Papers by Keyword: Rock Specimen

Abstract: Test point load test requires relatively small load, its instrument is portable, it can be easily applied to on-site testing,which may pave the way for the development of the fieldstrength of rock mechanics test, widely promoted in engineering construction, has a large space for development. When selecting the uniform rock do the load and saturation points uniaxial compression test respectively, and comparing the analysis of the two trials correlation between the results obtained by the method, the results showed that: point load test as a qualitative and semi-quantitative indicators are needed to meet the requiement of project, but if we put it as a fully quantitative indicators ,which will lead to large errors,and even lead to sweeping errors.

Abstract: In order to investigate the relation between uniaxial compressive strength and point load strength, several homogeneous rock specimens were tested, and the influence of the different rock type was investigated using regression analysis and the derived equations were statistically tested. The test result show that there are some correlations and trends between uniaxial compressive strength and point load strength, the shape size and lithology of rock specimens have important influence on the result of point load test, and the greain size, the mineral compositon and the structral compact are key factors. It is difficult to realize that using one or several function to describe all internal relations between uniaxial compressive strength and point load strength.

Abstract: The work is devoted to the problem of role of ambient factors (external electromagnetic field, in particular) in the process of ageing of mechanically burden nonmetallic solids (rocks). A specific research point is the effect of temporary activation of Acoustic Emission (AE) of rocks specimens during action of EM field pulses applied externally. Extended experimental studies of responses of AE have been conducted to evince the changes in defects accumulation process in loaded specimens due to external power impacts (EPI). The experiments have been held on noiseless rheological machines available at Bishkek Geodynamic Research Center - RS RAS. We have tested a number of specimens made of different materials and analyzed the temporal dependence of AE activity during exposure in electric field and crossed electric and magnetic fields; the compressive load being constant. The effect of AE stimulation by power pulses (triggering) has been verified. The obtained results allow to distinguish two kinds of AE activation. The first kind involves simultaneous well correlated growth of numbers of minor and major AEs (so-called selfconsistency of temporal plots of activity of different range acoustic events). The second kind represents dissimilar variations: the increment of activity of minor energy AEs, but the decrement of those of major energy. The first kind of solids material responses to EPI is prevailing when the compressive loads is under 0,85 of fracturing value. The episodes of dissimilar AE responses may signify that electromagnetic control of defects accumulation process inside rocks is possible, in principle.

Abstract: The failure process of heterogeneous rock specimen with initially random material imperfections in uniaxial plane strain compression and the macroscopically mechanical response are numerically modeled by using FLAC (Fast Lagrangian Analysis of Continua). A FISH function is generated to prescribe the initial imperfections within the heterogeneous specimen by using Matlab. The imperfection is weaker than the intact rock. Beyond the failure of the imperfection, it undergoes ideal plastic behavior, while intact rock exhibits linear strain-softening behavior and then ideal plastic behavior once failure occurs. The specimen with smooth ends is loaded at a constant strain rate and is divided into 3200 elements. The maximum numbers of the initial imperfections in five schemes are 100, 300, 500, 700 and 900. The effects of the number of the imperfections on the fracture process, the final fracture pattern and the complete stress-strain curve are investigated. Prior to the peak stress, some imperfections extend in the axial direction and then a part of them coalesce to form inclined shear bands. Beyond the peak stress, shear bands progressively intersect the specimen; in the process the number of the yielded elements approximately remains a constant. With an increase of the number of the initial imperfections, the spacing of shear fractures decreases, the peak stress and corresponding axial strain decrease; the post-peak branch of stress-strain curve becomes steeper; much more elements fail in tension; the number of the yielded elements in tension in the vicinity of the two lateral edges of the specimen remarkably increases.