Perspectives on Rock Behavior

State-of-art testing equipment allows new types of testing procedures to determine the mechanical parameters of joints and intact rock. High-response servo hydraulic systems with digital control technology, strain measurement equipment mounted onto the specimen and programmable control modes, enable new types of test procedures to be performed, which are tailored to the specific problem.

Rock mechanics laboratory tests contribute to understanding the behavior of the rock mass. Knowledge about mechanical properties of single rock specimens is just a statistically small representation of the global rock mass behavior.
The correct interpretation of test results depends on the quantity and especially on the quality of the laboratory tests with the goal of obtaining as much information as possible about the rock properties from each test or group of tests. In order to describe the behavior of rock and the rock mass, various parameters are used. Which parameters are used and how to get those parameters is one of the most intriguing questions in rock engineering.

Relevant boundary conditions for a certain project should be discussed in the investigation phase. The analysis of such complex matters requires a cooperation between geologists, geophysicists, engineers, and possibly experts from other fields. If a non comprehensive view is considered we can not expect reasonable results. Many parameters can be measured and calculated, but there are limits. The determination of these parameters in laboratory tests is an essential part of the characterization process. Because rock and the rock mass is inhomogeneous, we have to deal with wide distributions in the parameter values and to determine which parameters are necessary for a given rock or rock mass to properly convey lab behavior to the real situation. A data base system and statistical analyses are necessary to compile the test results and to make them available to the general engineer.

Teamwork between geologists and engineers, the laboratory and designers is necessry to adequately characterize complex geologic situations for engineering purposes. Specimens for rock testing that are representative of the rock mass behavior are extremely difficult to obtain. Even drilling cores, which are suitable for uniaxial or triaxial tests, often cannot be used due to sample defects. Therefore this biased selection of the specimens can have a great influence on the results.

This is especially true for soft rock or highly fractured rock, where the mechanical parameters are even more important for stability investigations. Putting numbers to the rock and rock mass behavior will always be a challenge, appropriate testing procedures and analyses are the first step for a more realistic evaluation.