International Journal of Rock Mechanics and Mining Sciences & Geomechanics Abstracts
Technical noteRock abrasiveness testing for tunnelling
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Cited by (179)
Tunnel boring machine (TBM) tunneling efficiency is influenced by surrounding rocks, TBM design, and interaction between the TBM cutter and rocks. Using a case study from a water conveyance tunnel project located in northwestern China and involving five different lithologies (metamorphic andesite, sandstone, granite, quartz schist, and quartz diorite), this work investigates the water saturation effects on Cerchar abrasivity index (CAI) and its correlations with other physical and mechanical rock properties and TBM disc cutter and energy consumption. The results show that water saturation reduces CAI for all examined rocks except for the quartz diorite at the 90 % confidence level. CAI of saturated rocks (CAIsat) has statistically better correlations with weighted Mohs hardness value of rock minerals (Ha), equivalent quartz content (EQC), and uniaxial compressive strength (UCS), than CAI of dry rocks (CAIdry). The in-situ construction data analyses suggest that the average disc cutter consumption increases exponentially with the rise of CAI values in both dry and saturated conditions, and the water saturation effects significantly reduce the disc cutter consumption within medium-hard and hard surrounding rocks. Both disc cutter and specific energy consumption have a quadratic relationship with the ratio of the maximum cutter spacing to penetration depth (Smax/P), and water saturation can significantly shift the quadratic relationships. Optimal Smax/P ranges for minimizing the disc cutter and energy consumption are recommended for different rocks under dry and saturated conditions. The findings from this study can support estimating cutter and energy consumption with considerations of groundwater effects.
Predicting the cutter consumption rate of mechanical excavators using the Cerchar abrasivity index (CAI) results is possible. However, changing operational parameters in the field may cause differences between the estimated cutter consumption rate based on CAI test results and the real cutter consumption rate observed in the field. One of the essential parameters in the field that affects the cutter consumption rate is the increase in the water content of the excavated rocks. In theory, an increase in the water content of rocks is expected to reduce their abrasivity. In addition, the prediction of cutter consumption rate is based solely on CAI test results conducted on dry surfaces. However, especially during the excavation of low-strength clay-rich rocks, the excavated rock material can adhere to the cutters and block them, leading to a higher cutter consumption rate than initially predicted. This study aims to analyze the rock-pin interaction in CAI tests conducted on wet surfaces of clay-rich rocks and investigate the effect of water saturation on CAI at different scratch lengths. CAI tests were conducted on dry and wet surfaces of 20 clay-rich rocks with low strength at 10, 30, 50, and 70 mm scratch lengths, respectively. The relationships between the CAI test results obtained on dry and saturated rock surfaces were statistically analyzed for each scratch length. A positive linear correlation was found between CAI values obtained on dry (CAIDry) and saturated surfaces (CAISat) at each scratch length. The percentage variations in CAI values at each scratch length were analyzed in detail. It was found that 90 % of samples have higher CAIDry than CAISat at 10 mm scratch length. However, it was observed that as the scratch length increased, the relationship between the CAI values obtained in dry and saturated conditions changed, and the proportion of samples with CAIDry higher than CAISat decreased to 65 %, 55 %, and 25 % at scratch lengths of 30 mm, 50 mm, and 70 mm, respectively. In CAI tests conducted on saturated surfaces, it was observed that the excavated rock material adhered to the test pins, and as the scratch length increased, the increase in CAISat values was considered to be due to this situation. This study revealed the importance of considering the adhesion potential of rocks to cutters at water-saturated conditions for the accurate prediction of cutter consumption in the excavation of clay-rich rocks.
Experimental study on the sandstone abrasiveness via mineral composition and microstructure analysis
2023, PetroleumRock abrasiveness is an important factor affecting the tool's lifetime and efficiency in breaking a rock. Characterizing rock abrasiveness helps in the design, optimization, and mean-life prediction of tools. X-ray diffraction, cast thin section analysis, and CERCHAR abrasiveness tests were performed on 18 different sandstones to characterize rock abrasiveness and explore new methods for characterization. The relationship between the mineral composition and microstructure of sandstone and abrasiveness was investigated. The results show that different structural maturities have varying effects on abrasiveness. In addition, the higher the structural maturity, the more the abrasiveness. Furthermore, in sandstones of the same structural maturity, the abrasiveness increases with equivalent quartz content (EQC). The texture coefficient (TC) and CERCHAR abrasiveness index (CAI) of sandstones with the same structural maturity showed a good linear relationship. Moreover, the correlation coefficients considering the combined parameters are above 0.85. Therefore, obtaining the microstructure and mineral composition of sandstone can effectively characterize rock abrasiveness. It also provides a new method for predicting the abrasiveness of the rock in the well.
Belt conveyors are currently one of the most commonly used technologies for transporting iron ore. Of the components of the conveyor system, the belt is the most expensive and susceptible to damage. Failures due to wear of the rubber cover lead to downtime for corrective maintenance, greater operational risks and performance and economic losses. To improve the tribological performance of conveyor belts, it is necessary to know the main parameters that influence their wear. As wear behavior is not an intrinsic property of a material, the most reliable results are obtained when the wear mechanisms produced in laboratory tests are similar to those in service. In this work, two types were investigated of belt rubber, one new and one worn in service, and four types of iron ore in two class sizes. Loose abrasive wear tests were carried out using the Dry Sand/Rubber Wheel apparatus with belt rubber test pieces and iron ores as abrasives. This work characterized the wear mechanisms that occur in service and in laboratory tests. The predominant wear mechanism found was the formation of Schallamach waves. In the wear tests, Friable Hematite samples presented the highest abrasiveness. In addition, the chemical, mineralogical and morphological features of the iron ore samples were characterized. The high abrasiveness of Friable Hematite was possibly due to the mineral assembly.
Development of a new test method for evaluating the abrasivity of granite building stones during polishing process based on weight loss of abrasive tool
2021, Construction and Building MaterialsAbrasivity of building stones is one of critical parameters during polishing stage in stone processing plants, which can significantly affect the abrasive tool consumption and the processing costs. Hence, the main purpose of this paper is to evaluate the building stone abrasivity based on the weight loss of abrasive tool during polishing process. For this purpose, a new laboratory test rig was developed, which can simulate the polishing process in laboratory scale as far as possible. Using this laboratory rig, a new test method was proposed, which gives an index herein called building stone abrasivity index (BSAI). This index was defined as the weight loss of abrasive tool during polishing process in order to estimate the building stone abrasivity. The proposed test method was carried out on 15 different types of Iranian granite building stones and the correlation of obtained BSAI with the physico-mechanical and petrographic properties of stone was investigated. Meaningful and reasonable relationships were observed. To evaluate the accuracy of proposed method, the correlation of BSAI with two most common abrasivity indices i.e. Schimazek abrasivity factor (F) and rock abrasivity index (RAI) was also discussed. The results indicated that there is a strong relationship between these indices, which verifies the accuracy of proposed method. Furthermore, the laboratory results were compared with data obtained from stone processing plants in order to validate the proposed test method. It was shown that the obtained BSAI has a good agreement with abrasivity of building stones in real conditions of stone processing plants. Therefore, the proposed test can be adopted as an accurate and rapid tool for evaluating the abrasivity of building stones in polishing process. Finally, relationship between BSAI and the abrasive tool lifespan (ATL) was examined and a model was suggested to predict ATL with acceptable accuracy.
Investigation on the relationship among the Cerchar abrasivity index, drilling parameters and physical and mechanical properties of the rock
2021, Tunnelling and Underground Space TechnologyRock abrasivity is an important factor that affects tool wear and tool parameter design, construction efficiency, and cost budgeting during rock excavation. The Cerchar abrasivity index (CAI) is used as a standard parameter to characterize the abrasiveness of rocks. It can be obtained through the Cerchar abrasivity test in a laboratory. However, conventional laboratory Cerchar abrasivity tests and petrophysical and mechanical tests are associated with certain problems, such as long cycles, high costs, and measurement delays, which cannot serve the determination of rock abrasiveness in field. Digital drilling technology is an efficient in situ test method that can effectively link drilling parameters with rock properties. Based on the test results for the CAI and physical and mechanical properties of 13 groups of rock samples collected from southwestern China, this paper focuses on the correlations of the CAI value with rock strength, petrographic characteristics and drilling parameters. By adopting a flat bottom diamond bit that mainly relies on grinding, according to the principle of mechanical balance and energy conservation during rock drilling, the grinding energy per unit volume of rock (ηe) is defined and derived. The univariate regression analysis results show that the uniaxial compressive strength (UCS) and equivalent quartz content (EQC) are the most important factors for explaining CAI and that the CAI can be well estimated using the ηe. Additionally, two optimal regression models for predicting CAI were established using stepwise multiple regression analysis. UCS and ηe were introduced into the model, and the use of both can predict approximately 96% of the variance in the CAI. In addition, a performance evaluation of the models proposed in this paper and previously published CAI prediction models that the prediction models established in this paper are verify statistically more reasonable and reliable than the previously proposed models. The research methods and results provide a new method for the rapid and accurate determination of rock abrasiveness in engineering field.