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Correlations between direct and indirect strength test methods

International Journal of Mining Science and Technology 2015年第3期25卷 355-360页

作者： kallu raj Roghanchi Pedram Department of Mining Engineering University of Nevada

The difficulties associated with performing direct compression strength tests on rocks lead to the development of indirect test methods for the rock strength assessment. Indirect test methods are simple, more economical, less time-consuming, and easily adaptable to the field. The main aim of this study was to derive correlations between direct and indirect test methods for basalt and rhyolite rock types from Carlin trend deposits in Nevada. In the destructive methods, point load index, block punch index, and splitting tensile strength tests are performed. In the non-destructive methods, Schmidt hammer and ultrasonic pulse velocity tests are performed. Correlations between the direct and indirect compression strength tests are developed using linear and nonlinear regression analysis methods. The results show that the splitting tensile strength has the best correlation with the uniaxial compression ***, the Poisson's ratio has no correlation with any of the direct and indirect test results.

关键词： Uniaxial compression strength test Indirect strength test methods Correlation Regression analysis

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Development of a multivariate empirical model for predicting weak rock mass modulus

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International Journal of Mining Science and Technology 2015年第4期25卷 545-552页

作者： kallu raj R. Keffeler Evan R. Watters Robert J. Agharazi Alireza Department of Mining Engineering University of Nevada RESPEC Consulting and Services University of Nevada Itasca Houston Inc.

Estimating weak rock mass modulus has historically proven difficult although this mechanical property is an important input to many types of geotechnical analyses. An empirical database of weak rock mass modulus with associated detailed geotechnical parameters was assembled from plate loading tests per- formed at underground mines in Nevada, the Bakhtiary Dam project, and Portugues Dam project. The database was used to assess the accuracy of published single-variate models and to develop a multivari- ate model for predicting in-situ weak rock mass modulus when limited geoteehnical data are available. Only two of the published models were adequate for predicting modulus of weak rock masses over lim- ited ranges of alteration intensities, and none of the models provided good estimates of modulus over a range of geotechnical properties. In light of this shortcoming, a multivariate model was developed from the weak rock mass modulus dataset, and the new model is exponential in form and has the following independent variables：（1） average block size or joint spacing, （2） field estimated rock strength, （3） dis- continuity roughness, and （4） discontinuity infilling hardness. The multivariate model provided better estimates of modulus for both hard-blocky rock masses and intensely-altered rock masses.

关键词： In-situ modulus Weak rock mass Preliminary design Elastic deformation

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Inflatable rock bolt bond strength versus rock mass rating (RMR)： A comparative analysis of pull-out testing data from underground mines in Nevada

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International Journal of Mining Science and Technology 2016年第1期26卷 19-22页

作者： Barnard Chase kallu raj R. Warren Sean Thareja Rahul Department of Mining Engineering University of Nevada Reno 89557 USA

The purpose of this paper is to establish confidence in anticipated minimum bond strength for inflatable rock bolts by comparing the bond strength to variable geotechnical conditions using the rock mass rating （RMR） system. To investigate a correlation between these parameters, the minimum bond strength of pull-out tested inflatable rock bolts was compared to the RMR of the rock in which these bolts were placed. Bond strength vs. RMR plots indicate that expected minimum bond strength is positively corre- lated with RMR; however, the correlation is not strong. Cumulative percent graphs indicate that 97~; of pull-out tests result in a minimum bond strength of 3.3 and 1.7 ton/m in RMR/〉 45 and 〈45, respectively. Although lower bond strengths are more commonly encountered in low RMR ground, high bond strengths are possible as well, yielding higher variability in bond strengths in low RMR ground. Bond strength of friction bolts relies on contact between the rock bolt and drill hole. Experience in Nevada indicates that RMR is known to affect both the quality and consistency of drill holes which likely affects bond strength. Drilling and bolting in low RMR ground is more sensitive to drilling and bolting practices, and strategies for maximizing bond strength in these conditions are discussed.

关键词： Rock mass ratingRMRRock boltPull-out testBond strength

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