Mechanical Characterization of Compact Basalt by using SHPB Device (original) (raw)
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High Strain Rate Response of Rocks Under Dynamic Loading Using Split Hopkinson Pressure Bar
Geotechnical and Geological Engineering, 2017
In the present work, dynamic stress-strain response of five sedimentary and three metamorphic rocks from different regions of India, e.g. Kota sandstone, Dholpur sandstone, Kota limestone, Himalayan limestone, dolomite, quartzite, quartzitic gneiss and phyllite have been investigated through split Hopkinson pressure bar test at different strain rates. The dry density, specific gravity, static compressive strength and tensile strength values of the rocks have also been determined. Petrological studies of the rocks have been carried out through X-ray diffraction test and scanning electron microscope test. It is observed from the stress-strain response of the rocks that the peak stress increases with increasing strain rate. Dynamic increase factors for the strength of these rocks have been determined by comparing the dynamic and the static peak compressive stresses and correlation equations are proposed.
New correlations between uniaxial compressive strength and point load strength of basalt
International Journal of Geotechnical Engineering, 2014
Although the mechanical and physical properties of many rocks have extensively been studied, little work is reported on basalt rock. This paper discusses the interrelationships between the mechanical and the physical properties of the basalt rock. Laboratory tests were conducted on rock cores collected from over 22 locations within the Mumbai city limits. The samples were tested in accordance with ISRM (1985) specifications. Correlations between the uniaxial compressive strength (UCS) and the point load strength index (I s.50) were developed. It was observed that other than the customary linear relations and power function between UCS and I s.50 , a bilinear relation best fitted the laboratory data.
Dynamic Response of Deccan Trap Basalt under Hopkinson Bar Test
Procedia Engineering, 2017
The Deccan trap is a large igneous rock province located on the Deccan plateau of west-central India. There are several important structures located on Deccan trap basalt like Koyna dam hydropower project, Konkan railways, Katraj twin tunnels to name a few. In order to safeguard the structures from dynamic loading arising from manmade or natural disastrous circumstances, it becomes necessary to characterize the dynamic behavior of rocks. In the present work, experimental studies have been performed to determine the dynamic stress-strain behavior of Deccan trap basalt rock as the same is not yet available in literature. The rock samples have been collected from various regions spread along the Western Ghats in Maharashtra. Tests have been performed to determine the physical and static mechanical properties. The dynamic tests have been carried out using 20 mm diameter split Hopkinson pressure bar (SHPB) at different strain-rates. From the analysis of results, the dynamic stress-strain response of the rocks, force equilibrium and dependence of dynamic strength on the strain rate have been examined for the first time.
Dynamic compressive properties of Kalgoorlie basalt rock
International Journal of Rock Mechanics and Mining Sciences, 2020
In this study, the basalt rock extracted from the Kalgoorlie region of Western Australia is intensively studied on its compressive properties under both static and dynamic loads covering strain rate between 2.22 × 10-6 /s to 408/s. The ultimate compressive strength and corresponding failure strain are quantified. The test results show that Kalgoorlie basalt rock exhibits high sensitivity to strain rate effect on its compressive strength especially above 100/s and dynamic increment factor up to 2.3 at strain rate 403/s. The failure strain also shows dependency to high strain rate. Discussion is made on fragment analysis which found the natural heterogeneous and anisotropic of WA basalt rocks cause variations on its compressive strength and dependent on the failure angle of the joints (layer formation). The dynamic increase mechanism on material compressive properties is observed to be correlated to the failure crack path formation, which can be explained through the fracture process captured from high-speed camera images analysis. Comparisons are also made on rock strengths with others' test data. A novel method based on numerical modelling is introduced which removes the influence of lateral inertia effect and specimen end friction effect out of the laboratory testing results. The true dynamic increase factor (DIF) for Kalgoorlie basalt rock at different strain rates are derived for more accurate analysis and design.
The paper presents experimental and numerical studies on the feasibility and validity of using prismatic rock specimens in split Hopkinson pressure bar (SHPB) test. Firstly, the experimental tests are conducted to evaluate the stress and strain uniformity in the prismatic specimens during impact loading. The stress analysis at the ends of the specimen shows that stress equilibrium can be achieved after about three wave reflections in the specimen, and the balance can be well maintained for a certain time after peak stress. The strain analysis reveals that the prismatic specimen deforms uniformly during the dynamic loading period. Secondly, numerical simulation is performed to further verify the stress and strain uniformity in the prismatic specimen in SHPB test. It indicates that the stress equilibrium can be achieved in prismatic specimen despite a certain degree of stress concentration at the corners. The comparative experiments demonstrate that the change of specimen shape has no significant effect on dynamic responses and failure patterns of the specimen. Finally, a dynamic crack propagation test is presented to show the application of the present work in studying fracturing mechanisms under dynamic loading.
Experiments to Determine Static and Dynamic Tensile Strength of Deccan Trap Rocks, India
Procedia Engineering, 2017
Tensile strength of rocks is an important parameter in the design of underground structures and for various engineering applications. Lack of literature and rapid development of infrastructure in central region of India calls for a need to characterize the mechanical behaviour of rocks in Deccan trap region which is mainly composed of Basalt. In this paper, characterization of tensile behaviour of Basalt rocks from Deccan trap is done at different loading conditions. Indirect test method namely Brazilian test is used to calculate the static indirect tensile strength at a loading rate of 0.2 kN/s. Tests are performed on different diameters samples and desirable failure modes are recorded. Tensile strength values recorded at slow loading are obtained to be different for specimen having different diameters. However, strength of rock in engineering problems like blasting, mining, rock bursting and breakage are affected by high loading rates. To consider the dynamic loading effect, a modified split Hopkinson pressure bar technique is used. For dynamic tensile experimentation, Brazilian disc specimen are used which are slightly flattened before testing. The flat ended Brazilian discs (FEBD) are placed diametrically in SHPB setup. Dynamic force equilibrium is successfully achieved for the initial stages of fracture propagation till complete failure of sample. The factor for increase in dynamic tensile strength of Deccan Basalt has been evaluated in this work. Scope of further research has been identified for experimentations on soft rocks to determine their dynamic tensile strength characteristics.
Stress–Dilatancy For Crushed Latite Basalt
Studia Geotechnica et Mechanica
In this article, the stress–dilatancy relationship for crushed latite basalt is analysed by using Frictional State Theory. The relationship is bilinear, and the parameters α and β determine these two straight lines. At the initial stage of shearing, the mean normal stress increment mainly influences breakage, but at the advanced stage, it is shear deformation that influences breakage. At the advanced stage of shearing, the parameter αpt represents energy consumption because of breakage and βpt mainly represents changes in volume caused by breakage during shear. It is also shown that breakage effect is significant at small stress levels and the η-Dp plane is important to fully understand the stress–strain behaviour of crushed latite basalt in triaxial compression tests.
Dynamic Characterization of Himalayan Quartzite using SHPB
Procedia Engineering, 2017
In the present work, dynamic stress-strain response of Himalayan quartzite is tested under high loading rates using split Hopkinson pressure bar (SHPB) device for the first time in the literature. The physical and static mechanical properties of quartzite e.g. dry and saturated density, specific gravity, static compressive strength and elastic modulus values are also determined. Petrological studies of quartzite are carried out through X-ray diffraction (XRD) test and scanning electron microscope (SEM) test. In the SHPB tests, it is observed from the stress-strain response that the dynamic peak stress increases with increasing strain rate whereas the elastic modulus does not show any clear trend with increase in strain rate. Dynamic force equilibrium at the incident and transmission bar ends of the rock samples is attained in all tests till the failure of the rock samples. Dynamic increase factor (DIF) for the rock is determined at a particular strain rate by comparing the dynamic to static peak compressive stress. Correlation equation for dynamic strength increase factor with respect to strain rate has been proposed herein.
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.