An analysis is given of a case history of the deterioration of a gallery along a long wall coal panel during the extraction of the coal. Many observations have been carried out during the winning of the panel and additional information was gathered during the winning of a second coal panel along the other side of the same gallery. The research gallery followed the strike of the seam. The dip of the coal seam was about 13 degrees in northern direction. The main elements and steps necessary for the analysis of the gradual deterioration of the gallery are described. The influence of the development of interacting fracture and failure mechanisms in the rock in a large area around the gallery is shown. A clear distinction has to be made between the primary fracturing processes, gradually developing into more complex fracturing systems, and the ultimate signs of failure in the gallery. The failure has to be seen as the result of the periodic development of fracture systems, related to the propagation of the coal face. The case history will be explained by a series of drawings. This article contains the approach of the basic phenomena of fracture and failure as an introduction in the phenomenology of brittle fracturing. A description is given of the case history with the course of the survey at the mine, the ordering of the different types of observations and the final analysis with the development of the diverse mechanisms in time. The description of this case history has to be seen as an example; the complete study is given by Gramberg (1969).
A failure of an excavation is in our opinion the final result of a process of interaction between a series of basic mechanisms, primary, secondary and more complicated combined mechanisms developing in time and in three dimensional space. This results in large deformations, making an excavation unfit for industrial use. Each mechanism has its own time scale and the result of one mechanism may cause the triggering of another. The mechanisms can propagate intermittently or may occur with a certain periodicity. The mechanisms are strongly influenced by the rock mass properties, including geological features, the destruction type of rock (brittle, non-brittle) and the loading history(-ies) (propagation rate of the front, excavation method, etc.). In solid rock the process of failure starts with permanent deformations, as a result of primary fracturing, developing via a number of successive elastic and cataclastic processes into the final failure of the excavation. In order to compose a more or less complicated case history a thorough knowledge of the destruction process of rock is required. The history of the knowledge of rock failure starts at the findings of Coulomb in 1783. His theory was firmly supported by the tests and analyses of Mohr between 1900 and 1912 and ever since failure is associated with the generation of shear fracturing following a pattern of conjugate oblique directions.