A total of 194 groundwater samples were collected from wells in hard rock aquifers of the Medak district, South India, to assess the distribution of fluoride in groundwater and to determine whether ...this chemical constituent was likely to be causing adverse health effects on groundwater user in the region. The study revealed that the fluoride concentration in groundwater ranged between 0.2 and 7.4 mg/L with an average concentration of 2.7 mg/L. About 57% of groundwater tested has fluoride concentrations more than the maximum permissible limit of 1.5 mg/L. The highest concentrations of fluoride were measured in groundwater in the north-eastern part of the Medak region especially in the Siddipeta, Chinnakodur, Nanganoor and Dubhaka regions. The areas are underlain by granites which contain fluoride-bearing minerals like apatite and biotite. Due to water–rock interactions, the fluoride has become enriched in groundwater due to the weathering and leaching of fluoride-bearing minerals. The pH and bicarbonate concentrations of the groundwater are varied from 6.6 to 8.8 and 18 to 527 mg/L, respectively. High fluoride concentration in the groundwater of the study area is observed when pH and the bicarbonate concentration are high. Data plotted in Gibbs diagram show that all groundwater samples fall under rock weathering dominance group with a trend towards the evaporation dominance category. An assessment of the chemical composition of groundwater reveals that most of the groundwater samples have compositions of Ca
2+
–Mg
2+
–Cl
−
> Ca
2+
–Na
+
–HCO
3
−
> Ca
2+
–HCO
3
−
> Na
+
–HCO
3
−
. This suggests that the characteristics of the groundwater flow regime, long residence time and the extent of groundwater interaction with rocks are the major factors that influence the concentration of fluoride. It is advised not to utilize the groundwater for drinking purpose in the areas delineated, and they should depend on alternate safe source.
Groundwater is a vital source of freshwater in both urban and rural regions of the world. However, its injudicious abstraction and rapidly increasing contamination are posing a severe threat for ...sustainable water supply worldwide. Geographical Information System (GIS)-based groundwater quality evaluation using Groundwater Quality Index (GQI) has been proved to be a cost-effective tool for assessing groundwater quality and its variability at a larger scale. However, the conventional GQI approach is unable to deal with uncertainties involved in the assessment of environmental problems. To overcome this limitation, a novel hybrid framework integrating Fuzzy Logic with the GIS-based GQI is proposed in this study for assessing groundwater quality and its spatial variability. The proposed hybrid framework is demonstrated through a case study in a hard-rock terrain of Southern India using ten prominent groundwater-quality parameters measured during pre-monsoon and post-monsoon seasons. Two conventional GIS-based GQI models GQI-10 (using all the ten groundwater-quality parameters) and GQI-7 (using seven ‘concerned/critical’ groundwater-quality parameters) as well as hybrid Fuzzy-GIS-based GQI (FGQI) models (using seven critical parameters) were developed for the two seasons and the results were compared. The Trapezoidal membership functions classified the model input parameters into ‘desirable’, ‘acceptable’ and ‘unacceptable’ classes based on the experts’ knowledge and water quality standards for drinking purposes. The concentrations of Ca2+, Mg2+, and SO42− in groundwater were found within the WHO desirable limits for drinking water throughout the year, while the concentrations of seven parameters (TDS, NO3−-N, Na+, Cl−, K+, F− and Hardness) exceed their permissible limits during pre-monsoon and post-monsoon seasons. A comparative evaluation of GQI models revealed that the FGQI model predicts groundwater quality better than the conventional GQI-10 and GQI-7 models. GQI modeling results suggest that the groundwater of most of eastern and southern parts (∼60% in pre-monsoon season; ∼90% in post-monsoon season) of the study area is unsuitable for drinking. Further, the groundwater quality deteriorates during post-monsoon seasons compared to pre-monsoon seasons, which indicates an increased influx of contaminants from different industries, mining areas, waste disposal sites and agricultural fields during monsoon seasons. This finding calls for the strict enforcement of regulations for proper handling of effluents from various contamination sources in the study area. It is concluded that the fuzzy logic-based decision-making approach (FGQI) is more reliable and pragmatic for groundwater-quality assessment and analysis at a larger scale. It can serve as a useful tool for the water planners and decision makers in efficiently monitoring and managing groundwater quality at watershed or basin scales.
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•Novel hybrid framework integrating Fuzzy Logic with GIS-based GQI is developed.•FGQI is more reliable and useful for water-quality evaluation at larger scales.•Groundwater polluted zones are in eastern and southern parts of the study area.•Groundwater quality in post-monsoon seasons is worse than in pre-monsoon seasons.•Comprehensive strategies for sustainable groundwater management are urgently needed.
The development of deep geothermal resources encounters challenges related to high temperatures and hard reservoir rocks. Abrasive water jets (AWJ) offer a potential solution to enhance the ...efficiency of breaking high-temperature hard rocks in deep ground. This mainly originated from their combined characteristics of jet cooling impact and high-speed abrasive grinding. In order to investigate the dynamic deformation process and rock-breaking mechanism of high-temperature hard rocks cut by AWJ, laboratory tests were conducted on high-pressure abrasive water jets cutting granite, sandstone, and marble. Rock strains were monitored using dynamic strain gauges and the digital image correlation (DIC) technique. The results indicate that in the process of abrasive jet cutting high-temperature hard rock, the rock strain is divided into three stages: compression deformation, deformation release, and stable deformation. The strain response zone can be divided into strain concentration zone, strain transition zone, and strain weak response zone. The high strain region and heat exchange region of high-temperature hard rock during AWJ cutting process are almost consistent. Jet vaporization weakens the water cushion effect during the water hammer stage, leading to high strain concentration at the stagnation point of the jet. During the stagnation stage, the fluid weakens the binding of particles, the abrasive becomes more divergent, and the range of high strain response region expands. Unlike the dynamic strain generated by jet erosion of hard rock, when jet cutting rocks, the strain in the vertical jet direction is generally greater than that along the jet direction. The cutting effect increases with the increase of rock temperature. When the rock temperature is 300 °C, the cutting depth of sandstone, granite, and marble increases by 50 %, 120 %, and 180 %, respectively. Under the combined effects of high-frequency jet impact, high-speed abrasive grinding, and thermal stress, hard rock undergoes varying degrees of damage and failure.
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•The friction process between disc cutter and hard rock is analyzed.•The relationship between rolling force work and thrust force work of disc cutter is examined.•A method to identify ...the friction work is developed.•The hard rock TBM cutterhead energy equation is deduced.•A method for the prediction of disc cutter wear for a hard rock TBM cutterhead is advanced.
Disc cutter wear is a crucial problem that influences the working efficiency and security of hard rock tunnel boring machines (TBMs). This wear results from friction energy accumulation and conversion. In this study, the process of hard rock TBM disc cutter wear is identified and analyzed by quantifying the collective energy change. This study starts with an analysis of the friction process between the disc cutter and hard rock. The relationship between the rolling force work and thrust force work of the disc cutter is examined. As a result, the disc cutter energy equation is determined, and the meaning of the upper and lower bounds of this equation are discussed. Based on the above results, the hard rock TBM cutterhead energy equation is then deduced. A method to identify the friction work is developed. According to the energy wear theory, the cutter wear law on hard rock for a TBM cutterhead is revealed, and a method for predicting disc cutter wear for a hard rock TBM cutterhead is advanced. Furthermore, the validity of this prediction method is confirmed by utilizing data from project cases.
Sixty-one groundwater samples collected from the hard rock terrain of Nanganur region in South India, were evaluated for hydrogeochemistry as well as groundwater quality for drinking and irrigation ...purposes. Additionally, the probabilistic non-carcinogenic human health risks associated with fluoride and nitrate concentrations were assessed using the US Environmental Protection Agency (USEPA) mathematical model. The hydrogeochemical facies, i.e. Ca2+-Mg2+-SO42− and Na+-Cl--SO42−, are result of weathering and dissolution of rocks, ion exchange between Ca2+ and Na+, and precipitation of CaCO3, and influences of anthropogenic sources. Molar ratio Na+/Cl-, and distributions of Ca2++Mg2+ versus HCO3-+SO42−, Ca2++Mg2+ versus total cations (TC), and Na++K+ versus TC indicate that silicate weathering is the prime source for the ions. Gibbs diagram also suggests that rock-water interaction is the primary process of ionic concentrations in this groundwater system. About 18% groundwater samples show medium salinity and low sodium hazards and 73% of them, however, have high salinity and low sodium hazards. Wilcox diagram indicates that most groundwater samples (92%) are suitable for irrigation. However, 66% of them exceeded the prescribed limits of nitrate (45 mg/L) and 62% these groundwater samples exceeded limit of fluoride (1.5 mg/L) for drinking purpose. Hazard quotient of nitrate (HQNitrate) and HQFluoride as well as total non-carcinogenic health risk of fluoride and nitrate (HITotal) indicates that infants and children are more vulnerable to non-carcinogenic risk than adults. Based on these results, we recommend regulation of fertilizer application and appropriate remediation for defluoridation of drinking water to prevent the further health risk.
Triaxial compression tests were conducted on fine-to-medium–grained granite specimens, with initial confining pressures of 10, 20, 40, and 60MPa, under various loading and unloading stress paths. The ...energy evolution characteristics of granite specimens from a quarry in Miluo city (China) were studied in the triaxial deformation and failure process of the rocks. The results show that the time history curves of the total strain energy, elastic strain energy, and dissipative strain energy exhibit significant stage features. In particular, the ratio of the dissipative strain energy to the total strain energy can be used to describe the deformation and degree of damage to rock specimens during the triaxial loading and unloading processes. Under the same initial confining pressure, the maximum values of the total strain energy, elastic strain energy, and dissipative strain energy occur in the conventional triaxial compressive testing of group I, and the minimum values occur in test group II with constant axial stress and decreasing confining pressure. The total strain energy, elastic strain energy, and circumferential strain energy all increase as the initial confining pressure increases, whereas the dissipative strain energy does not. During the process of unloading the confining pressure, the increase of the circumferential strain is considerably larger than that of the axial strain. Under unloading conditions, rock bursts may occur more easily for hard rocks than under conventional triaxial loading conditions, especially under the conditions of test group III with increasing axial stress and decreasing confining pressure. The micro-difference in the granite micro-cracks was identified using a scanning electron microscope (SEM) combined with an energy dispersive spectrometer (EDS). Shear failure characteristics were observed in a conventional triaxial test, and the combined tension and shear failure was identified through unloading confining pressure tests. The tensile failure characteristics of the granite in group III are more pronounced than those of group II. This indicates that the triaxial failure of rock results from the development of micro-extension cracks and volumetric expansion in the granite specimen under unloading confining pressure tests.
•Triaxial tests with different loading and unloading paths have been carried out on granite specimens.•The energy evolution characteristics were studied to understand the deformation and failure process of granite specimens.•The micro differences of granite failure mechanism were identified by SEM-EDS analysis under different stress paths.•Rock burst phenomenon may more easily occur for hard rocks under triaxial unloading conditions.
Historical mining left a legacy of abandoned mines and waste rock in remote headwaters of major river systems in the western United States. Understanding the influence of these legacy mines on ...culturally and ecologically important downstream ecosystems is not always straightforward because of elevated natural levels of mineralization in mining‐impacted watersheds. To test the ecological effects of historic mining in the headwaters of the upper Salmon River watershed in Idaho (USA), we measured multiple community and chemical endpoints in downstream linked aquatic–terrestrial food webs. Mining inputs impacted downstream food webs through increased mercury accumulation and decreased insect biodiversity. Total mercury (THg) in seston, aquatic insect larvae, adult aquatic insects, riparian spiders, and fish at sites up to 7.6 km downstream of mining was found at much higher concentrations (1.3–11.3‐fold) and was isotopically distinct compared with sites immediately upstream of mining inputs. Methylmercury concentrations in bull trout and riparian spiders were sufficiently high (732–918 and 347–1140 ng MeHg g−1 dry wt, respectively) to affect humans, birds, and piscivorous fish. Furthermore, the alpha‐diversity of benthic insects was locally depressed by 12%–20% within 4.3–5.7 km downstream from the mine. However, because total insect biomass was not affected by mine inputs, the mass of mercury in benthic insects at a site (i.e., ng Hg m−2) was extremely elevated downstream (10–1778‐fold) compared with directly upstream of mining inputs. Downstream adult aquatic insect–mediated fluxes of THg were also high (~16 ng THg m−2 day−1). Abandoned mines can have ecologically important effects on downstream communities, including reduced biodiversity and increased mercury flux to higher order consumers, including fish, birds, and humans. Environ Toxicol Chem 2022;41:1696–1710. Published 2022. This article is a U.S. Government work and is in the public domain in the USA.
This investigation aims to explore the effects of stress conditions and rock cutting rates on hard rock fragmentation through indentation tests on a newly designed triaxial testing apparatus. This ...apparatus was designed to realize a triaxial loading and indentation test of cylindrical specimens using inserted tooth cutter. The boreability and crushing efficiency of granite rock was investigated by analyzing the change rules of the thrusting force, penetration depth, characteristics of chippings and failure patterns. Several quantitative indexes were used to evaluate rock boreability in this investigation. The granite rock samples all had a chiselled pit and a crushed rock core. Under initial stress conditions, only flat-shape chippings were stripped from the rock surface when the thrusting force reached 20 kN. The rock cutting special energy had a close correlation with the initial stress conditions and inserted tooth shape. Moreover, a thrusting force prediction model was proposed in this paper. The contribution of this study is that for the first time the influence mechanism of the initial triaxial stress conditions on rock fragmentation is investigated using an inserted tooth and the newly designed testing apparatus. This study has a crucial importance for practical underground hard rock crushing in geoengineering.
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•Three MCDA methods are compared to assess groundwater prospect in hard-rock regions.•Novel approach is adopted to verify the results of geospatial and MCDA techniques.•AHP technique ...was found most reliable compared to Catastrophe and Entropy methods.•Findings are useful to the decision makers for sustainable groundwater management.•The demonstrated methodology is replicable in other regions of the world.
Groundwater is a treasured underground resource, which plays a central role in sustainable water management. However, it being hidden and dynamic in nature, its sustainable development and management calls for precise quantification of this precious resource at an appropriate scale. This study demonstrates the efficacy of three GIS-based multi-criteria decision analysis (MCDA) techniques, viz., Analytic Hierarchy Process (AHP), Catastrophe and Entropy in evaluating groundwater potential through a case study in hard-rock aquifer systems. Using satellite imagery and relevant field data, eight thematic layers (rainfall, land slope, drainage density, soil, lineament density, geology, proximity to surface water bodies and elevation) of the factors having significant influence on groundwater occurrence were prepared. These thematic layers and their features were assigned suitable weights based on the conceptual frameworks of AHP, Catastrophe and Entropy techniques and then they were integrated in the GIS environment to generate an integrated raster layer depicting groundwater potential index of the study area. The three groundwater prospect maps thus yielded by these MCDA techniques were verified using a novel approach (concept of ‘Dynamic Groundwater Potential’). The validation results revealed that the groundwater potential predicted by the AHP technique has a pronounced accuracy of 87% compared to the Catastrophe (46% accuracy) and Entropy techniques (51% accuracy). It is concluded that the AHP technique is the most reliable for the assessment of groundwater resources followed by the Entropy method. The developed groundwater potential maps can serve as a scientific guideline for the cost-effective siting of wells and the effective planning of groundwater development at a catchment or basin scale.
To investigate the matching rules of cutters with different blade widths in hard rock and extremely hard rock environments, this study carries out a full-scale cutting test of 432-mm disc cutters ...with blade widths of 12 mm, 19 mm and 30 mm. A multifunctional cutter performance experimental system was used to test the cutting loads and rock-breaking quantity of rust stone granite (hereinafter referred to as hard rock) and granite (hereinafter referred to as extremely hard rock) as well as to analyse the specific energy consumption for rock breaking under different cutting parameters. The experimental results show that (1) the blade width has a greater influence on the normal force than on the rolling force. The rock-breaking resistance of the 12-mm-blade-width cutters under extremely hard rock conditions is 36.7% lower than that of conventional cutters. (2) Under the same conditions, the smaller the blade width is, the smaller the specific rock-breaking energy consumption is and the smaller the optimal cutter spacing is. Under extremely hard rock condition, the specific energy consumption of the 12-mm-blade-width cutters is 37.9% lower than that of conventional cutters. (3) With a certain gross thrust of a single cutter, the rock-breaking quantity of a single 12-mm-blade-width cutter is much larger than that of the 19-mm-blade-width cutter, regardless of the types of rock. Under extremely hard rock conditions, the
S
/
P
of the 12-mm-blade-width cutter with the highest rock-breaking efficiency is approximately 10–12.
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