Intact rock strength (original) (raw)
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Considerations on strength of intact sedimentary rocks
Engineering Geology, 2004
This study presents the results of laboratory testing of sedimentary rocks under point loading as well as in uniaxial and triaxial compression. From the statistical analysis of the data, different conversion factors relating uniaxial compressive and point loading strength were determined for soft to strong rocks. Additionally, the material constant m i , an input parameter for the Hoek and Brown failure criterion, was also estimated for different limestone samples by analysing the results from a series of triaxial compression tests under different confining pressures. The uniaxial compressive strength (UCS) of intact rocks, as estimated from the point load index using conversion factors, together with the Hoek -Brown constant m i , and the Geological Strength Index (GSI) constitute the parameters for the calculation of the strength and deformability of rock masses. D
Symmetry, 2021
The objective of the current study was to compare results relating to the compressive and tensile strength of rocks obtained during research undertaken according to Polish Standards (as part of the European standards known as Eurocodes), American Society for Testing and Materials (ASTM) Standards, and the recommendations of the International Society for Rock Mechanics (ISRM). A total of 130 experiments for uniaxial compression on axisymmetric samples, point loads, and transverse compression (so-called Brazilian tests) were performed on rock samples comprising granite, limestone, and sandstone. Geometric properties of the samples were selected depending on the applied research method, and the relationship between the specimen’s slenderness and shape, and the obtained values of compressive and tensile strength, were analyzed. The results of the study showed that values of compressive and tensile strength obtained in a laboratory depend significantly on specimen slenderness, different ...
Evaluation of empirical methods for measuring the uniaxial compressive strength of rock
International Journal of Rock Mechanics and Mining Sciences & Geomechanics Abstracts, 1990
Eight sandstones, three limestones, one dolomite, one marble and one syenitic gneiss were tested to evaluate the correlations between the compressive strength values, as determined by the standard uniaxial compression test, and the corresponding results of the point load, the Schmidt hammer, the Los Angeles abrasion, and the slake durability tests. Ten cores of each rock type were used for the uniaxial compression, point load and Schmidt hammer tests, whereas an average of three tests for each rock type was used to determine the Los Angeles abrasion loss and the slake durability indices. Results indicate that strong linear correlations exist between the results of uniaxial compression vs the point load and Schmidt hammer tests, the correlation for the Schmidt hammer being dependent on rock type. The correlation between uniaxial strength and the Los Angeles abrasion loss in non-linear but becomes linear when a log-log scale is used. The slake durability index does not exhibit a significant correlation with the uniaxial strength for the rocks tested. The correlation equations for predicting compressive strength using different methods are presented along with their confidence limits. All empirical tests used, other than the slake durability test, provide reliable estimates of compressive strength, with Schmidt hammer slightly underestimating at higher strength (> 150 MPa).
Determination of Rock Strength and Deformability of Intact Rocks
The paper presents the results of laboratory tests performed on a large number of intact sedimentary rock specimens (limestone, sandstone, siltstone) and metamorphic rocks from Greece. The physical properties (porosity, dry density), mechanical properties (uniaxial compressive strength), Young's modulus, point load index, Schmidt hardness) and dynamic properties (wave velocity) were determined. Furthermore, laboratory results of intact rock properties were collected and evaluated. From the statistical analysis of the data, regression equations were established amongst intact rock parameters. The ratio of rock strength and deformation modulus was investigated and its range was determined for all rock types. A comparison was made between existing empirical equations for the correlation of uniaxial strength, Schmidt hardness and dry density (σ c -SHV-ρ d ). This comparison proved that chart yields the better prediction of the uniaxial compressive strength. Additionally, the correlation between uniaxial compressive strength, σ c , and point load strength, Is 50 , shows that an exponential fit gives a significantly better fit than a linear one. Finally, a multivariable analysis was done between tangent Young's modulus, uniaxial compressive strength and wave velocity (E t -σ c -V p ) and an empirical correlation is proposed.
Influence of Specimen Size and Shape on the Uniaxial Compressive Strength Values of Rocks
2021
The most significant factors affecting the results of Uniaxial Compressive Strength (UCS) test are the size, slenderness ratio h/d (ratio of height to diameter), and the shape of the rock specimen. The proposed experimental study shows the variable impact of these parameters on UCS values by implementing several lithological types. Standard strength tests were performed on four lithological types: granodiorite, limestone, sandstone and andesite. Cylindric and cube-shaped test specimens of different sizes were prepared from each rock. Cylindric specimens with diameter 20 mm, 35 mm, 50 mm and 70 mm with height to diameter ratio of 1:1 and 2:1, and cubic and prismatic specimens with an edge dimension of 50 mm were tested and analyzed. Obtained results of strength tests confirmed a high variability of current research opinions on how the size and shape of specimens influence the strength values of rocks. The study revealed the impossibility of conclusive correlations between the UCS and...
2014
Unconfined compression strength is one of the most important engineering parameters in rock mechanics; it is used to characterize and study the behavior of solid rocks. A good correlation between the unconfined compression strength test (UCS) and the point load strength (PLS) can be very useful because it allows for faster and cheaper testing than others with the same security to calculate the structures and performances of solid rocks. A preliminary step to implement the correlation is to have a good method to determine resistance to point load. This determination is quite correct if you have a sufficient number of tests on specimens of the same nature, but usually it does not occur and it is necessary to apply a size correction factor, F = (De / 50)α, with α = 0.45. This paper is based on limestone from Comunidad Valenciana (Spain) because it represents a very high percentage of their rocks. The implementation has been conducted over 700 field and laboratory tests of which 255 are...
Determination of the uniaxial compressive strengths of rocks
Soviet Mining Science, 1970
The most used parameter in rock engineering practice is the Uniaxial Compressive Strength (UCS). It is often estimated on the field or trough Index-to-strength conversion factors proposed by various researchers for a specific rock type. The research presented in the paper involved field estimation of Uniaxial Compressive Strength using Schmidt rebound hammer and Point Load laboratory testing on limestone rock samples. The results of the estimated UCS were compared to the Uniaxial Compression Strength laboratory testing results on limestone specimens taken from the same location, in order to compare corresponding UCS of limestone rocks. These results can contribute to better estimation of the local design parameters, when direct determination of the UCS in the laboratory is not possible, rather than adopting the values from around the world case studies.
International Journal of Geo-Engineering
In this study, various rock and cementitious rock-like material specimens with same ratio of length to diameter and different sizes were tested under various deformation controlled loading rate (mm/min) and load controlled rate (kN/s) conditions. According to the results obtained from 93 specimens of 5 different types of rock material and 2 different rock-like materials (cement paste and a concrete mix including sand) tested in this study, uniaxial compressive strength (UCS) values were found to significantly decrease with an increase in the specimen size under the condition of a load controlled rate (kN/s) selection. To practically remove the size effect on UCS values, the uniaxial compression test is suggested to perform selecting the loading rate as strain controlled (s-1) and proportional to diameters of specimens with different sizes and same geometry. In addition to the UCS values, Modulus of elasticity values, stress and strain graph shapes and deformation characteristics were found to significantly change with the change of the specimen size and loading rate. According to the results, both modulus of elasticity values and brittleness were found to notably increase as a result of increase in loading rate values.
Strength and strain quantities under brittle compression process of hard rocks
Mining of Mineral Deposits, 2018
Purpose. To examine the relationships between strength properties and strain quantities associated with the brittle compression process of hard brittle rocks. Methods. The data used in this paper were obtained from laboratory uniaxial compression tests carried out on 84 different types of hard rocks in accordance with Ulusay (2015) proposed standards. The strength properties and the strain quantities were coordinated so that each of the strain quantities or their ratios is compared individually with the strength properties of the rocks as for their relationship. Findings. In all the cases the relationships between the strain ratios and the strength parameters are stronger than when compared with individual strain quantities. A threshold level for strain ratio Ɛ vf / Ɛ cd may be assumed as the limit for fracture initiation above which the rock may experience brittle fracture failure. Originality. Scientific sources demonstrate few laboratory studies as for strength properties-strain quantities ratio. Most of the published research has been concentrated on crack damage stress (σ cd) and uniaxial compressive strength (σ c) of characteristic stress levels during compression. The paper has performed detailed analysis of the problem using experimental results of the relationships between strength properties and strain quantities under the deformation process of hard rocks. Practical implications. The relationships can improve our knowledge to evaluate correctly the stability of excavations, design of stable structures such as tunnels and excavations for mining and civil engineering purposes.
Mining of Mineral Deposits
Purpose. The research aims to investigate how the load influences the ultimate compressive strength of rocks at failure. It uses both a uniaxial compression test, which involves incremental displacements, and a triaxial compression test, which applies varying confining stresses while maintaining a constant axial compression stress and incrementally increasing the displacement. Methods. To conduct the investigation, the researchers used RS2D, a rock-soil software, to examine the impact of different incremental displacements and confining stresses on the strength properties of various rock samples. The numerical analysis includes Fayum argillaceous sand, Sinai coal, Aswan granite, Assiut limestone, and Red-Sea phosphate. Findings. The research findings indicate that the ultimate compressive strength of rocks at failure is achieved with minor incremental displacements. Conversely, an increase in the confining stress leads to higher ultimate tensile strength, deviatoric stresses, and vo...