Cerchar Abrasivity Test Research Articles

Abrasivity database of different genetic rocks based on CERCHAR Abrasivity Test

Rock abrasivity is one of the main factors affecting the wear of rock-cutting tools, which is usually quantified by the CERCHAR Abrasivity Index (CAI). Researchers and engineers study tool wear and predict tool life based on the CAI of rocks. However, there is still a lack of a dataset on rock properties, especially the abrasivity of various rocks. This paper reports the abrasive dataset of 10 kinds of rocks, including sedimentary rocks, metamorphic rocks, and igneous rocks, with the aid of the CERCHAR Abrasivity Test and digital measurement techniques. The dataset comprises rock abrasivity data, point cloud data for visualization, scratch photos, CERCHAR Abrasivity Test force data, and mechanical properties (uniaxial compressive strength) of rock samples. This dataset facilitates future research on rock abrasivity and rock-cutting tool wear.

Analysis of the effect of a banded structure on jaspilite abrasiveness

Ore fragmentation is the most expensive step of mineral processing. The choice of lining materials on this type of machinery is based on ore abrasiveness. However, traditional abrasiveness tests do not consider particularities, such as the ore structure. The effect of the banded structure on jaspilite abrasiveness by conducting a CERCHAR abrasiveness test was investigated. A factorial design was applied, and the analysis included three test directions: parallel to the band of quartz minerals, parallel to the band of iron oxide minerals, and perpendicular to the bands. A hypothesis test was executed, and the difference in abrasiveness between the direction parallel to the quartz band and that parallel to the iron oxide minerals was found to be nonsignificant. However, the difference in abrasiveness between the direction parallel to the iron mineral band and the perpendicular direction was significant. Analysis of the forces monitored during the tests showed similar behavior for the different conditions. The normal load and friction force were correlated with mineral removal and characteristics of the jaspilite, such as porosity and the banding boundary. Furthermore, the observed wear mechanisms were in the transition region between mild and severe wear for all test conditions.

Laboratory Test Campaign Aimed at the Analysis of an Uncommon Wear Phenomenon in a Marble Quarry

The use of ornamental stones has a historical value that makes them strategically precious in Italy; marble can offer high performance in architectural applications, even though the variability of the rock mass requires detailed studies to optimize the exploitation techniques and reduce waste. Italy is world famous for its marble, which is extracted mainly through chainsaw cutting machines, which are currently used intensively due to their high-safety working conditions compared to alternative techniques and for their great versatility, especially in underground applications. Although this cutting technique is well-rooted, an uncommon problem of tool wear was found in the quarry under study, which strongly affected productivity. A series of laboratory test were carried out to estimate the wear potential of the rock and the suitability of the tools. The Cerchar abrasivity test highlighted a mean wear potential for the marble of 2.77, while microhardness outcomes pointed out the presence of quartz veins in the tested material (values over 10,000 MPa). Finally, additives typically used in the conditioning process of EPB machines in tunneling were tested with the purpose of reducing the extent of wear. A reduction of about 50% in the wear (in terms of weight lost) was obtained for a moisture content of 9%.

Investigation on the relationship among the Cerchar abrasivity index, drilling parameters and physical and mechanical properties of the rock

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.

Study of some testing condition-based factors affecting the Cerchar abrasivity index (CAI)

Since the development of the Cerchar abrasivity test, various factors affecting the Cerchar abrasivity index (CAI) have been investigated by many researchers. However, some dominant factors, such as surface condition, testing distance, and velocity, are still under discussion due to their sensitivity to the test results. For this purpose, a newly designed Cerchar test device is proposed and applied, by which the testing distance is controlled and the testing velocity can be pre-set and kept constant. Using this device, the effect of some testing condition-based factors on the CAI is studied based on four types of rocks (granite, sandstone, slate, and gneiss). In addition, since not much attention was paid to the effect of rock anisotropy on the CAI, this factor is investigated based on two intact foliated metamorphic rocks, slate, and gneiss.

Temperature-dependent abrasivity of Bukit Timah granite and implications for drill bit wear in thermo-mechanical drilling

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.

Cerchar Abrasivity Index Estimation of Andesitic Rocks in Ecuador from Petrographical Properties Using Artificial Neural Networks

Abstract 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 pe...

Investigation of scratching specific energy in the Cerchar abrasivity test and its application for evaluating rock-tool interaction and efficiency of rock cutting

Wear occurs on mechanical tools during rock cutting and drilling, or any other kind of mechanical based excavation of rocks. The determination of rock abrasivity plays therefore a key role for estimating the tool's lifetime and for evaluating the economic efficiency. Due to simple design and convenient handling, the Cerchar abrasivity test is commonly used to assess the rock abrasivity and to predict the tool wear. However, the abrasivity index reflects only the abrasion of the stylus, and does not consider what happens on the tested rocks, as well as on how the stylus interacts with the rock during the scratching process. In this paper, an instrumented West apparatus is used to determine the applied horizontal force in the Cerchar test. The area under the force-displacement curve represents the consumed scratching energy. The material removed from the rock surface is measured using a digital microscope. Then, a new parameter called Cerchar specific energy, which is defined as the ratio of scratching energy to material removal volume, is proposed to assess the rock abrasivity, to describe the rock-stylus interaction, as well as to evaluate the efficiency of rock scratching, which can be used as indicator for rock cutting or drilling efficiency.

Development of a GEP model to assess CERCHAR abrasivity index of rocks based on geomechanical properties

The CERCHAR abrasivity test is very popular for determination of rock abrasivity. An accurate estimation of the CERCHAR abrasivity index (CAI) is useful for excavation operation costs. This paper presents a model to calculate CAI based on the gene expression programming (GEP) approach. This model is trained and tested based on a database collected from the experimental results available in the literature. The proposed GEP model predicts CAI based on two basic geomechanical properties of rocks, i.e. rock abrasivity index (RAI) and Brazilian tensile strength (BTS). Root mean square error (RMSE), mean absolute error (MAE), Nash-Sutcliffe efficiency (NSE), and coefficient of determination (R2) are used to measure the model performance. Furthermore, the developed GEP model is compared with linear and non-linear multiple regression and other existing models in the literature. The results obtained show that GEP is a strong technique for the prediction of CAI.

Performance of roadheaders in low strength pyroclastic rocks, a case study of cold storage caverns in Cappadocia

Roadheaders are one of the mechanical excavators widely used in mine roadway excavation or tunneling projects. Therefore, researchers have usually investigated the performance of roadheaders only for these working areas. However, roadheaders can be also used in excavations of the other underground spaces which can be designed as cold storages, hotels, restaurants etc. In Cappadocia region, cold storage caverns (CSC) are excavated also by roadheaders and CSCs are generally constructed in tuff formations that are very soft, homogeneous, and can be carved out easily. The use of roadheaders for the excavation of CSCs may show some different characteristics in mining and tunneling projects. For example, the excavated formations are generally accepted as massive and since the drainage problem, water is not used during the excavations of CSCs. For such reasons, the performance of a roadheader may differ from the estimated performance calculated in the previous models. In this study, field performance of roadheaders were analyzed in eight different CSCs excavated in low strength pyroclastic rocks, in Cappadocia region. The excavation performance and cutter consumptions of the roadheaders were recorded in detail and the instantaneous cutting rates (ICRs) of the machines were determined. The Cerchar abrasivity tests and physico-mechanical tests were carried out on the core samples collected from the project areas. Relationships between field ICRs and results of physico-mechanical tests were analyzed. Based on the uniaxial compressive strength (UCS), a new site specific model for predicting roadheader performance was proposed for low-strength rocks with up to 10 MPa UCS. The ICRs of the roadheaders were calculated using some previously developed empirical models and compared with the field performance of the roadheaders and the results of the newly developed model. Similarly, a new model based on the Cerchar abrasivity index (CAI) for predicting cutter consumption rate of roadheaders was proposed to excavate low-strength tuffs. The amount of cutter consumption was also calculated using some previous models for each CSC project and compared with the field data.

Assessment of cerchar abrasivity test in anisotropic rocks

There have been developed a number of methods to assess the abrasivity of rock materials with the increased use of mechanized rock excavation. These methods range from determination of abrasive and hard mineral content using petrographic thin section analysis to weight loss or development of wear flat on a specified cutting tool. The Cerchar abrasivity index (CAI) test has been widely accepted for the assessment of rock abrasiveness. This test has been considered to provide a reliable indication of rock abrasiveness for isotropic rocks. However, a great amount of rocks in nature are anisotropic. Hence, viability assessment of Cerchar abrasivity test for the anisotropic rocks is investigated in this research. The relationship between CAI value and quartz content for the isotropic rocks is well known in literature. However, a correlation between EQ, F-Schimazek value, Rock Abrasivity Index (RAI) and CAI of anisotropic rocks such as phyllite was done first time in literature with this research. The results obtained with this research show F-Schimazek values and RAI values should be considered when determination of the abrasivity of anisotropic rocks instead of just using Cerchar scratch test.

Assessing the uniaxial compressive strength of extremely hard cryptocrystalline flint

Cryptocrystalline flint is an extremely hard siliceous rock that is found in chalk formations. The chalk is frequently a prefered rock type, which in recent decades is often used as a host for underground rock caverns and tunnels in Europe and North America. A reliable estimation of the uniaxial compressive strength (UCS) of the extremely strong flint, with an average UCS of about 600 MPa will provide guidance for a proper engineering design, where flint is encountered, thereby avoiding project progress delay, litigation as well as economic consequences. Conventional UCS measurement using core samples is cumbersome for flint due to the extreme strength and hardness of the rock, for which the core sample preparation process is often extremely difficult. In this study, the UCS prediction models of flints collected from the North-West Europe were developed and the validity of the developed models was investigated. A series of laboratory index tests (comprising the three-point-bending, point load, ultrasonic velocity, density, Shore hardness and Cerchar Abrasivity tests) were perfomed. The index test results were correlated with the UCS values previously determined in the laboratory using both cylindrical and cuboidal specimens to develop the UCS prediction models. Regression analysis of the UCS and the index test results was then performed to evaluate for any potential correlations that can be applied to estimate the UCS of the cryptocrystalline flint. Intensive validity and comparison studies were performed to assess the performance of the proposed UCS prediction models. This study showed that UCS of the tested flint is linearly correlated with its point load strength index, tensile strength and compressional velocity, and is parabolically correlated with its density. The present study also demonstrated that only a couple of the previously developed empirical UCS models for estimating UCS are suitable for flint, which should be used with care.

Identification of abrasion regimes based on mechanisms of wear on the steel stylus used in the Cerchar abrasiveness test

The wear of tools in rock excavation is a challenging and costly issue. To predict the added costs arising from wear, field and laboratory investigations can be conducted during the early stages of a project. Accordingly, a measure of particle abrasivity is needed. Abrasivity is defined as the capability of different kinds of soils and rocks to cause abrasive wear of metallic surfaces. The Cerchar abrasiveness test is a well-recognized lab test for assessing rock abrasivity. The Cerchar Abrasiveness Index (CAI) is determined by measuring the crater diameter [mm] produced by a conical steel stylus moving under a fixed load and sliding distance. Many authors have been trying to correlate CAI with rock properties, but no consensus has been achieved. The main reason for this difficulty arises from the effects of the microstructural complexity of rocks and their tribological response. This investigation proposes a new approach based on the use of a scanning electron microscope to identify the wear mechanisms acting on the Cerchar stylus (AISI A2 tool steel) during testing, and comparing these observations to the corresponding CAI values for nine different rock types (0.1 < CAI < 6). The observed wear mechanisms were classified into two extremes (mild and severe) with a transition region between them. The mild regime is characterized by the polishing action of rocks (CAI ≤ 1.8). The severe regime is characterized by microcutting with extensive plastic deformation (CAI ≥ 3.1). The reliability of the current findings is discussed in the light of a theoretical conversion of CAI values into their respective wear coefficients. Our proposed approach of using wear coefficients is expected to provide better correlation between the results of the Cerchar laboratory test and real drilling rates.

Geotechnical Challenges of Tehran Metro Line 7 (South Northern Route)

Tunneling in urban areas, has raised the level of difficulty and challenge in respecting the constraints deriving from human presence and, therefore, the necessity for the study of geological and geotechnical properties and parameter, classification of the soils according to their engineering behavior, choosing the right TBM, determine groundwater level and determining possible geological hazards. In this paper some geological and geotechnical study took place along the tunnel route. This investigation is done by the result of 73 machinery borehole and 32 manual borehole that took place in the process of studying the tunnel route and continued by the result of field tests and laboratory tests and according to the result, the geological zone classified in 6 zone in tunnel route; due to the result of Cerchar abrasivity test and since Alluvial soil is the main soil in most of the tunneling route, the excavation soil classified as highly abrasive. In some part of tunneling there is a risk of clogging due to the high amount of clay. Based on the results of Lofran tests the permeability of most of the classified soils in route of the tunnel was obtained less that 10E-7 m/s.

Estimation of Cerchar abrasivity index of andesitic rocks in Ecuador from chemical compounds and petrographical properties using regression analyses

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.

A study to correlate LCPC rock abrasivity test results with petrographic and geomechanical rock properties

Rock abrasivity is very much influenced by the petrographic and physico-mechanical properties of rock and hence its assessment from common geomechanical rock properties is helpful for rock engineers in estimating excavation costs. In this paper LCPC and CERCHAR abrasivity tests, as well as a complete suite of mechanical and physical rock properties tests, were conducted on 51 rock samples collected from different locations in Pakistan. Moreover, petrographical studies of 48 rock specimens were performed along with the computation of Schimazek's F-value (F-value) and Rock Abrasivity Index (RAI). For the analysis of test results least square regression was employed. Initially the LCPC abrasivity coefficient (ABR) values were correlated with CERCHAR abrasivity index tests and reasonable relationships were observed. Statistically meaningful relationships were found between ABR and geotechnical wear indices (F-value and RAI). Possible correlations of LCPC test results with rock properties are also discussed. Finally multiple regression analysis was applied to find statistically significant correlation of ABR with petrographical and physico-mechanical rock properties. Test results show that RAI, Brazilian tensile strength and mean quartz grain size (Ø-qtz) prove to be the statistically best predictors of ABR from the rock properties determined. The developed correlations are specifically intended for rock engineers involved in designing excavation projects.

Effects of variation in the particle size of the rock abrasion powder and standard rotational speed on the NTNU/SINTEF abrasion value steel test

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.

Investigation of Various Parameters Effect on Cerchar Abrasivity Index with PFC3D Modeling

The Cerchar test is one of the appropriate and routine tests for determining the rock abrasion; but as for the costs and pin wear measurement errors in laboratory procedures and lack of access to laboratory equipment, using of numerical modeling can lead to use of greater number of samples required during the course of mechanized excavation and reduce the costs and errors in the laboratory test. In this study, the Cerchar abrasivity test was modeled using PFC3D (Particle Flow Code in 3 Dimensions) software. In order to verify the simulation results, Cerchar laboratory test results obtained by Rostami (Rock Mech Rock Eng 47(5):1905–1919, 2014) were compared with the numerical modeling results. In modeling studies, the effects of some parameters such as apply load, test speed, pin hardness and scratching distance on pin wear were investigated. As a conclusion of the study, good agreement between modeling and experimental results was obtained for a given condition. As in the experiment with various loads in both laboratory tests and modeling, with increasing applied load the Cerchar abrasivity index also increased in the experiment with Rockwell hardness HRC (An abbreviation for Rockwell Hardness measured on the C scale. The Rockwell test determines the hardness by measuring the depth of penetration of an indenter under a large load compared to the penetration made by a preload, that on the C scale use from a indenter with 120° cone and 150 kgf load) 42.

Investigation into effect of scratch length and surface condition on Cerchar abrasivity index

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 2mm and 20mm with an increment of 2mm, 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 10mm while about the final CAI value of 99% is reached at 15mm. 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.

Statistical evaluation of CERCHAR Abrasivity Index (CAI) measurement methods and dependence on petrographic and mechanical properties of selected rocks of Pakistan

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 p). 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 (CAIs) and freshly broken (CAIfb) 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 CAIs and CAIfb values measured from top view of the test stylus were 17 and 19 % higher, respectively, in comparison to CAIs and CAIfb 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.