Uniaxial Compressive Strength Values Research Articles

Bearing Capacity Equations for Intact Argillaceous and Arenaceous Rocks in Malaysia Derived from P-Wave Velocity

This paper presents the derivation of the bearing capacity equation of shallow foundations using P-wave velocity based on the seismic refraction method on argillaceous rocks (shale) and arenaceous rocks (sandstone). Various theories of bearing capacity equations were developed over the years for the calculation of bearing capacity under vertical central loading. But, the most widely used on rock is the Mohr-Coulomb failure criterion given by Meyerhof (1963). Based on this theoretical development, the empirical equation of ultimate bearing capacity was obtained. The detailed derivation of these parameters is comprised of the results from Uniaxial Compressive Strength (UCS) and P-wave velocity values. The proposed empirical equation of bearing capacity derived from P-wave velocity herewith can be used as an alternative method in designing shallow foundations. There is a good agreement on the bearing capacity determination from P-wave velocities.

Experimental study on I/II/III mixed mode fracture characteristics of a combined rock mass under creep loading

I/II/III mixed mode fractures of intersecting joint fissures often occur in natural rock masses, and jointed rock masses are prone to rockbursts in deep underground engineering when subjected to long-term crustal stresses. However, most studies of the mechanical mechanisms of these intersected joints have been conducted by simplifying two-dimensional joint model tests. Furthermore, the fracture mechanisms of two-dimensional intersected joints under tension and compression are completely different from those of three-dimensional joints. This paper presents a novel prefabricated specimen with combinations of intersecting joints capable of detecting the failure behaviours of rock I/II/III mixed mode fractures under creep loading. Uniaxial compression and multistage creep tests are performed on prefabricated sandstone specimens with intersecting joints of 0°/0°, 0°/30°, 0°/60°, and 0°/90°. The experimental results show that with the increase in the number of prefabricated intersecting joints, the uniaxial compressive strength and elastic modulus values of the sandstone specimens gradually decrease. In addition, the sandstone specimens experience relatively few AE events and minor axial strain variations in the first creep stage and the second creep stage of the multistage creep test. The axial strain increases sharply due to the sharp increase in the number of AE events in the third creep stage. The 0°/60° sandstone specimen undergoes accelerated creep failure, resulting in mixed X-shaped tensile‒shear rupture. The RA value is high based on the quantification of the creeping cracks using the acoustic emission parameters of the rise angle (RA) and average frequency (AF). The AF values of the 0°/0°, 0°/30°, and 0°/90° sandstone specimens are high. The experimental results show that a larger joint intersection angle leads to greater mutual restraints and greater effects of prefabricated crack propagation in the rock specimens, thus increasing the final failure strength. Finally, based on the acoustic emission count, a characteristic variable D suitable for characterizing the creep damage evolution of a joint rock mass is established. The findings of this paper can facilitate an effective understanding of the creep effect of I/II/III mixed mode fracture and its micromechanism. The research results will have a certain reference value for the detection and risk mitigation of instantaneous and time-delayed rockbursts.

An experimental study on the strength values of resin added sand samples with different types of fiber reinforcements

In this study, uniaxial compressive strength values of a sand type soil reinforced with polypropylene fiber and silicate-based resin additives with different amounts were investigated. Micro grid fiber (MGF) was tested as a new polypropylene fiber additive in the experiments to compare it with a widely used polypropylene fiber type geosynthetic product used in soil fill improvement applications. According to the findings obtained from the uniaxial compressive strength (unconfined compressive strength) tests, it was determined that the new MGF type fiber usually increased the strength values at higher rates in comparison with the conventional fiber product. As another outcome, it was found that target strength values can be supplied by using less resin amounts for the specimens with fiber additives. It was determined that proper strength improvements can be obtained more economically by the fiber additive use together with the resin, rather than the resin added mixtures without the fiber.

Usability of Trabzon stone as a natural building stone and aggregate

This study investigated the suitability of Trabzon stone, which is used as a building stone in many areas in and around Trabzon province, as an aggregate. It was found that the uniaxial compressive strength values of the samples taken from the quarry were 87-130 MPa, P-wave velocities were 5048-5642 m/s, density value was 2.58 g/cm3, apparent porosity values were 2.77-4.54%, water absorption values by weight were 1.04-1.78% and water absorption value by mass was 2.0%. Weight loss in the freeze-thaw test was 0.36%, weight loss in the wet-dry test was 0.22%, loss in the magnesium sulfate test was 13%, Los Angeles fragmentation resistance in coarse aggregate was 22%, abrasion resistance value was 18% and methylene blue value was 0.9%. When the results were analyzed, it was found that the mass water absorption rate and the magnesium sulfate test results were above the values required by the standards. Although these rocks are used as marble, it has been determined that the waste material is not suitable for use as ballast, crushed stone, stone fill, pere, and masonry for road and concrete construction. Despite this result, it is necessary to investigate the usability of materials from other marble quarries in the region as aggregates.

Оценка влияния скорости нагружения на прочность скальных горных пород при одноосном сжатии и характер их разрушения

When studying physical and mechanical properties of rocks, one of the main parameters to be determined is their uniaxial compressive strength. During laboratory experiments, the value of this parameter can be influenced by both loading conditions and the shape of the prepared samples. By studying the impact of these factors, it is possible to give an adequate assessment of changes in the strength of rocks, as well as to predict their failure behavior. The paper presents the results of experimental studies of hard rocks from the Kola region deposits under uniaxial compression. The values of the rock strength at loading rates from 0.01 to 50 kN/s were established. On the basis of the obtained data it was revealed that the V.A. Fokin criterion can be used to determine the rated strength of rocks. It is shown that the values of uniaxial compressive strength of brittle elastic rock (urtite) and non-brittle elastic-plastic rock (carbonatite) will also increase with the increasing loading rate. It is established that for hard rocks prone to dynamic failure, an increase in the loading rate will lead to an increase in the intensity of their failure. Increasing the loading rate for non-brittle elastic-plastic rocks can cause them to start failing dynamically. The obtained conclusions indicate that the failure behavior of rock samples depends on the time factor of loading.

Study on damage characteristics and application of gypsum pillar strengthened with FRP

The instability of mine pillars has posed a serious threat to the safety of mines in China. In order to reduce the risk of pillar instability, this study used fiber-reinforced polymer (FRP) to reinforce gypsum specimens and conduct mechanical loading experiments. The study investigates the reinforcement effect of gypsum specimens with different height-diameter ratios and different FRP wrapping thicknesses, and analyzed the uneven distribution of constraint force along the height direction of FRP-reinforced gypsum specimens. An optimized wrapping method was proposed, and a stress–strain constitutive model for gypsum materials under optimized wrapping was established. By utilizing a statistical method based on strain energy density for heterogeneous rock damage identification, a simulation study was conducted on FRP-reinforced gypsum-like specimens. A comparative analysis was carried out with experimental results to verify the feasibility of the constitutive model. The research findings indicate that the use of FRP reinforcement significantly improves the uniaxial compressive strength and strain values of gypsum-like specimens. Moreover, the smaller the aspect ratio, the more pronounced the effect of FRP reinforcement on gypsum-like specimens. The stress–strain curve of FRP-reinforced gypsum-like specimens shows a distinct combination of curves and straight lines, which can be divided into two distinct stages based on different elastic moduli. The peak value of acoustic emission energy of FRP-reinforced gypsum specimens appears at the junction of the first and second stages of the stress–strain curve, and then the acoustic emission energy curve becomes relatively flat, with an increase in peak energy before failure. The constraint force acting on FRP-reinforced gypsum specimens exhibits an obvious uneven distribution along the height direction, based on which an optimized reinforcement scheme is proposed. Based on the established constitutive model, numerical simulation was conducted using real data from a specific mine. The research findings demonstrate that when the optimized reinforcement method is employed, the load-bearing capacity of the mine pillars was significantly enhanced. The maximum displacement was reduced by 33%, the maximum vertical stress was reduced by 3.2%, and the volume of the plastic zone was reduced by 39.87%.

Use of microgrid fibre as a new reinforcement additive to improve compressive and tensile strength values of cemented rock fill mixes

ABSTRACT In this study, use of microgrid fibre (MGF) was tested as a new polypropylene fibre additive for cemented rock fill (CRF) mixes and compared with the conventional polypropylene fibre type geosynthetics. Changes in the uniaxial compressive strength and indirect tensile (splitting) strength values of CRF specimens were investigated for the use of different fibre types. In this experimental study, cemented basalt aggregate type rock fill materials were tested in case of using different amounts of fibre additives and cement contents. According to the results obtained from this experimental study, it was determined that MGF type new fibre additives can supply better increases in strength values in comparison with the conventional polypropylene fibre products. It was assessed that MGF type novel additives can be used to make better adherence in the CRF mixes and reinforcement performances under both compression and tension cases than those of the conventional fibre additive products.

Correlations between mineral composition and mechanical properties of granite using digital image processing and discrete element method

This study investigated the correlations between mechanical properties and mineralogy of granite using the digital image processing (DIP) and discrete element method (DEM). The results showed that the X-ray diffraction (XRD)-based DIP method effectively analyzed the mineral composition contents and spatial distributions of granite. During the particle flow code (PFC2D) model calibration phase, the numerical simulation exhibited that the uniaxial compressive strength (UCS) value, elastic modulus (E), and failure pattern of the granite specimen in the UCS test were comparable to the experiment. By establishing 351 sets of numerical models and exploring the impacts of mineral composition on the mechanical properties of granite, it indicated that there was no negative correlation between quartz and feldspar for UCS, tensile strength (σt), and E. In contrast, mica had a significant negative correlation for UCS, σt, and E. The presence of quartz increased the brittleness of granite, whereas the presence of mica and feldspar increased its ductility in UCS and direct tensile strength (DTS) tests. Varying contents of major mineral compositions in granite showed minor influence on the number of cracks in both UCS and DTS tests.

Acoustic and mechanical tests of sandstone-shale composites in Songliao Basin and prediction of uniaxial compressive strength

Rock uniaxial compressive strength is a vital rock mechanics parameter, which accurate assessment is critical for high-efficiency unconventional reservoir development. However, its realization for standard cores is quite problematic due to difficulties and high costs related to the collection and preparation of samples. Unconventional fracturing treatment have evolved from single to composite lithology. This study collected shale and sandstone samples at different bedding angles (0°, 45°, 90°)to prepare the sandstone-shale composite samples at different interlayer ratios. It measured the prepared composites’ longitudinal wave and transverse wave velocities with ultrasonic velocity testing. The uniaxial compressive strength of the sandstone-shale composites with various bedding angles were tested via a servo rock triaxial testing machine. The anisotropic characteristics of the prepared sandstone-shale composites with various bedding angles were analyzed, and relation between the uniaxial compressive strength of the anisotropic sandstone-shale composite and P-wave velocity was derived and experimentally validated. The results show that: the wave velocity test results of the sandstone-shale combination show that with the increasing proportion of shale, the wave velocity of the longitudinal wave and the transverse wave both increase; The wave velocity results of different bedding planes in shale are as follows: Vp(0°)> Vp(45°)> Vp(90°). The average P-wave and S-wave velocities at 45° are 0.92, while the average P-wave and S-wave velocities at 90° are 0.85 compared to 0°; the P-wave and S-wave anisotropy of shale are both 0.14, and the shale shows significant anisotropy. In the sandstone-shale composite, the uniaxial compressive strength gradually decreases and the strain increases with the increase of shale proportion. The value of uniaxial compressive strength is UCS(0°) > UCS(90°) > UCS(45°). Based on the P-wave modulus, a fitting relationship formula for the uniaxial compressive strength of sandstone-shale composites with different bedding angles and interlayer ratios was established and verified. The anisotropic strength predictive formula established based on experimental data is simple, precise, and easy to obtain, with strong practicability. The present research results can provide proper technical support for sandstone-shale composite fracturing optimization and reservoir development.

Experimental Study on the Mechanical Properties and Acoustic Emission Characteristics of Different Bedding High-Rank Coals.

Bedding has an important influence on the macroscopic and microscopic mechanical properties of coal, and the mechanical properties of coal and rock mass and acoustic emission characteristics are very important for rock burst monitoring and warning. In order to explore the influence of different beddings on the mechanical properties and acoustic emission characteristics of high-rank coal, using the RMT-150B electrohydraulic servo rock mechanics test system and the DS5 acoustic emission analyzer, the uniaxial compression and acoustic emission characteristics of high-rank coals with different beddings (parallel bedding 0°, oblique bedding 30, 45, 60°, and vertical bedding 90°) were investigated. The results show that the uniaxial compressive strength and deformation modulus of vertical stratified coal samples are the largest, which are 28.924 MPa and 2.95 GPa, while the average values of uniaxial compressive strength and deformation modulus of oblique stratified coal samples are the smallest, which are 10.91 MPa and 1.776 GPa, respectively. With the increase of the bedding angle, the uniaxial compressive strength of high-rank coal decreases first and then increases. The stress-strain process of coal varies greatly with different high stratification grades (parallel bedding 0°, oblique bedding 30°, 45°, 60° and vertical bedding 90°). The loading times of parallel, oblique, and vertical beddings are 700, 450, 370, 550, and 600 s, and the acoustic emission mutation point values are 495, 449, 350, 300, and 410 s. The mutation point value can be used as precursor information to judge the failure of high-rank coal in different beddings. Research results to find the high-rank coal destruction instability prediction method and the index provide a basis; further damage to the acoustic emission testing high order coal provides reference significance; and the use of acoustic emission in the monitoring and early warning of percussive ground pressure, the bedding surface of coal, and the actual stress on site should be considered.

CORRELATION OF UNIAXIAL COMPRESSIVE STRENGTH AND ELASTIC MODULUS BASED ON PARAMETER PHYSICAL PROPERTIES AND POINT LOAD OF LIMESTONES IN GUNUNG KIDUL DISTRICT

In mining design, it is necessary to know in advance the characteristics of physical and mechanical properties, especially in the case of limestone. Laboratory tests need to be carried out to determine the physical and mechanical characteristics of limestone. Two important parameters that are often used for geotechnical analysis are the uniaxial compressive strength (UCS) and elastic modulus (E) values. Uniaxial compressive strength and elastic modulus values can be interpreted indirectly by using statistical relationships, which are simple regression and multiple regression, to interpret the correlation between the parameters of specific gravity, porosity, and point load index (PLI). Based on the results of statistical analysis, the strongest correlation is found between the point load index (PLI) and UCS, where the correlation value is 0.85. The correlation between the point load index (PLI) and the elastic modulus also has a strong relationship, with a correlation value of 0.74. In the multiple regression analysis, with independent variables (density, porosity, and PLI) and dependent variables (UCS and elastic modulus), the average error for the uniaxial compressive strength (UCS) value is 1.7811 (multiple regression) and 1.5542 (multiple non-linear regression) while the average error for elastic modulus (E) is 0.2460 (multiple regression) and 0.1841 (multiple non-linear regression).

Investigation of changes in geomechanical properties of sandstones under different saturation and anisotropy conditions: Example from Gümüşhane (NE Türkiye)

In this study, the changes in various geomechanical properties were studied for sandstones cropped out at the Mescitli region of the Gümüşhane city under different saturation and anisotropy conditions. For this purpose, 225 specimens were prepared considering the lamination planes of those were chosen to have orientation of 0, 30, 45, 60 and 90° relative to loading direction. Index properties of the sandstones such as dry unit weight (dry), saturated unit weight (sat), water absorption by weight (Aw) and water absorption by volume (Av) were assigned. In accordance with the objective of study P wave velocity, uniaxial compressive strength and indirect tensile strength values were determined based on different saturation and anisotropy conditions. It was noted as a result of the observations carried out that specimens parallel to lamination have higher wave velocities in general when compared with specimens that are perpendicular to lamination planes. While uniaxial compressive strength values for sandstones are high for specimens which are parallel and perpendicular to lamination, the lowest strength value was observed in specimens with an anisotropy angle of 30°. In addition, it was also observed that the strength values decrease at a significant level with increasing saturation conditions. Strength anisotropy ratio (RUCS) for sandstones varies between 1.28–1.49 based on different saturation conditions. Similarly, while indirect tensile strength values were higher in specimens that were parallel and perpendicular to lamination, they were lower for other anisotropy orientations. Indirect tensile strength values also decreased with increasing degree of saturation.

Investigation of the Leeb hardness test in rapid characterisation of rock cores with particular emphasis on the effect of length to diameter ratio

ABSTRACT The Leeb hardness is a practical, economical and non-destructive test method in rock characterisation in engineering. Hardness measurements on core samples with lower values of length-to-diameter (L/D) ratios cause unstable measurements, and as a result, erroneous evaluations can be made. To overcome this limitation, this study aimed to reveal the effect of different L/D ratios both in axial and diametral measurement directions. Eleven types of rock samples were prepared and tested. Mineralogical and petrographic examinations were performed and evaluated together with the hardness values. Equations have been proposed to estimate correct hardness and uniaxial compressive strength values for all rock types.

CORRELATION OF UNIAXIAL COMPRESSIVE STRENGTH WITH BRAZILIAN TENSILE STRENGTH AND INDEX PROPERTIES FOR SOFT SEDIMENTARY ROCKS

Sedimentary Rocks composing the Thar Lignite basin Pakistan are of clastic origin. These rocks have comparatively low uniaxial compressive strength (UCS) values, and hence recognized as ‘soft sedimentary rocks’ in this study. UCS is a fundamental property of rocks, used by mine design engineers in designing the surface and underground excavations. The purpose of this study is to investigate the relationship between UCS with Brazilian tensile strength (BTS), and index properties of soft sedimentary rock formations at Thar Lignite basin. Various correlations between mechanical and physical properties of rocks have been developed previously. However, no significant correlation has been developed on UCS with BTS and index properties for soft sedimentary rocks. Numerous Rock samples from Two complete geotechnical drillholes at Block-IX Thar Coalfield were selected. Standard test procedures were implemented to determine the UCS, indirect Tensile and index properties such as point load strength, and shore Scleroscope hardness. The correlations between rock properties were established using simple and multiple regression techniques, and empirical equations were obtained. These equations can be used to predict the UCS and tensile strength of soft sedimentary rocks by performing simple index tests; which are quick, economical, and easier to be performed on the site.

Meso-mechanical anisotropy and fracture evolution of reef limestones from the Maldives Islands and the South China Sea

Reef limestone is a biogenic sedimentary rock widely distributed in coral reef areas, acting as an important foundation for coast construction. Due to its special biogenic origin, reef limestone is different from conventional rocks both in terms of rock structure and mechanical properties. In this study, mesoscale uniaxial compression experiments with five different loading directions were conducted on two kinds of reef limestones from the Maldives Islands and the South China Sea, respectively. The real-time high-resolution videos and images of failure processes were recorded simultaneously to investigate the fracture evolution and fracture surface roughness of reef limestones. It demonstrated that the reef limestones belonged to extremely soft to soft rocks, and their uniaxial compressive strength (UCS) values fluctuated with high discreteness. The mesoscale mechanical properties of reef limestones were highly anisotropic and mainly controlled by pore structure. The occurrence of dissolution pores in reef limestone tended to intensify mechanical anisotropy. With the integration of the fracture initiation and propagation features of reef limestones, it is supposed that the intrinsic mechanism of anisotropy was probably attributed to the differences in coral growth direction and dissolution. Furthermore, the quantified fracture surface roughness was revealed to have a good consistency with density and UCS for the reef limestones from the South China Sea. The findings are helpful for providing theoretical and experimental references for engineering construction in coral reef areas.

Geotechnical and environmental radioactivity investigations at Al Sādis Min Uktōber city, Cairo municipality (Egypt), for the high-speed railway construction

The present study aims to evaluate the possibility of constructing a new high-speed railway (HSR) at Al Sādis Min Uktōber city, Cairo (Egypt): geotechnical and environmental radiological hazards are estimated from several collected soil and water samples. A variety of laboratory geotechnical tests such as grain size, free swelling test, liquid and plastic limits, chemical analysis and uniaxial compression strength are applied to sixty-one drill holes. A geotechnical examination of the coarse-grained soil at the foundation level classified it as poorly graded soil. The results of the investigation of fine-grained soil at the foundation level shown that the liquid limit ranges from 22% to 55%, the plastic limit ranges from 12% to 28%, the plasticity index varies from 11% to 33%, free swelling varies from 51% to 71%. Mechanically, the uniaxial compressive strength values on rock samples range from 6.96 MPa to 142.39 MPa. The radioactive study is performed to detect the 226Ra, 232Th, and 40 K activity concentrations of the soil samples: their mean values are 34 ± 10 Bq·kg−1, 14 ± 5 Bq·kg−1 and 552 ± 20 Bq·kg−1, respectively. The values of radiological hazard indexes are not exceeded the permissible limits: e.g. the mean value of absorbed dose rate is 47 ± 6 nGy h−1; the annual gonadal dose equivalent is 0.3 ± 0.04 mSv·y−1; the lifetime cancer risk is 02 ± 0.2·10−3. Thus, the soil in the studied railway area is safe to use in building materials and infrastructure applications: the radiological hazards and the geotechnical studies confirmed the studied area is suitable to construct a new community having a HSR. According to the SWOT-PEST and environmental impact analyses, the construction of the HSR meets the criteria of the Kyoto Protocol, the EU Climate and Energy policy, and other international treaties.

The Effect of Cyclic Impact Loads on Rock Properties

This study was conducted mainly in the laboratory to evaluate the effect of cyclic impact loads on rock properties. The test sample was a rock-like material made of cement, sand, and water. The sample was given an impact load from a metal pounder that was dropped at various heights. The load was repeatedly applied to the sample until it was damaged and/or until failure. The test results revealed four stages in the fracturing process, starting with cratering of the upper surface of the sample, formation of initial fractures, fracture development along the sample, and finally sample failure. The test results also revealed that with an increase of impact load, the number of cycles until failure decreases. Furthermore, the value of uniaxial compressive strength and Young’s modulus decreases with increasing number of cyclic loads. The decrease is proportional to the increase of the damage value.

Evaluation of the Effect of Rock Strength on Drilling Penetration Rate and Index of Rotation Energy–A Case Study

Proper knowledge of the rocks and properties of rock will allow proper selection of the bit and speed of rotation of the drill for fast penetration and reduce the cost of drilling. Since the rock fragmentation process requires the drilling of small diameter holes for the placement of explosive material, this makes the evaluation of rock properties' effect on this operation important. This study focus on evaluating the effect of rock properties and drill parameters on drill bit penetration rate, specific energy, and index of rotational energy. Two case studies mine in southwest Nigeria were considered for this study. Rock properties, penetration rate, and index rotation energy of the drill quarry machines were determined. The obtained parameters for different drilling operations were used to develop datasets for different observations. The uniaxial compressive strength, point load, and hardness values of the case study granite have an average value of 90.56-121.43 MPa, 6.8-8.54 MPa, and 45.648.01 respectively. Prediction models were developed for the prediction of the drill penetration rate, specific energy, and index of rotation energy as a function of the rock properties. The developed regression models show a very high correlation having R2 value close to unity. Hence the proposed regression models can reasonably predict drill penetration rate, specific energy, and index of rotation energy for practical purposes.

Numerical Test and Strength Prediction of Concrete Failure Process Based on RVM Algorithm

Recycled aggregate concrete (RAC) based on the machine learning (ML) method predicts the nonlinear uncertainty relationship between various mixing ratios and strength. Uniaxial compressive strength is one of the important indices to evaluate its performance. Machine learning is one of the essential methods for solving this nonlinear uncertainty relationship. To realize the selection of concrete raw materials and the learning and application of other influencing factors and provide guidance for engineering construction and application, this paper establishes a database of concrete uniaxial compressive strength based on Abaqus simulation software. The simulation results are highly consistent with the actual values. Based on the simulation database, with different water-cement ratios, different curing days, and recycled aggregate replacement rates as the input data set, the uniaxial compressive strength of concrete is the output data set. The data set is divided into a training set and a test set. A prediction model of the uniaxial compressive strength of concrete based on a relevance vector machine (RVM) algorithm is established. The results show that the maximum error between the simulated and experimental uniaxial compressive strength values is only 0.2 MPa. The correlation coefficient R between the predicted and simulated values of the concrete uniaxial compressive strength prediction model based on the RVM algorithm is 0.975. The model can effectively predict the compressive strength of RAC to meet the engineering requirements.

A novel equation for calculating uniaxial compressive strength values using the point load test

A novel equation for calculating uniaxial compressive strength values using the point load test