The use of models made of equivalent materials is a universally acknowledged method of investigation. Proposed and developed at VNIMI (All-Union Scientific-Research Mine Surveying Institute), it is being used ha scientific institutes doing research on rock mechanics and rock pressure phenomena in varied mining-geological conditions and on a wide range of technical mining problems. The method has recently been increasingly recognized abroad.This book deals with the latest progress in development of this method. It gives a very complete and systematic exposition of the theoretical principles of the method and the techniques for its application. The theoretical principles of equivalent-material models have been developed further, giving a sounder basis for selection of criteria of similarity of materials in work on problems characterized by the mechanical state of the solid rock and the conditions of its fracture. The need for such development of the method is urgent in connection with the extension of its range of application.A thorough going examination of the initial state of the solid rock, its mechanical properties and the parameters and depth of the working has enabled the authors to make quite accurate determinations of the range of application of three-dimensional and plane models. They give an estimate of the errors involved in determining the stresses in roof strata with a plane model, and show how to allow for them.The authors have developed sections dealing with preservation of the initial and boundary conditions in the models, the choice of equivalent materials for solving various problems, selection of model scale, and methods of determining the mechanical characteristics of the material. They give a fairly complete description of the methods developed by themselves for testing equivalent materials for strength, and of the devices used for this purpose.The book explains the methods and apparatus most widely used at VNIMI and other scientific organizations for observing displacements, deformations, and states of stress in the rock and in the model, together with structures imitating the operation of the supports at the face and their interaction with the wait rocks.The authors generalize the methods of investigation based on models, and give methods of processing the results. This generalization of methods of testing models and use of standard methods of processing results is very useful for getting comparable data.Of great value is the development of a method of using models to study phenomena connected with blastings. The book analyses the action of waves on the stability of exposed rocks, and shows the possibility of investigating the influence of wave processes on plane models of limited dimensions. The authors give criteria of similarity which must be observed in making models of the action of blasting and methods of achieving such similarity in models made of equivalent materials. They develop technical methods of setting up the experiment.The provision of a sound basis for model research on the a...

Abutment pressure is one of the main sources of the complications involved as the depth of mine workings increases in the Prokop'evsk-Kiselevsk region of the Kuzbass. Its effect is to reduce the stability of the solid coal and the roads driven in the seam. Particular difficulties occur where abutment pressure zones originate from contiguous takes or where they lie on a boundary with upper levels already worked out (zones of residual abutment pressure).Planar models made from materials with scaled properties were used to study abutment pressure ahead of a face advancing in the direction of dip. These planar models simulate workings of considerable extent, for which the ends have no effect on roof deformations. Conditions of this kind will be found where a large area along the strike of a seam (e.g., a take 200-300 m in length) is being worked by a shield system, or where the pillars left between the shields are allowed to break up.The models were made on a test rig enabling us to study the effect of the surface on deformation of the strata, and the way in which the abutment pressure was formed, A 1 : 100 scale model was made of an area of solid rock 200 m deep and reaching 230 m across the strike (Fig.

The optically sensitive materials --epoxy gels --developed in the Rock Pressure Laboratory of the Skochinskii Institute of Mining are a pale yellow transparent elastic material with a high optical sensitivity (3000-3400 units -i0-') at room temperature and a very modulus of elasticity (usually less than 2-25 kgf/cm z) [I]. As a result of their high optical sensitivity, epoxy gels can be used successfully to make photoelastic gauges for measurements in such relatively soft media as equivalent materials.This possibility was noted by MalkisAt the Institute of Mining of the Siberian Branch of the Academy of Sciences of the USSR, epoxy gel gauges are used to investigate deformations and stresses in planar models of equivalent materials in research on the stress--strain state of the stowing during working of steep seams.The FDP-ID gauges operate in transmitted light and are small cylinders 20 or 40 mm in length; they are made of epoxy gel and have an axial hole.The gauges have an external diameter of 10 or 18 mm; the axial hole diameters are 2 and 3 mm, respectively.One (for the I0 mm gauges) or three (for the 18 mm ones) scale circles are marked on the front face of the gauge to serve as a coordinate grid for observing the optical pattern within it (Fig. la).In addition to these FDP-ID gauges, intended mainly for operation as deformometers, there are FDP-OS-I gauges, intended to operate as stress gauges.These differ from the former by the fact that they are additionally equipped with Plexiglas rings in which the sensing elemsnt of epoxy gel is enclosed (Fig. Ib). Note that during the manufacture of epoxy gel gauges a preliminary optical pattern in the form of narrow annular isochromes is near the outer and inner edges of the gauges; this must be taken into account when the readings are interpreted.The gauges are designed to operate in transmitted light and can be used with any polarlscope of transmitted light.To observe the optical pattern in them, one can use with good effect magnifying glasses or special lenses which bring the objects observed nearer or magnify them.Before us the gauges were calibrated in a special loading chamber, consisting of a transparent vessel measuring 20 x 20 • 10 cm. The chamber was filled with the appropriate equivalent material.A hole was made in the middle and the gauge was placed in it. The walls of Institute of Mining, Siberian Branch, Academy of Sciences of the USSR, Novosibirsk.

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i 5,0-3,G I,o ~O o ,b z6 J~ 46 ~ Distance to face, m a b Fig. i. Layout of mining operation: a) plan; b) section.Institute of Mining, Siberian Branch, Academy of Sciences of the USSR, Novosibirsk.