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The CERCHAR abrasivity test is a widely used index test in earth and subsurface works, delivering numerical values for abrasion that are critical to the selection of excavation tools, TBM performance or cost and project schedule estimates. The test evaluates the wear of the tip of a standardized metal pin after a scratch test on a rock surface. However, excavatability is not considered in this test. The present study presents an approach to assessing the material removal of a rock specimen due to the scratching action of a steel pin. The concept is tested for a broad range of sedimentary, metamorphic and igneous rocks. The volume of removed rock material is determined by measuring the width of the scratch groove and assuming an idealized trapezoid geometry. The CAI and volumetric removal are used to calculate the CERCHAR abrasivity ratio (CAR), and the results are in good agreement with those from the literature where specialized equipment was used. A classification scheme to estimate the excavatability of rock based on the CAI in combination with the material removal of a rock specimen is introduced. Based on the amount of material removed and the wear on the pin, an estimate can be made as to whether the excavation is likely to be economical in terms of time and material costs. The approach does not require additional testing, but rather makes use of the inherent geometry of the steel pin and the scratch groove on the rock specimen. The approach can be implemented as a complementary analysis to the existing CERCHAR test with little additional effort. [ABSTRACT FROM AUTHOR]

The abrasivity of materials is of vital importance in selecting an affordable excavation method in the early stages of a tunneling project. The amount of specific energy and the Mode I and Mode II stress intensity factors in the eroded disc is more than the non-eroded disc. Vickers hardness number rock (VHNR), rock abrasivity index (RAI), Cerchar abrasivity index (CAI), LCPC abrasivity coefficient, and Norwegian University of Science and Technology (NTNU) abrasion test are among the methods for estimating rock abrasivity. Correlations were proposed in this study for estimating the CAI of sandstone and tuff. To achieve reliable comprehensive results, various kinds of sandstone and tuff with different geological properties were selected. Sandstone and tuff samples were collected from different regions. Various tests were then carried out on prepared rock specimens to determine the uniaxial compressive strength (UCS), tensile strength, longitudinal waves velocity, Schmidt hammer rebound hardness, and the equivalent quartz content (EQC). Two correlations were presented by analyzing the experimental results with the help of SPSS and Excel. The first correlation estimated the CAI of sandstone based on the UCS and EQC with a coefficient of determination (R2) of 0.81. Moreover, using data analysis in Excel, another correlation was proposed to estimate the CAI of tuff. The second correlation estimated the Schmidt hammer rebound hardness of tuff with an R2 of 0.88.

Rock abrasivity is an important parameter that influences tool design and wear, the efficiency of tools, and cost during rock excavation. Generally, the abrasiveness of rocks is measured with the Cerchar abrasivity index (CAI). In this research, several Cerchar abrasivity parameters such as penetration of stylus (Ps), the volume of material scratched in the groove (Vm), scratching force (SF), scratching energy (SE), and Cerchar scratching specific energy (CSSE) were determined using an Cerchar device. For evaluating Cerchar abrasivity parameters, 24 rock samples were used comprising igneous, metamorphic, and sedimentary rocks. The new classification was presented based on the Cerchar abrasivity index and Cerchar abrasivity parameters. In this research, the specific energy of the Sievers J miniature drill test (SJ) was calculated for comparison with the specific energy of the Cerchar abrasivity test. Then, the relationship between Cerchar abrasivity parameters with SJ was investigated, new relationships between Cerchar abrasivity parameters and SJ with accurately acceptable presented. The results indicated that the Cerchar abrasion ratio (CAR) is a good parameter for measuring rock abrasivity and cutting. The SJ exhibited a good relation (R2 = 0.78) with CAR. In addition, CAR showed a good correlation (R2 = 0.97) with the specific energy of the rock cutting test (SEcut). The CAR can be used to evaluate abrasivity laboratory tools and the specific energy of a rock cutting test. [ABSTRACT FROM AUTHOR]

The most known and applied method for determining the abrasivity of rocks is the Cerchar Abrasivity Index (CAI). Properties of rocks such as abrasive mineral content, density, strength, and degree of cementation are the main factors affecting abrasivity, and these parameters likewise control their hardness properties. In this study, the average scratch depth formed on the rock surface after the CAI test was determined and it was investigated whether this calculated new parameter had the properties to represent the rock. Measurements were taken from four points along the scratch line formed on the surface with the help of a comparator and the average value was defined as the Cerchar Indentation Depth (CID). Measurements have shown that igneous rocks have CID values in the range of 0.01 mm-0.68 mm. Apart from the CID parameter, nine different properties (hardness, abrasivity, and physical) of fifty igneous rocks were tested. Statistically significant results were obtained by establishing relationships between CID and other rock mechanics tests. In CAI tests, it has been shown that CID measurements can be determined very sensitively if well-leveled core samples with parallel lower and upper surfaces are used. It has been determined that the CID value is directly related to the investigated rock properties and can be used as very useful experimental data in estimation studies. [ABSTRACT FROM AUTHOR]

In any underground excavation project, choosing the best excavation technique and careful preliminary assessments of wear costs and production rates are crucial aspects to consider. The production rate and costs of tools, as well as the frequency of tool replacement, deeply affect the duration and cost‐effectiveness of the whole project. Among the rock‐specific characteristics affecting tool wear, Cerchar abrasivity index (CAI) and uniaxial compressive strength (UCS) play an important role. In this article, the relationship between these two parameters was examined by regression analyses for 237 different rocks with the aim to define a preliminary and expected wear potential of three groups of rocks: sedimentary, metamorphic and igneous rocks. The analysis of the results showed that 86 % of the igneous rocks analysed have a CAI > 2, which is a medium or high level of abrasiveness. In sedimentary rocks, over 70 % of the samples are characterised by low abrasiveness behaviour (CAI < 2). Results obtained for these rocks can represent an instrument for predicting the abrasiveness potential of a rock when the UCS is known associating it with an expected range value of CAI. Metamorphic rocks, on the other hand, cannot be classified in specific ranges of UCS and CAI. For this rock group, therefore, a univocal tool for forecasting could not have been obtained, but analyses of rock type and quartz content show that the mineralogical content cannot be considered the only parameter for a wear analysis. [ABSTRACT FROM AUTHOR]

Since ancient times, rocks and their geomechanical and mineralogical properties have played a fundamental role for realising construction and infrastructure projects. Workability and excavability of the material itself are still decisive factors controlling tool wear and advancement rates. In engineering geology, standardised tests and analyses related to the strength, hardness, abrasivity and mineralogical composition are commonly conducted in this context. The uniaxial compressive strength (UCS), CERCHAR Abrasivity Index (CAI) and equivalent quartz content are widely used parameters for such an assessment, in order to estimate and predict drillability and associated wear of drill bits, cutting discs or chisels. In this article, the correlations between strength, abrasivity and mineral content of various rock types are investigated. The concept of hardness in geotechnics and engineering geology is elaborated in greater detail, shedding light on hardness definitions, testing methods and how hardness parameters are interrelated. Under the aspect that the CAI shows a good correlation with the Mohs hardness commonly used in mineralogy, a novel approach for estimating the CAI is presented. It is suggested that the CAI of a rock can be estimated within 50 % of the actual value, if its UCS exceeds »60 MPa. On the data basis of various rock types analysed from national and international construction projects, the potential and limitations of this method are discussed. [ABSTRACT FROM AUTHOR]

The Cerchar test is the most commonly used method for evaluating rock abrasivity and estimating tool wear. The conventional test results are reported based on the measured changes of the wear parts, and little attention is paid to what happens on the rock surface and scratching force. Since the cutting process is the interactive behavior between cutting tools and rock materials, the changes in both parts are important to represent rock-tool interaction and evaluate cutting efficiency. In the present study, the Cerchar tests have been carried out on eleven types of monomineralic rocks by using an improved West apparatus. The related abrasive parameters have been comprehensively and systematically analyzed, including stylus tip wear, rock material loss, applied horizontal force, and scratching energy. The variation characteristics of those abrasive parameters have been studied. The specific abrasivity ratio (SAR) and scratching specific energy (SSE), which represent the tool wear and energy consumption per unit of rock removal respectively, have been developed to evaluate the cutting efficiency of different rocks. The results show that the SAR and SSE values of the tested rocks have comparable data ranges and variation trends due to the same mathematical treatment of the indices. Under the given rock removal volume, the SAR and SSE could be used to compare and classify the relative cutting efficiency of different rocks. The lower the SAR and SSE values, the less stylus wear and lower energy consumption in the cutting process, indicating higher cutting efficiency. According to their values, the cutting efficiency of the tested rocks is divided into four categories: high cutting efficiency, medium cutting efficiency, low cutting efficiency, and very low cutting efficiency. The SAR -based and SSE -based classifications are consistent for most of the tested rocks, and the SAR -based classification is lower to higher abrasive rocks (pyroxene, hematite, and quartz) due to it considering the influence of stylus tip wear. Hence the SAR -based classification is more suitable for hard and highly abrasive rocks. [ABSTRACT FROM AUTHOR]

The equivalent quartz content – historic review and its future application in abrasivity prediction The assessment of the abrasion resistance of minerals and their influence is an important aspect in engineering geology and rock mechanics. Questions with regard to rock excavation and the expected wear parameters play a decisive role. Various test methods have been developed over the decades to assess the hardness properties and abrasiveness of minerals and rocks. These include direct tests on rock samples, hardness tests but also parameters derived from mineralogical and petrographic data, such as the equivalent quartz content FEQ. The values used today for determining the FEQu exist since more than 100 years, and are named after August Rosiwal (1860–1923), the pioneer in the field of grinding tests, referred to as Rosiwal factors. The present work deals with this approach, compiles the factors of various authors, and establishes correlations with other hardness parameters. Using laboratory data, the FEQu are calculated and compared amongst the different sources. It is also shown how the FEQu can be directly related to the widely used cerchar test, on the basis of cerchar abrasivity index (CAI) values of selected reference minerals. The FEQu cannot record structural influences, but quartz as a common reference in the cerchar test and FEQu offers the possibility of directly linking the two parameters. [ABSTRACT FROM AUTHOR]

Disc cutter wear is a crucial problem that influences the working efficiency and security of hard rock tunnel-boring machines (TBMs). When tunneling and rock breaking with TBM, the cutters at the forefront of the cutter head directly contact the tunnel face, where wear is serious due to a harsh working environment. In this study, the Cerchar abrasivity index (CAI) of various rock samples was obtained by using the ATA-IGG I rock abrasion servo system. Additionally, a series of small-size cutter wear experiments were carried out on an SP3-I composite abrasion test platform, and the fitting relationship between cutter wear and rock abrasion value was obtained. A cutter wear prediction method was established by measuring the cutter wear and rock CAI of the project built section and the rock CAI of the project unbuilt section. Based on the experimental results, the effects of different tunneling parameters (penetration speed, rolling speed) and tip width on cutter wear were analyzed. In the study of cutter wear, attention should be paid to the influence of load, vibration and temperature on the cutter wear removal mechanism. It is suggested that wide-tip and narrow-tip cutters should be arranged alternately on a TBM cutter head to give full play to the lateral rock crack ability developed by the wide-tip cutter and the radial rock crack ability developed by the narrow-tip cutter, so as to reduce wear on the cutter and improve the efficiency of TBM rock breaking. The results of this research provide a reference for optimization design and performance selection of a TBM cutter ring and cutter head. [ABSTRACT FROM AUTHOR]

Thermo-mechanical drilling combines the advantages of flame thermal treatment and rotary head drilling to achieve a high penetration rate in granitic rocks and a low wear rate of drill bits. This drilling strategy has been recognized as a potential technique to develop deep geothermal energy, but further improvement is still needed to optimize the drilling efficiency, such as the reduction in drill bit wear in thermally treated rocks. We use the Cerchar abrasivity test to investigate the abrasivity characteristics of Bukit Timah granite after the thermal treatment at different high temperatures. The Cerchar abrasivity index (CAI) decreases from 3.5 at 25 °C to 3.0 at 400 °C, remains constant between 400 and 600 °C and subsequently increases to 4.1 at 800 °C. Based on the meso-scale and micro-scale observations using polarizing microscope, 3D scanner and scanning electron microscope, the reduction in CAI value at lower temperatures is due to the abrasive wear of stylus tip, while the mechanical interaction between the stylus cone and abrasive minerals causes the increase in CAI value at higher temperatures. The Cerchar abrasivity test results indicate that overheating rocks may result in the exposure of drill bits to more abrasive minerals and enhance drill bit wear. [ABSTRACT FROM AUTHOR]

The prediction of rock cuttability to produce the lignite deposits in underground mining is important in excavation. Moreover, the certain geographic locations of rock masses for cuttability tests are also significant to apply and compare the rock cuttability parameters. In this study, sediment samples of two boreholes (Hole-1 and Hole-2) from the Sagdere Formation (Denizli Molasse Basin) were applied to find out the cerchar abrasivity index (CAI), rock quality designations (RQD), uniaxial compressive strengths, Brazilian tensile strengths and Shore hardnesses. The Sagdere Formation deposited in the terrestrial to shallow marine conditions consists mainly of conglomerates, sandstones, shales, lignites as well as reefal limestones coarse to fine grained. A dataset from the fine grained sediments (a part of the Sagdere Formation) have been created using rock parameters mentioned in the study. Dataset obtained were utilized to construct the best fitted statistical model for predicting CAI on the basis of multiple regression technique. Additionally, the relationships among the rock parameters were evaluated by fuzzy logic inference system whether the rock parameters used in the study can be correlated or not. When comparing the two statistical techniques, multiple regression method is more accurate and reliable than fuzzy logic inference method for the dataset in this study. Furthermore, CAI can be predicted by using UCS, BTS, SH and RQD values based on this study. [ABSTRACT FROM AUTHOR]

Cerchar Abrasion Ratio (CAR) as a New Indicator for Assessing Rock Abrasivity, Rock-Stylus Interaction and Cutting Efficiency Keywords: Cerchar abrasion ratio; Cerchar abrasivity index; Cutting efficiency; Rock abrasivity; Rock-stylus interaction EN Cerchar abrasion ratio Cerchar abrasivity index Cutting efficiency Rock abrasivity Rock-stylus interaction 3363 3371 9 07/02/20 20200701 NES 200701 Introduction Similar to stiffness, strength or fracture toughness, abrasivity is a characteristic property of rocks. In medium to low abrasive limestone and dolomite, since material removal volume and stylus wear volume increase or decrease simultaneously, a medium CAR value is calculated. The CAI value for sandstone is very similar to that of greywacke and only slightly lower than that of gneiss, but the CAR value is about 1.5 times higher than that of greywacke or gneiss. [Extracted from the article]

Rock abrasivity is the main factor that causes erosion of excavation tools and is usually quantified by the Cerchar Abrasivity Index (CAI). Although Cerchar abrasivity tests are easy to perform, they are time consuming and require a relatively high volume of rock samples. Having good correlations of CAI values and other faster and simpler tests is therefore of great interest, since it results in time and budget savings when controlling excavating tool wear. Based on the results of 73 andesitic rock samples coming from the central area of Ecuador, this paper presents a series of artificial neural networks developed to find a good estimation of CAI values of andesitic rocks from their petrographical properties. The network showing the best performance (R2 equal to 97%) is identified and a detailed process to estimate CAI value using the network developed is described. [ABSTRACT FROM AUTHOR]

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 (CAI sat) has statistically better correlations with weighted Mohs hardness value of rock minerals (H a), equivalent quartz content (EQC), and uniaxial compressive strength (UCS), than CAI of dry rocks (CAI dry). 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 (S max / P), and water saturation can significantly shift the quadratic relationships. Optimal S max / 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. • Water saturation tends to reduce Cerchar abrasivity index at the 90 % confidence level. • Saturated Cerchar abrasivity index can be estimated with various rock properties. • Water reduces disc cutter wear for medium hard and hard rocks by up to 57 %. • Optimal cutter spacing and penetration depth ratios are recommended. [ABSTRACT FROM AUTHOR]

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 (CAI Dry) and saturated surfaces (CAI Sat) 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 CAI Dry than CAI Sat 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 CAI Dry higher than CAI Sat 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 CAI Sat 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. • A problem encountered during the excavations in the field was investigated through the approximately 800 CAI tests. • The effect of rock materials adhering to the test pin on CAI was investigated. • Standard CAI test results may be inadequate for predicting cutter consumption in water-saturated clay-rich rocks. • To estimate an accurate cutter consumption rate, the adhesion potential of clay-rich rocks has to be considered. [ABSTRACT FROM AUTHOR]

An experimental study that contributes to the understanding of the relationships between petrographic features and engineering properties of igneous rocks is conducted. To this end, a wide range of igneous rocks were tested for their engineering properties including abrasivity (Cerchar abrasivity index), mechanical (point load strength index Is(50)), basic physical (dry density and porosity) and dynamic (P-wave velocity) characteristics. Moreover, a semi-automatic method has been developed to analyze petrographic data that relies on digital image acquisition from representative parts of representative thin sections of samples, semi-automatic image segmentation and image analysis. The method quantifies 18 petrographic features including size descriptors (area, perimeter, equivalent circular diameter, minimum Feret's diameter, maximum Feret's diameter), shape descriptors (elongation, orientation, eccentricity, compactness, rectangularity, solidity, convexity), rock fabric coefficients (index of interlocking, index of grain size homogeneity, texture coefficient) and mineralogical indices (saturation index, feldspathic index, colouration index). The Pearson's correlation coefficient and multivariate regression analysis are employed to analyze the relationships between extracted petrographic features and engineering properties. In general, fine-grained and basic igneous rocks compared to the acidic and coarse-grained ones possess higher engineering quality and lower abrasiveness potential. The results imply that mineralogical composition tends to be more important than rock fabric characteristics in determining the engineering properties of igneous rocks. Furthermore, among rock fabric characteristics, size descriptors have significant influence on the engineering properties. Overall, it was found that mineralogical composition and rock fabric characteristics provide a suitable complement to reliably predict engineering properties of igneous rocks. [ABSTRACT FROM AUTHOR]

An important issue in any rock engineering project is the adequate prediction of tool consumption. Excavation tools are subjected to wear, and repair/replacement of those tools is usually an important expense on any excavation budget. The key factor that affects wear of excavation tools is rock abrasivity. In mining and civil engineering, rock abrasivity is typically measured by the Cerchar abrasivity index (CAI), which is obtained in laboratory from a Cerchar abrasivity test. This paper studied the relation between CAI and the chemical compounds and petrographical properties of andesitic rocks from the central area of Ecuador. A series of regression analyses are performed to study the influence of the different chemical compounds and petrographical properties on the CAI value. Results show that it is possible to make a good estimation of CAI from the plagioclase grain size and/or the content of SiO2, FeO, MgO, CaO, Na2O and K2O compounds. [ABSTRACT FROM AUTHOR]

Ten potentially abrasive rock samples selected from various locations of Pakistan covering igneous, metamorphic and sedimentary rocks were subjected to a comprehensive laboratory testing program. The experimental work includes the NTNU/SINTEF abrasion value steel (AVS) and Sievers' J-miniature drill (SJ) tests accompanied by CERCHAR and LCPC rock abrasivity tests. The results of SJ tests and AVS tests were further utilized to compute the cutter life index (CLI), which estimates the life of tunnel boring machine (TBM) disc cutter rings in boring hours. In this research, a comparative study was performed on an NTNU/SINTEF rock abrasivity device by varying the particle size of rock abrasion powder and rotational test speed of the steel disc. The NTNU/SINTEF AVS test results showed a gradual decrease in abrasivity with the corresponding decrease in grain size of test fractions. An increase in the wear of the test piece was observed at a test speed of 10 rpm as compared to the standard test speed of 20 rpm. Relevant correlations of CLI, SJ-value and AVS with CERCHAR abrasivity index (CAI) and LCPC abrasivity coefficient (ABR, g/t) were also discussed. [ABSTRACT FROM AUTHOR]

The wear evolution indicated that abrasive wear is the dominant wear mechanism for disc cutter wear. Considering the uneven rolling force distribution on the cutterhead, the relative installation radius is introduced to reflect the influence of installation radius on the rolling force, and the CSM rolling force model is corrected based on linear assumption. To accurately predict disc cutter wear, the relative sliding distance between disc cutters and rock is derived based on corrected rolling force and contact theory. The effect of installation radius, cutters radius and penetration on the relative sliding distance is investigated, the results illustrated that the relative sliding distance increase with the installation radius and penetration, conversely, the relative sliding distance increase with the disc cutter radius decrease. In addition, the relationship between wear coefficient and Cerchar Abrasivity Index (CAI) is analyzed by a series CAI test. According to CAI change trend as stylus sliding distance, the effect of stylus shear failure on the abrasivity property within initial test stage was excluded. Furthermore, A new model is proposed to predict disc cutter wear based on the relative sliding distance and wear coefficient. And the effect of installation radius, cutters radius, Uniaxial Compressive Strength (UCS), CAI et al. on the disc cutter wear is investigated, the results illustrate that the disc cutter wear increase with installation radius, penetration, UCS, CAI and spacing between adjacent cutter, conversely, the disc cutter wear increase with the cutter radius and thickness decrease. Finally, the accuracy of proposed model is verified by Yintao water conveyance tunnel project. The research of parameters provides a theoretical basis for optimizing excavation parameters and reducing cutters wear. • Rolling force is corrected by installation radius to ensure slip ratio's accuracy. • The slip ratio model is proposed to estimate cutter sliding distance when cutting. • The wear coefficient and Cerchar abrasivity index are exponentially correlated. • A novel wear model is proposed based on wear coefficient and sliding distance. • Penetration, cerchar index and cutter thickness significant effect disc cutter wear. [ABSTRACT FROM AUTHOR]

The Cerchar abrasivity index (CAI) is one of the most widely known index method for identification of rock abrasivity. It is a simple and fast testing method providing reliable information on rock abrasiveness. In this study, the relationships between the CAI and some rock properties such as uniaxial compressive strength (UCS), point load strength, Brazilian tensile strength and Schmidt rebound hardness, and equivalent quartz content (EQC) are examined. The relationships between the CAI and drill bit lifetime is also investigated and the type of drill bit wear observed is mentioned. Additionally, the CAI is modeled using simple and multiple linear regression analysis based on the rock properties. Drill bit lifetime is also modeled based on the CAI. The results show that the CAI increases with the increase of the UCS, point load strength, Brazilian tensile strength, L-type and N-type Schmidt rebound hardness, and the EQC. It is concluded that the higher and the lower bit lifetime are obtained for marl and andesitic-basaltic formation, respectively. Moreover, flushing holes, inserted button, button removal, and failures of button on the bits are determined as the type of drill bit wear. The modeling results show that the models based on the UCS and the EQC give the better forecasting performances for the CAI. [ABSTRACT FROM AUTHOR]

The Cerchar abrasivity index (CAI) obtained from Cerchar abrasivity tests is an indicator of abrasiveness of rocks, and widely used for the estimation of bit/cutting tool life and wear rates in various mining and tunnelling applications. The effect of scratch length on CAI is investigated in this study by use of West apparatus and 6 different steel styluses with Rockwell Hardness of HRC40-42, HRC44-46, HRC48-50, HRC50-52, HRC54-56, and HRC58-60. The tests are carried out on 15 different rock samples (sedimentary, igneous, and metamorphic) on which rough and sawn cut surfaces with scratch lengths varying between 2 mm and 20 mm with an increment of 2 mm, thus resulting in total 27,000 scratches. It is observed that the CAI values between 85% and 93% are reached at the sliding distance of 10 mm while about the final CAI value of 99% is reached at 15 mm. It is also observed that the CAI values on rough surfaces are about 18% higher than those on sawn cut surfaces. Besides, it is determined that the most suitable surface condition in CAI test is sawn cut surfaces according to the coefficient of variation of CAI values in measurement depending on the stylus hardness and the measurement surface condition. [ABSTRACT FROM AUTHOR]

During the last decades, the rapid developments in mining operations and tunnel construction have lead to a rapid increase in the number of excavation machines. In order to achieve the expected benefits of mechanical excavation machines, these machines should be selected in accordance with the characteristics of rocks. Tool abrasion is an important factor in hard rock tunnelling, mining, and it is highly affected by rock abrasivity. There are several methods to identify the rock abrasivity. One of the commonly used abrasion test in rock is the Cerchar abrasivity index (CAI). Before selection and implementation of excavating machines, physical and mechanical properties of the rocks should be determined. It’s known that, physical-mechanical properties of granitic rocks are generally better than those of many rock types although they cause some difficulties (tool wear, lost time, etc.) in excavation and increase the cutter costs. The purpose of the present study is to determine empirical relationships between CAI and physical-mechanical properties of different granitic rocks using regression method. In this study, some laboratory experiments were conducted on samples collected from granite quarries in different parts of Turkey, particularly from the Marmara Region. Firstly, petrographical, mineralogical and physical-mechanical characteristics of the collected granitic rocks were determined. Then, empirical relationships between these properties and CAI were determined using method of regression analysis. According to the results obtained, a strong correlation is found between CAI value, quartz content and quartz size of the granitic rocks. In addition, the uniaxial compressive strength and indirect tensile strength of the studied granitic rocks increase as CAI increases. Surface roughness, waviness and peak number of granitic rocks lead to an increase in CAI. On the contrary, Bohme abrasion resistance increases while CAI decreases. [ABSTRACT FROM AUTHOR]

Forty-six rock units selected from various locations of Pakistan comprising of igneous, sedimentary and metamorphic rocks were subject to a comprehensive laboratory testing program consisting of two parts. The first part included CERCHAR abrasivity tests and measurement of physical rock properties including uniaxial compressive strength (UCS), Brazilian tensile strength (BTS), dry density, porosity, and P-wave velocity ( V ). The second part involved petroghraphic thin section analyses of 40 selected abrasive and non-abrasive rock samples along with the determination of wear factors such as Schimazek's F value and Rock Abrasivity Index (RAI). The CERCHAR abrasivity tests were conducted on sawn (CAI) and freshly broken (CAI) rock surfaces employing top and side viewing methods for the measurement of wear flat of the stylus tip. This paper statistically confirms the previous work on the influence of wear flat measurement methods and rock surface conditions on the CERCHAR Abrasivity Index (CAI) values. It was found statistically that CAI and CAI values measured from top view of the test stylus were 17 and 19 % higher, respectively, in comparison to CAI and CAI values measured using side viewing stylus measurement technique. Further the correlations of CAI with RAI, Schimazek's F value, petrographic, and physico-mechanical rock properties are also discussed. [ABSTRACT FROM AUTHOR]

The estimation of abrasivity on granitic rocks is very important in mechanical excavators. The mineralogical composition and physico-mechanical properties of the rock affects of abrasivity properties such as the type and size of the mineral grains and strength. Tool wear is an important parameter in hard rock tunnelling and mining applications that are highly affected by rock abrasivity. The estimation of the Cerchar abrasivity index (CAI) from geological properties is useful for excavation costs. For this purpose, CAI, chemical, petrographical, physical and mechanical tests were carried out on 12 granitic rocks taken from different regions of Turkey. The test results were analysed using the method of least squares regression. Multiple regression models having good correlation coefficients were obtained for the granitic rocks. The CAI tests were correlated with chemical compound and a weak relation was determined. The regression analysis was also repeated for petrographical, physical, and mechanical properties. Statistically meaningful correlations were determined between all geological properties and CAI. Then multiple regression analysis was applied to all geological properties to find the more significant relations. Results show that shore scleroscope hardness, water absorption, and the waveness average prove to be the best for estimating CAI of granitic rocks. [ABSTRACT FROM AUTHOR]

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The wear rate of working tools during the cutting and drilling of rocks is closely related to the abrasiveness of those rocks. As the contact area of the tools increases, due to wear, the specific cutting energy will also increase, and that directly affects the overall consumption of excavation tools. A new artificial intelligence (AI) based model has been developed. It utilizes acoustic emission (AE) and rock properties as main indicators of rock abrasivity, estimated by Cerchar Abrasivity Index (CAI). AE sensors are attached to both the Cerchar testing apparatus and the rock in question while conducting scratch tests using hardened steel pins of 42 and 56 HRC. Prior to the implementation of Artificial Neural Network (ANN) modeling, the selection of independent variables was carried out via Gamma test and V-ratio analyses. As a result, AE parameters, such as total number of events and root mean square of signal, in addition to testing parameters (i.e. uniaxial compressive strength, Young׳s Modulus, quartz content and pin hardness) are found to be the optimum model input combination needed to accurately predict CAI. [ABSTRACT FROM AUTHOR]

The present paper mainly describes the prediction methodology to determine the Cerchar Abrasiveness Index and Penetration Rate related to rock excavation using simple geomechanical parameters as predictors. As abrasiveness of rocks is influenced by many geomechanical parameters, an attempt is made to use these parameters for its prediction using Multivariate Regression Analysis and Artificial Neural Networking. Abrasiveness Index as well as Penetration Rate are very vital in deciding the economics of the excavations as they directly govern the wear and tear of drill bit. It was observed that ANN shows a better prediction capability than MVRA using UCS, Point load index, P wave velocity and Young’s modulus as predictors. [ABSTRACT FROM AUTHOR]

Schmidt hammer hardness values ( SHH 1 , SHH 2 , and deformation coefficient) are used to determine the performance of large diameter circular saws. The measured Schmidt hammer hardness values are correlated with the physical and mechanical properties of natural stones and areal slab production rates of large diameter circular saws. Two statistical models for prediction of the areal slab production rates for these machines are developed, which is very important in decision making for engineers. A simple statistical model is suggested taking into account the deformation coefficient and a multiple regression model is also suggested by using the deformation coefficient and Cerchar abrasivity index. The reliability of these models is tested against actual performance of large diameter saws. Verifications and comparisons showed that the models suggested in this study may be a very useful and reliable tool for prediction of areal slab production rates for large diameter circular saws. [ABSTRACT FROM AUTHOR]

The development of some predictive models for the geomechanical properties of fault breccias will be useful for geo-engineers, because the preparation of smooth specimens from the fault breccias is usually tedious and expensive. In this study, simple and multiple regression analysis were applied to the data pertaining to Misis Fault Breccia to develop predictive models for the differential stress (Δ σ) from non-destructive methods including the Cerchar abrasivity index (CAI). As a result of simple regression analysis, strong relations between Δ σ and indirect properties were not found. The CAI was included in the best multiple regression model for the prediction of Δ σ. The significance of derived models was statistically tested. It was concluded that the CAI is a useful property for the prediction of Δ σ of Misis Fault Breccia. [ABSTRACT FROM AUTHOR]

The Cerchar abrasion index is commonly used to represent rock abrasion for estimation of bit life and wear in various mining and tunneling applications. Although the test is simple and fast, there are some discrepancies in the test results related to the equipment used, condition of the rock surface, operator skills, and procedures used in conducting and measuring the wear surface. This paper focuses on the background of the test and examines the influence of various parameters on Cerchar testing including pin hardness, surface condition of specimens, petrographical and geomechanical properties, test speed, applied load, and method of measuring wear surface. Results of Cerchar tests on a set of rock specimens performed at different laboratories are presented to examine repeatability of the tests. In addition, the preliminary results of testing with a new device as a potential alternative testing system for rock abrasivity measurement are discussed. [ABSTRACT FROM AUTHOR]

Shore hardness has been used to estimate several physical and mechanical properties of rocks over the last few decades. However, the number of researches correlating Shore hardness with rock cutting performance is quite limited. Also, rather limited researches have been carried out on predicting the performance of chain saw machines. This study differs from the previous investigations in the way that Shore hardness values (SH, SH, and deformation coefficient) are used to determine the field performance of chain saw machines. The measured Shore hardness values are correlated with the physical and mechanical properties of natural stone samples, cutting parameters (normal force, cutting force, and specific energy) obtained from linear cutting tests in unrelieved cutting mode, and areal net cutting rate of chain saw machines. Two empirical models developed previously are improved for the prediction of the areal net cutting rate of chain saw machines. The first model is based on a revised chain saw penetration index, which uses SH, machine weight, and useful arm cutting depth as predictors. The second model is based on the power consumed for only cutting the stone, arm thickness, and specific energy as a function of the deformation coefficient. While cutting force has a strong relationship with Shore hardness values, the normal force has a weak or moderate correlation. Uniaxial compressive strength, Cerchar abrasivity index, and density can also be predicted by Shore hardness values. [ABSTRACT FROM AUTHOR]

Abstract: The derivation of some predictive models for the geomechanical properties of fault breccias will be useful due to the fact that the preparation of smooth specimens from the fault breccias is usually difficult and expensive. To develop some predictive models for the uniaxial compressive strength (UCS) and elastic modulus (E) from the indirect methods including the Cerchar abrasivity index (CAI), regression and artificial neural networks (ANNs) analysis were applied on the data pertaining to Misis Fault Breccia. The CAI was included to the best regression model for the prediction of UCS. However, the CAI was not included to the best regression model for the prediction of E. The developed ANNs model was also compared with the regression model. It was concluded that the CAI is a useful property for the prediction of UCS of Misis Fault Breccia. Another conclusion is that ANNs model is more reliable than the regression models. [ABSTRACT FROM AUTHOR]

Abstract: The determination of index properties of rock, such as Cerchar Abrasivity Index, Shore Hardness, Protodyakonov Index and Vickers Hardness in laboratory or insitu conditions is time-consuming and requires special equipment and expertise. However, the use of P-wave technology to measure the P-wave velocity of rock is a relatively simple task because the portable equipment can be used in the laboratory or in the field without tedious preparation of rock cores and it is non-destructive. This paper presents an experimental study of the measurement of P-waves of several types of igneous, sedimentary and metamorphic rock. The index properties were also determined in the laboratory to obtain correlations between P-waves and various index properties. Good linear relationships were found between all the index properties determined and the P-wave measurements. [Copyright &y& Elsevier]

Abstract: This paper examines the relations between Cerchar abrasivity index (CAI) and petrographic properties of Coal Measures Rocks in the Zonguldak Coal Basin, Turkey. In this study, petrographic properties and abrasivity indices of 29 sedimentary rock samples were determined and the values of CAI and petrographic analysis results were compared. A good linear relationship between CAI and average quartz grain size parameters was found. The test results also showed that abrasivity was affected by the mineralogical composition, cement type, degree of cementation, quartz content, and average quartz grain size. It was found that abrasivity of rock was decreased by the low grade of cementation between abrasive minerals. CAI values and petrographic properties were used to estimate tool consumption in underground works in the Zonguldak Coal Basin. It was observed that when CAI values increased, tool consumption increased. [Copyright &y& Elsevier]

• The mathematical model between rock grinding energy and drilling parameters is established. • EQC and UCS are the most important parameters for explaining the CAI. • The rock grinding energy is used to quickly and easily estimate the CAI without laboratory testing. • The rock grinding energy is an important parameter to evaluate the rock abrasiveness in field. Rock 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. [ABSTRACT FROM AUTHOR]