A series of low-strain triaxial compression and high-strain torsion experiments were performed on marble and limestone samples to examine the influence of stress, temperature, and strain on the ...evolution of twin density, the percentage of grains with 1, 2, or 3 twin sets, and the twin width—all parameters that have been suggested as either paleopiezometers or paleothermometers. Cylindrical and dog-bone-shaped samples were deformed in the semibrittle regime between 20°C and 350°C, under confining pressures of 50–400MPa, and at strain rates of ~10−4–10−6s−1. The samples sustained shear stresses, τ, up to ~280MPa, failing when deformed to shear strains γ>1. The mean width of calcite twins increased with both temperature and strain, and thus, measurement of twin width provides only a rough estimation of peak temperature, unless additional constraints on deformation are known. In Carrara marble, the twin density, NL (no of twins/mm), increased as the rock hardened with strain and was approximately related to the peak differential stress, σ (MPa), by the relation σ=19.5±9.8NL. Dislocation tangles occurred along twin boundaries, resulting in a complicated cell structure, which also evolved with stress. As previously established, the square root of dislocation density, observed after quench, also correlated with peak stress. Apparently, both twin density and dislocation cell structure are important state variables for describing the strength of these rocks.
•Carbonate rocks were experimentally deformed in the semibrittle regime.•Twin density increased roughly proportional to the square of peak stress.•Dislocation cell structures and densities are important state variables for strength.•Twin width increased with both temperature and strain.
Ductile crustal shear zones play an important role during the formation of orogenic wedges but the softening mechanism controlling their formation and evolution are still debated. We perform ...two-dimensional thermo-mechanical numerical simulations of lithospheric shortening, including an underlying asthenosphere, to investigate the mechanism for ductile shear localization and to quantify the evolution of differential stress, temperature and strain rate inside shear zones that form in the ductile part of the upper crust. The simulations show the development of an intra-continental subduction zone whereby the lower crust and mantle lithosphere subduct beneath the adjacent mantle lithosphere. The upper crust forms a doubly-vergent wedge in which shear zones form subsequently. Shear zone formation is exclusively caused by thermal softening due to shear heating and temperature dependent viscosity, and is initiated by locally elevated shear stresses. The shear zone thickness is physics-controlled, hence mesh-insensitive and numerically resolved in the simulations. Temperature increase inside crustal shear zones is ca. 100 °C. The tectonic overpressure inside upper crustal shear zones is up to 250MPa and can be twice the value of the corresponding deviatoric stress. Stresses inside the shear zone decrease during its formation and are hence smaller inside the shear zone than outside. Surface processes influence the location and orientation of shear zones, but not their formation and propagation by thermal softening. The numerically calculated differential stress (30–260MPa), temperature (280–380 °C) and strain rate (∼ 10−13s−1) inside ductile crustal shear zones agree with corresponding estimates for natural shear zones. This agreement between modelled differential stress, temperature and strain rate with corresponding natural estimates supports previous results which indicate that thermal softening is a controlling softening mechanism for natural shear zone formation.
•Thermal softening causes spontaneous ductile shear zone formation and propagation.•Shear zones are initiated in regions with locally elevated shear stresses.•Calculated stresses and temperatures agree with estimates from natural shear zones.•Stresses decrease inside shear zone favouring paleowattmeter for grain size reduction.•Surface processes do not impact the general shear localization mechanism.
Ductile shear zones evolve through complex feedbacks between microstructure and rheology. In the mantle, shear zones often display mylonitic or ultramylonitic microstructures, characterized by ...extensive grain-size reduction and well-mixed polymineralic domains. The feedback between the formation of these microstructures and grain-size sensitive deformation is often considered an important weakening mechanism in high-temperature mantle shear zones. To understand better the processes that transform coarse-grained tectonites into fine-grained and well-mixed mylonites, we have performed triaxial deformation experiments on synthetic peridotite samples comprised of mm-scale olivine and orthopyroxene clasts. Experiments were conducted in a Griggs apparatus at a confining pressure of ∼1 GPa, temperatures of 1400 to 1550 K and strain rates of 10−5–10−6 s−1 under nominally dry conditions. Experiments yield deformed samples with macroscopic natural strains ranging from 0.31 to 0.74. Samples are partially recrystallized, with neoblasts ranging in grain size from 2–25 μm. At these deformation conditions, unrecrystallized mm-sized clasts deform by grain-size insensitive dislocation creep, while recrystallized grains deform by grain-size sensitive dislocation accommodated grain boundary sliding (disGBS). Using electron-backscatter diffraction (EBSD) we investigate the interfaces between recrystallized olivine and orthopyroxene domains. At the majority of these interfaces no mixing is observed. However, many boundaries are serrated, which is interpreted to be the result of surface tension driven phase boundary migration. In a few cases we observe small degrees of mixing, with enclaves of one phase completely surrounded by the other phase. This mixing occurs only within a few recrystallized grain length scales of the interface. These results demonstrate that the serial processes of dynamic recrystallization, phase boundary migration and disGBS deformation are a plausible mechanism for solid-state phase mixing. However, more extensive deformation may be needed to reproduce the near steady-state microstructure observed in highly deformed mantle shear zones.
•Recrystallization, GBS and phase mixing explain observations from shear zones.•Dynamic recrystallization and phase mixing preserve weak mantle shear zones.•Phase mixing does not initiate shear localization.
The Indus Delta is an endangered wetland on the Ramsar list due to a continued decrease of river flow toward the delta, resulting in seawater intrusion into the inland areas and deteriorating the ...potable patches of shallow groundwater and wetland areas. The groundwater in the lower Indus Basin is brackish, except for a few potable pockets, which are shrinking due to water extraction for drinking purposes. The gap thus occupied by saline water permanently degrades the potable groundwater. This paper correlates the potable patches with surface seepage due to either rainfall or river flows, to recommend a continuous flow of fresh water in the river system, and a revival of the ruined wetlands and lagoons. Twelve nested piezometers at various depths have been installed in the study area to monitor the groundwater quality temporally transformation. The water samples have been periodically collected to analyze physical and chemical properties for three years. The data trend indicates the rapid changes in shallow groundwater quality (up to the depth of 10 m) to the surface availability of freshwater. An area of 378 km2 was turned from saline to fresh groundwater with only two spells of rainfall. The result confirms the positive impact on groundwater quality improvement due to rainfall and water in river tributaries. Based on this analysis, it is recommended to replenish the lagoons and shallow lakes with fresh water. Canals should run continuously to constantly recharge the shallow groundwater as the only source of drinking water in the study area.
•Original well instrumented leachate pumping and injection tests in landfills.•The permeability decreasing with depth drives strongly the flow behaviour.•Richards model provides a satisfying ...description of the experimental results.•Hysteretic effects probably due to the gas entrappement and release are sensitive.
During the lifespan of a Municipal Solid Waste landfill, its leachate drainage system may get clogged. Then, as a consequence of rainfall, leachate generation and possibly leachate injection, the moisture content in the landfill increases to the point that a leachate mound could be created. Therefore, pumping the leachate becomes a necessary solution. This paper presents an original analysis of leachate pumping and injection in an instrumented well. The water table level around the well is monitored by nine piezometers which allow the leachate flow behaviour to be captured. A numerical model based on Richards equation and an exponential relationship between saturated hydraulic conductivity and depth is used to analyze the landfill response to pumping and injection. Decreasing permeability with depth appears to have a major influence on the behaviour of the leachate flow. It could have a drastic negative impact on the pumping efficiency with a maximum quasi-stationary pumping rate limited to approximately 1m3/h for the tested well and the radius of influence is less than 20m. The numerical model provides a reasonable description of both pumping and injection tests. However, an anomalous behaviour observed at the transition between pumping and recovery phases is observed. This could be due to a limitation of the Richards model in that it neglects the gas phase behaviour and other double porosity heterogeneous effects.
In the current study, subsurface characteristics within the complex formation of the Shilabati basin system of West Bengal, India, extending over an area of 3888 km
2
, have been estimated using a ...cost-effective piezometer and MIKE FEFLOW package based on a steady-state numerical model. Pore size and fine particle content of streambeds are affected by two opposing flow contraptions. Such opposite flow conditions are likely to affect the hydraulic conductivity of the streambed. However, analogies of the hydraulic conductivity (
K
h
) of streambeds for losing and gaining streams have not been well documented in the recent past. The
K
h
value from the piezometer has been highest at the Dakshin Pairachali site (6.765 m/day), with the stream gaining water from the discharge of the local aquifer. Analysis of the stream-aquifer interaction using the FEFLOW model has allowed us to understand the groundwater water head of the basin ranging from 160.33 to 0.32 m.a.s.l (meters above sea level). The present study also constitutes the first attempt for the identification of suitable sites for the implementation of managed aquifer recharge (MAR) technology in West Bengal, India, to manage extreme drought events. The suitable sites have been identified by means of three fuzzy multi-criteria decision analysis based on nine criteria: river discharge, moisture content, porosity, drainage type, rainfall, land use type, geology, aquifer material, and hydraulic conductivity. To design a radial collector well and infiltration gallery for the selected site in an anisotropic, homogeneous, unconfined, and semi-infinite aquifer near a fully penetrating stream, a pumping test has been conducted to optimize a safe yield of 12.096 MLD (megaliters per day).
Hydraulic conductivity is an essential parameter for groundwater investigation and management. A simple technique for determining the hydraulic conductivity of aquifers is the slug test, which ...consists of measuring the water level in a well after the sudden removal or injection of a small amount of water. The interpretation of a slug test is based on a geometry-dependent shape factor, for which various empirical relationships and approximate solutions have been proposed in the literature. In this study, shape factors are derived numerically for slug tests performed in monitoring wells with screens unaffected by aquifer boundaries. Also presented is a new approximate analytical solution for predicting shape factors for well screens with a large aspect ratio. A comparison with earlier methods reported in the literature shows that our results match or exceed them in terms of accuracy. The approximate analytical solution is promising because it is accurate and very easy to apply in practice.
Using earthen liners at the base of an integrated constructed wetland (ICW) maintains a hydraulic continuum between the ICW and the underlying groundwater body. This may enable migration of reactive ...carbon (dissolved organic and inorganic carbon (DOC, DIC)) and reactive nitrogen (Nr) across this liner to groundwater along this continuum to groundwater. Therefore, in terms of a holistic assessment of ICWs, quantification of these losses is important and indeed from an environmental perspective comparing such losses to other ICW dis-connected areas within the same groundwater body is critical. The main objective of the present study on an ICW site in SE Ireland was to compare reactive forms of C and N in groundwater (three piezometer nests) representing the continuum end point of ICW Cell 2 and 3 with that of groundwater dis-connected to the ICW system. For this purpose two control planes consisting of shallow and deep groundwater piezometer nests were installed and monitored at 1 and 4 m depths, respectively underneath the earthen liners at 0.2 m adjacent to the ICW cells. Fieldwork was conducted between Nov 2013 and Nov 2014 and results showed that groundwater beneath the ICW liner had a highly reduced signal with C and N concentrations being significantly higher to those of the disconnected up-gradient groundwater. The DOC, DIC and dissolved CO2 and CH4 concentrations in groundwater beneath the ICW cells were significantly higher than the up-gradient groundwater. All the reactive forms of C were higher in Cell 2 than in Cell 3. With respect to depth, all forms of reactive C were higher in deeper groundwater than the shallow equivalents except for DOC. Equally, Nr concentrations (NH4+, DON, NO3−-N and N2O) were higher in groundwater beneath the ICW cells than the up-gradient groundwater. They were higher in Cell 2 than in Cell 3 and higher in shallow rather than deep groundwater. The fate of the reactive C and N is unknown. Typically DOC delivery from groundwater to surface water drives many biogeochemical processes as an electron donor to microbes or can be converted to CO2 and CH4 emissions and the dissolved CO2 and CH4 can be indirectly exchanged to the atmosphere. The results suggest that nutrient delivery from the ICW cells to the underlying groundwater needs to be evaluated and the design of earthen-lined ICWs should consider this nutrient loss continuum across the liner.
•Significant natural purification of farm wastewaters takes place in the lagoons.•The major portion of metals from wastewater is concentrated in the solid manure.•Positive statistical correlation ...shows that shallow groundwaters on the farms are contaminated.•Shallow groundwater contains elevated amounts of organic matter and ammonia.•No deterioration of the quality of drinking water was detected in the deeper wells on the farms.
The objective of this study was to determine the degree of contamination of the shallow groundwater and the quality of drinking water, on the locations of three pig farms employing liquid manure cleaning systems, in lagoons without hydroisolation for storing wastewaters.
For the purpose of monitoring the quality of shallow groundwater and its level, ten piezometers were installed on three pig farms, whereas the quality of drinking water was followed using samples from the local wells.
The minimum fluctuations of shallow groundwater level were measured in the reference piezometers, whereas the highest variations (up to 4.19m) were detected in the piezometers drilled near the lagoons, indicating the infiltration of water from the lagoon. A significant correlation (P<0.001) between the amount of rainfall and the level of water in the piezometers, indicates the possible penetration of the pollutants from the earth surface to the groundwater. The measurements encompassed the physico-chemical parameters that characterize pig farm wastewater, viz. organic and suspended matter and dry matter. The results of measuring the parameters of wastewater, solid manure, and lagoon sediment indicate that efficient water purification occurred in the lagoons under natural conditions. The organic matter content in the lagoons was reduced by 85–90%, dry matter by 56–69%, suspended matter by 94–96%, total P by 31–50%, total N by 39–55%, Cu by 69–85%, and Zn by 83–89%. The results also show that most of the metals settled on the bed of the lagoon, reducing thus the risk of contamination of surface water and groundwater.
The investigation showed large variations in the parameters of shallow groundwater on the locations of the farms. The concentrations of NH4+-N in water of the reference piezometers ranged between 0.02 and 1.52mg/L, while in the piezometers close to the lagoons they were up to 52.6mg/L. The content of total N in the reference piezometers was between 0.14 and 22.4mg/L, while in the piezometers close to the source of contamination it reached 90.4mg/L. Also, at one of the farms the amounts of P and Cl− measured in the piezometers close to the lagoon were up to 7 and 5 times higher than in the reference piezometer. The correlations between electrical conductivity (EC) and Cl−, SO42−, Na+, K+, between total N and NH4+-N, NO3−-N and organic N by Kjeldahl (ONK) and various metals in the shallow groundwater, indicate their common origin from farm wastewaters.
On the other hand, the results clearly indicate that there was no degradation of the quality of the drinking water in the deeper layers, and none of the drinking water quality parameters showed significant variation during the investigation period. This is explained by the presence of 4–6m thick clay layer between the lagoon and the drinking water aquifer.
Overall, this study clearly shows that the pollution of shallow groundwater on the farms is of a local character, and that here is no significant pollution of groundwater sources, despite the fact that farms employing liquid manure cleaning systems have been in operation for many decades.
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