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31.
Kananathan Amalan Amila Sandaruwan Ratnayake Nalin Prasanna Ratnayake Shanaka Maduranga Weththasinghe Nimila Dushyantha Nalika Lakmali Ranjith Premasiri 《Environmental Earth Sciences》2018,77(21):737
Beach sediments in Sri Lanka contain industrial-grade heavy mineral occurrences. Samples of both offshore and onshore sediments were collected to examine the provenance, mineralogy and geochemical compositions of the heavy mineral occurrences. Coastal morphodynamic changes along the coastline of Sri Lanka were analyzed using the time-series satellite images. These coastal morphodynamic changes were used to identify the prominent directions of monsoon-influenced longshore currents, coastal sediment accretion and depositional trends and their relationships to the provenance of the heavy minerals. Results show the concentrations of detrital ilmenite, zircon, garnet, monazite, and rutile vary in the onshore and offshore sediments. The heavy mineral potential of the northeastern coast is high (average contents of about 45–50% in the Verugal deposit, 70–85% in the Pulmoddai deposit, and 3.5–5.0% in offshore samples stretching from Nilaveli to Kokkilai), compared to sediments in southwest (average content about 10% in onshore sediments and 2% in offshore sediments from the mouth of the Gin River). Therefore, no economic-grade heavy mineral placers were identified in the offshore environments. The high concentrations of heavy minerals in beach sediments and low concentrations in offshore sediments suggest operation of a panning system in the surf zone to form enriched placer deposits. Major and trace element compositions of beach sediments show marked enrichments of TiO2, Fe2O3, La, Ce, Zr, Cr, Nb, Th and V compared to average Upper Continental Crust (UCC) values. Analysis of prominent coastal longshore transport patterns identifies bidirectional sediment transport in the northeast coast of Sri Lanka. In the southwestern coast, two transport directions occur with anti-clockwise transport from Galle to Hambantota, and clockwise transport from Hikkaduwa to Wadduwa. The heavy minerals in the placers were mainly derived from Precambrian metamorphic rocks, and transported to the coast through the river systems of Sri Lanka. 相似文献
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Length–weight relationships are a fundamental tool for assessing populations and communities in fisheries science. Many researchers have collected length–weight data throughout New Zealand, yet parameters describing these relationships remain unpublished for many species of freshwater fish. We compiled 285,124 fish records from researchers and institutions across New Zealand to parameterise length–weight equations, using both power and quadratic models, for 53 freshwater species belonging to 13 families. The influence of location and sex on length–weight relationships was also assessed. Location, in particular, generated different length–weight relationships for 65% of the species examined. Length–weight equations were validated by comparing predicted weights against independently measured weights from 25 electrofished sites across New Zealand and the equations were highly accurate (R2>0.99). Recommendations are made about how to robustly apply this new resource which should assist freshwater fisheries researchers throughout New Zealand. 相似文献
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Wai Loong Chong Asadul Haque Ranjith Pathegama Gamage Akm Shahinuzzaman 《Arabian Journal of Geosciences》2013,6(5):1639-1646
Rock mass is a highly complex entity where the strength and deformation behaviour can be significantly affected by its secondary structures such as joints, fissures and bedding planes. Whilst many research works have been conducted to study the behaviour of a specific rock mass, a thorough understanding of its strength and deformation behaviour incorporating different joint sets has not been established. In this study, a comprehensive numerical modelling using a three-dimensional distinct element code, 3DEC, was undertaken to study the strength and deformation behaviour of a mudstone, locally found in Melbourne, in unconfined and confined states. The initial unconfined model established for intact mudstone was calibrated against the well-established laboratory-based empirical strength relationships and subsequently compared with some strength test data available for field samples. The intact unconfined model was then extended to study the strength behaviour in the confined state. The results obtained from this confined intact model were compared with existing strength criteria and were found in good agreement. The confined model was extended further to investigate the effects of joint sets and dip angles on the rock mass strength and deformation behaviour by incorporating two different joint configurations (one-joint and two-joint) with varying dip angles (0°–90°). This study found that the rock mass strength in a confined state varied significantly between the two joint configurations. 相似文献
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It is of great importance to investigate the effect of loading rate on the behaviour of brittle material such as concrete and rock because engineering structures are subjected to multiple loading conditions. Although material behaviour under single loading mode has been extensively studied, very limited research has been conducted to investigate the performance of brittle materials subjected to varying loading conditions. This paper presents an experimental study of the effects of single and multiple strain rates (ε) on cement mortar samples. The first set of samples was loaded at constant strain rates until failure. For the remaining samples, the first strain rate (0.005 mm/s) was applied to the sample up to a predetermined load, and then the second strain was initiated immediately by using the specially-designed gear system in place in the compression rig. As expected, the increase in strain rate showed an increase in peak strength of the sample with reduced ultimate strain. For multiple strain modes, it was observed that the highest peak strength occurred when the second strain was applied at 50 % of the peak strength of the first strain. 相似文献
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A Novel Testing Apparatus for Hydromechanical Investigation of Rocks: Geo-Sequestration of Carbon dioxide 总被引：1，自引：0，他引：1
R. Shukla P. G. Ranjith S. K. Choi A. Haque 《Rock Mechanics and Rock Engineering》2012,45(6):1073-1085
This paper presents the design, development and application of a new multi-phase high-pressure and elevated temperature rock hydromechanical testing apparatus for the investigation of reservoir and cap rock behaviour in carbon geo-sequestration projects. The triaxial apparatus is designed to support high confining stress, injection pressures and higher temperatures to imitate the natural thermo-hydro-geomechanical conditions of deep underground geological formations. The apparatus also includes an acoustic emission device for the study of the mechanical failure behaviour of rocks under compression. The apparatus is designed to support a range of different rock specimen sizes from 34 to 54?mm in diameter. Since sequestration projects involve the injection of supercritical carbon dioxide, which is extremely sensitive to temperature and pressure, and is highly corrosive in nature, special precautions were taken in the design and manufacture of the apparatus. The data acquisition system is powered and calibrated in accordance with each of the sensors and is guided by a series of in-house developed and commercial softwares for data storage and analysis. The methodology for conducting advanced testing on cap rock and reservoir rocks with the injection of water and supercritical CO2 is presented with the appropriate theory. Some preliminary tests have been carried out on sandstone specimens sourced from the Melbourne region using the newly designed apparatus and the results are presented in this paper. 相似文献
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Bandara K. M. A. S. Ranjith P. G. Rathnaweera T. D. 《Natural Resources Research》2019,28(3):1139-1161
Proppant crushing, a major proppant failure mechanism, occurs in geothermal energy and oil/gas stimulation production stages when the level of net stress exerted on the proppant exceeds the actual crush resistance of the material. Loss of effective reservoir conductivity due to proppant crushing can result in significant loss in productivity, and so it is crucial to understand the realistic proppant mechanical performances under deep reservoir conditions. This review provides a comprehensive overview of proppant crushing at the micro- to macro-levels by analyzing single proppant breakage, as well as re-arrangement and breakage mechanisms of proppant packs under in situ fracture environments. The choice of an appropriate proppant type based on the fracture treatment plays a key role in effective geothermal and oil/gas recovery. In addition, injection of proppants with better characteristics (higher sphericity, lower size, better gradation and lower granular porosity) can significantly influence the reduction of the extent of proppant crushing. Moreover, this study compares the performances and responses of different types of proppants upon proppant interaction with geothermal and oil/gas reservoir environments. Furthermore, this paper discusses various proppant types and their enhanced characteristics, which can be utilized as controlling measures for proppant crushing during unconventional energy extraction.
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Bandara K. M. A. S. Ranjith P. G. Zheng W. Tannant D. D. De Silva V. R. S. Rathnaweera T. D. 《Acta Geotechnica》2022,17(11):4837-4864
Acta Geotechnica - Proppant crushing and embedment in hydraulically-induced fractures is a major drawback to the recovery of unconventional oil/gas and geothermal energy production. This study... 相似文献
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Richa Shukla P. G. Ranjith S. K. Choi A. Haque Mohan Yellishetty Li Hong 《Rock Mechanics and Rock Engineering》2013,46(1):83-93
Acoustic emissions (AE) and stress–strain curve analysis are well accepted ways of analysing crack propagation and monitoring the various failure stages (such as crack closure, crack initiation level during rock failure under compression) of rocks and rock-like materials. This paper presents details and results of experimental investigations conducted for characterizing the brittle failure processes induced in a rock due to monocyclic uniaxial compression on loading of two types of sandstone core samples saturated in NaCl brines of varying concentration (0, 2, 5, 10 and 15 % NaCl by weight). The two types of sandstone samples were saturated under vacuum for more than 45 days with the respective pore fluid to allow them to interact with the rocks. It was observed that the uniaxial compressive strength and stress–strain behaviour of the rock specimens changed with increasing NaCl concentration in the saturating fluid. The acoustic emission patterns also varied considerably for increasing ionic strength of the saturating brines. These observations can be attributed to the deposition of NaCl crystals in the rock’s pore spaces as well some minor geo-chemical interactions between the rock minerals and the brine. The AE pattern variations could also be partly related to the higher conductivity of the ionic strength of the high-NaCl concentration brine as it is able to transfer more acoustic energy from the cracks to the AE sensors. 相似文献