Scale effects in rock strength properties (original) (raw)
Related papers
Point-load strength: An index for classification of rock material
Bulletin of the International Association of Engineering Geology, 1991
Point-load strength (Is) as a measure for the determination of rock strength and for estimating uniaxial (unconfined) compressive strength (UCS) are described and both put together and used for rock strength classification of brittle and hard rocks. The estimated point-load strength values of ~,pecimuns of ',';trying sizes and also the ',alue~, corrected t,) a standard thickness (d" 50 ram, and die resultant point-load strength ,,,;dues (Is-50) have been used tt~ estimate the uniaxial (unconfined) compre~,sive strength which c~wrelates well v. ith actual recorded uniaxial (unconfined) compression test results. Using graphical and mathematical relations, hips between the obser'~ed and estimated tICS and ls values, a conversion factor of 16 is obtained for estimating uniaxinl (unconfincdl compressixe strengtb ',';dues from point load strength resulb, A nomogram for computing point-load strength index and a system for the classification of rock material are presented. Rdsumd La resistance au fendage sous charge ponctuelle (Is) constitue une d.valuation de ]a resistance de la roche et permet d'estimer la resistance en compressi~m uniaxiale (UCS): les deux ess;,is sont utilis,Ss pour dtablir une classification des roches rdsistantes de type fragile. l_es valeurs de resistance au fendage sous charge ponctuelle rdalisdes sur des dchantilhms de differentes tallies, ainsi que les valeurs ramendes par corrections :', une dpaisseur standard de 50 mm fournissent une valeur resultante Is-50 qui a ere utilisde pour estimer la resistance en compression uniaxiale a,,ec uric bonne correlation. En utilisant des comparaisons graphiques et math,Smatiques entre les valeurs UCS et b,. un facteur de conversion de 16 est obtenu pour a;oir la valeur UCS b. partir de la valeur Is. Un nomogramme pour calculer la valeur de resistance au fendage sous charge ponctuelle, et un syst~me de classification des roches son presentes.
Correlation between uniaxial strength and point load index of rocks
Japanese Geotechnical Society Special Publication, 2016
Determination of rock engineering properties is important in civil, mining and geotechnical engineering. Uniaxial Compressive Strength (UCS) is one of the most important properties of rocks. Point Load Test (PLT) is practically used in geotechnical engineering to determine rock strength index. Despite that the PLT is fast, economical and simple in either field or laboratory, Uniaxial Compressive Test (UCT) is time-consuming and expensive. UCS can be estimated using Point Load Index (PLI). So, implementation of correlation between results of PLT and UCT is of interest. In this research correlation between the results of point load test and uniaxial compressive test are presented for rock samples from three sites in Iran. Two rock types including Shale and Marlstone have been utilized in this research. Correlations between UCS and PLI in this study are verified with proposed equation by pervious researchers.
Characterizing Intact Rock Strength using Field Estimates and the Point Load Index Test
A number of guidelines for the field estimate of intact rock strength are available. Although all vary slightly in terms of the boundaries of the strength classes, they generally rely on reaction to a number of simple index tests. The errors and uncertainties associated with estimation of strength using these schemes are high and strength estimates need to be treated with caution. Undertaking point load index testing in the field is a useful tool that can provide data to augment field strength estimates and laboratory test data. Field point load index test data can be converted to an equivalent uniaxial compressive strength (UCS) but this relationship should be calibrated through twinned UCS and point load index tests. A case study is presented for an investigation in highly anisotropic banded iron formation of the Hamersley Province, West Australia. The relationship between UCS and point load index strength for the site is shown to be strength dependent. The calibrated field point load index test data is provides additional information on the variability of the rock strength that could not be captured by limited laboratory testing.
Point load testing is used to determine rock strength indexes in geotechnical practice. The point load test apparatus and procedure enables economical testing of core or lump rock samples in either a field or laboratory setting. In order to estimate uniaxial compressive strength, index-to-strength conversion factors are used. These factors have been proposed by various researchers and are dependent upon rock type. This study involved the extensive load frame and point load testing of coal measure rocks in six states. More than 10,000 individual test results, from 908 distinct rock units, were used in the study. Rock lithologies were classified into general categories and conversion factors were determined for each category. This allows for intact rock strength data to be made available through point load testing for numerical geotechnical analysis and empirical rock mass classification systems such as the Coal Mine Roof Rating (CMRR).
Bulletin of Engineering Geology and the Environment, 2015
The strength conversion factor (k) is the ratio between the uniaxial compressive strength (UCS) and the point load index (PLI). It has been used to estimate the UCS from the PLI since the 1960s. Many researchers have investigated the relationship between UCS and PLI for various rock types of different geological origins, such as igneous, sedimentary, and metamorphic rocks. In this study, the k values for subclasses of igneous (pyroclastic, volcanic, and plutonic), sedimentary (chemical and clastic), and metamorphic (foliated and nonfoliated) rocks were evaluated. For this purpose, UCS and PLI data for a total of 410 rock samples extracted from literature published around the world as well as UCS and PLI data obtained in this work for 80 rock samples taken from the Eastern Black Sea Region in Turkey were evaluated together to determine the k values of different rock classes. Strength conversion factors were obtained using zero-intercept regression analysis, formulation, and a graphical approach. This study confirmed that there is no single k value that is applicable to all rock classes. According to statistical analyses, k varied between 12.98 and 18.55 for the rocks studied. These findings demonstrate that the k values derived in this work can be reliably used to estimate the strengths of rock samples with specific lithologies.
Rock material particle size and its correlation with the point load test index
Minerva
This work proposes the methodology to obtain a correlation between the particle size of the rock material and the point load test index (Is 50), in order to characterize the materials, present in mining projects in terms of resistance. For a correct development of mining activities, both open pit (quarries) and underground (mines), it is important to determine the compressive strength of the rocks, since, through it, geomechanical classifications are obtained, and thus calculate safety factors to define stabilization and/or fortification systems for mining operations. This work was developed on the basis of samples from a geological formation and subsequent preparation of specimens, then they were subjected to physical tests, which can be carried out without problem in the field and finally the respective relationships were obtained. The results are encouraging and the equations are proposed to characterize the rock and achieve the proposed objective.
Rock Mechanics and Rock Engineering, 2020
The point load strength index is a widely used index in rock engineering, and cylindrical core and irregular shaped specimens are used in its determination. But, in mine sites, the borehole cores are cut axially into two equal parts to obtain half-cut cores and one part of these half cores is sent to laboratory for geochemical analyses. This situation causes a problem that the remaining half of the cores from the specimens cannot be used not only in the strength and deformability tests, but also in the point load test. In this study, it is aimed to investigate the applicability of the point load test on half-cut cores, to adopt the previously suggested size correction formulations to the half-cut core specimens and to estimate the uniaxial compressive strength from the point load strength index determined from the half-core specimens. To achieve these goals, point load strength index and uniaxial compression tests were conducted on a number of half-cut and cylindrical core samples prepared from 12 different rock types and the test results were assessed based on the statistical analyses. The analysis results indicated that the point load strength index may also correctly be determined from the half-cut cores and uniaxial compressive strength may be estimated from the size corrected point load strength index values of half-cut cores with a low error margin using average size correction factor.