Many workers [1][2][3] have shown that the structures and properties of real rocks are inhomogeneous in space and nonuniform in time. The inhomogeneity of the rock may be manifested in cracks, stratification, stress, inclusions, and cavities, and may be regular (smoothly varying) or random. The scale of inhomogeneities in the rock can vary over a very wide range; for example, cracks can be from 10 -7 cm to 1 cm wide and 10 -I cm to tens of meters long; inclusions and cavities vary from 10 -1 cm to several tens or hundreds of meters; and stress concentration zones have dimensions from tens of centimeters (around a borehole) to tens of meters (tectonic stresses).The chief problem of physical methods of surveying and monitoring is to discover and assess various types of inhomogeneity, i.e., to obtain an objective picture of the distribution of properties and of the state of the rock by making measurements in the solid rock and interpreting the results.The principal requirement imposed on physical methods of investigation and control of the properties and state of the solid rock is objectivity of the results in conjunction with technological feasibility of the measurer merits -i.e., detail and accuracy of measurement, reliability of interpretation, and attainability of quantitative data on the solid rock.At present there are many methods of investigating and monitoring the state of the solid rock -in particular physical methods based on wave fields of various types (elastic and electromagnetic waves and penetrating radiation), which are finding increasing application in engineering-geological surveys and exploitation control of the properties and state of the solid rock in mining. These methods are based on finding various types of inhomogeneity in the part of the solid rock under observation by means of changes in the parameters of the wave field which are used as indicative signs.Analysis reveals that the chief causes reducing the effectiveness of measurements in solid rock are experimental-methodological errors and inhomogeneity of the rock which is scarcely taken account of in present methods of control. The selection of an indicative sign for control and of a base for measurement without taking account of the statistical inhomogeneity of the rock will greatly reduce the reliability with which zones of high stress are distinguished near mine workings; the error in the estimation of the fissuring parameters of the rock may reach hundreds of percent.The maximum detail attainable in investigations of the spatial inhomogeneity of the rock is governed both by the absolute dimensions of the inhomogeneities and by the nature of their interaction with the wave field. Thus the measurement procedure and the methods of interpretation should be closely linked with the real structure of the rock. In other words, to increase the effectiveness of measurement it is necessary to match the parameters of the measuring system with the characteristics of the subject of investigation. Here by the parameters of the measuring system we ...
In the creation and introduction of methods of monitoring and investigation of the properties and state of rock in situ there are two goals: minimization of costs of monitoring, and getting the maximum of objective information about the rock. Solution of these problems primarily involves optimization of methods of measurement in situ and corresponding interpretation of the results.One of the most important features of optimization of measurements is a well-founded choice of the information parameter for monitoring, which must be carried out with consideration of the main requirement: --detail, accuracy, and reliability of geomonltoring.In this article we discuss the comparative assessment of information parameters used in acoustic measurements of rock in place, and establish a relation between the index of Information content of the parameter | and the reliability of monitoring of the state of the rock.In geoacoustic investigations, the information parameters of monitoring are usually the following characteristics of the acoustic signal: a) Velocities of propagation of longitudinal Vp and transverse V s elastic waves. b) Amplitude A or damping factor u of elastic vibrations.To increase the effectiveness of geomonitoring, in a number of problems (e.g., in studying Jolnting in rocks) use is made of the spectral correlation characteristics of the acoustic signals (the displacement ~f/fo of the maximum of the spectral density towards lower frequencies, the correlation interval T of noise signals propagated in a fissured medium, etc.).The lack of an objective criterion for the information content of a control parameter has the result that the control parameter is chosen without sufficient consideration of the properties of the test object --the rock in place which exists in particular mininggeological and mining-technical conditions. Since a set of different factors {F} influences the characteristics of the acoustic signal propagated in the rock, including the structure of the rock and physical fields of various natures, not usually sufficiently well taken into account by experiments, we get a situation in which changes in the characteristics {| of the acoustic signals are random and the experimenter cannot uniquely determine which factor F(i) is causing an observed change in the information parameter | (Fig. i).Furthermore, by experimental investigations it has been established [i, 2] that one acoustic information parameter | is correlated with several factors F~, F2, ..., Fn, and conversely, one factor F is correlated with various acoustic parameters. Because these correlations are not equivalent, we must make'a quantitative estimate of the information content of the control parameters with allowance for inhomogenelty of the rock and the conMining Institute, Moscow.
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