Institute of Fundamental Technological Research

Measurements of the state of stress in rocks are of vital importance in mining operations. These stresses are very difficult to measure. The reason for this is the necessity of making measurements inside the rock mass, usually at a distance of several meters from the rock face. Moreover, working conditions in mines are often arduous, which makes the application of more sophisticated measuring techniques difficult.

The paper briefly presents principles of strain determination in steel elements by using photoelastic coatings. Some innovations of the method are proposed, especially in the case of investigations on actual full-size structures. Examples of experimental data obtained by the authors in investigations of engineering structures (full-size elements) are given. Practical remarks on carrying on such investigations are given.

The authors have presented some results of the investigations of plastic deformations in component parts of steel structures obtained by means of photoelastic layer method. Attention was paid to characteristic features of the strain field exhibiting considerable nonuniformity with a stepwise yield zone propagation. Attempt was made to explain the sources of the phenomenon. Possible simplifications of experimental techniques have been indicated.

Describes three dimensional model investigations of a buttress dam. Coating techniques in metal moulds were used to make spatial models with holes and galleries. Gravity loading was investigated, by centrifuge and 'stress freezing' techniques. Non-uniform mass force effects were considered. Hydrostatic pressure at the stress freezing temperature was applied by a lever type loading arrangement. Stresses were determined from the 'frozen' photoelastic effects, demonstrated on slices from the models. Presents some characteristic fringe patterns, stress trajectories and boundary stresses.

A three-dimensional photoelastic model investigation of a body with voids loaded by uniform pressure on the external surface is presented. The model represents a certain rock region weakened by the crossing of a shaft with a horizontal excavation. The ″stress freezing″ technique was applied by loading the model hydraulically in a special container. The results are presented in the form of stress diagrams in the characteristic cross sections. In the introduction a short review of the most important prublications dealing with photoelastic rock investigations in mining is given.

The authors present a certain method of investigation of twodimensional photoelastic models with rigid constraints. It consists in the fact that cementing of constraints with the model is performed under
load, and photoelastic investigation — without external loads.
In the paper are presented advantages of the method , particularly when being used together with a conventional investigation.
The method is presented on an example of a halfplane under uniaxial load, the boundary of which is attached to a rigid constraint of finite length.

The paper contains an example of application of the photoelastic method to designing of a dam buttress. Testing procedures are described, special attention being paid to the method of realization of a uniform loading along the boundary of the model. Program of investigations is suggested rendering it possible to determine an optimum crosssection of the dam buttress.
In the paper is described the optimization procedure of the shape of the dam buttress based on the results of photoelastic investigations. As the optimization criterion is assumed the condition of minimum volume of the buttress at a determined stress value on the upstream side. Optimum section parameters calculated on the ODRA 1204 computer are presented in the form of tables and diagrams.