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Rocks are formed from particles and the interaction between those particles controls the behaviour of a rock’s mechanical properties. Since it is very important to conduct extensive studies about the relationship between the micro-parameters and macro-parameters of rock, this paper investigates the effects of some micro-parameters on strength properties and the behaviour of cracks in rock. This is carried out by using numerical simulation of an extensive series of Uniaxial Compressive Strength (UCS) and Brazilian Tensile Strength (BTS) tests. The micro-parameters included the particles’ contact modulus, the contact stiff ness ratio, bond cohesion, bond tensile strength, the friction coefficient and the friction angle, and the mechanical properties of chromite rock have been considered as base values of the investigation. Based on the obtained results, it was found that the most important micro-parameters on the behaviour of rock in the compressive state are bond cohesion, bond tensile strength, and the friction coefficient. Also, the bond tensile strength showed the largest effect under tensile conditions. The micro-parameter of bond tensile strength increased the rock tensile strength (up to 5 times), minimized destructive cracks and increased the corresponding strain (almost 2.5 times) during critical stress.

This study investigated the changes in the physical parameters of sandstone (solution pH, mass, P-wave velocity, and porosity) and mechanical strength (tensile strength) under acidic drying-wetting cycles. Additionally, the particle flow code (PFC) was used to simulate the drying-wetting cycles. The results reveal that the pH range of the acidic solution is much larger than that of the neutral solution. The changes of the mass and P-wave velocity are consistent and both exhibit a decreasing trend, which slowed down in stage IV. Compared with the neutral solution, the acidic solution could accelerate the damage peak of the specimen and cause early destruction. The "S" curve variation of porosity indicates that the decrease of physical parameters in stage IV was caused by the slowdown of porosity growth. In turn, this indicates that the soluble material in the specimen decreased, and the number of drying-wetting cycles could not excite new crack generation, which resulted in the slowdown of the loss rate. The results obtained by the Brazilian splitting test (BTS) reveal that the damage in the acidic solution of the specimen first deformed by compression and then by splitting damage, which is different to the direct splitting damage in the neutral solution. The simulation also proves that the specimen mainly exhibited extrusion deformation in the y-direction and tensile damage in the x-direction. The contact between the particles inside the specimen gradually decreased as the cycles progressed. Finally, damage occurred under low pressure. [ABSTRACT FROM AUTHOR]

Due to difference in mineral composition, cementation, and porosity, the strength behavior of sandstone after exposure to different high temperatures is complex. From literature review, it is found that a transition temperature in the treatment exists at which the strength of sandstone changes from slow increase or decrease to fast decrease. This paper studies the effect of high temperature treatment on mechanical behavior of a fine-grained sandstone with a focus on discussion of the controlling factor that affects the various strength behavior of sandstone in response to thermal loading. The results in this study show that the transition temperature is about 500 °C for the examined sandstone. When the treatment temperature is below 500 °C, the Brazilian tensile strength (BTS), uniaxial compressive strength (UCS), and elastic modulus increase with increasing temperature in the treatment. However, when the treatment temperature exceeds 500 °C, the three parameters are found to decrease with a further increase in the treatment temperature. The relation between brittleness and treatment temperature is also examined. The brittleness indices B3 and B4 are found to be more effective than B1 and B2 to assess the brittleness of thermally damaged rock. The results in this study are useful for better understanding the mechanism of thermal damage effect on strength behavior of sandstone. [ABSTRACT FROM AUTHOR]

Rock drillability characteristic is one of the important properties for mining and tunneling operations. The rock drillability can be determined by using the drilling rate index (DRI) for engineering applications. The present study attempts to develop a practical and convenient DRI estimation model by using rock strength and abrasivity properties. For this purpose, fuzzy inference system (FIS) being an accurate prediction model was applied to predict DRI by using experimental data obtained with 37 different rocks. The predictive FIS based on experts knowledge by taking mechanical and abrasivity properties as input parameters was created on MATLAB. This structure was carried out by using Mamdani extraction method. DRI values obtained experimentally and estimated from the FIS model were compared. This comparison is given with statistically reliable (R2=0.9277) results. In order to prove the validity of the FIS model for DRI prediction, a validation process has been performed by using test data as well. The performance determination coefficients (R2) are found as 0.9513 by using test data. As a result, it was found that DRI values can be predicted very efficiently and accurately with the proposed prediction method. [ABSTRACT FROM AUTHOR]

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Abstract Various testing methods have been proposed to measure rock abrasiveness as an input into the prediction models for estimating the tool wear in mechanized tunneling and mining. Among the proposed tests, LCPC test has been used by many researchers for assessment of rock abrasivity. In this study, 20 rock samples from various locations in Pakistan were subjected to comprehensive testing of various properties. The tests included LCPC (Laboratorie Central des Ponts et Chaussees) rock abrasivity tests as well as a complete suite of standard rock physical and mechanical property tests. Whilst the standard LCPC test is run in dry samples, this study compared the results of the LCPC method in dry and saturated conditions, performed at water contents of 15, 30, 45 and 60%. Overall abrasivity [measured as ABR (g/t)] decreased with the increase in water content with peak values of ABR (g/t) attained at 15% water contents for low porosity rocks and 30% water content for high porosity rocks when compared to dry tests. Similarly, a gradual decrease in the LCPC Breakability Index (BR%) was noted in the case of low porosity rocks with the corresponding increase in water content. However, for high porosity rocks there was a cyclic fall and rise in breakability (BR%) at 15% and 30% moisture levels, respectively. This was in contrast to dry tests. A steady drop in BR% was also observed at higher water contents. This paper discusses the result of the testing as well as practical implications of these measurements on predicted wear of cutting tools used in mechanized excavation in mining and tunneling applications. Preliminary statistical analysis of the data and correlations between ABR, water contents, and petrographic and engineering rock properties are also included in this paper. [ABSTRACT FROM AUTHOR]

Discrete element method is a commonly used numerical method in rock mechanics and rock engineering. In this research, the flat-joint contact bond model is used to reproduce the macro-properties of basalt on an assembly of particles. A series of laboratory tests, including uniaxial compression test, Brazilian tension test, and fracture toughness test are used to simulate progressive degradation of rock mass strength in a size-independent model with a unique set of micro-properties. The work involves a detailed analysis for estimating compressive elastic modulus, Poisson's ratio, bimodularity, mode I fracture toughness, crack closure, crack initiation, and crack damage thresholds, as well as the tensile and compressive strengths. The constructed flat-jointed material yields a realistic uniaxial compression to tensile strength ratio and nonlinear stress-strain response through sustaining adequate particle interlocking and embedded pre-existing microcracks. The role of sample size on the compressive elastic modulus, crack initiation and crack damage stress limits is demonstrated in detail. A model size-independency analysis was also performed to examine the effect of particle size on the results. The numerical results presented in this study are within 10% of the laboratory results. [ABSTRACT FROM AUTHOR]

The Earth Mechanics Institute (EMI) was established at the Colorado School of Mines (CSM) in 1974 to develop innovations in rock mechanics research and education. During the last four decades, extensive rock mechanics research has been conducted at the EMI. Results from uniaxial compressive strength (UCS), Brazilian tensile strength (BTS), point load index (PLI), punch penetration (PP), and many other types of tests have been recorded in a database that has been unexamined for research purposes. The EMI database includes over 20,000 tests from over 1,000 different projects including mining and underground construction, and analysis of this database to identify relationships has been started with preliminary results reported here. Overall, statistically significant correlations are identified between bulk density and mechanical strength properties through UCS, BTS, PLI, and PP testing of sedimentary, igneous, and metamorphic rocks. In this paper, bulk density is considered as a surrogate metric that reflects both mineralogy and porosity. From this analysis, sedimentary rocks show the strongest correlation between the UCS and bulk density, whereas metamorphic rocks exhibit the strongest correlation between UCS and PP. Data trends in the EMI database also reveal a linear relationship between UCS and BTS tests. For the singular case of rock coral, the database permits correlations between bulk density of the core versus the deposition depth and porosity. The EMI database will continue under analysis, and will provide additional insightful and comprehensive understanding of the variation and predictability of rock mechanical strength properties and density. This knowledge will contribute significantly toward the increasingly safe and cost-effective geostructures and construction. [ABSTRACT FROM AUTHOR]

Efficient use of waste materials is a proven solution to the problems associated with their disposal. Fly ash is one such material produced from thermal power plants that requires a huge disposal area and creates environmental problems. Stabilization of weak soils with fly ash not only improves the engineering properties of soil, but also provide answers to the issues of fly ash disposal. This paper reports the results of laboratory investigation carried out on clayey soil stabilized with fly ash and hydrated lime. Effects of lime, fly ash and the days of curing studied on Unconfined Compressive Strength (UCS), California Bearing Ratio (CBR) and compaction parameters of the stabilized soil were also analyzed. An attempt was made for establishing a relationship between the tensile strength and compressive strength of the 56 days cured stabilized mixes. Brazilian Tensile Strength (BTS) of lime-fly ash stabilized soil at 56 days curing varied in the range of 22 to 143 kN/m² and UCS from 143 to 2172 kN/m². Remarkable strength increase indicates that the clayey soils can productively stabilize with fly ash and hydrated lime. [ABSTRACT FROM AUTHOR]

India will generate about 283,470 MW of electricity by 2022. Seventy percent of the proposed energy demand is fulfilled by fossil fuel, out of which 54 % of demand is contributed by coal as reported by Krishna (2001). The coal production would be 850 Mt per year to fulfil the demand. Opencast mining plays a major role in meeting the demand of coal for thermal power generation leading to the use of large-capacity haul trucks. Carrying capacity of trucks/dumpers used in opencast mines has grown from 30 to 250 t in recent years. These ultra-capacity trucks/dumpers need well-designed haul roads. At present, design of new haul roads is based on past experience and empirical methods. The sub-grade, sub-base and/or base of haul road typically uses the overburden (O/B) materials which could be replaced by composite material at a particular layer for better performance. There are more than 165 opencast coal mines and many are near to thermal power stations. Present-generation fly ash (FA) from coal-based thermal power plants in India is 135 Mt/year and it is expected to increase to 300-400 Mt/year by 2016-2017 as reported by Çimento (2004). The usage percentage of fly ash is about 60 % leaving the rest as plant waste occupying a huge land area and creating environmental problems. The investigation has characterised fly ash (FA), mine overburden material (O/B) and lime (L). Geotechnical properties of untreated fly ash, mine overburden, fly ash-mine overburden mixes and lime-treated fly ash-mine overburden mixes were investigated using response surface methodology (RSM). Design-Expert software was used to establish the design matrix and to analyse the experimental data. The relationships between the percentage parameters (%FA + %O/B + %L) and experimentally obtained three responses (California bearing ratio (CBR), unconfined compressive strength (UCS) and BTS) were established. RSM was performed to optimize the interactions of input parameter which showed the best conditions for preparation of composite material. According to the obtained results, the model was developed and further analysis was conducted. The experimental values agreed with the predicted ones, thus indicating suitability of the model employed and the success of RSM in optimizing the composite material. Lime percentage, curing period was observed to have strong influences on the strength parameters of the developed FCMs. The best composite material obtained with highest CBR and UCS values. [ABSTRACT FROM AUTHOR]

The article presents a study which investigates the strength of rocks by the use of point load test on meta-sedimentary rocks and its correlation to Uniaxial compressive strength (UCS) and Brazilian tensile strength (BTS). The study involves several methods including the Point Load Test Methods, coring of rocks, and the correlation. The study reveals that most of the rock specimens tested fail in typical tensile splitting failure modes under the point load test.