Rock Hardness Research Articles

Preliminary geomechanical analysis on limestones in PPSDM Geominerba campus, Padalarang, West Java

The research location is in the PPSDM Geominerba field campus. The campus is located in Padalarang, West Java that is surrounded by the open-pit mining of limestone and marble. This limestone was formed in Oligo-Miocene of Rajamandala Formation. The research objective was to determine the condition of the slopes around the campus based on geomechanical characteristics. Based on field observations, the slope angle in the area is dominated by steep slopes. The rock hardness level is dominated by hard rock with a hardness ranging from 50-100 MPa. Rock Mass Rating shows that the are a is dominated by good rocks. While the S lope Mass Rating calculation show that the maximum slope angle is between 52-75 ° . L evel of deformation and intensive weathering process will reduce the strength of the rock in the future. Several rock fall occurrences on this research area support this assumption . Yet , some local open pit mining area activity near the toe hill of the area need to be concerned regarding the effect of the local rock fall occurrences.

Analysis of Basin Geometry in Ataq Region, Part of Shabwah Yemen: Using Remote Sensing and Geographic Information System Techniques

Study of drainage and basin is important to understand the character of any basin geometry for implication of conservation of natural resources. Remote sensing and GIS is valuable tool and widely used in recent research for geometric analysis of basin. SRTM data was used to delineate the drainage network as well as sub-basin boundary; digital elevation model, aspect grid and slope map were prepared using SRTM data. Morphometric parameters (linear, areal and relief) has been analysed with the help of ArcGIS 10.2. in this analysis mean RB varies from 2.31–3.97, elongation ratio is 0.63–0.9 and relief ratio is 0.033 to 0.06; indicates that the area is highly structural controlled, steep ground slope, high drainage density and sub-dendritic to sub-parallel nature. These studies are very useful for understanding the structural control and inequalities in the rock hardness for the Ataq region.

Rock mass properties and edifice strength data from Pinnacle Ridge, Mt. Ruapehu, New Zealand

Volcanic edifices exhibit spatially variable physical and mechanical properties. Magmatic intrusions are common at shallow depths within the volcanic edifice and are a poorly-understood contributor to this spatial variability. Intrusion-related alteration has been found to weaken rock mass strength through the development of joints and fractures; however, there is a paucity of research investigating how intrusions affect rock mass strength specific to the geotechnical units that define the rock masses. In this study, we employ a range of field techniques—field permeametry, rock hardness assessment, rock mass classification, and discontinuity mapping—to characterise an exposed fossil geothermal system produced by a shallow intrusion at Pinnacle Ridge, Mt. Ruapehu (New Zealand). We find that intrusions detrimentally affect the rock mass characteristics of altered brecciated lava margins. The resulting change in rock mass strength may be offset by an increase in intact rock strength as a product of alteration mineral precipitation in microfractures. Consequently, the final strength of the rock mass of the altered brecciated lava margins has the potential to be lowest of any of the geotechnical units in the volcanic edifice. We also conclude that these discontinuities increase permeability of the host rock at distances from the intrusion roughly proportional to 1–2 times the thickness of the intrusion itself under near-surface conditions. The data and conclusions presented in this study help to bridge the gap between the lab- and the field-scale and have immediate relevance to engineering geology and geothermal applications worldwide, and to rock mass classification assessments in volcanic environments.

The correlations between the Cerchar abrasivity index and the geomechanical properties of building stones

Cerchar abrasion index (CAI) value is one of the most important test parameters for determining the abrasion value of a cutter or drilling bit. This study aims to present the relation between CAI and various geomechanical properties of building stones. Herein, single and multiple regression analyses were performed to determine the best measure of the relation between CAI and three geomechanical properties. The CAI value is strongly related to the Shore hardness. However, the correlation coefficient increases when we jointly consider the Shore hardness, porosity, and uniaxial compression strength of rock. On the contrary, the analyses results show that the significance level of the CAI value is lower when the CAI value is less than 1. The correlation between CAI and Shore hardness is higher when the CAI values greater than 1 are considered. Also, the R2 value increases from 0.843 to 0.946 in multiple regression analysis.

Rock fabric and origin of the expandable phyllosilicates in the sands of the Ashdown Formation, East Sussex, UK

Abstract Phyllosilicate minerals have the potential to be used as indicators of past environmental conditions and climate. However, the appropriate use of this tool requires that the origin of the phyllosilicates be ascertained to correspond to the age under investigation, as mineralogical changes postdating it would lead to wrong conclusions. The soft sandstone of the Ashdown Formation (south-central and southeaster UK) contains fine-grained Al-phyllosilicates of limited interlayer expandability that have been described by other authors as vermiculite, smectite, interstratified illite-vermiculite and interstratified illite-smectite. The origin of these mineral phases is not yet agreed, with some authors reporting them as detrital and some as authigenic, generated by the weathering of detrital mica in the sandstone. In order to investigate whether or not these fine-grained minerals are detrital, four samples of the sandstone of variable softness were studied because they most likely had different clay content and because the different clay content could be possibly due to differential weathering. Investigation of mineralogy (X-ray diffraction), chemistry (bulk and SEM-EDS microanalysis) and rock fabric (image analysis of SEM micrographs) indicated that the sandstone consists of quartz, microcline, albite, anorthite, muscovite/illite, kaolinite, interstratified illite-smectite and smectite, where smectite layers expand only partially. Kaolinite is mainly detrital. Rock hardness was controlled by quartz abundance in the original sediment, not by later weathering. Alteration of the investigated sandstone samples after deposition was limited but reaction models are compatible with partial (

Influence of physico-mechanical properties of Indian dimension stones on cutting rate of diamond wire saw

Cutting performance of diamond wire saw is a key factor influencing mine planning, production scheduling, and equipment selection for dimension stone quarries. It is normally measured in terms of cutting rate. Rock samples collected from various granite and marble quarries in India were tested in laboratory to determine their physico-mechanical properties. Cutting rate of diamond wire saw was measured in the field studies during the actual cutting process in quarries. Using these laboratory determined properties and the cutting rate, a multiple linear regression model has been developed to predict the cutting rate of diamond wire saw. Physico-mechanical properties of rocks determined in laboratory are used as independent variables and cutting rate as predictor variable in the regression model. The study indicates that the cutting rate increases with a decrease in most of the hardness and strength parameters of rock. The final model is tested for its goodness of fit indicating a significant linear relation between cutting rate and physico-mechanical properties, namely tensile strength, slake durability index, and Cerchar hardness index with regression coefficient of 94%. The resulting model can be used suitably for different types of hard to medium hard and soft dimension stones. The generalized model for estimating the cutting rate becomes a handy tool for mining engineers to work out operating efficiency, expenses, planning etc. of the dimension stone block cutting.

Examination of the relationship between rate of penetration and mud weight based on unconfined compressive strength of the rock

The rate of penetration (ROP) plays a major role in drilling optimization, which makes it an important area of investigation. In this work, sensitivity and statistical analysis were carried out using a big set of data gathered from over 800 wells in the Basra oil fields, Iraq. The main objective of this investigation is to assess the effect of mud weight (MW) on ROP and to provide a method for estimating the recommended range for operational mud weight based on the rock hardness.The collected data for the drilling intervals from the drilling reports for over 800 wells in the Basra oil fields, Iraq, were categorized as weak, medium, hard, and very hard, based on the unconfined compressive strength (UCS), depth, and lithology. Statistical and sensitivity analyses were conducted and correlation coefficients (CC) were developed to describe relationships between rock hardness, ROP, and MW from field data. This methodology combines data from mud logging, daily drilling reports, and geological information to investigate the relationship between ROP and MW for different rock types and strengths.Several previous studies focused directly on MW, where the effect of MW on bit conditions, and thus the ROP was clearly demonstrated. However, these studies did not take into consideration the rock hardness or lithology. There is also a strong discrepancy between results from different studies, where some studies showed an inverse relationship between MW and ROP, while other studies showed it was a direct relationship.In this study, field data have been gathered (more than 800 wells) to further investigate the relationship between MW and ROP, and how it varies with rock hardness. The results showed that MW has an inverse relationship with ROP for the weak formation with a CC of −0.57, suggesting that the MW should be maintained as minimum as possible when drilling through the weak formation. On the other hand, MW showed a direct relationship with ROP for medium, hard, and very hard formations with CC of 0.31, 0.4, and 0.42 respectively. Hence, MW has to be maintained as high as possible to maximize ROP for medium, hard, and very hard formations.Large-scale collection and interpretation of field data were collected to demonstrate the effects of MW on ROP with varying rock hardness and lithology. While field data of this scale is inherent of interest, this analysis also investigates relationships previously unexplored and extends understanding of how MW effects ROP.

Prediction of coal-bearing strata characteristics using multi-component seismic data—a case study of Guqiao coalmine in China

The longwall mining method has been widely used in underground mining of coal seams. For longwall mining, the stability of coal-seam roofs and hardness of coal rocks in coal-bearing strata are particularly important. High-precision multi-component seismic exploration technology can obtain more parameters for characterizing coalbed reservoirs than conventional methods, and it is gradually replacing conventional P-wave technology in coalfield exploration. We have obtained multi-component seismic data from the central mining area of Guqiao Coal Mine, in the Huainan area, China. Using constraints from logging information, and seismic data, joint PP- and PS-wave inversion and interpretation have been performed. The coal seam 13-1, located in a Permian formation, was studied to determine the lithology of the coal-seam roof and floor, evaluate the stability of the coal-seam roof, and determine the hardness of coal rocks in coal seam 13-1. The distribution characteristics of lithology, roof stability, and hardness of coal rocks in coal seam 13-1 were also investigated. To achieve this, we used P- to S-wave velocity ratios to identify the lithology, evaluated the roof stability with parameters LambdaRho and MuRho, and used Young’s modulus to evaluate the hardness of the coal rocks. Our predicted results are in good agreement with the interpretative results from logging information, which shows the accuracy of our method. The joint PP- and PS-wave inversion and interpretation used in this paper can obtain more accurate information for evaluating coalbed reservoirs than conventional methods, which are valuable in assessing mine safety.

Numerical simulation and analysis of drill rods vibration during roof bolt hole drilling in underground mines

Structural deterioration in the roof in an underground mine can easily cause roof fall, and deterioration is difficult to detect. When drilling holes for roof bolts, there is a relationship between the vibration of the drill rod and the properties of the rock being drilled. This paper analyzes transverse, longitudinal, and torsional vibrations in the drill rod by using vibration theory. Characteristic indexes for three kinds of vibration are determined. Using the finite element analysis software ABAQUS, a model for drill rod vibration during the drilling of roof bolt holes was established based on the geological and mining conditions in the Guyuan Coal Mine, northern China. Results from the model determined that the transverse and the longitudinal vibration decrease as the rock hardness decreases. In descending order, sandstone, sandy mudstone, mudstone, and weak interbeds cause progressively less vibration when being drilled. The ranking for strata that cause decreasing torsional vibration is slightly different, being, in descending order, mudstone, sandstone, sandy mudstone, and weak interbeds. These results provide a theoretical basis for predicting dangerous roof conditions and the presence of weak interbeds to allow for adjusting bolt support schemes.

Lithology and the distribution of Early Roman-era tombs in Jerusalem’s necropolis

During the last 150 years, various archaeological excavations and surveys revealed approximately 900 rock-cut tombs in the extensive necropolis surrounding ancient Jerusalem, dated to the late Hellenistic and Early Roman periods. The research goals are to examine the spatial distribution of these tombs in relation to the lithological units and rock hardness and to examine the diverse methods by which the ancient masons solved various lithological defects they encountered during the tomb excavation. We used field observations and Schmidt hammer tests to determine the rock hardness and the lithological properties. Our study demonstrates that the substrate played a crucial role in the establishment of the city and residents’ living conditions and that the presence or absence of caves in certain areas can be explained lithologically. Most tombs found west of the city were excavated in the Weradim Formation (13.7%); those found north of the city were mainly hewn into the well-bedded Nezer Formation (20.7%); and the tombs hewn east or south of the ancient city mainly met the soft Menuḥa Formation (56%). Excavating in the hard limestone of the Shivta Formation required high levels of effort and funding and, therefore, the number of tombs is limited (3%). In some cases, owners of estates located in soft lithologies granted burial rights to additional families, as proved by the large number of tombs and the clusters of burial systems in the Menuḥa Formation. Rock surfaces are mostly decayed by chemical dissolution, enhanced by structural fissures in the rock. Condensation corrosion and excess moisture were observed on the ceilings of some structures, along with bio-erosion. Two types of defects are common in the local rock: (a) major defects, endangering the stability of the rock-cut chamber that required complementary building with ashlar stones and (b) superficial defects that required only aesthetic solutions.

The weathering of granitic rocks in a hyper-arid and hypothermal environment: A case study from the Sør-Rondane Mountains, East Antarctica

Weathering processes in hyper-arid and hypothermal environments are key to our understanding of geomorphological processes and landscape evolution in Antarctica and likely on Mars. A number of studies have focused on the weathering of basaltic rocks in Antarctica; however, the nature of the weathering of quartzofeldspathic rocks, a common rock type on Earth, has received less attention and remains unclear. Here, we explore the weathering of granitic rocks, which are a type of quartzofeldspathic rock, and the associated weathering products, in the Sør-Rondane Mountains of East Antarctica to obtain quantitative information regarding the physical and chemical weathering of granitic rocks in hyper-arid and hypothermal environments. Various petrological techniques were used to analyze the physical and chemical weathering of the rocks. Loss on ignition (LOI) values and the major element composition obtained from the crust and core of the rock samples indicate that the production of hydrous clay minerals in this area is very limited. Examination under a microscope, together with laser-Raman microspectroscopy, of thin sections from the crust and core of the samples indicate that goethite grains form mainly in veins within the crust, which is consistent with the contrasts seen in the Fe3+/Fe2+ and color strength index (CSI) values obtained from the core and crust. A negative correlation between rock hardness and degree of weathering, as measured from the crust of the samples, indicates that the weathered samples are softer than the core. This indicates that cracking and subsequent vein formation cause a reduction in the hardness of the crust and an increase in staining via the formation of goethite grains that develop in the veins. Furthermore, electron probe microanalyzer (EPMA) analysis indicates that the original Fe–Ti oxide grains are altered by weathering and change to hematite or a non-stoichiometric Fe–Ti compound associated with ilmenite grains in the case of a greater degree of weathering. These findings reveal that the weathering of granitic rocks in a hyper-arid and hypothermal environment is controlled mainly by oxidation, including iron hydroxide formation in veins formed by the thermal expansion and contraction of rock-forming minerals, frost shattering and/or salt fretting, and Fe–Ti oxide alteration in the rock interior. Importantly, these physical and chemical weathering processes are unlikely to require a liquid water supply from the environment (snow or vapor). Hence, the restricted supply of liquid water and salt is the most probable explanation for the extremely slow weathering rates in the Sør-Rondane Mountains. We therefore conclude that the weathering process observed in this area is a typical feature of quartzofeldspathic rocks under hyper-arid and hypothermal conditions, and potentially also on Mars. In situ color measurements essentially express the amount of iron hydroxide on the rock surface; thus, in situ and satellite measurements of the color of exposed rocks in Antarctica can potentially provide quantitative information regarding the degree of weathering.

Shore platform downwearing in eastern Canada; A 9–14 year micro-erosion meter record

Downwearing rates (erosion in the vertical plane) were measured with a micro-erosion meter (MEM) in eastern Canada, on an argillacious, sub-horizontal shore platform at Mont Louis in eastern Québec, and on two sloping, basaltic and sandstone platforms at, respectively, Scots Bay and Burntcoat Head in the Bay of Fundy, Nova Scotia. The original data covered a period from 2002 to 2009. This dataset was extended by measurements repeated at surviving MEM stations in 2017, producing records ranging over 9–14 years, depending on when each station was installed. Because of rapid surface downwearing, many of the original MEM stations were inoperable in 2017, especially at Burntcoat Head. Nevertheless, data were obtained from 19 stations at Burntcoat (35% of the 2009 original), 25 at Mont Louis (83% of the original), and 38 at Scots Bay (75% of the original). For the stations at Mont Louis and Scots Bay that were still functioning in 2017, there were no significant differences in rates of downwearing over the shorter (from station installation up to 2009) and extended periods (from installation to 2017). Mean rates of downwearing calculated from all the stations in each area declined through time, however, due to the loss of the more rapidly eroding stations. A simple procedure, which was proposed to compensate for this decrease, produced mean downwearing rates that were broadly similar to those reported over the original measurement period. There were significant relationships between downwearing rates and elevation (R2 = 0.32) and downwearing rates and rock hardness (R2 = 0.41) in the extended record at Scots Bay, and a small but significant relationship between downwearing rates and rock hardness at Mont Louis (R2 = 0.17). Differences in downwearing rates across the platforms suggest that salt weathering and wetting and drying are dominant weathering mechanisms at Scots Bay and Mont Louis. Chemical weathering of the sandstone cementing agent and the premature removal of weathered grains by wave-generated bottom currents may, however, be more important at Burntcoat Head.

Rotary ultrasonic machining of rocks: An experimental investigation

Rock drilling is widely used to explore and mine energy resources. It has also been used to extract samples to study the earth’s geological composition and topography and to explore different planets. Percussive drilling is, as of right now, the most commonly used rock drilling method. Due to the high hardness and abrasiveness of rock, tool wear in rock drilling is severe, thus limiting its penetration rate and resulting in high cost. Therefore, it is crucial to develop more cost-effective rock drilling processes. Rotary ultrasonic machining has been used to drill many materials including metal alloys, ceramics, and composites, and its cost advantages have been demonstrated in many previous studies. This article presents the first experimental investigation of rotary ultrasonic machining of rocks. Three types of rocks (basalt, marble, and travertine) were used. Six input variables (tool rotation speed, feedrate, ultrasonic power, abrasive size, abrasive concentration, and drill bit diameter) were examined...

Characterizing the two principal rock types comprising the Woodford Shale resource play: Application to shale geomechanics

This paper provides a comprehensive analysis and documentation of a popular outcrop (roadcut) of the Woodford Shale, known as the I-35 outcrop. At the bed scale, based on outcrop weathering responses, the lithology of the Woodford Shale is cyclically represented by two distinctive, intercalated rock types: soft (incompetent, ductile) siliceous shales and hard (competent, brittle) cherts. The detailed geologic characterization integrated results from several laboratory techniques: X-ray diffraction, X-ray fluorescence, total organic carbon (TOC), thin-section petrography, scanning electron microscopy, rock hardness, and uniaxial compressive strength (UCS) tests. Experimentally, soft beds are ductile because they sustained significant plastic deformation before failure on UCS tests; these beds are finely laminated, clay-rich ([Formula: see text]), have very high TOC content ([Formula: see text]), very high concentrations of organic proxies (Mo, U) and detrital proxies (Ti, Zr, K, Al), and low Si/Al ratios. In contrast, hard beds are brittle because they sustained little to no plastic deformation before failure; these beds are massive (not visibly laminated), quartz-rich ([Formula: see text]), and have lower TOC content ([Formula: see text]), lower organic proxies (Mo, U), and lower detrital proxies (Ti, Zr, K, Al). The results from our study attest the outcrop-based distinction between soft and hard beds, as determined by systematic contrasts in composition, rock fabric, and mechanical properties. In addition, our results provide insights for the prediction of rock properties for the two principal rock types within the Woodford Shale, giving rise to speculation that if a proper physical distinction is made between soft and hard beds in cores or outcrops, few samples would work well for upscaling rock properties within larger intervals with incomplete sets of data, thus helping to reduce the costs/time related to acquiring large data sets. In addition, observations from this and other outcrops indicate the potentially best horizontal targets are those with approximately equal proportions of the two rock types.

Determining point load strength loss from porosity, Schmidt hardness, and weight of some sedimentary rocks under freeze–thaw conditions

Rocks are subjected to various atmospheric, climatic, and seasonal effects, and those effects can cause partial or complete deterioration. To understand the degree of deterioration of rocks, especially in cold regions, the influences of freeze–thaw cycles on physico-mechanical properties need to be investigated. This study assesses the influence of freeze–thaw cycles on some physical and mechanical properties of some rocks of sedimentary origin in Turkey. For this purpose, samples were subjected to 30 freeze–thaw cycles, and porosity, point load strength, Schmidt hardness, and weight loss were determined after every five cycles. The freeze–thaw cycle progression led to decreases in point load strength, Schmidt hardness, and weight and an increase in porosity of the specimens. The increase and decrease ratios were calculated at the end of every five freeze–thaw cycles, and the relationships were determined for estimated point load decrease ratios. At the end of 20 cycles, there was a strong relationship between point load strength loss and Schmidt hardness loss (R2 = 0.903), which can be very useful for predetermination of point load strength decrease after freeze–thaw cycles without testing.

Relationship between the Power of the Two-Bit Cutting Body Rotation Drive of the Roadheader and Hardness of Broken Rock

The motion patterns of the cutting body of a roadheader with two kinematically connected reversible radial bits equipped with a disk tool on trihedron prisms are presented. The regularity of the disks motion under the action of forces applied to them is considered with allowance for the moments of inertia. The scheme of forming the depth of intrusion by the biconical disc tool of radial bits into the face rock strata is substantiated. The calculated dependences of the total torques ΣMk on the cutting body of the roadheader are obtained from the angle ρ of the bitsrotation, taking into account the contact strength Pk of the rock strata to be broken. The calculation is made of the power of the rotation drive of the two-bit cutting body with a disk tool on trihedral prisms in breaking the rock strata in the range of strength characteristics for the mines of Kuzbass.

Technology Focus: Bit Technology and Bottomhole Assemblies (December 2017)

Technology Focus Drilling-efficiency improvements, needed to ensure continuous reductions in project cycle time, require holistic drilling-system evaluations. Bottomhole assemblies (BHAs), as part of the drilling system, have dominating effects on the functionality and effectiveness of other system components. BHA design, usage, and monitoring must promote drilling-system compatibility, efficiency, and reliability. BHA design must provide or contribute to the creation of operational conditions that ensure efficient failure and removal of rocks. Additionally, it must enable the use of appropriate drilling parameters as needed by specific applications without compromising efficiencies of other drilling-system components. Research continues to investigate rock-failure mechanisms and the implications the processes have on drilling performance. Through this effort, it has been identified that different drilling parameters are needed for dissimilar rock types, even when rock hardness, hole sizes, well profiles, and hydraulic considerations are the same. In most cases, these findings dictate the need for different BHAs to accommodate appropriate parameter ranges and sweet spots. BHA usage must not create conditions that initiate or promote dynamic dysfunctions. Such a condition, while compromising the functional efficiencies of other drilling-system components, also promotes premature downhole-tool failures. The contributions of micro-doglegs to dynamic dysfunctions, excessive torque and drag, poor weight-on-bit transfer, and other issues have been known for a long time. Research into this area is providing a deeper understanding, together with findings that are bound to improve drilling-parameter management and overall drilling efficiency. Appropriate parameter ranges, and improved BHA compliance with regard to vibrations, improve drilling efficiency. These conditions, though beneficial, are not sufficient to ensure BHA reliability. Considering the effect that BHA failures (e.g., twistoff) have on project cycle time and operational costs, investigators have taken a deeper dive into this issue. With the “whys” and “hows” of BHA failures identified, work flows have been developed to address these reliability issues. Ensuring BHA efficiency and reliability is critical for drilling performance. These requirements must thread through BHA design, usage, and monitoring. Yes, the industry has the tools and know-how, and it can be done. Recommended additional reading at OnePetro: www.onepetro.org. SPE 183870 A Modified Three-Point-Contact Approach for Dogleg-Severity Modeling by Hossam Gharib, Halliburton, et al. SPE 183037 Testing and Characterization of Shock and Vibration Loads To Enhance Drilling-Tool Reliability and Efficiency by Dennis Heinisch, Baker Hughes, a GE company, et al. OTC 27575 Applying Real-Time Data Analytics To Detect Underreamer Failure Early During Hole Enlargement While Drilling in Deepwater Gulf of Mexico by Xianping Wu, Shell, et al.

Research on rock-breaking mechanism of cross-cutting PDC bit

Cross-cutting PDC (Polycrystalline Diamond Compact) bit is an efficient drilling technology that increases the rock-breaking efficiency and prolongs the service life of the bit through forming mesh-like pattern in the bottom-hole. This paper studies the rock-breaking mechanism of the cross-cutting PDC bit with the combination of both experiment and numerical simulation. With the nonlinear dynamical model being established, the stress status within rock units, sliding fracture characteristic, plastic energy consumption and stress distribution along the cutter edge are analyzed in the cross-cutting process. Compared with unidirectional cutting, cross-cutting generates larger tensile stress within the rock unit and achieves lower plastic energy consumption. Moreover average stress on the cutter edge in cross-cutting is much smaller than that in unidirectional cutting. When cutters break the rock protrusions formed during cross-cutting process, cracks inside of the rock will rapidly run through the protrusion, generating brittle fractures within the rock and consequently producing sizable volumetric fractures. During cross-cutting, the rock is damaged not only because the shear failure, but also brittle fracture, which is conductive to improving the rock-breaking efficiency. Through unit experiment under cross-cutting condition, this paper studies the influencing regularity of experimental parameters (including the cutter diameter, back rake angle, cross-cutting angle, cutters spacing and rock hardness etc.) on the cutting load, the research achievements are conductive to the deeper understanding of rock-breaking mechanism of the new bit and provides theoretical basis for the application of the technology.

Bioerosive and bioprotective role of barnacles on rocky shores

Bioerosion and bioprotection (bio-remodeling) is the action exerted by biota colonizing rocky shores. It represents an important component among processes responsible for shaping coastal landforms, and a clear evidence of interaction between the biosphere and the solid earth. Barnacles extensively colonize the midlittoral belt of rocky shores in the Mediterranean Basin. Previous research, mostly based on laboratory evidence, suggests that barnacles are bioprotectors, in that they protect the rock surface from different types of physical and chemical weathering. In this paper, we present the results of a field experiment carried out at different spatial scales at two study areas along the moderately energetic and microtidal coast of NW Italy. Barnacles were removed from the sandstone bedrock in replicated plots (manipulated plots) arranged according to a hierarchical spatial design. After four months rock hardness was tested on each plot with both Schmidt hammer and Equotip Piccolo devices, as well as on a corresponding number of control plots. Data were processed by means of a multifactorial analysis of variance (ANOVA). In control plots, rock hardness tested with Schmidt hammer exceeded that measured in previously manipulated plots. Testing with Equotip yielded the opposite results. This experimental evidence confirmed that barnacles play a bio-protective role in the midlittoral at sub-surficial level, while adding the key aspect that this effect is generalizable to spatial scales ranging from a few centimeters up to tens of kilometers. In addition, our results showed, for the first time, that at surface level they can simultaneously act as bioeroders, likely causing corrosion of the rock surface by fostering dissolution of the sandstone carbonate matrix.

Correlation relationships between mechanical parameters of Bulgarian crushed-rock aggregates utilized in railway construction

Crushed-rock aggregates from 11 railway ballast-producing quarries in Bulgaria have been investigated. The test materials consist of igneous and sedimentary rocks of different ages: basaltic andesite, trachyte, diabase, andesitic tuff, quartz-cemented sandstone, dolomite and five varieties of limestone. The standard laboratory tests (Los Angeles, micro-Deval and point load) and in-situ test (Schmidt hammer) were carried out for determination of the following mechanical properties of aggregates: resistance to fragmentation; wear resistance; strength; and rock hardness. Results show that Los Angeles coefficient (LA) values range from 11.9% to 28.4%. The micro-Deval coefficient (MDE) varies between 3.7% and 22.4%. The point load strength index (IS(50)) is between 4.0 MPa and 8.8 MPa. The Schmidt hammer rebound value (SHV) ranges from 34.4 to 60.2. The possibility of predicting the Los Angeles and micro-Deval coefficients from the Schmidt hammer rebound value and the point load strength index was studied. Regression analysis shows a strong correlation between Los Angeles coefficient and point load strength index (coefficient of determination R2=0.93), a good correlation between the Los Angeles coefficient and the Schmidt hammer rebound value (R2=0.62) and moderate correlation between the micro-Deval coefficient and the Schmidt hammer rebound value (R2=0.51).