Faculty Publications

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An Investigation on the Influence of Thermal Damage on the Physical, Mechanical and Acoustic Behavior of Indian Gondwana Shale
(Springer, 2020) Srinivasan, V.; Tripathy, A.; Gupta, T.; Singh, T.N.
In the present study, the effect of thermal treatment on the physical, mechanical and fracturing behavior of Gondwana shale samples from India was investigated. Acoustic Emission signals were used to identify the changes brought in by temperature variations on the crack damage zones and failure attributes in shale. The results suggested that mechanical parameters such as uniaxial compressive strength, tensile strength (?t), elastic modulus, mode-I fracture toughness (KIC), cohesion, and brittleness index (B1) exhibited a strong negative correlation with thermal damage (Dt). But, the internal angle of friction and brittleness index (B2) showed a reasonable positive relation with thermal treatment. The deformation of the shale was dominated by its clay mineral enrichment, the characteristics of which changed with heating. The intensity of fracturing as observed from acoustic signals was chiefly controlled by the orientation of bedding planes and the degree of thermal treatment. The initiation and propagation of macro-crack were found to be greatly influenced by the degree of thermal damage. Under compression, thermally damaged samples showed similar deformation pattern, while under Brazilian tensile load, the deformation path became inconsistent with increasing temperatures. It was observed that thermal damage in tested shale decreased the layer compaction, which eased the fracturing intensity, thereby reducing the overall strength of the samples. The present investigation concludes that even a slight change of the thermal conditions can substantially alter shale fracturing behavior and failure attributes posing serious safety concerns of deep geo-engineering structures. © 2020, Springer-Verlag GmbH Austria, part of Springer Nature.
An experimental study on rock damage and its influence in rock stress memory in a metamorphic rock
(Springer, 2020) Srinivasan, V.; Gupta, T.; Ansari, T.A.; Singh, T.N.
Rock stress memory, often referred as Kaiser effect, in rocks can be an effective tool to estimate the in situ stress conditions, if the uncertainties in rock damage and its behavior during loading conditions are properly understood. In view of this, the present study is an attempt to investigate the variations in rock stress memory, i.e., the Kaiser effect in a metamorphic rock under multi-stage uniaxial compression. The khondalite rock samples from Eastern Ghats Mobile Belt (EGMB) belonging to southeastern part of Indian subcontinent having complex geological history are examined. The effects of multi-stage compression on the damage evolution and subsequent variations in rock stress memory are investigated. The samples were categorized into different levels of rock stress memory, depending on the stress the rock was able to withhold after loading stages. The damage evolution in the tested rocks was predominantly controlled either by initial loading or failure stress. Higher damage imparted by initial loading and intense fracturing could be the possible reason for poor stress memory function in the investigated rock. Felicity ratio, an indicative of rock damage with stages of loading, supported the observation that rock damage was dominant during initial loading stage. Rock heterogeneity has played a dominant role in decay of Kaiser effect, with intense fracturing during subsequent loading stages in the investigated rocks. To summarize, Kaiser effect can be used to infer rock damage and stress conditions, provided the geological history of the region is also taken into consideration. With rocks from complex geological conditions, Kaiser effect or rock stress memory should be supported by other tools to infer in situ stress, but the method can be effectively used to understand the stress changes and damage mechanism of multiple loading. © 2020, Springer-Verlag GmbH Germany, part of Springer Nature.
Experimental study on failure and fracturing attributes of granite after thermal treatments with different cooling conditions
(Elsevier B.V., 2022) Srinivasan, V.; Hasainar, H.; Singh, T.N.
Thermal damage is one of the fundamental mechanisms affecting the stability of rocks encountered in many deep geo-engineering ventures such as nuclear waste isolation, geothermal extraction etc. In the present study, the findings on influence of heating and subsequent cooling conditions on the fracturing and mechanical behaviour of an Indian granite are discussed. The granite samples from Jalore region of India were heated from room temperature to 600 °C followed by slow cooling and water quenching treatments. It was observed that rapid cooling through quenching had a greater impact on strength, elastic properties than slow cooling rate. Moreover, a drastic shift in terms of fracturing thresholds was witnessed, as a function of both temperature and sudden thermal shock experienced by rock at higher cooling rate. The simultaneous AE monitoring results suggested an early crack damage at higher thermal regimes. With help of microscopic observations, it was observed that inter-granular crack boundaries widened with increasing thermal damage experienced by minerals under both cooling conditions. However, the fracturing process was intense under rapid cooling treatment due to the invasion of water due to quenching which accelerated severe intra-crack growths, especially at higher thermal stress because of the rapid cooling rate than the slow cooling. The increased intensity of thermal cracks with temperatures and with variation in cooling rate was inferred as the primary reason for decay of rock characteristics. This was very well supplemented by decay in strength properties and changes in fracturing attributes of the tested granite as inferred from acoustic monitoring. © 2022

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