Subsurface Zone Research Articles

Urban environment and sustainable water supply: a comprehensive analysis of Darjeeling city, India

This article is an attempt to analyse the link between the condition of city environment and availability of water in Darjeeling city. Darjeeling, located in the Eastern Himalayan Region of India, is such a city which faces acute water scarcity in most part of the year, except during monsoon. The city cannot use ground water directly, and there is no river as source of water as well. It only uses spring water and rain water. The climatic condition and local environmental conditions have higher control over the availability of daily water. This article analyses the city’s 100-year climatic conditions as well as the condition of vegetation cover and built-up areas using NDVI and BUI methods, respectively. The present study explores that the deterioration of natural environmental conditions and increasing demand from both the permanent population and transitory population accelerate the intensity of water scarcity. Measuring the fluctuation of discharge (during pre-monsoon and post-monsoon period), the paper discusses how except in monsoon, most of the spring’s discharge gets reduced and increases the level of water stress in the city. Using quantitative methods, this empirical study explores that the loss of vegetation and haphazard constructions have enormous impact on the fragile hill ecosystem and reduce the rate of infiltration of water in the sub-surface zones, thus reducing the discharge ultimately. Therefore, the study recommends immediate actions to protect the city environment and to revive those springs for the city’s water security.

Probabilistic characterization of subsurface stratigraphic configuration with modified random field approach

Accurate and precise characterization of the subsurface stratigraphic configuration (geological model) at a given site is crucial to geotechnical engineering work. The uncertainty in the derived stratigraphic configuration can be significant, due to the strata's complexity and inherent spatial variability coupled with the limited availability of borehole data. The characterization and reduction of this uncertainty should be part of any site characterization project. This paper presents a method for characterization of the subsurface stratigraphic configuration with limited borehole data. Within the framework of the proposed method, the spatial correlation between the existence of a stratum in one subsurface zone and that in the other subsurface zone (or the spatial correlation of the existence of the stratum) is captured by an autocorrelation function determined with the maximum likelihood principle. The initial stratigraphic configurations are first sampled with the conditional random field theory. Next, the maximum-a-posteriori (MAP) estimates of the initial stratigraphic configurations are derived using Markov Chain Monte Carlo (MCMC) and taken as the final stratigraphic realizations. The effectiveness of the proposed method and its advantages over the existing stratigraphic characterization methods are demonstrated through a series of comparative analyses. The versatility of the new approach in modeling the 3-D stratigraphic configuration is further revealed through a case study of a site in Western Australia. This paper adds to the literature on stratigraphic uncertainty characterization and provides a basis for a risk-based geotechnical assessment that considers geological and geotechnical uncertainties.

Classification of soil quality using K-Nearest Neighbors methods

The damage or deterioration of the material due to reaction with the environment is called corrosion. The corrosive of soil can cause natural disasters such as landslides. Soil corrosivity is a serious problem in industrial and infrastructure activities. Soil corrosivity is also a problem at PT. IPMOMI, because of the large number of metal pipes that are planted underground which functions to drain fluid in the form of seawater as the main material for steam production. PT. IPMOMI wants to install metal pipes underground, Therefore PT. IPMOMI requires information about the status of soil corrosivity at that location. To overcome soil corrosivity, PT. IMOMI will install cathodic protection on the soil with high corrosivity. One of the efforts to deal with this problem is by mapping the subsurface corrosion zone. Before mapping the corrosion zone, it is necessary to know the level of soil corrosivity whether it is very high, high, medium, low, or very low. So that to determine the level of soil corrosivity whether very high, high, medium, low, or very low, a classification method is needed. In this study, the classification method used is the nonparamteric classification method, namely K Nearest Neigbors. The results of classification accuracy were 83.3% and variable chargebility had a higher contribution than the depth level in the classification model.

Integration of finishing and surface treatment of Inconel 718 alloy using high-speed ultrasonic vibration cutting

The successful implementation of high-speed ultrasonic vibration cutting (HUVC) to improve the machinability of the Inconel 718 alloy has been reported in literature. However, the influence of HUVC on the surface integrity of the Inconel 718 alloy has not been investigated. In this context, this study is the first attempt to integrate cutting operations and mechanical surface treatment into one step via HUVC. To this end, an experiment was performed to compare the surface integrity of conventional cutting (CC) and HUVC using coated carbide tools at high cutting speeds (80–240 m/min). The experiment revealed that HUVC led to a lower surface roughness, regular surface micro-texture, deeper subsurface deformation zone (up to 104.47 μm), higher surface micro-hardness rate (by up to ~50%), and higher surface compressive residual stress (−1772 to −2323 MPa) compared to CC. In some occasions, a single HUVC step can be used to satisfy requirements originally addressed over two distinct steps (cutting operation and mechanical surface treatment) by improving surface integrity.

Identification of the typical frequency range associated with subsurface gas zones: a study using Hilbert-Huang transform and wavelet analysis

Frequency attributes embedded in nonlinear geophysical signals such as well-log data or seismic data can provide vital clues in the effective characterization of the subsurface reservoir. Therefore, it is always important to recognize suitable mathematical techniques that need to be employed to extract such vital information from the nonlinear geophysical data. Several nonlinear mathematical techniques include wavelet analysis, fractal and multifractal analyses, and the fully data-adaptive Hilbert-Huang transform (HHT) technique. In the present study, we employ the HHT and the wavelet analysis techniques to seismic data of the Dutch sector of southern North Sea. We use a small portion of the seismic data, consisting of inline section 133 and time slice section 520 ms of the F3 block, to extract the instantaneous frequency associated with the subsurface gas zone. HHT constitutes two independent techniques, namely, the empirical mode decomposition (EMD) technique and the Hilbert spectral analysis (HSA). While the EMD technique facilitates to decompose the data into different signals of varied frequencies, called intrinsic mode functions (IMFs), the HSA helps to determine the instantaneous amplitudes and frequencies of the IMFs. EMD technique, together with HSA, has delineated a low-frequency spectral signature, believed to be a subsurface gas zone in the chosen data, corroborating the results of earlier studies of the same data sets. The instantaneous frequency range of the gas zone estimated by HSA was validated with the two-dimensional continuous wavelet transform (CWT) of the data sets using a suitable frequency range of Morlet wavelet. Results of the combined HHT and CWT analyses confirmed that the subsurface gas zone could be well identified in the frequency range 14–18 Hz. Results have direct implications in situ, in the sense that, by performing CWT analysis of seismic data using a Morlet wavelet in the frequency range 14–18 Hz, one can easily identify the location of subsurface gas zones.

Curve splitting analysis of synthetic MT data to identify permeable zone at geothermal field “X”

The permeable zone is one of the important parameters in the geothermal system. Its existence is influenced by fractures or faults generated within the geothermal reservoir. Due to the continuous influence of both high temperature and pressure, reservoir rocks are stressed and tend to cause a fracture. Unfortunately, some fractures are generally not continuous to the surface, so that geological data are not able to map out the presence of this structure. While the presence of the fracture zone greatly facilitates fluid mobility in the reservoir including heat transfer from the heat source convectively. Mapping the presence of a subsurface fracture zone is not easy. The study aims to identify the existing fracture zone through curve splitting analysis of MT data (magnetotelluric). The data used here is synthetic MT data. The fracture zone is a heterogeneous zone and anisotropy for EM waves. Splitting TE and TM curves will happen when the MT wave passes through this zone. The analysis of curve splitting provides depth penetration value. Therefore, the existence of fault as the cause of curve splitting can be mapped. From the results of forward modelling, the curve splitting approach can map very well the existence of the subsurface fault. For medium/rock resistive, the deviation of its dip value is only 1.36%. When the rock medium is highly conductive the deviation of its dip value up to about 3.48%. This is due to the absorption of EM waves by the conductive layer so that it is not effective in mapping the underlying layer.

Seismic Ambient Noise Analyses Reveal Changing Temperature and Water Signals to 10s of Meters Depth in the Critical Zone

AbstractThe critical zone sustains terrestrial life, but we have few tools to explore it efficiently beyond the first few meters of the subsurface. Using analyses of high‐frequency ambient seismic noise from densely spaced seismometers deployed in the forested Shale Hills subcatchment of the Susquehanna Shale Hills Critical Zone Observatory (SSHCZO), we show that temporal changes in seismic velocities at depths from ∼1 m to tens of m can be detected. These changes are driven by variations at the land surface. The Moving‐Window Cross‐Spectral (MWCS) method was employed to measure seismic‐velocity changes in coda waves at hourly resolution in 10 different frequency bands. We observed a diurnal signal, a seasonal signal, and a meteorological‐event‐based signal. These signals were compared to time‐series measurements of precipitation, well water levels, soil moisture, soil temperature, air temperature, latent heat flux, and air pressure in the heavily instrumented catchment. Most of the velocity changes can be explained by variations in temperature that result in thermoelastic strains that propagate to depth. But some double minima in seismic velocity time‐series observed after large rain events were attributed in part to the effects of water infiltration. These results show that high‐frequency ambient noise data may in some locations be used to detect changes in the critical zone from ∼1 to ∼100 m or greater depth with hourly resolution. But interpretation of such data requires multiple environmental data sets to deconvolve the complex interrelationships among thermoelastic and hydrological effects in the subsurface critical zone.

Simulation and modeling of the residual stress state in the sub-surface zone of BTA deep-hole drilled specimens with eigenstrain theory

The BTA (Boring and Trepanning Association) deep-hole drilling process is used to machine bores with large diameters (D > 40 mm) and a bore-length (l) to diameter ratio lager than ten (l/D >10). The resulting bore surface and its sub-surface zone are influenced by the cutting action and the self-guiding effect of the tool. The Guide pads support the asymmetric tool on the bore surface while burnishing the surface. The mechanical/thermal loads induced by the process lead to hardening, microstructure alteration and substantial residual stresses in the sub-surface. Particularly the residual stress state influences the fatigue strength and reliability of the machined part. To predict the residual stress in BTA deep-hole drilling, for the first time a novel analytical modeling approach is developed based on eigenstrain theory, integrating the machining process of cutting insert and the burnishing process of guide pad. A semi-analytical 3D contact model is built for the cycling incremental plasticity due to the equivalent mechanical/thermal loading of cutting process. Furthermore, an approximate estimation is provided for the contact condition between the inclined guide pad and bore hole, which facilitates the incremental contact analysis in the burnishing process. With the induced inelastic deformation known, residual stress distribution in the machined surface is constructed based on the eigenstrain theory. The results of the model are compared to X-Ray-Diffraction (XRD) measurements of BTA deep-hole drilled specimens.

Integration of multisources data for quarry slope stability assessment in the Itaoca district (Southeastern Brazil).

Usually, stability conditions of excavation slopes are evaluated by means of kinematic analysis and geomechanical classification systems. However, field surveys are concentrated at the slope toe and information about the upper and internal portions of rock masses are not taken into account. In order to tackle with these issues multisources data were integrated. The studies were carried out in a marble quarry located in one of the largest Brazilian poles of dimension stones. Results have shown that drone images actually help in the structural characterization of rock masses because they allow to classify variable degrees of fracturing and to identify structural domains in the entire slope face. In addition, the number of discontinuities interpreted from drone images was much larger than that determined by scanline survey methods. This demonstrates that the subsampling of classical survey methods may significantly affect slope stability assessment. Results have also shown that the intensive use of explosives as a method for rock dismantling was an important mechanism of fracture generation. The electrical resistivity tomography method coupled with the other survey methods employed in this work, proved an important tool for rock mass characterization and quarry exploitation, since it allowed identifying and assessing subsurface fractured zone.

The influences of process parameters on the thermo-mechanical workpiece load and the sub-surface residual stresses during peripheral milling of Ti-6Al-4V

The residual stress state of the sub-surface zone is a significant influencing factor, which determines the strength, lifetime and reliability of a component after machining. A reliable adjustment of this surface characteristic during peripheral milling is currently not possible. It is desired to control the milling process using a model-based approach in order to generate defined residual stresses in titanium components. This paper focuses on the determination of the thermo-mechanical load leading to the residual stress state during peripheral milling of Ti-6Al-4V. A newly developed sensory tool holder for the in-process measurement of the temperatures in the process zone was used. The influence of the process parameters cutting speed, feed per tooth, and radial depth of cut on the residual stress condition is shown. In addition, the varying microgeometry of the tool due to tool wear is taken into account as an observable disturbance variable.

Hydrological Modelling of Small Gauged and Ungauged Mountainous Watersheds Using SWAT—A Case of Western Ghats in India

Mountainous forested watersheds are important hydrologic systems that are responsible for much of the water supply and run-of-the-river hy-dropower schemes in many parts of the world. In India, the Western Ghats are one of such important hydrologic systems located in southern peninsular region. Several of these watersheds are ungauged. The Soil and Water Assessment Tool (SWAT) has been used to model streamflows for two mountainous forested watersheds, namely, Gurupur (699 km2) (a gauged watershed) and Upper Payaswini (44.6 km2) (an ungauged wa-tershed). Model calibration and validation are performed using monthly and daily streamflow data for the gauged watershed. Sample flow values obtained over a limited period were used for validation of ungauged wa-tershed. Flow duration curves (FDCs) have been derived to assess per-centile flow distributions. Model performance is evaluated using Nash-Sutcliffe coefficient (ENS), percent bias (PBIAS), coefficient of de-termination (R2) and comparison of percentile flow values obtained from observed and simulated FDCs. Sensitivity analysis with Latin Hypercube One-factor-At-a-Time (LH-OAT) indicates five soil-land use related pa-rameters namely, soil available water capacity (SOL_AWC), soil evapora-tion compensation factor (ESCO), soil depth (SOL_Z) and layers, groundwater baseflow (ALPHA_BF), and curve number (CN2 (forest & agriculture)), to be sensitive for simulating both gauged and ungauged wet mountainous forested watersheds. Study shows that lateral flows from dynamic sub-surface zones in such watersheds contribute substan-tially to the total water yield.

Reverse migratory behaviour of the earthquakes aftershock sequences along Himalayan Seismic Belt, Northwest Himalaya

The Anderson's theory (Anderson, 1951) can be utilized to understand the allocation of principal stresses. For various tectonic regimes, the global seismicity trend for crustal earthquakes of less than 20 km depth suggests that the source fault inclination also plays a critical part in the propagation of the aftershocks in the subsurface rupture with respect to the mainshock earthquake. It has also been observed that majority of the compression earthquakes that display upward seismicity migration typically occur along steep faults. However, in the context of Himalaya seismicity, the opposite migratory behaviour of the aftershock sequence is observed even along the gentle dipping source faulting. The failure envelope Mohr's diagram is used to understand the alteration in the dynamics of the subsurface locked zone of Himalayan Seismic Belt (HSB). This study discusses the alteration in the effective strength of the rock mass which imply the variation in the crustal hydrostatic fluid pressure at shallow depth (0–15 km). Different earthquakes and their aftershocks sequence of Himalayan terrain have been incorporated to corroborate the role of orientation of tectonic principal stresses, subsurface morphology and fluids/partial melts if present. In addition, topography contributes to the vertical loads and development of the subsurface geometry, therefore its role and its influence on seismicity has been discussed. This study highlights the controlling factors and the trend of the principal applied stresses and subsurface fluids in the distribution of aftershock sequences along tectonic regime of the Himalayan arc.

Tilt angle and lifetime of sunspot groups

ABSTRACT We use the Catalogue of Solar Activity (CSA) to study the latitudinal variations of tilt of solar active regions. The tilt angles β are computed taking into account changes of the heliographic grid with latitude φ. We show that when sunspot groups of different sizes and lifetimes are included, a classical representation of the Joy’s law as a linear function of latitude (β ∝ φ) is only the first approximation valid within a limited range of latitudes (−25° ≤ φ ≤ +25°). Outside this range, the functional dependence β = f(φ) becomes non-linear. Separating the data set on large long-living groups (LLG) and small short-living groups (SSG) reveals two quite different dependencies in β = f(φ): non-linearity in tilt is only present in LLGs and the steepness of linear section of β = f(φ) fit is higher for LLGs. This suggests a difference in the physical properties of two populations of solar groups, which could be hypothesized as an indication of different localization of subsurface zones of their formation in the framework of a distributed dynamo. However, since CSA contains the coordinates of sunspots averaged over the lifetime (or disc passage) of each group, one cannot rule out that the difference in tilts of SSG and LLG groups may be affected by the evolution of tilt angles during the lifetime/disc passage of the groups.

Mathematical Model for the Electric and Temperature Fields in the Heat-Affected Zone during Electrocontact Welding

The mechanism of formation of softened zones during electrocontact welding is considered. A calculation method is proposed, and the influence of the main electrocontact welding parameters on the surface and subsurface softened zone sizes and the decrease in the hardness of the metal in these zones is investigated.

Production and Properties of FeB-Fe2B-Fe3(B,C) Surface Layers Formed on Tool Steel Using Combination of Diffusion and Laser Processing

The paper presents the study results of laser remelting diffusion boronized layers produced on CT90 tool steel. A diffusion boronized layer was produced at 950 °C in a powder mixture containing boron carbide as a source of boron. A needle-like microstructure of iron boride was obtained. After diffusion boronizing, the specimens were subjected to laser processing, which was carried out using a diode laser with a nominal power of 3 kW. Three laser beam power values were applied (600, 900, and 1200 W). The aim of the study was to investigate the microstructure, microhardness, chemical, and phase composition as well as the wear and corrosion resistance of newly formed FeB-Fe2B-Fe3(B,C) layers. As a result of the laser beam interaction, the needle-like borides occurring in the subsurface zone were remelted, and three characteristic areas were obtained: the remelted zone, the heat-affected zone, and the substrate. The properties of newly formed layers have improved in comparison to diffusion boronized layers (except for corrosion resistance). It should be noted that using the highest laser beam power contributed to a slight reduction in wear resistance. Both the reduced corrosion and wear resistance were caused by greater remelting of the steel substrate and thus by the increased iron content in the formed layer.

Methods for Delivery and Distribution of Amendments for Subsurface Remediation: A Critical Review

AbstractThe ability to reliably deliver and widely distribute remedial amendments through the subsurface environment is of paramount importance to achieve cleanup objectives for contaminated sediments and groundwater for protection of sensitive environmental habitats and natural resources. A wide range of amendments, delivery techniques, and subsurface access methods are available. However, the applicability of these approaches is dependent on a multitude of site‐specific factors. In this review, an overview of amendments and access/distribution methods is provided, along with discussion of the maturity level, advantages, and limitations that relate to the potential effectiveness of each approach in the context of site‐specific factors. Each amendment and delivery approach are further evaluated for applicability to the following subsurface target zones: saturated, unsaturated, and perched water, with specific focus on high and low permeability regions in each zone. The review highlights a critical need for field‐tested approaches targeting unsaturated and perched water zones, as well as low‐permeability regions within all subsurface regions. The intent of this review is to provide critical information and insight into how amendments can be delivered, emplaced, and/or distributed effectively in the subsurface environment to effectively manage subsurface contamination.

Structural analysis and metamorphism of the Barlow Fault Zone, Chibougamau area, Neoarchean Abitibi Subprovince: implications for gold mineralization

Faults and deformation zones are important features of Archean terranes because of their significance for structural evolution and the formation of large gold districts. In the Chibougamau area, northeastern portion of the Abitibi Subprovince, an Apogee Metal Earth seismic reflection survey identified an association between an exceptional shallow-dipping subsurface reflector zone and the Barlow Fault Zone visible at the surface. This fault zone is located adjacent to the Opatica Subprovince and shares many characteristics with well-documented major gold-bearing faults in the more gold-endowed southern portion of the Abitibi Subprovince. This study aimed to reconstruct the kinematic evolution of the Barlow Fault Zone, determine its position within the structural setting of this section of the Abitibi Subprovince, and evaluate its importance for gold potential in the northern part of the Chibougamau area. The fault zone can be divided into three segments that differ markedly in dip. Structural reconstruction and field observations are compatible with a reverse south-over-north movement related to a ductile north–south shortening event, which culminated with amphibolite metamorphism. A late normal movement is deduced at the final stage. Geothermobarometers indicate peak metamorphism conditions of 550 ± 50 °C and 6 ± 1.2 kbar. Results from this study suggest that amphibolite facies metamorphism covers a much wider area within the Chibougamau region than previously documented. The Barlow Fault Zone shares similar geometric characteristics and evolutionary history with other gold-bearing structures in the Abitibi Subprovince, but ultimately it was unable to provide optimal conditions for channelling fluid and precipitating gold. High-grade metamorphism and the limited crustal extent of the fault likely prevented the tapping of deep metamorphic fluid and magma reservoirs. The Barlow Fault Zone is interpreted as a back-thrust fault that belongs to a more extensive south-dipping fault system encasing juxtaposed tectonic slivers. This system, with amphibolite facies metamorphism, is a defining feature of the northern portion of the Chibougamau area and developed during the accretion between the Opatica and Abitibi subprovinces.

Emerging organic compounds in European groundwater.

In Europe, emerging organic compounds (EOCs) in groundwater is a growing research area. Prioritisation for monitoring EOCs in Europe was formalised in 2019 through the development of the first voluntary groundwater watch list (GWWL). Despite this, groundwater occurrence data in the peer reviewed literature for Europe has not been reviewed to date. Questions surrounding the effect, toxicity, movement in the subsurface and unsaturated zone make the process of regulating EOC use difficult. The aim in Europe is to develop a unified strategy for the classification, and prioritisation of EOCs to be monitored in groundwater. This paper compiles evidence from the recent published studies from across Europe, since 2012, when the last major literature global review of EOCs in groundwater took place. A total of 39 studies were identified for review based on specific selection criteria (geography, publication date, sample size>10, inclusion of EOCs data). Data on specific compounds, and associated meta-data, are compiled and reviewed. The two most frequently detected EOCs, carbamazepine and caffeine, occurred in groundwater at concentrations of up to 2.3 and 14.8μg/L, respectively. The most frequently reported category of compounds were 'Pharmaceuticals'; a highly studied group with 135 compounds identified within 31 of the 39 studies. In Europe, the majority of reviewed studies (23) were at a regional scale, looking specifically at EOCs in a specific city or aquifer. The use of analytical methods is not uniform across Europe, and this inevitably influences the current assessment of EOCs in groundwater. A correlation between the number of compounds analysed for, and the number detected in groundwater highlights the need for further studies, especially larger-scale studies throughout Europe. For the development of EU and national regulation, further work is required to understand the occurrence and impacts of EOCs in groundwater throughout Europe and elsewhere.

Estimating of the Size of the Maximum Non-Metallic Inclusions in Martensitic Steels and their Influence on Fatigue Properties

Fatigue cracks can start from non-metallic inclusions in the subsurface zone at low stress amplitude level and high number of cycles. This phenomenon was observed mainly at high strength steels and parts with hardened surface zone. Fatigue strength of steel can be then estimated on the basis of hardness and maximum size of defect/inclusions measurements. Many inclusions rating methods exist, some of which have been adopted as the standards. However, “standard” methods for characterization of inclusion content are not convenient for assessment of their influence on fatigue strength of materials. This contribution deals with assessment of maximum sizes of inclusions in three types of martensitic steels used for production of rotating blades of steam turbines (Böhler T552, Böhler T671, and MLX 17) using extreme value statistics methods. Murakami´s concept of √AREAmax parameter and procedure according to ASTM E2283-08 were applied. Results were compared one another and also with the result of standard methods, too. Founded parameters were used for calculation of expected limit of the fatigue strength and compared with results of fatigue test of these steels.

Clumping in the Winds of Wolf–Rayet Stars

Abstract We attempt to determine the driver for clumping in hot-star winds by extending the measure of the spectral variability level of Galactic Wolf–Rayet stars to by far the hottest known among them, the WN2 star WR 2 and the WO2 stars WR 102 and WR 142. These three stars have T ⋆ = 140 and 200 kK, the last two being well above the bulk of WR stars with T ⋆ ∼ 40–120 kK. This full temperature range for WR stars is much broader than that of their O-star progenitors (∼30–50 kK), so is better suited to look for any temperature dependence of wind clumping. We have obtained multiple observations with high signal-to-noise, moderate-resolution spectroscopy in search of small-scale variability in the strong emission lines from the dense winds of these three extreme stars, and find a very low-level of variability in both stars. Temperature and terminal velocity are correlated, so faster winds show a lower variability, though this trend goes against any predictions made involving Line Deshadowing Instability (LDI) only, implying that instabilities intrinsic to LDI are not the main source of wind clumping. Instead, it could be taken as support for the suggestion that clumps are caused by a subsurface convection zone (SSCZ) at T ∼ 170 kK, since such an SSCZ would have little opportunity to operate under the hydrostatic surface of these hottest WR stars. It is still possible, however, that an SSCZ-related driver could interact with nonlinear line instability effects to enhance or possibly even produce clumps.