Geomechanical conditions for quasi-resonances in geomaterials and block media

Conclusions  Based on voluminous information about relations between the dimensions of the central zones of crustal earthquakes and various energy classes of underground explosions, as well as mine shocks and man-induced tremors, therefore, the hypothesis that we had previously advanced relative to the quasi-resonant mechanism of their manifestation is confirmed. Here, the geomechanical conditions for the development of quasi-resonances associated with the inducement of pendulum waves are characterized by the dimensionless energy criterion k:

Change in properties of geophysical medium during underground explosions

Mechanisms of strength loss of rocks in a slightly fractured mass during confined explosions are considered. It is shown that, at small depth (H ≤ 400m) beyond the boundary of radial crack zone, local rock failure is possible under the action of hoop tensile stresses during a single explosion and under the action of shear stresses in wave superposition zones during a group explosion. At great depths, local failure and strength loss of rocks in the indicated area are possible by shear failure in zones of blast wave interaction. Scientific-Research Institute of Labor Protection, Kiev. Translated from Fiziko-Tekhnicheskie Problemy Razrabotki Poleznykh Iskopaemykh, No. 3, pp. 45–50, May–June, 1999     

Model of the effects of an explosion in a well

Conclusions A new model of explosions in wells was proposed on the basis of the "inverse" (in terms of the factor of rock pressure) zonal disintegration of rocks around underground workings (Discovery No. 400) and the anomalously low friction in block media detected experimentally by the authors in an investigation of pendulum-type waves. Considerable weight was given to the empirical finding that for certain energies of shock loading of models of block media, friction "vanishes" between interacting blocks of geologic materials in directions orthogonal to the line of action of the external impulse. The geometric parameters of the quasi-cylindrical system of blocks formed around an exploded well are determined by the scale factor of the zonal disintegration process, this factor being linked to the radius of the well; the dynamic—kinematic characteristics of geologic blocks capable of moving along the annular "inverse" disintegration zones are determined by the type of stress state of the surrounding rock masses. Institute of Mining, Siberian Branch of the Russian Academy of Sciences, Novosibirsk. Translated from Fiziko—Tekhnicheskie Problemy Razrabotki Poleznykh Iskopaemykh, No. 2, pp. 37–46, March–April, 1997.     

Relations between rock bursts in pits and periodically varying astronomical factors

Conclusions Rock bursts in underground coal pits are not only affected by geological and mining-technological factors, but also depend on the following astronomical factors. The probability of rock bursts increases with the tidal influence of the moon on the earth. The probability of rock bursts is highest when the moon is at perigee, and lowest when it is at apogee. The probability of rock bursts falls as solar activity increases. The probability of bursts is highest in years of minimum solar activity and lowest in years of maximum solar activity. Eastern Mining Research Institute (Vost NII), Kemerovo. Translated from Fiziko-Tekhnicheskie Problemy Razrabotki Poleznykh Iskopaemykh, No. 4, pp. 33–37, July–August, 1969.     

Alteration of the permeability tensor around a grouped explosion

Conclusions The results derived in the paper indicate that the permeability of the medium deteriorates along a straight line connecting the chamber centers. At the same time, the components k_r and k_ω of the permeability tensor increase. This gives a new confirmation to the conclusion made earlier that infiltration flows between spherical cavities will be practically absent along the shortest distance, and that the hydrodynamic connection between the cavities will occur through areas marked by circled minuses in Fig. 4. Our calculations thus indicate that the distribution of permeability factor near the destruction zone of confined explosions is a rather complex function of three-dimensional coordinates, described qualitatively in Fig. 4 (the increase and decrease areas). This distribution of is bound to affect the pattern of infiltrational interaction of the destruction zones and should be taken into consideration when planning a cluster blast. Institute of Engineering Physics, Moscow. Translated from Fiziko-Tekhnicheskie Problemy Razrabotki Poleznykh Iskopaemykh, No. 5, pp. 43–50, September–October, 1985.     

On some features of evolution of harmonic acoustic signals in loading block media with a cylindrical cavity

The results are presented for physical modeling, which make it possible to answer a question whether there are any bases for the hypothesis (proposed by M. V. Kurlenya and V. N. Oparin) that at the prefailure stages, the focus zones of rock bursts, earthquakes, and other dynamic events become similar to a peculiar “geomechanical laser system,” i. e., an acoustically active medium capable of coherent seismic-energy radiation. In this context, possible consistency of the acoustic signals formed in structural elements of block media, in terms of both the frequency spectrum and the phase component, is a key issue. In existing approaches to the analysis of the mechanisms of focus zones of dynamic rock-pressure manifestation, as a rule, the fact that quasi-static processes of elastic energy accumulation in the forming focus zones always proceed against an acoustic background (from natural microseisms to complex wave phenomena accompanying pulsed seismic effects from remote earthquakes, explosions, etc.) is ignored. In view of the anomalously low friction in block media (discovered at the Institute of Mining, Siberian Branch, Russian Academy of Sciences), the type of the stress-strain state in geoblocks and the amplitude-period characteristics of the “seismic background” may be decisive in the realization of dynamic event. Therefore, it is natural to ask what happens, for example, to microseisms or acoustic wave packets, that are regular in frequency, in the focus zones of future dynamic events depending on the level of stresses prevailing there. Experimental data are considered for one of the most simple cases where the focus zone is modeled by a set of homogeneous blocks with a stress concentrator in the form of a cylindrical cavity (a “plane” model), while the quasi-static process of external loading is represented by uniaxial compression from a press with weak lateral thrust. The “acoustic background” is specified in a peripheral block of the model in a monochromatic regime. This model relates directly to the acoustic monitoring of the limiting states of rocks around underground workings. It is proved that the prefailure stages of model are characterized not only by convergence of the resonance frequencies in the block system but also by amplification of the harmonic-signal amplitude due to conversion of the stored elastic energy of the structural elements to energy of acoustic signals. The law of exponential decay of harmonic signals from a radiation source is violated here, and the model of the geomaterials becomes an acoustically active medium operating as a peculiar “geomechanical laser system.” Institute of Mining, Siberian Branch, Russian Academy of Sciences, Novosibirsk. Translated from Fiziko-Tekhnicheskie Problemy Razrabotki Poleznykh Iskopaemykh, No. 6, pp. 10–32, November–December, 1999.     

Hydrogeomechanical problems in mining

The hydrogeomechanical problems of mining are considered, which deal with rocks and ground water as a single mechanical system. Among these problems are the openpits slopes stability, rocks consolidation and surface subsidence due to ground water level lowering, water inrushes into mine workings, rock bursts prevention by using the water injection into the advance boreholes, etc. The paper contains the basic theoretical grounds, as well as in-situ and laboratory methods for the investigation of these processes. The combined study of ground water regime and rock deformations has resulted in the theoretical substantiation of the hydrodynamic and geomechanical processes within the scope of unique scientific direction-hydrogeomechanics (Mironenko, 1974). The hydrogeomechanical models are widely used now for the analysis and forecasting the extremely important processes connected with the safe and efficient mining operations, as well as with the protection of geological medium. Among these processes are:

Energy content of the nonexplosive excavation of rock by excavators with a dynamic scoop

Conclusions  

Stress-field evaluation by geostructural and geomechanical prospection: The case history of the machaerus rock-mass (Hashemite Kingdom of Jordan)

On the bases of a field geostructural and geomechanical survey, we evaluate the stress field and structural regime responsible for the deformation of the rock-mass in the Machaerus area, the Hashemite Kingdom of Jordan, on the eastern side of the Dead Sea Transform Fault. The resulted data are compared to those from deep mines and base tunnels in order to evaluate the potentiality of using geostructural data to envisage the stress-field for new geoengeneering projects. It resulted the Machareus rock mass was deformed at a depth of about 500–900 m with a deviatoric stresses of the order of σ ₁ =15 MPa, σ ₂ =10 MPa and σ ₃ =−25 MPa, being σ ₃ vertical. The stress field orientation is consistent with the left-lateral kinematics of the nearby Dead-Sea transform fault.     

Specific Energy Prediction for Circular Diamond Saw in Cutting Different Types of Rocks Using Multivariable Linear Regression Analysis

Circular diamond saw performance is affected by a variety of factors. The principal factors requiring consideration when predicting cutting rates are the type and operating features of a diamond saw and the rock characteristics. The laboratory experimental tests are carried out on three groups of rocks (16 types) cut with the help of three types of diamond disk saws with different feed rates and cutting depths at constant peripheral velocity. The quantitative determinations of a wide range of textural, mechanical, and intact properties of rocks are also made. The relationship between the specific cutting energy SE _cut of the sawblade operating parameters and rock properties is established. Applying multivariable linear regression analysis, the predictive model of SE _cut is developed based on the rock property data. Models verified by statistical tests prove their practical validity. __________ Translated from Fiziko-Tekhnicheskie Problemy Razrabotki Poleznykh Iskopaemykh, No. 3, pp. 56–80, May–June, 2005.     

Nonlinear effects in the radiation and propagation of vibro-seismic signals in a rock mass

Results are presented from measurements of the vibro-seismic field of a surface source in a rock mass at depths of up to 1.5 km. Effects connected with the grouping of sources are examined along with the transformation of the signal spectrum during passage through an oil stratum. It is shown that the absorption coefficient of vibro-seismic monochromatic signals by sedimentary rocks is within the range 0.63–0.75 dB/λ_p, where λ_p is the length of the longitudinal waves. Institute of Mining, Siberian Branch, Russian Academy of Sciences, Novosibirsk. Translated from Fiziko-Tekhnicheskie Problemy Razrabotki Poleznykh Iskopaemykh, No. 2, pp. 3–10, March–April, 1999.     

Features of forming an explosive fracture zone in a hard rock mass

The effect of extended discontinuities in a hard rock mass on regularities of forming explosive fracture zones is considered. The comparison of the numerical and in situ experimental results permits to conclude that, in common with the known effect of seismic blast wave screenage, transformation of the wavefront configuration is of drastic importance. In a number of cases, that results in the generation of complex-structured fracture zones: new fractured zones can form beyond unbroken areas. It is demonstrated that the similar effects may cause redistribution of the blast energy and, as a consequence, the higher seismic efficiency produced by flat charge blasting as compared with concentrated charge blasting. __________ Translated from Fiziko-Tekhnicheskie Problemy Razrabotki Poleznykh Iskopaemykh, No. 3, pp. 65–76, May–June, 2007.     

Single-borehole measuring method for broken rock zone in gently inclined thin layer weakness structure

According to the structural characteristics of gently inclined thin layer rock mass in which lots of weak interlayer existed, the concept of gently inclined thin layer weakness structure was proposed. If single-borehole measuring method of the acoustic along the conventional arrangement mode was used in measuring the broken rock zone in this structure, the change of the relationship curves (V _p -L) between acoustic p-wave velocity (V _p ) and borehole depth (L) would present the irregular feature due to the mechanical characteristics of layered rock mass and harmful effects of weak interlayers, and the scope of broken rock zone couldn’t be defined quickly. Based on the analysis of the mechanical characteristics of layered rock mass, the propagation rule of acoustic and distributions characteristics of plastic zone and slip zone in layered rock mass, new arrangement mode of acoustic measuring boreholes for broken rock zone in gently inclined thin layer weakness structure was proposed. Namely, the measuring boreholes in two sides were parallel to the strata, the measuring boreholes in the roof and floor perpendicular to the strata. Besides the controlling depth of the measuring boreholes in the scope of the large plastic zones or the large slip zones should be increased. Engineering example showed that new acoustic measuring boreholes arrangement mode had the better applicability and could determine the scope of the broken rock zone in the gently inclined thin layer weakness structure quickly. Supported by the National Natural Science Foundation of China(50490274); National Key Project of Scientific and Technical Supporting Programs of China(2006BAB02A02); Guangxi University Research Foundation (X061068)     

Features of the thermally stressed state of a rock mass with flame-jet drilling taking account of thermal changes in its physical properties

Conclusions A detailed calculation has been carried out for the thermal and stressed-strained state of a solid mass, in particular rock, for temperature dependences of only thermal conductivity coefficient λ(θ), thermal expansion coefficient, α(θ), and Young's modulus E(θ), and also with combined dependence of them. Comparison of these calculations with the case of constant values λ₀, α₀, E_o [7] showed that the latter appear to be very close to the most accurate calculation with λ(θ), α(θ), E(θ). Consideration of the dependence on temperature alone for individual properties may lead to more serious deviations. Institute of Mining, Siberian Branch, Academy of Sciences of the USSR, Novosibirsk. Translated from Fiziko-Tekhnicheskie Problemy Razrabotki Poleznykh Iskopaemykh, No. 6, pp. 9–13, November–December, 1989.     

Devices for Continuous Recording of the Parameters of Deformation — Wave Processes in Rock Mass. Part I: Measurement of Longitudinal Movements of Rocks in a Borehole and Design of the Position Sensor

A sensor for measuring movements in block rock mass through boreholes is presented. Being an organic part of multichannel instrumental set, the sensor ensures revealing of deformation changes in the controlled zones of block geomedia, which is of key importance when stress variations and fatigue failure in rock mass are determined. __________ Translated from Fiziko-Tekhnicheskie Problemy Razrabotki Poleznykh Iskopaemykh, No. 3, pp. 106–115, May–June, 2005.     

Microcracking of salt under creep

Conclusions During creep in rock salt samples, the concentration of microcracks decreases, due to their amalgamation and formation of larger cracks at rates proportional to the load. Moreover, the increase in the number of cracks, according to the acoustic emission and the electromagnetic radiation data, is the result of the formation of sub-micron cracks, which were undetected because of inadequate sensitivity and resolution of the microanalyzer. The parameters of the superimposed microcracking varied proportionally with the load and the duration of the tests. After 35 days under loads of 0.5 σ_c and 0.7 σ_c, the average crack length had increased by 29% and 50%. After 45 days, the increases were 42% and 54% (Fig 1). The average widths of the open cracks increased in the first case by 19% and 25%, and in the second, by 27% and 38%. The results can be used to evaluate the change in the void volume with time, as a result of expansion in rock salt deposits. G. V. Plekhanov Mining Institute, Leningrad. Translated from Fiziko-Tekhnicheskie Problemy Razrabotki Poleznykh Iskopaemykh, No. 4, pp. 37–40, July–August, 1991.     

Modeling the failure of rock blocks by blasting a cylindrical charge

The calculation model of breaking action exerted by a cylindrical charge blasted in a block rock mass is proposed. The deformation of a block medium in the zones of elasticity and heavy fragmentation is described by a continuum, properties of which are changed as compared with monolithic rocks. It is shown that the accounting of the block rock strength decrease in the massif influences greatly the calculated failure parameters and provides an opportunity to obtain fragmentation zone sizes, close to those observed in actual rock blasting. __________ Translated from Fiziko-Tekhnicheskie Problemy Razrabotki Poleznykh Iskopaemykh, No. 1, pp. 31–38, January–February, 2006.     

Ratio of the cavity volumes in confined explosions of concentrated and linear charges

Numerical calculations are performed to obtain a formula showing that confined cavities obtained from the explosions of linear charges are smaller in volume than those obtained from the explosions of concentrated charges containing the same mass of explosive. This phenomenon is explained by the fact that the energy similarity law governing the effect of explosions is satisfied approximately. Institute of Geosphere Dynamics, Russian Academy of Sciences, Moscow. Translated from Fiziko-Tekhnicheskie Problemy Razrabotki Poleznykh Iskopaemykh, No. 3, pp. 58–63, May–June, 1999.     

Hydrogeochemistry of the Getchell Underground Mine––Part 1: Mine Water Chemistry

The Getchell underground operations in Northern Nevada intersect groundwater associated with marble and hornfel lithologies and a sulfide bearing ore hosted within a 30-km long shear zone system. The deposit is classified as Carlin-type gold mineralization. A distinct feature of the mineralization is the high proportion of arsenic sulfides present in the ore and associated altered wallrock. This results in an intense arsenic enrichment, with some zones containing as much as 30% arsenic, and 0.5–2% arsenic throughout the mineralized envelope. Most of the groundwater in the area is well buffered by the calcareous host rocks and show a macrochemistry of Ca-Na-HCO₃. Along the shear zone and in zones within the hornfel host rock, the waters are less alkaline and more saline, and have a chemistry of Na-Mg-Ca-SO₄-HCO₃. This latter water type occurs in sulfide-bearing zones. Arsenic speciation analysis and theoretical predictions demonstrate that higher arsenic concentrations are associated with reducing conditions, with higher Na/Ca ratios, and with low concentrations of Fe. In these waters, As occurs as arsenite, along with trace concentrations of mono-methyl arsonic acid and di-methyl arsinic acid. Natural attenuation of As appears to occur along groundwater flow paths due to co-precipitation and adsorption onto hydrous ferric oxide particles. However, elevated As is still a notable feature of groundwater quality throughout the Kelly Creek basin. This elevated As occurs in bedrock groundwater during underground mine development, rather than in near-surface alluvium groundwater. Due to this and the protracted history of mining, it is not possible to define a true background value for water quality in the area other than acknowledging that bedrock groundwater is mineralized and has little association with seasonal recharge and water quality in the alluvium cover.