Subsurface Behavior Research Articles

Predictive Crack Growth Technique for Laser Peening Process Development

Laser peening (LP) has shown excellent fatigue life extension in numerous tests with typical treatments garnering 2-4 times the fatigue performance of an untreated component. Initially, large test programs were implemented to determine the best LP parameters for a given scenario, eventually being augmented by physics-based modeling due to the large design space available to the LP process. Approval for these processes continues to be on a case-by-case basis, contingent on multiple factors: cost, applicability, time, % fatigue life extension, and ability to track crack growth. Because LP induces compressive residual stresses in the near surface region, the compensatory tensile residual stresses are shifted sub-surface. While an axial tensile load would be mitigated by surface compressive stresses, sub-surface a crack can propagate rapidly via tensile stresses. Current predictive methods lack the ability to track this sub-surface behavior, limiting the accuracy of fatigue crack growth predictions throughout the various design stages of an LP treatment. This work demonstrates a framework that incorporates user-defined geometry, material data, crack growth data, mechanical loading, and residual stresses to predict the crack front shape evolution in 3D solids. A baseline case with no residual stresses is simulated and compared with a closed form solution.

Temperature sensitivity of reactive ester tracers for measuring CO2 residual trapping capacity

An understanding of the fundamental properties of chemical tracers (e.g. partitioning and sorption) is critical for assessing their subsurface behavior and to accurately model and interpret field tracer data. Carbon dioxide–water (CO2/H2O) partition coefficients have been previously determined for the reactive ester tracers, propylene glycol diacetate, triacetin and tripropionin, suggesting their suitability for assessing the residual trapping capacity of a geological formation for CO2 in a single well chemical tracer test. Understanding the temperature dependent behavior of chemical tracers significantly enhances their utility in field trials leading to a more accurate estimate of reservoir properties. However, very little information is known on the relationship between temperature and the partitioning process for these chemical tracers. In this paper, the temperature dependence of the partitioning process has been determined for temperatures ranging from 60 to 120°C. The variations in the partition coefficient with temperature were shown to correlate reasonably well with the van't Hoff equation for all tracers. The enthalpy associated with the partitioning process was determined by a regression fit to this equation and was shown to be the smallest for propylene glycol diacetate and the largest for tripropionin. It was found that the estimated enthalpy is approximately linearly correlated with the number of carbon atoms in the organic ester. Furthermore, we have shown that the temperature dependence of the tracer partition coefficient causes significant variation in the estimate of residual saturation.

Electro-osmotic transport of nano zero-valent iron in Boom Clay

One of the many problems that impede the successful remediation of soil and groundwater contaminated with chlorinated hydrocarbons occurs when pollutants diffuse into low permeability zones, and become difficultly accessible. Remediation by reductive dechlorination using nanoscale zero-valent iron (nZVI) is possible, but its delivery into contaminated hot spots is difficult using solely hydraulic gradients.Recently, electrokinetics has been proposed to transport nZVI, with the assumption that both electrophoresis and electro-osmosis are involved. However, so far no study has focused solely on transport driven by electro-osmotic flow. This driving force could significantly improve field remediation, allowing nZVI to reach low permeability hotspots.This work describes the experiments carried out to evaluate if nanoscale zero-valent iron can be transported by electro-osmotic advection in a dense clay using a specifically designed laboratory apparatus. It explores how working parameters (such as voltage, injection point and pH) influence transport, and provides an insight into the subsurface behaviour of nanoparticles using micro-XRF.The results confirm the transport of nZVI by electro-osmotic advection, with an electro-osmotic conductivity in the range (0.5-1.0)·10−10 m2V−1s−1. The presence of nZVI decreases electro-osmotic conductivities by approximately half and affects geochemical conditions of the system, inducing sharper pH profiles and enhancing cation exchange in the clay.

Subsurface Behavior of Ductile Material by Particle Impacts and its Influence on Wear Mechanism

Erosion is observed in many industrial situations such as pneumatic conveying pipelines, shot peening and sand blasting where interaction between particle and surface is expected. A number of particle impact parameters and material surface properties are involved in the erosion process. Extensive studies have been conducted to understand the effects of the process parameters on erosion; however, only limited studies can be found in the literature associated with material surface and subsurface properties. In order to get a better understanding of the material surface and subsurface behaviour due to particle impacts for different parameters, erosion tests were performed for different impact angles and different particle velocities using a micro-sandblaster. Angular silicon carbide (SiC) particles were impacted on two different ductile surfaces, mild steel and aluminium, with a constant particle flux. Wear mechanisms were studied in terms of particle kinetic energy. Subsequently, the worn surfaces and their cross-sections were observed using scanning electron microscope (SEM) to relate the subsurface damage characteristics to different impact conditions, and to wear mechanisms. Results showed that at a lower impact angle, material was removed through cutting mechanism, while at a higher angle; material removed through predominantly deformation process. Also, subsurface cracking and subsurface damage were observed up to a certain depth from the worn surface. It appears both the depth of subsurface cracking and subsurface damages increases with increasing impact velocity. The variation is consistent with increase in surface and subsurface temperature at higher velocities. With increased temperature, the depth of the heat affected zone increases, which increases the work hardening layer thickness. In addition, subsurface microstructural damage is consistent with attainment of higher temperature which can be explained through the high strain-rate deformation and thermo-physical properties of the surface.

Engineering classification of soil masses for design of tunnel support based on observations in Tehran eastern main sewerage tunnel

The need to provide an index of subsurface soil behaviour which would include allowances for intact soil strength, soil texture and its matrix properties, discontinuity frequency, groundwater condition together with stress condition at the depths encountered has led this author to develop a soil mass classification system to isolate in a qualitative manner categories of soil which, under a particular set of engineering constraints, will behave in a similar way. The principle on which this classification system is based is that the selected parameters which are important in determining soil mass behaviour can be determined quickly and easily by a field geologist or engineer. For a particular soil stratum, a numerical assessment is made within designated limits of the quality of the soil as it relates to a particular parameter. These numbers are then summed to give an index number which can be related to the behaviour of soil mass culminating in the prediction of excavation procedures and support system density for a 3⋅5 m diameter hand excavated tunnel. The classification provided very good feed-back for the NATM tunnelling method, including stand-up time and support requirements.

Conservation applications of baseline acoustic tag data from right whales

Data collected from archival acoustic tags have dramatically improved our understanding of marine mammal subsurface behavior. Some of the earliest tag deployments were made on the endangered North Atlantic right whale (Eubalaena glacialis) to better understand their behavior and to contribute to their conservation. Over the past 15 years, the database of acoustic tag records collected from a diverse cross section of the population has served as a valuable resource for research. Acoustic tag data have provided critical behavioral information including details on individual calling behavior in designated critical habitat feeding grounds, behavioral responses to controlled exposures of acoustic signals including conspecific and man-made signals, acoustic responses to vessel noise, and ground truth data for passive acoustic monitoring efforts. Current studies continue to utilize tag data to shed light on the individual, seasonal, and regional variation in acoustic behavior of right whales, particularly focused on the shallow water coastal habitats of the calving grounds off of Florida and Georgia and in the migration corridor off the Eastern United States. These studies have contributed data that are crucial for targeted conservation efforts and highlight the value of long-term databases of tag data in baleen whale research.

Dynamics of convective dissolution from a migrating current of carbon dioxide

During geologic storage of carbon dioxide (CO2), trapping of the buoyant CO2 after injection is essential in order to minimize the risk of leakage into shallower formations through a fracture or abandoned well. Models for the subsurface behavior of the CO2 are useful for the design, implementation, and long-term monitoring of injection sites, but traditional reservoir-simulation tools are currently unable to resolve the impact of small-scale trapping processes on fluid flow at the scale of a geologic basin. Here, we study the impact of solubility trapping from convective dissolution on the up-dip migration of a buoyant gravity current in a sloping aquifer. To do so, we conduct high-resolution numerical simulations of the gravity current that forms from a pair of miscible analogue fluids. Our simulations fully resolve the dense, sinking fingers that drive the convective dissolution process. We analyze the dynamics of the dissolution flux along the moving CO2–brine interface, including its decay as dissolved buoyant fluid accumulates beneath the buoyant current. We show that the dynamics of the dissolution flux and the macroscopic features of the migrating current can be captured with an upscaled sharp-interface model.

From Fourier to Darcy, from Carslaw to Theis: the analogies between the subsurface behaviour of water and heat

The analogy between the behaviour of groundwater in an aquifer and the conductive behaviour of heat in an aestifer is almost perfect. The development of groundwater flow theory has consistently drawn upon thermal analogues to find mathematical solutions: Darcy’s Law is analogous to Fourier’s. Charles Theis drew on Horatio Scott Carslaw’s heat conduction equations to develop his analysis of radial groundwater flow. Ogata and Banks refer to Carslaw and Jaeger’s work on heat diffusion to solve the longitudinal dispersion of solutes in flowing groundwater. The hydrogeologist is thus admirably equipped with the necessary conceptual models, mathematical tools and computer codes to become a practising thermogeologist

Lock-in thermographic inspection of squats on rail steel head

The development of squat defects has become a major concern in numerous railway systems throughout the world. Infrared thermography is a relatively new non-destructive inspection technique used for a wide range of applications. However, it has not been used for rail squat detection. Lock-in thermography is a non-destructive inspection technique that utilizes an infrared camera to detect the thermal waves. A thermal image is produced, which displays the local thermal wave variation in phase or amplitude. In inhomogeneous materials, the amplitude and phase of the thermal wave carries information related to both the local thermal properties and the nature of the structure being inspected. By examining the infrared thermal signature of squat damage on the head of steel rails, it was possible to generate a relationship matching squat depth to thermal image phase angle, using appropriate experimental/numerical calibration. The results showed that with the additional data sets obtained from further experimental tests, the clarity of this relationship will be greatly improved to a level whereby infrared thermal contours can be directly translated into the precise subsurface behaviour of a squat.

Asset Management and Safety Assessment of Levees and Earthen Dams Through Comprehensive Real-Time Field Monitoring

Assessing the health of and maintaining civil infrastructure has been an increased concern in the wake of natural disasters such as Hurricane Katrina in 2005 and the summer 2007 flood events in the UK. The variability of properties within geotechnical systems makes predictions of soil behavior extremely difficult, especially when soil models are not calibrated with field-measured performance. Unfortunately the current state of the art in geotechnical system health assessment is either based on very expensive monitoring systems for real-time information or on periodic measurement of ground surface displacements. Accordingly, a need has arisen for a system capable of in situ, real-time monitoring of levees, embankments, and other earthen structures. The work presented herein highlights the development of novel, affordable sensing technologies for use in a framework to monitor, manage and ensure the safety of geotechnical infrastructure. MEMS (micro-electro-mechanical systems)-based in-place inclinometer system, Measurand’s ShapeAccelArray (SAA), is now established as a sensing tool for simultaneous measurement of 3D soil acceleration and 3D ground deformation up to a depth of one hundred meters, with an accuracy of ±1.5 mm per 30 m. Each sensor array is connected to a wireless sensor node to enable real-time monitoring as well as remote sensor configuration. This system is now being further developed to include digitally integrated pore pressure measurement in the form of vibrating wire piezometers equipped with microprocessors (called SAAPs). The SAAPs are able to convert vibrating wire data to digital data downhole, and they integrate easily into the SAA system. In situ testing was conducted in a levee in England subjected to significant tidal loading (up to 6 m of fluctuation during spring tides) through collaboration with the European Union’s UrbanFlood project. In addition to the SAAs and SAAPs installed in three sections of the levee, the site was also instrumented with other sensors from Alert Solutions and TenCate, providing values for comparison. The likelihood of this levee to experience deformation and the density of instrumentation installed in the bank made this the ideal location to test the new SAAP system. The additional insight into subsurface behavior provided by the SAAPs is integral in the development of a comprehensive system for monitoring and management of civil infrastructure. The preliminary testing indicates the suitability of this new multi-parameter system for inclusion in a multi-scale monitoring and health assessment framework, which will be implemented in New Orleans, LA in 2012.

Subsurface behavior of bottlenose dolphins (Tursiops truncatus) interacting with fish trawl nets in northwestern Australia: Implications for bycatch mitigation

AbstractMost studies of delphinid‐trawler interactions have documented the surface behavior of dolphins feeding on discarded bycatch, but not their subsurface behavior around demersal trawl gear. Using video cameras mounted inside trawl nets, we recorded the subsurface behavior of common bottlenose dolphins (Tursiops truncatus) in a demersal fish trawl fishery in northwestern Australia. Footage from 36 trawls across the fishery was analyzed to determine the extent of dolphin‐gear interactions and the behavior of dolphins inside the nets. Interaction rates were high, with dolphins present inside and outside the nets during 29 and 34 trawls, respectively, and for up to 99% of the trawl duration. The proportion of foraging behaviors exhibited inside the nets was higher than the proportions of traveling and socializing behaviors. Twenty‐nine individuals were identified inside the net, seven of which returned repeatedly within and between trawls and fishing trips, but were observed primarily in the same localized areas in which they were first recorded. Our results suggest that entering trawl nets may be a frequently occurring, yet specialized behavior exhibited by a small subset of trawler‐associated dolphins. We propose that gear modifications, not spatial or temporal adjustments to fishing effort, have the greatest potential to reduce dolphin bycatch.

Long-term electrical resistivity monitoring of recharge-induced contaminant plume behavior

Geophysical measurements, and electrical resistivity tomography (ERT) data in particular, are sensitive to properties that are related (directly or indirectly) to hydrological processes. The challenge is in extracting information from geophysical data at a relevant scale that can be used to gain insight about subsurface behavior and to parameterize or validate flow and transport models. Here, we consider the use of ERT data for examining the impact of recharge on subsurface contamination at the S-3 ponds of the Oak Ridge Integrated Field Research Challenge (IFRC) site in Tennessee. A large dataset of time-lapse cross-well and surface ERT data, collected at the site over a period of 12months, is used to study time variations in resistivity due to changes in total dissolved solids (primarily nitrate). The electrical resistivity distributions recovered from cross-well and surface ERT data agrees well, and both of these datasets can be used to interpret spatiotemporal variations in subsurface nitrate concentrations due to rainfall, although the sensitivity of the electrical resistivity response to dilution varies with nitrate concentration. Using the time-lapse surface ERT data interpreted in terms of nitrate concentrations, we find that the subsurface nitrate concentration at this site varies as a function of spatial position, episodic heavy rainstorms (versus seasonal and annual fluctuations), and antecedent rainfall history. These results suggest that the surface ERT monitoring approach is potentially useful for examining subsurface plume responses to recharge over field-relevant scales.

Evaluation of Burnished Subsurface Mechanical Behavior Using Nanoindentation

The performance and life of machined components in service are mainly effect by their surface integrity. Burnishing process is a kind of chipless processing which improve the surface integrity obviously. A subsurface “hardness film” is formed during the processing. Subsurface mechanical behavior is the main part of surface integrity. Since the very small scale of the subsurface in burnished surface nanoindentation is used to identify how the local changes of microstructure influence the hardness distributions of subsurface mechanical properties. This study focuses on the relationships between burnishing parameters (burnishing feed and burnishing depth) and nanohardness. A series of burnishing processing experiments and nanoindentation tests were conducted on the surface of the burnished samples. The microstructure and nanoindentation research results indicate that there is no visible phase transformed region in the subsurface of burnished specimens, the hardening film is larger than 4 micro meters, the nanohardness is about 2.2~3.5Gpa which depends on the burnishing parameters and distribution and position of the second phase particles, while the nanohardness in turned material is about 1.8Gpa.

Enhanced gas recovery, CO2 storage and implications from the CO2CRC Otway Project

Successful completion of the first stage of the CO2CRC Otway Project demonstrated safe and effective CO2 storage in the Naylor depleted gas field and confirmed our ability to model and monitor subsurface behaviour of CO2. It also provided information of potential relevance to CO2 enhanced gas recovery (EGR) and to opportunities for CO2 storage in depleted gas fields. Given the high CO2 concentration of many gas fields in the region, it is important to consider opportunities for integrating gas production, CO2 storage in depleted gas fields, and CO2-EGR optimisation within a production schedule. The use of CO2-EGR may provide benefits through the recovery of additional gas resources and a financial offset to the cost of geological storage of CO2 from gas processing or other anthropogenic sources, given a future price on carbon. Globally, proven conventional gas reserves are 185 trillion m3 (BP Statistical Review, 2009). Using these figures and Otway results, a replacement efficiency of 60 % (% of pore space available for CO2 storage following gas production) indicates a global potential storage capacity—in already depleted plus reserves—of approximately 750 Gigatonnes of CO2. While much of this may not be accessible for technical or economic reasons, it is equivalent to more than 60 years of total global stationary emissions. This suggests that not only gas—as a lower carbon fuel—but also depleted gas fields, have a major role to play in decreasing CO2 emissions worldwide.

Abiotic subsurface behaviors of As(V) with Fe(II)

Subsurface geochemical behavior of As(V) with Fe(II) was studied under strict anoxic conditions. Abiotic reduction of As(V) (0.1 mM) to As(III) by aqueous Fe(II) and sorbed Fe(II) in pH range 5.0-7.0 and Fe(II)(aq) concentration (0.6-1.2 mM) was investigated along with the effect of As(V) on the oxidation of Fe(II) by dissolved oxygen (DO). Although the reduction was thermodynamically feasible for homogeneous chemical conditions, practically no As(V) reduction by aqueous Fe(II) was observed. Similarly, no sorbed As(V) reduction was observed under the heterogeneous experimental conditions by sorbed Fe(II) onto synthetic iron oxide (hematite, α-Fe₂O₃). Experimental results on Fe(II) oxidation by DO in the presence of 0.1 mM As(V) showed a significantly slower Fe(II) oxidation, which might be due to the formation of Fe(II)-As(V) complex in the aqueous phase. The results of this study demonstrate that As(V) is relatively stable in the presence of Fe(II) under subsurface environment and interfere the oxidation of Fe(II).

AN ESTIMATE OF THE DETECTABILITY OF RISING FLUX TUBES

The physics of the formation of magnetic active regions (ARs) is one of the most important problems in solar physics. One main class of theories suggests that ARs are the result of magnetic flux that rises from the tachocline. Time–distance helioseismology, which is based on measurements of wave propagation, promises to allow the study of the subsurface behavior of this magnetic flux. Here, we use a model for a buoyant magnetic flux concentration together with the ray approximation to show that the dominant effect on the wave propagation is expected to be from the roughly 100 m s −1 retrograde flow associated with the rising flux. Using a B-spline-based method for carrying out inversions of wave travel times for flows in spherical geometry, we show that at 3 days before emergence the detection of this retrograde flow at a depth of 30 Mm should be possible with a signal-to-noise level of about 8 with a sample of 150 emerging ARs.

Influence of cyclic freeze-thaw on the mobilization of LNAPL and soluble oil in a porous media

Abstract Subsurface behavior of spilled fuel in freezing and frozen porous media including fractured bedrock is not well understood. To simulate a bedrock fracture, a freezing cell consisting of two parallel glass plates filled with glass beads was constructed to study the impact of cyclic freeze–thaw on LNAPL movement. The test procedure involved introduction of LNAPL atop the cell that contained water mixed with fluorescein dye. Freezing progressed from the top down, with observation and measurement of the LNAPL migration using a high-resolution digital camera and time-lapse photography. Both diesel and soluble oil were used for the experiments. Tests with soluble oil involved thorough mixing at 12.5% volume ratio with the fluorescein–water mixture in the freezing cell. The results showed upward mobility of the LNAPL under cyclic freezing and downward progressive expulsion of the soluble oil ahead of the advancing freezing front. The results corroborated literature findings on organic solute expulsion ahead of freezing front, and provided insight into the behavior of trapped LNAPL below the water table when subjected to freeze–thaw conditions. Additionally, micro fissures were observed in the formed ice inside the freezing cell under prolonged freezing. Such micro fissures may provide potential migration pathways for fresh spilled fuel in permafrost environments.

The role of crystal orientation and surface proximity in the self-similar behavior of deformed Cu single crystals

We report on novel 3D spatially resolved X-ray diffraction microscopy studies of self-affine behavior in deformed single crystals. This study extends surface profile measurements of self-affined morphology changes in single crystals during deformation to include local lattice rotations and sub-surface behavior. Investigations were made on the spatial correlation of the local lattice rotations in 8% tensile deformed Cu single crystals oriented with [1 2 3], [1 1 1] and [0 0 1] axes parallel to the tensile axis. The nondestructive depth-resolved measurements were made over a length scale of one to hundreds of micrometers. Self-affined correlation was found both at the surface and below the surface of the samples. A universal exponent for the power-law similar to that observed with surface profile methods is found at the surface of all samples but crystallographically sensitive changes are observed as a function of depth. Correlation lengths of the self-affine behavior vary with the [1 2 3] crystal exhibiting the longest self-affine length scale of 70 μ m with only 18 μ m for the [1 1 1] and [0 0 1] crystals. These measurements illuminate the transition from surface-like to bulk-like deformation behavior and provide new quantitative information to guide emerging models of self-organized structures in plasticity.

Insights into Habitat Utilization by Green Turtles (Chelonia mydas) During the Inter-Nesting Period Using Animal-Borne Digital Cameras

AbstractMany marine turtle habitat utilization studies have historically relied on inferences from logged data or direct visual observation. Here we remotely investigate aspects of the habitat utilization of inter-nesting female green turtles (Chelonia mydas) nesting on the Mediterranean island of Cyprus. Using an animal-borne digital video camera set to take only still images, with an integrated time-depth recorder, we recorded a total of 2,375 images and 2,899 dives for two nesting female green turtles. Both turtles spent over 80% of their time at depths of 5 m or less. Photographic evidence allowed us to categorize sub-surface behaviors from 66 of the deeper dives (turtle A with 40 dives and turtle B with 26 dives) containing more than 900 images into three categories: swimming, probable foraging and resting. Methodologically, our study highlights future utility in using camera technologies to clarify at-sea behavior of marine organisms, with a view to generating reliable time budgets.

Fate of Sulfamethoxazole, 4-Nonylphenol, and 17β-Estradiol in Groundwater Contaminated by Wastewater Treatment Plant Effluent

Organic wastewater contaminants (OWCs) were measured in samples collected from monitoring wells located along a 4.5-km transect of a plume of groundwater contaminated by 60 years of continuous rapid infiltration disposal of wastewater treatment plant effluent. Fifteen percent of the 212 OWCs analyzed were detected, including the antibiotic sulfamethoxazole (SX), the nonionic surfactant degradation product 4-nonylphenol (NP), the solvent tetrachloroethene (PCE), and the disinfectant 1,4-dichlorobenzene (DCB). Comparison of the 2005 sampling results to data collected from the same wells in 1985 indicates that PCE and DCB are transported more rapidly in the aquiferthan NP, consistent with predictions based on compound hydrophobicity. Natural gradient in situ tracer experiments were conducted to evaluate the subsurface behavior of SX, NP, and the female sex hormone 17beta-estradiol (E2) in two oxic zones in the aquifer: (1) a downgradient transition zone at the interface between the contamination plume and the overlying uncontaminated groundwater and (2) a contaminated zone located beneath the infiltration beds, which have not been loaded for 10 years. In both zones, breakthrough curves for the conservative tracer bromide (Br-) and SX were nearly coincident, whereas NP and E2 were retarded relative to Br- and showed mass loss. Retardation was greater in the contaminated zone than in the transition zone. Attenuation of NP and E2 in the aquifer was attributed to biotransformation, and oxic laboratory microcosm experiments using sediments from the transition and contaminated zones show that uniform-ring-labeled 14C 4-normal-NP was biodegraded more rapidly 130-60% recovered as 14CO2 in 13 days) than 4-14C E2 (20-90% recovered as 14CO2 in 54 days). There was little difference in mineralization potential between sites.