Brazilian Tensile Strength Test Research Articles

Analysis of tensile failure mechanism in intact, foliated, and cracked rocks using distinct element method: Influence of anisotropy

A thorough numerical analysis was conducted to understand the failure mechanisms and behaviour in intact rocks, foliated rocks and rocks with pre-existing cracks using the Brazilian tensile strength tests. The dominant anisotropy in rocks, especially foliated rocks like phyllites, slates and schists, as well as sedimentary rocks like sandstone, limestones and shale, leads to complex failure mechanism. The presence of cracks leads to anisotropy causing different mechanisms of failure and variation in tensile strengths of rock mass. Numerical simulations were conducted based on experimental studies of foliated phyllite and dolomitic limestone from the Tejam Group, Lesser Himalaya. The variations in failure behaviour and strength of foliated rocks were studied for samples at different foliation angle using the particle distinct element model. The simulation results show that with increase in foliation angle to the loading direction (from 0° to 90°), the peak tensile strength of rocks remains almost same for specimens with θ = 0° to 30° and then increases linearly till 90°. The influence of cracks as anisotropy was also studied by changing crack length (from 5 mm to 30 mm) and angle (from 0° to 90°). The development of failure patterns in rocks with pre-existing cracks leads to a better understanding of the failure modes and makes it possible to interpret failure behavior, pattern, and strength parameters. With increase in crack length, the tensile strength of rocks decreases. Overall, this study depicts the influence of anisotropy and microparameters on failure modes and behavior in Brazilian tensile strength tests on foliated and pre-cracked rocks.

Dynamic response, durability, and carbon footprint analysis of the marl clay treated with sodium lignosulfonate as a sustainable-environmentally friendly approach

In the current study, the marl clay was improved by different contents of sodium lignosulfonate (NLS) and cured at different times and then, all samples were subjected to Bender Element (BE), Unconfined Compressive Strength (UCS), and Brazilian Tensile Strength (BTS) tests considering two different dry condition (DC) and wet condition (WC). The durability of the samples was further controlled by a special technique, namely the soaking test. The carbon footprint analysis was undertaken for a low-volume trench project to address the sustainability benefits associated with replacing cement and lime as traditional stabilizers with NLS. The results show that the reuse of NLS as a non-traditional alternative for stabilizing marl soil can play an influential role in improving dynamic parameters as well as sustainable development. It has been observed that the CO2 emission decreases up to 5.6 and 4.4 times compared to lime and cement, respectively. Additionally, the use of NLS enhances the UCS by 249%, BTS by 208%, and small strain shear modulus by 117%. Furthermore, reducing the adverse effects of the WC on soil properties, among others, was the main finding of utilizing the NLS in marl stabilization with curing time. NLS-treated marl samples were able to preserve the integrity of their particles even after being soaked in water for a period of 3 weeks. In contrast, the particles of the untreated sample started to disintegrate within a few seconds of initiating the soaking test. Finally, possible equations correlating the dynamic and static moduli were reported in this study.

Exploring for the Future: new geomechanical data in frontier Australian basins

Led by Geoscience Australia, Exploring for the Future (EFTF) is a A$225 million Australian Government program dedicated to exploring Australia’s resource potential and boosting investment. The EFTF program energy component aimed to attract industry investment by delivering a suite of new precompetitive geoscience data in prospective Australian sedimentary basins. Through EFTF, Geoscience Australia has acquired significant amounts of new geomechanical data from underexplored onshore sedimentary basins with identified hydrocarbon prospectivity, from both legacy and newly acquired samples. These data were acquired to build a better understanding of basin sediment rock properties, particularly looking at the reservoir and seal potential of postulated unconventional and conventional targets. Four major datasets are presented herein, representing prospective intervals from the Paleozoic Canning Basin of Western Australia, the Neoproterozoic-Paleozoic Officer Basin of South Australia and Western Australia, the Paleo-Mesoproterozoic South Nicholson region of the Northern Territory and northwest Queensland, and the Paleo-Mesoproterozoic Birrindudu Basin of the Northern Territory and Western Australia. Additionally, the Paleo-Mesoproterozoic McArthur Basin of the Northern Territory is represented by a small number of analyses. Tests include unconfined compressive strength tests, laboratory ultrasonic measurements, single and multi-stage triaxial tests and Brazilian tensile strength tests. These datasets are a precompetitive resource that can facilitate investment decisions in frontier regions, helping to identify elements of conventional and unconventional hydrocarbon systems as well as providing essential data to assess geological storage opportunities.

Measurement of true tensile strength from Brazilian tensile strength laboratory tests

Brazilian tensile strength (BTS) testing in standard practice is a practical method to approximate tensile strength for rock core using the conversion of axial compressive vertical and diametral loading to horizontal tensile stress in the centre of the core disk. The method, however, routinely inflates tensile strength, using peak tensile stress calculated from the BTS, versus true tensile stress (TTS) from direct tensile strength (DTS) tests. This study presents a novel technique to measure TTS directly from the BTS test via the onset of nonlinearity in horizontal strain response. TTS is equivalent to the peak strength of a DTS test. While not yet standardized, the modification to achieve TTS measurements is to instrument the BTS specimen with a horizontal strain gauge on each flat side. Over 100 BTS specimens of varying lithologies were instrumented, tested, and analyzed to measure their TTS and compare to peak BTS. Results demonstrate the average measured TTS is 0.81BTS, 0.75BTS, 0.85BTS for granitoid, carbonate, and metamorphic rocks, respectively. This concurs with previous studies, validating the proposed novel TTS measurement method. We recommend measurement of TTS be adopted into standard practice for BTS laboratory testing to improve accuracy of tensile strength data in rock engineering design.

Geotechnical performance of isotropic and foliated quartzite waste as aggregate for road base and asphalt mixture

Quartzite mines produce a large amount of waste. Although the reuse of materials is essential for sustainable constructions, little is known about the geotechnical properties of isotropic (massive) and foliated (discontinuous) quartzite waste. In this paper, the potential use of these wastes as base layers and asphalt mixtures were examined by a series of laboratory tests and numerical simulations. This paper presents an analysis of the particle properties, durability, strength, and deformation response of quartzite waste in isotropic (IGM) and foliated granular (FGM) mixtures. Asphalt mixtures with isotropic (IAM) and foliated (FAM) quartzite waste as aggregates are evaluated using Brazilian tensile strength, moisture susceptibility, and repeated-load indirect tension tests, such as the resilient modulus and fatigue. To estimate the performance of these materials as pavement layers, numerical experiments are also carried out using the mechanistic-empirical design framework of the MeDiNa software package. As a base material, the mixtures showed plastic creep responses at the highest stress level (higher permanent strain of 1.2 % at σ3/σd = 360/120 kPa) and negligible expansion. The California bearing ratio (higher than 130 % for both IGM and FGM) and resilient modulus (average of 224 and 130 MPa for IGM and FGM, respectively) greatly exceeded the minimum requirement of Brazilian standards. As asphalt mixtures, both IAM and FAM met the minimum limit of tensile strength, but IAM showed greater stiffness. According to the stress–strain analysis of the MeDiNa software, granular and asphalt mixtures incorporating quartzite waste fulfilled the fatigue crack area and rut depth criteria, falling within the allowed thickness ranges for road pavements subjected to up to 5×106 repetitions (medium heavy traffic). This study provides support for the transformation of quartzite waste into a valuable byproduct.

Comparison of machine learning and statistical approaches to estimate rock tensile strength

Tensile strength is very important in drilling operations. The main objective of this study was to assess petrography, physical, and mechanical properties and predict the Brazilian tensile strength of sedimentary rocks by leveraging key parameters such as Schmidt hardness, compressional wave velocity, density, and porosity. A diverse array of predictive models was employed, encompassing simple regression, multivariate linear and nonlinear regression, backpropagation artificial neural network, gaussian process regression, classification and regression tree, K-nearest neighbor, random forest, and support vector regression. Based on thin section analysis and X-ray diffraction, the samples were identified. The sandstone samples were meticulously categorized into two distinct groups: arenite and litharenite. Additionally, the limestone samples were stratified into the categories of packstone to mudstone based on texture. The highest failure mode frequency of the samples under the Brazilian tensile strength test was identified as central fracturing. Upon meticulous examination, it was discerned that compressional wave velocity exerted the most substantial influence on Brazilian tensile strength estimates, while density exhibited the least impact. Comparing the outcomes derived from the diverse modeling techniques, it was unequivocally established that the support vector regression model showcased the highest level of performance for forecasting Brazilian tensile strength. This was evidenced by the remarkable coefficient of determination of 0.99 along with an impressively low root mean square error of 0.03.

An efficient Kriging-based calibration framework for FDEM

The combined finite-discrete element method (FDEM) is a powerful numerical tool to simulate the transition of materials from continuous deformation to discontinuous fracturing and fragmentation. Calibrating parameters using laboratory data is crucial for applying FDEM to engineering-scale analysis. Considering the high computational costs in existing calibration schemes, this study proposes an effective FDEM calibration framework employing the Kriging surrogate model rooted in Uniaxial Compressive Strength (UCS) and Brazilian Tensile Strength (BTS) tests. The sensitivity analysis is first conducted on mesh size, loading rate, and numerical parameters to find a suitable set that balances computational efficiency and accuracy. Subsequently, an efficient mapping relationship between input fracture parameters and simulated strengths is established based on the Kriging surrogate model, replacing the expensive FDEM program for forward calculations. With the fracture parameters treated as unknown variables and experimental strengths available, the objective function is formulated and then solved to estimate fracture parameters. The effectiveness of the proposed method is validated through a numerical example. Compared to the conventional methods, the proposed approach requires fewer simulations of UCS and BTS, which highlights a significant computational efficiency advantage.

The needle penetration index for estimating the physico-mechanical properties of pyroclastic rocks

Preparation of suitable core specimens for physico-mechanical testing s not always possible, particularly for soft and clay-bearing rocks. Although several indirect test methods have been proposed to predict the properties of rocks, specimen preparation from soft rocks for some indirect tests is still difficult. For such cases, the needle penetration test has been developed. In this paper we present a study on the predictability of the physico-mechanical properties of pyroclastic rocks from the needle penetration index (NPI). The NPI, uniaxial compressive strength (UCS), Brazilian tensile strength (BTS), density, and porosity tests were performed in the laboratory on specimens from ten different locations in Turkey. Correlations were established between the NPI values and the physico-mechanical properties. Strong correlations were observed between NPI and both UCS and BTS. General correlations were found between NPI and both density and porosity.

Paint Speckle Application Recommendations for Digital Image Correlation Analysis of Brazilian Tensile Strength Tests on Low-Porosity Rocks

Paint Speckle Application Recommendations for Digital Image Correlation Analysis of Brazilian Tensile Strength Tests on Low-Porosity Rocks

Prediction of Tensile Strength in Tight Sandstone Based on Well Logging Data

The tensile strength of tight sandstone reservoirs has a direct impact on crack initiation, hydraulic fracture propagation, and the connectivity between hydraulic fractures and natural fractures during hydraulic fracturing processes. To overcome the limitations of experimental testing methods and field hydraulic fracturing techniques, this study conducted Brazilian tensile strength tests to obtain tensile strength data for 16 sets of tight sandstone samples. By comparing these experimental results with well logging data, a predictive model for the tensile strength of tight sandstone was established based on geophysical well logging data, with a correlation coefficient exceeding 0.92. The research findings indicate a positive correlation between tensile strength and sample density. This study provides support for fracture design, assesses fracturability, and aids in the selection of optimal drilling locations for hydraulic fracturing operations.

Modeling Brazilian Tensile Strength Tests on a Brittle Rock Using Deterministic, Semi-deterministic, and Voronoi Bonded Block Models

Modeling Brazilian Tensile Strength Tests on a Brittle Rock Using Deterministic, Semi-deterministic, and Voronoi Bonded Block Models

Tensile strength of anisotropic rocks from enhanced Brazilian laboratory testing and data analysis protocols

The tensile strength of rock and rock-like materials is a critical material property in rock engineering design and the prediction of rockmass behaviour to mitigate any potential failure that may affect personnel safety or damage property. This study presents new instrumentation guidelines to the Brazilian Tensile Strength (splitting tensile strength) test to enhance the data processing techniques to determine true tensile strength. For this study a total of eighteen (18) specimens of two lithologies (Pointe Du Bois tonalite gneiss and Key Anacon metabasalt) were instrumented, tested, and reviewed to determine the true tensile strength of the material. This paper also identifies three potential failure modes and presents a failure envelope based on the identified potential failure modes.

Effect of geogrid reinforcement on tensile failure of high-strength self-compacted concrete

In this study, the tensile strength, failure mechanism and ductile behaviour of geogrid-reinforced high-strength self-compacting concrete discs subjected to both the Brazilian tensile strength test and a biaxial compressive test are studied. To determine the combined effects of geogrid layer numbers and inclination angle on the ultimate tensile strength of concrete samples, 21 experiments were conducted with up to three layers of geogrids inclined at angles of 0° to 90°, at increments of 15°. In addition, discrete-element numerical simulations were conducted using two-dimensional particle flow code to examine the failure behaviour of geogrid-reinforced high-strength self-compacting concrete discs. The numerical models were first calibrated by the experimental results and then the failure behaviour of models containing geogrids was investigated. Both experimental and numerical results demonstrate that augmenting the concrete discs with geogrids increases the ductility of specimens, especially after failure. As the number of geogrid layers increased, the tensile strength of specimens also increased, whereas the tensile strength and absorbed energy were the same for specimens with different numbers of geogrid layers and inclination angles of 75° and 90°. The specimen with three horizontal geogrid layers had the highest tensile strength, biaxial compression strength and ductility of all specimens tested.

Geoscience Poster G8: Geomechanical rock properties of the Officer Basin

Poster G8 The Officer Basin spanning South Australia and Western Australia is the focus of a regional stratigraphic study being undertaken as part of the Exploring for the Future (EFTF) program, an Australian Government initiative dedicated to increasing investment in resource exploration in Australia. Despite numerous demonstrated oil and gas shows, the Officer Basin remains a frontier basin for energy exploration with significant uncertainties due to data availability. Under the EFTF Officer–Musgrave Project, Geoscience Australia acquired new geomechanical rock property data from forty core samples in five legacy stratigraphic and petroleum exploration wells that intersected Paleozoic and Neoproterozoic aged intervals. These samples were subjected to unconfined compressive rock strength tests, Brazilian tensile strength tests and laboratory ultrasonic measurements. Petrophysical properties were also characterised via X-ray computerised tomography scanning, grain density and porosity-permeability analysis. Accurate characterisation of static geomechanical rock properties through laboratory testing is essential. In the modern exploration environment, these datasets are a precompetitive resource that can simplify investment decisions in prospective frontier regions such as the Officer Basin. To access the poster click the link on the right. To read the full paper click here

Experimental Study on Mechanical Properties of 3D-Printed Specimens of Iron Oxide, Quartz, and Bedded Composites Under Uniaxial Compression and Indirect Tensile Strength.

The heterogeneity of natural rocks produces increased variations in the results of geomechanical and metallurgical tests making the repeatability of experimental work questionable. Fabricated test specimens have, therefore, become more attractive for fundamental studies. In this study, quasi-identical 3D-printed (3DP) specimens with 10 and 16 mm diameters were fabricated and tested to study material strength and understand the breakage characteristics at a scale more suitable for comminution. Cylinder specimens composed of quartz (named Si) and iron oxide (named Fe), with sorted grains of ∼100-150 μm in the form of homogeneous specimens (3DP-Si and 3DP-Fe) and heterogeneous specimens (bedded) (3DP-SiFeSi, 3DP-SiFe, and 3DP-FeSiFe) were tested. This article presents the results for experimental Unconfined Compressive Strength (UCS) and Brazilian Tensile Strength (BTS) tests. The elastic property was obtained from the UCS tests, while tensile strength was obtained from BTS tests. The strength of 3DP specimens of similar diameter decreases following the types: 3DP-Si (most competent), 3DP-Si-Fe, 3DP-SiFeSi, 3DP-FeSiFe, and 3DP-Fe (less competent). The results show that heterogeneous 3DP specimens were influenced by bedding angle, thickness, and mineral group composition. It also seems that the sequence of mineral composition and the number of beds play a role, rather than the overall grain percentage area for each cylinder, in influencing the strength and variability of fragments. Finally, the brittleness indices for 3DP specimens were calculated as a function of UCS and BTS.

Geomechanical rock properties of the Officer Basin

The Officer Basin spanning South Australia and Western Australia is the focus of a regional stratigraphic study being undertaken as part of the Exploring for the Future (EFTF) program, an Australian Government initiative dedicated to increasing investment in resource exploration in Australia. Despite numerous demonstrated oil and gas shows, the Officer Basin remains a frontier basin for energy exploration with significant uncertainties due to data availability. Under the EFTF Officer–Musgrave Project, Geoscience Australia acquired new geomechanical rock property data from forty core samples in five legacy stratigraphic and petroleum exploration wells that intersected Paleozoic and Neoproterozoic aged intervals. These samples were subjected to unconfined compressive rock strength tests, Brazilian tensile strength tests and laboratory ultrasonic measurements. Petrophysical properties were also characterised via X-ray computerised tomography scanning, grain density and porosity-permeability analysis. Accurate characterisation of static geomechanical rock properties through laboratory testing is essential. In the modern exploration environment, these datasets are a precompetitive resource that can simplify investment decisions in prospective frontier regions such as the Officer Basin.

Investigation of the shear failure of rock joints using the four-dimensional lattice spring model

This research adopts the four-dimensional lattice spring model (4D-LSM) to investigate the shear strength and failure mechanism of irregular rock joints and the influence of rock heterogeneity. The 4D-LSM has been used for a wide range of rock engineering applications, however its ability for simulating direct shear tests has not been investigated in detail. The material strength parameters were calibrated using uniaxial compressive strength (UCS) and Brazilian tensile strength (BTS) tests on granite specimens while the joint parameters were calibrated from direct shear tests on saw-cut UCS specimens and rock joints containing a single triangular asperity. From UCS tests, a calibration method is proposed to adjust the excessive machine deformation due to the high brittleness of granite, which is further applied to the direct shear test results. It was found that the strength of rock joints is strongly influenced by the intact rock properties. To investigate the influence of joint geometry and rock heterogeneity, three joint asperity angles and five heterogeneous models were simulated using the calibrated 4D-LSM model. Simulation results were able to capture the influence of different joint asperity angles on the shear strength and failure mechanism as reported in previous experimental and numerical studies. With larger asperity angles, higher shear strengths were obtained. Meanwhile, rock heterogeneity represented by particles with lower strength will reduce the shear strength and alter the failure mechanism, especially at a high porosity. This strength reduction was observed to be greater for steep-angle asperities and becomes less significant for flatter asperities. Similar conclusions were also obtained based on the simulations of natural joint profiles. From these findings, it is suggested that the characterisation of rock heterogeneity is crucial to estimate the strength of rock joints. In addition to the roughness parameters , heterogeneity parameters such as porosity are fundamental for rock engineering applications. • The ability of the (4D-LSM) for simulating the direct shear of irregular rock joints is verified against experimental results. • A calibration is developed for 4D-LSM to model rock joints by integrating uniaxial compressive and direct shear tests. • The influence of rock joint surface on its shear strength is investigated numerically by using the calibrated 4D-LSM. • The influence of different rock heterogeneities on the shear strength of the joints is numerically studied.

Using ground blast-furnace slag grouts with biopolymer additives for improving sandy soils

The mechanical performance of microfine ground-granulated blast-furnace slag grouts for improving sandy soils was evaluated using unconfined compressive strength, drained triaxial compression and Brazilian tensile strength tests of grouted sand specimens. Two activator types, namely sodium hydroxide and rapid-hardening cement (RHC), and two biopolymer additives, namely xanthan gum (XG) and diutan gum (DG), were investigated for slag-based grouts prepared at various water–binder (w/b) ratios. The bench-scale investigation examined the cured strength properties of grouted sand specimens. It was observed that the RHC activator with modest biopolymer additive and smaller w/b ratio resulted in markedly higher strength gains. In terms of activator type, compared to sodium hydroxide, the RHC resulted in significantly better performance, mobilising increased cohesion in specimens tested in drained triaxial compression. When used together with slag grouts, XG and DG mostly showed comparable strength improvements, but DG proved more effective at lower dosage in increasing tensile strength of grouted sand.

FEM-DEM simulation of Brazilian Tensile Strength (BTS) laboratory tests

A Brazilian Tensile Strength (BTS) laboratory test for meta-andesite was modeled using a Finite/Discrete Element Method (FDEM or FEM-DEM). These hybrid methodologies allow modeling the transition from continuous to discontinuous that happens on mechanical tests of rock samples. This article presents the calibration and the simulation of BTS tests using some parameters previously calibrated on UCS modeling of the same material. Irazu, a two-dimensional software developed by Geomechanica, was used to simulate the tests based on the tensile strength and the fracture pattern. The model shows that, in BTS test simulation, the mode II (shear) happens mainly on the rock-platen contact. The mode I (traction) rules the fractures on the BTS test as observed in laboratory tests. The model represents, with great fidelity, the results obtained in the physical test.

Experimental evaluation of multi-functional effects of fibers on mechanical and performance properties of Roller-compacted concrete pavements (RCCP)

The weak performance of asphalt pavements in different climatic conditions, quick decay of pavement, and lack of necessary durability have caused engineers and constructors to try to find Roller Compacted Concrete Pavement (RCCP) for use in various conditions and applications with outstanding properties such as higher durability, and lower maintenance costs. This paper aimed to investigate the mechanical and durability of RCCP by considering different types and amounts of fibers. Cylindrical specimens (with two diameters of 100 and 150 mm) and bending beams with four different fiber types (steel, Kortta Emboss, Kortta Twist, and Sinusoidal plastic) and different percentages were used and subjected to various tests. The compaction time (VB or Vebe) test on fresh concrete, the compressive strength, elastic modulus, the flexural strength, the Brazilian tensile strength, impact resistance, electrical resistance, and skid resistance tests on hardened concrete were conducted. A total of 17 fiber-reinforced concrete mixtures in addition to plain specimen were considered. The test results indicated that compressive, flexural, and tensile strengths of the specimen containing steel fibers were improved up to 27, 83, and 25%, respectively. Moreover, the flexural and tensile strengths of specimens containing Kortta Emboss fibers were improved up to 80 and 19%, respectively. The impact resistance of specimens containing steel and Kortta Emboss fibers were significantly improved up to 270 and 290%. Based on evaluating the results obtained from all tests, Kortta Emboss fiber was proposed as the best option among the studied fibers to improve the properties and functions of RCCP.