Rock Strength Properties Research Articles

Selection and Justification of Design Variables for Strength Properties of Rocks in Slope Stability Analysis for Open Pits

Selection and Justification of Design Variables for Strength Properties of Rocks in Slope Stability Analysis for Open Pits

Blastability and Ore Grade Assessment from Drill Monitoring for Open Pit Applications

Blasting performance is influenced by mechanical and structural properties of the rock, on one side, and blast design parameters on the other. This paper describes a new methodology to assess rock mass quality from drill-monitoring data to guide blasting in open pit operations. Principal component analysis has been used to combine measurement while drilling (MWD) information from two drill rigs; corrections of the MWD parameters to minimize external influences other than the rock mass have been applied. First, a Structural factor has been developed to classify the rock condition in three classes (massive, fractured and heavily fractured). From it, a structural block model has been developed to simplify the recognition of rock classes. Video recording of the inner wall of 256 blastholes has been used to calibrate the results obtained. Secondly, a combined strength-grade factor has been obtained based on the analysis of the rock type description and strength properties from geology reports, assaying of drilling chips (ore/waste identification) and 3D unmanned aerial vehicle reconstructions of the post-blast bench face. Data from 302 blastholes, comprised of 26 blasts, have been used for this analysis. From the results, four categories have been identified: soft-waste, hard-waste, transition zone and hard-ore. The model determines zones of soft and hard waste rock (schisted sandstone and limestone, respectively), and hard ore zones (siderite rock type). Finally, the structural block model has been combined with the strength-grade factor in an overall rock factor. This factor, exclusively obtained from drill monitoring data, can provide an automatic assessment of rock structure, strength, and waste/ore identification.

Анализ зависимости между акустическими и физико-механическими свойствами горных пород терригенных отложений

During the entire development of an oil and gas field, it is necessary to carry out a complex of various studies aimed at identifying the parameters of the productive layer. One of such studies is the analysis of core material, as a result of which the following parameters of the rock are determined: porosity, permeability, Young's modulus and others. The listed characteristics must be taken into account when building a geological and hydrodynamic model of a field. In addition to these parameters, the strength properties of the rock should be determined, since they are necessary in the design of the wellbore. Such characteristics can be obtained by conducting research in specialized laboratories. This is not always possible due to various reasons. A number of studies confirm the fact of the relationship between the acoustic properties of a rock (the velocity of the longitudinal and transverse waves) and the strength characteristics. The acoustic properties of the rock must be taken into account when interpreting the acoustic logs of the wells, which allows to reveal the distribution of rocks along the wellbore. Based on the velocities of ultrasonic waves propagation, it is possible to calculate the elasticity dynamic modulus, which let assess the tendency of the rock skeleton to compaction as a result of the effective stress action. Therefore, the determination of the rock acoustic properties is necessary when planning the development of a field and its implementation. The results of laboratory studies aimed at establishing the relationship between the strength and acoustic properties of rocks are presented. During the experiment, the dynamic Young's modulus was also determined and its relationship with the speed of ultrasonic waves propagation was revealed. As a result of laboratory studies, empirical dependences of the ultimate strength in volumetric compression (σс), elasticity dynamic modulus (E ) and the velocity of transmission of longitudinal (vp) and transverse waves (vp) were obtained. An assessment of the obtained values was given over the entire measurement range.

Prediction of drilling rate index from rock strength and cerchar abrasivity index properties using fuzzy inference system

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

Simulating tunnel support integrity using FEM and FDEM based on laboratory test data

The West Vaughan Sewer System (WVSS) tunnel, at the time of writing, is planned to be constructed in Toronto, Ontario, Canada. A geotechnical program was conducted to characterize the mechanical properties of the anisotropic bedrock, Georgian Bay shale, and was determined to exhibit weak rock strength properties, moderate to fair anisotropy, and extremely low abrasivity. Following characterization, the shale was numerically calibrated using the hybrid finite-discrete element method (FDEM) and used to qualitatively simulate the WVSS tunnel. The major advantage of FDEM is its ability to explicitly simulate fracturing in geomaterials allowing for the excavation damaged zone (EDZ) to be estimated. In addition, anisotropic elastic and fracture models were used to appropriately simulate shale. The objective of the simulations is to explicitly compare the difference between the finite element method (FEM) and FDEM in estimating the deformation and stress in the rock mass and support liner. In FDEM simulations where the virgin stress conditions did not cause the rock to fracture, the FEM and FDEM results are very similar. However, in simulations where the rock is fractured, predominantly consisting of bedding plane slippage due to the orientation of the maximum in-situ stress relative to the strata, several key differences are evident. The liner simulated in FDEM has an asymmetric distribution of stress and strain, liner deformation is approximately 60% greater, stresses can be up to four times larger, and the stresses in the liner are purely compressive.

Characterization and correlation of engineering properties of basalts

Basalts are a common lithology found beneath Lisbon and are the predominant rocks of the Volcanic Complex of Lisbon (CVL) (72 Myr). These basalts exhibit variable texture and composition. Given the vast extent of the CVL, which encompasses Lisbon and its surroundings, and the establishment of several present and future engineering works upon this rock mass, the geotechnical study of the CVL is relevant. This type of information is scarce in comparison to petrographic and geochemical studies already available. From this perspective, a study of the intact rock was carried out, involving a total of 349 specimens of seven samples of basalts collected at five distinct locations and displaying different grades of weathering and fracture spacing. Non-destructive and destructive tests were conducted to characterize the physical, mechanical, and dynamic properties of the intact rock. The test results are in agreement with those established for basalts around the world. However, the correlations for basalts presented in the literature cannot be applied to the CVL materials due to several variations in its texture and structure and therefore on the mechanical, physical, and dynamic properties. Consequently, some new correlations of index, strength, and deformational properties of intact rocks are presented. These are intended to be applied in future studies involving basalts of this complex or similar rocks.

Lithological Parameters Controlling Rock Strength and Elastic Properties of Peritidal and Deep Marine Carbonate Mudrocks, Lower to Upper Jurassic Succession, Central Saudi Arabia

The study integrated lithofacies analysis and measurement of total organic carbon "TOC," porosity, and mechanical properties to evaluate the main factors controlling rock strength and elastic properties of three carbonate mudrocks units within the Jurassic succession of Central Saudi Arabia. Textural and microstructural analyses revealed that the former two units (Hanifa Formation Hawtah Member and Tuwaiq Formation) have five lithofacies interpreted as a lower shoreface intra-shelf basin deposition, respectively. Two mudrock lithofacies within the Upper Marrat Formation were recognized, both deposited under peritidal low ramp setting. Weak to moderate correlations between mechanical properties and porosity in all studied formations were observed; coefficient of determination R2 values range between 0. 1 and 0.7. Tensile strength has the strongest correlation with porosity and mineral composition. Hard phase mineral (quartz, feldspar, and pyrite) abundance has a more robust correlation with elastic moduli compared to the other minerals. Relatively higher R2 values were observed for the correlations between rock strength and clay + TOC content in Tuwaiq and Hanifa compared with Marrat mudrocks. Marrat and Tuwaiq mudrocks lithofacies have a stronger correlation between particle size and unconfined compressive strength, whereas particle size is weakly correlated with elastic moduli. Sedimentary layering and associated anisotropy significantly control these correlations. Deep lower shoreface deposits of Hanifa mudrock are mechanically stiffer than intra-shelf basin outer ramp deposits of Tuwaiq mudrock lithofacies. Peritidal Upper Marrat mudrock lithofacies have slightly higher stiffness than Tuwaiq mudrock and lower stiffness than Hanifa mudrock. The results are useful to predict the rock brittleness of these Jurassic intervals and their worldwide equivalent.

Technological aspects of cased wells construction with cyclical-flow transportation of rock

A high-performance technology for constructing cased wells is proposed. Essence of the technology is the advance insertion of the casing pipe into the sedimentary rock mass and the cyclical-flow transportation of the soil rock portions using the compressed air pressure supplied to the open bottomhole end of the pipe through a separate line. Results of mathematical modeling for the process of impact insertion of a hollow pipe into a soil mass in horizontal and vertical settings are considered. Modeling of the technology is implemented by the finite element method in the ANSYS Mechanical software. Parameters of the pipe insertion in the sedimentary rock mass are determined - value of the cleaning step and the impact energy required to insert the pipe at a given depth. Calculations were performed for pipes with a diameter from 325 to 730 mm. Insertion coefficient is introduced, which characterizes the resistance of rocks to destruction during the dynamic penetration of the casing pipe in one impact blow of the pneumatic hammer. An overview of the prospects for the application of the proposed technology in geological exploration, when conducting horizontal wells of a small cross-section using a trenchless method of construction and borehole methods of mining, is presented. A variant of using the technology for determining the strength properties of rocks is proposed. Some features of the technology application at industrial facilities of the construction and mining industry are considered: for trenchless laying of underground utilities and for installing starting conductors when constructing degassing wells from the surface in coal deposits. Results of a technical and economic assessment of the proposed technology efficiency when installing starting conductors in sedimentary rocks at mining allotments of coal mines are presented.

Probabilistic analysis of the disc cutter failure during TBM tunneling in hard rock

TBM disc cutters used in a long-distance tunneling particularly in cutting through hard rock would undergo substantial and intense wear. The cutting efficiency may greatly reduce and potentially facing complete suspension if the worn-out cutters were not ascertained in a timely manner. Due to the uncertainty of both geological and technical factors, it is undoubtedly arduous to predict the failure of the disc cutter. In this study, the rock abrasiveness and strength properties of 267 rock specimens, including 9 different rock types were investigated. The uncertainty characteristics of the rock abrasiveness and TBM operational parameters were summarized based on the collected data. The rock abrasiveness, compressive strength, tensile strength, TBM advancing rate and rotation speed of the cutter head were considered as random variables in this study. A probabilistic analysis was performed to investigate the cutter failure and cutters group failure in hard rock excavation. The results show variability in the geological and technical factors withhold an important influence on the cutter failure, in particular on the cutters group failure. It is therefore essential to analyze the performance of the cutter wear in the probabilistic framework to avoid overestimation of the cutters’ lifespan. Lastly, a reliability design chart is proposed for the adoption in the industries to estimate the potential failure of the cutter.

Fracture Morphology Analysis of Frozen Red Sandstone under Impact

The deformation and failure characteristics of red sandstone under subzero temperature were studied by the split Hopkinson pressure bar (SHPB) dynamic impact test. The effects of different subzero temperatures on rock strength properties, fractal dimension, and dissipated energy were analyzed combined with microfracture morphology. The reasons for rock dynamic mechanical property deterioration under lower subzero temperatures were revealed. The research shows that low subzero temperature will cause “frostbite” of red sandstone. Under high strain rate loading, the rock will quickly lose its bearing capacity, and its dynamic mechanical strength will drop sharply. The dissipated energy WL of the frozen rock specimen is positively correlated with the fractal dimension D and closely related to the macroscopic failure characteristics. It could be concluded that greater dissipation energy leads to more serious damage of rock and accordingly results in a larger fractal dimension. Fracture morphology analysis shows that the lower subzero temperature generated remarkable cracks in the material interface of the red sandstone. The damage of the red sandstone could be explained by the fact that the crack tip had low plastic deformation ability under high strain rate loading and the composition of cement was vulnerable to the subzero temperature effect.

Deformations and fracture of rock strata during deep level potash mining

Increased mining depths entail both increased rock pressures and complicated rock mass structures. When it comes to mining mineral salts, there is a significant difference in the strength and deformation properties of rocks developed in the geological section, which affects the nature of deformation and the destruction of underworked strata. During the initial development stage of the Gremyachinskoye deposit, where the mining of potash salts at depths of more than 1,000 meters has been planned, a mathematical model of the undermined mass has been developed, reflecting the main features of its geological structure and the design parameters of a pillar mining system. The mathematical modelling estimated safe conditions of undermining the waterblocking strata and the expected deformations at the earth’s surface. This was carried out with an elastic-plastic plane formulation using the finite element method. The time factor was accounted for based on the developed modification of the method of alternating deformation moduli. Based on the mathematical modelling performed, it was shown that geomechanical models of new deposits of potash salts being prepared for development can be calibrated using the information available from analogous deposits; this information can be subsequently corrected, reflecting certain differences in the geological structure and parameters of the mining system. Based on the numerical modelling results, an increase in the boundary angle of the subsidence trough of the earth’s surface was established due to the significant depth of mining and the presence of hard rock strata in the geological section, which allowed the linear dimensions of the protective pillars under critical facilities to be reduced, alongside minimising losses of potash ore.

Selection and Justification of Design Variables for Strength Properties of Rocks in Slope Stability Analysis for Open Pits

Selection and Justification of Design Variables for Strength Properties of Rocks in Slope Stability Analysis for Open Pits

The role of underground urbanization in Samara city geological processes

In all largest cities due to lack of territory there is an intensification of underground space use - underground urbanization. It allows finding solutions to transport and environmental problems while preserving the unique appearance of the city’s historical cents. However, the process of underground space development leads to activation of some exogenous processes, which may lead to negative consequences. More than one million people live in Samara city, subway line is built, there are subway objects of industrial and defense importance (bunkers) reaching considerable depth. Active underground construction leads to strengthening of geological processes (weathering, karst formation, suffosia, etc.), change of strength properties of rocks, violation of natural hydrological regime of the territory. By the example of Samara, stages of underground urbanization of the city were studied and its influence on geological processes was considered. Results of studying existing use of city underground space are described. Taking into account geological and geomorphological regionalization of the city, the areas, which underground space development is the most undesirable, were identified.

Geomechanical evaluation of a middle Cambrian unconventional oil and gas play in the southern Georgina Basin, northern Australia

Middle Cambrian sediments in the southern Georgina Basin contain multiple organic-rich source rocks and have been suggested to be prospective for both conventional and unconventional hydrocarbons. We present new geomechanical data collected from the middle Cambrian Arthur Creek Formation and Thorntonia Limestone in four wells (Baldwin 1, MacIntyre 1, Owen 2, Todd 1) in the southern Georgia Basin, and compare the data to mineralogical and geochemical datasets. Geomechanical test intervals were selected to allow geomechanical test results to be directly compared with the mineralogical and geochemical datasets (X-Ray Diffraction, HyLogger and organic geochemistry). Approximately 25 m of core was tested for unconfined compressive strength (UCS) using the scratch-testing technique, and results indicate values in the range of 60–150 MPa. Triaxial testing was also conducted to measure the poroelastic properties of core, and results indicated that Young’s modulus is generally in the range of 45–67 GPa. UCS and Young’s modulus are positively correlated and increase with depth through the prospective Arthur Creek Formation. The mechanical properties of the tested core are relatively indurated and stiff compared with young sedimentary rocks and broadly similar to proven shale gas plays in Australia and internationally. Mineralogically, the Georgina Basin rocks tested have lower clay contents than rocks from other Australian and international basins but no clear correlation was observed between geomechanical properties and mineralogy, suggesting that multiple factors contribute to the poroelastic and strength parameters. For example, parameters such as sonic velocity and porosity are weakly correlated to rock strength. Geomechanical data can be used alongside other datasets (e.g. sedimentological, geophysical and structural data) to better inform predictions of hydrocarbon prospectivity. KEY POINTS Middle Cambrian rocks from the Georgina Basin, Australia are prospective for conventional and unconventional hydrocarbons. Rock mechanical tests are conducted to determine how the organic-rich sediments might respond to stimulation. Mechanical analyses are evaluated alongside mineralogical, geochemical and well-log data to assess controls on rock strength properties. Geomechanical behaviour is complex and appears to be driven by multiple factors.

Mechanical characterization of Laffan and Nahr Umr anisotropic shales

Geomechanics-related wellbore instability has become a major source of non-productive time in highly deviated wells drilled in oil and gas fields in offshore Abu Dhabi. These wells are drilled through two highly anisotropic shale formations, namely the Laffan shale formation and the Nahr Umr shale formation. Most of the models used in the oil and gas industry do not account for the strength and elastic anisotropy of shale. Therefore, a laboratory study was conducted to examine the strength and elastic anisotropy of shales using uniaxial compression tests and triaxial compression tests.Jaeger's Plane of Weakness (JPW) model was used to understand the anisotropic failure behavior of highly laminated shales of the Laffan and Nahr Umr formations. This model assumes that for an anisotropic rock, there exists a plane of weakness that has strength properties (cohesion and angle of internal friction) different than the strength properties of the intact rock. By minimizing the Root Mean Square Error (RMSE), the experimental strength values of the samples, as measured at different orientations, were fitted to the JPW model.Elastic moduli were also measured on these shales, as a function of orientation angle. The results showed that the moduli vary with angle according to the expected tensor transformation law. Therefore, the transverse isotropy assumption is a reasonable model to be used when dealing with these laminated sedimentary rocks.

The physics of fault friction: insights from experiments on simulated gouges at low shearing velocities

Abstract. The strength properties of fault rocks at shearing rates spanning the transition from crystal–plastic flow to frictional slip play a central role in determining the distribution of crustal stress, strain, and seismicity in tectonically active regions. We review experimental and microphysical modelling work, which is aimed at elucidating the processes that control the transition from pervasive ductile flow of fault rock to rate-and-state-dependent frictional (RSF) slip and to runaway rupture, carried out at Utrecht University in the past 2 decades or so. We address shear experiments on simulated gouges composed of calcite, halite–phyllosilicate mixtures, and phyllosilicate–quartz mixtures performed under laboratory conditions spanning the brittle–ductile transition. With increasing shear rate (or decreasing temperature), the results consistently show transitions from (1) stable velocity-strengthening (v-strengthening) behaviour, to potentially unstable v-weakening behaviour, and (2) back to v strengthening. Sample microstructures show that the first transition seen at low shear rates and/or high temperatures represents a switch from pervasive, fully ductile deformation to frictional sliding involving dilatant granular flow in localized shear bands where intergranular slip is incompletely accommodated by creep of individual mineral grains. A recent microphysical model, which treats fault rock deformation as controlled by competition between rate-sensitive (diffusional or crystal–plastic) deformation of individual grains and rate-insensitive sliding interactions between grains (granular flow), predicts both transitions well. Unlike classical RSF approaches, this model quantitatively reproduces a wide range of (transient) frictional behaviours using input parameters with direct physical meaning, with the latest progress focusing on incorporation of dynamic weakening processes characterizing co-seismic fault rupture. When implemented in numerical codes for crustal fault slip, the model offers a single unified framework for understanding slip patch nucleation and growth to critical (seismogenic) dimensions, as well as for simulating the entire seismic cycle.

On experimental determination of the elastic and strength properties of anisotropic rocks

Influence of anisotropy of elastic and of strength properties on the stress-strain state near wells and openings is considered. The choice of parameters characterizing both types of anisotropy is discussed. A method of experimental determination of the parameters characterising anisotropy of both elastic and strength properties from the direct measurements using true triaxial loading systems is described.

Apparent moduli and strength differences between cylindrical and prism specimens caused by edge confinement effects

Rock samples obtained from excavation and fault damage zones are friable, and it is challenging to obtain cylindrical specimens from such rocks using coring bits in the lab. On the other hand, preparation of prismatic specimens may be less destructive because it does not exert excessive rotational torque around the sides of the rock as in the preparation of cylindrical specimens. Therefore, prism-shaped specimens could become a more favorable sample geometry when working with highly fragile rock samples. However, prism specimens may experience shape-specific boundary effects during mechanical deformation due to the presences of corners and edges, which might cause differences in the measured rock strength and elastic properties compared to a cylindrical specimen. This study aims to investigate how the corners and edges of prism specimens affect the apparent strength and moduli of samples via comparison of laboratory data and finite element modelling results. We find that the prismatic samples can have higher apparent elastic moduli due to the enhanced confinement at the sample edges, which in turn also increases the measured compressional strengths of prism samples compared to cylindrical samples. Whether this apparent strengthening effect influences laboratory data interpretation will also depend on the degree of sample variability and how well specimen edge boundary conditions are controlled.

АНАЛІЗ ПІДХОДІВ ЩОДО ВИЗНАЧЕННЯ МІЦНІСНИХ ХАРАКТЕРИСТИК ГІРСЬКИХ ПОРІД ДЛЯ ПРОГНОЗУ ЗСУВОНЕБЕЗПЕЧНОСТІ УКОСІВ

The paper is based on a comparative analysis of modern approaches using deterministic, statistical and graphic-analytical models and techniques for determining the strength properties of soft rocks to predict slope failure and landslide hazard. To assess the stability of natural and man-made slopes, the Mohr-Coulomb failure criterion is often used, the main values ​​of which are the cohesion (C) and the angle of internal friction (φ). The deterministic approach involves obtaining the values ​​of these properties as a result of laboratory testing of soft rock specimens on shearing devices under the impact of normal and tangent loads. However, these calculated values ​​depend on how to draw a direct line tangent to Mohr circles, which is a significant disadvantage. The probabilistic approach for determining the strength properties takes into account a certain range of C and φ values ​​for soft rocks in changing geo-climatic conditions for adequate prognosis of slope stability and landslide danger. The results of calculations of stability for hypothetical slopes with heights of 20 m and 30 m are obtained by means of determined parameters C and φ and with probabilistic values of these indicators. A graphic-analytical approach for determining the strength characteristics of mine rocks is proposed. The technique for determining the strength properties of soil or mine rocks through the construction of a curve of boundary states at three points tangential to the boundaries of the Mohr circles corresponding to the limits of tensile strength, compression strength and shear strength is substantiated. The scientific novelty of the technique is to combine the results of laboratory tests of rocks specimens due to compression and shear, the analytical determination of the tensile strength through the formula and drawing the boundary state curve. The practical value of the proposed technique of the plotting a passport of the rock strength is the ability to more accurately calculate the physical and mechanical properties of rocks and predict the processes of their failure.

Smart Software Assessment of Effects of Rock Properties on Blast-Induced Ground Vibrations

The drilling and blasting method considered most economical method in civil and urban construction process. Ground vibrations are one of the major problem in blasting activity. Velocity of blast induced ground vibrations influenced by mainly three parameters such as properties of the rock mass properties, the explosive characteristics and the blast design and execution. In those parameters, rock mass properties of blasting area are unchangeable, so study of influence of rock properties very essential to minimize the effect of vibration on nearby structure. This study investigated the effect of rock strength parameters on vibration velocity. In this study, the blasting vibration monitored at a blasting site with different rock masses. This paper, presented a review on prediction models and rock properties influence on peak particle velocity. This paper also presented the relation between peak particle velocities different mines with their respective rock properties. This paper critical analysis on previous studies. This paper presented correlation between rock strength properties like compressive strength and tensile strength on vibration velocity.