types with the petrogenetic evolution that caused the differences in the properties of these various rock types.
Study of the heterogeneity and anisotropy of both rock materials and rock masses.
Delimitation of rock masses which are approximately uniform in physical properties (quasihomogeneous units).
Delimiting of the quasihomogeneous rock masses is the main contribution that the engineering geologist can make to rock mechanics. This delimiting is based on the evaluation of many complex geologic factors, not on test results alone, and therefore is most effectively done by trained engineering geologists.
The foregoing types of studies are being used in Czechoslovakia for several purposes, including: 1) the compilation of regional engineering petrologic data--that is, the systematic definition of the main rock types of the country in terms of their representative physical characteristics; 2) the determination of effective systems of rock sampling with the aim of obtaining a greater accuracy in interpretation of test results in a given rock unit as well as their extrapolation to similar units; 3) the selection of the most appropriate field and laboratory tests, the most suitable combinations of such tests, and correlation of their results; and 4) the most effective locations for in-situ tests and the extrapolation of the results to surrounding areas of the rock mass by correlation with less expensive rapid tests.
The basic assumption from which all the foregoing studies must proceed is that in order to understand the physical properties and causes of heterogeneity and anisotropy in rocks, we must first understand the origin and geological evolution of the rock masses; such an understanding can then be used to predict the properties of rock masses not exposed for direct observation some users of rock mechanics data often forget that during the evolution of a rock, the rock mass is exposed to constantly changing environments in which it must continually adjust to new dynamic and physical-chemical conditions. The more extensive the changes of conditions the more radical the changes in the mineralogic and structural characteristics of the rock. As a result of all these processes properties such as the strength and deformability of the rocks are changed.
An example of the necessity for analysis of petrogenetic evolution is provided by a quartzite in the Carpathians which is of uniform age and original composition.
In the large area of the Alpine-Carpathian geosynclines huge masses of Homogeneous sand were deposited in a monotonous environment of sea Beaches during the lower Triassic period.
