Subsurface Irregularities Research Articles

Effects of surface topography and subsurface structural irregularities of river embankments on Rayleigh wave propagation

A numerical investigation of surface wave propagation in the surface wave exploration of river embankments is implemented using 3D shallow soil models with different subsurface shapes and S-wave velocities. The focus is on the effects of surface and subsurface irregularities on the propagation and dispersion characteristics of Rayleigh waves generated by a surface source and observed at points along the crest of the embankment. Rayleigh wave dispersion curves observed along the embankment crest are found to be contaminated by reflected waves, with the amount of contamination affected more by the position of the velocity boundary at the bottom edge of the embankment than the surface topography. When the velocity boundary is close to the ground surface, especially at the toe of the slope, the effect of reflected waves is sufficiently large to generate biases in the phase velocity estimates.Graphical

Utilizing Drone-Based Ground-Penetrating Radar for Crime Investigations in Localizing and Identifying Clandestine Graves.

The decomposition of a body is influenced by burial conditions, making it crucial to understand the impact of different conditions for accurate grave detection. Geophysical techniques using drones have gained popularity in locating clandestine graves, offering non-invasive methods for detecting surface and subsurface irregularities. Ground-penetrating radar (GPR) is an effective technology for identifying potential grave locations without disturbance. This research aimed to prototype a drone system integrating GPR to assist in grave localization and to develop software for data management. Initial experiments compared GPR with other technologies, demonstrating its valuable applicability. It is suitable for various decomposition stages and soil types, although certain soil compositions have limitations. The research used the DJI M600 Pro drone and a drone-based GPR system enhanced by the real-time kinematic (RTK) global positioning system (GPS) for precision and autonomy. Tests with simulated graves and cadavers validated the system's performance, evaluating optimal altitude, speed, and obstacle avoidance techniques. Furthermore, global and local planning algorithms ensured efficient and obstacle-free flight paths. The results highlighted the potential of the drone-based GPR system in locating clandestine graves while minimizing disturbance, contributing to the development of effective tools for forensic investigations and crime scene analysis.

Non-destructive control of roads by georadars (review article, part I)

Relevance. The relevance of the studies outlined in the article is due to their focus on the implementation of the state strategy for ensuring the reliability and extending the resource of transport and engineering structures, the implementation of which is associated with the methods and means of obtaining information and processing it in real time; methods for assessing the state of engineering structures, a feature of which is a significant heterogeneity of geometric and physical-mechanical parameters, which complicates the use of diagnostic results. With the obvious advantages of wave sounding methods, their application is constrained by the complexity of the tasks of interpreting the results obtained and the associated errors in determining the parameters of structures; the multifactorial nature of the problems of evaluating the parameters of multicomponent materials of structures, the imperfection of flaw detection methods. Purpose of work – a review of the capabilities of modern georadars and means of processing ultra-wideband signals together with computer-oriented systems for numerical modeling, optimization of methods for processing georadar data for solving problems of detecting and identifying subsurface irregularities in building structures that are a flat-layered medium. Materials and methods. The first part of the article provides a brief overview of the main methods of processing data sets obtained using pulsed GPR. A new method of data processing using specialized software is proposed GeoVizy. The possibilities of using the methods of the modern theory of diffraction and methods of signal analysis in the space-time domain for solving the problems of flaw detection are also briefly considered. Results. The results obtained in this work are based on remote sensing data, proposed mathematical models and methods for processing sensing data. Based on the results of the comparative analysis of the capabilities of georadars, practical recommendations were proposed to improve the reliability of the data sets obtained, and possible directions for further research were substantiated. Conclusions. The results of numerical modeling and laboratory experiments obtained in this work confirmed the previously stated theoretical assumptions about the degree of influence of the key parameters of ultra-wideband GPR on the reliability of the results obtained. The significance of the new scientific results obtained consists not only in the use of new sensing means and new models of processing and subsequent interpretation of the data obtained, but also in the considered prospects for progress in the field of non-destructive testing and diagnostics.

A Probability Electrical Resistivity Tomography Imaging of complex tectonic features in the Kissamos and Paleohora urban areas, Western Crete (Greece).

A number of 2D Electrical Resistivity Tomographies (ERT) were conducted in northwest and southwest Crete with the aim to model geotectonic features at selected urban sites. The study area is located within the central forearc of the Hellenic subduction zone. Thirteen ERT profiles were realized using the dipole–dipole electrode and/or the Wenner-Schlumberger arrays . In order to model the resistivity distribution, the probability-based electrical resistivity tomography inversion (PERTI) method has been applied . The main features of the PERTI method are: (i) unnecessity of a priori information; (ii) full, unconstrained adaptability to any kind of dataset, including the case of nonflat topography; (iii) independence from data acquisition techniques and spatial regularity; (iv) capability to resolve complex continuous resistivity variation. Since the present case-study is the first application of the PERTI algorithm to locate fault zones and near subsurface irregularities, its routine has been tested using the well-known RES2DINV commercial software as reference. The comparison has shown a common coherence between the results of the two inversion methods and confirmed the better filtering capacity and greater versatility of the PERTI algorithm, already outlined in a number of previous papers dealing with archaeological applications.

Quantifying the influence of failure surface asperities on the basal shear resistance of translational landslides

For active landslides, drained shear strength is often determined from either a forensic slope stability analysis or laboratory residual shear testing. Both analyses often yield different shear strength values, often attributed to the complex, micro-scale behavior of the sheared material. However, subsurface asperities, such as cobbles, boulders, discontinuities, steps, and other geologic anomalies, may also influence the effective resistance realized along a highly sheared slip surface, thus influencing slope stability, and consequently landslide forensics. In this study, the influence of subsurface irregularities on effective mobilized residual shear strength, ϕr, and shear resistance from basal asperities, ϕa, is considered for idealized geometry under plane strain and three-dimensional conditions. The results demonstrate that even a modest presence of subsurface asperities may impart significant shear resistance, effectively reducing the drained residual shear strength that yields equilibrium. These effects are amplified when three-dimensional asperities are considered. There are significant uncertainties towards actually quantifying the geometry of subsurface asperities; however, this study highlights the potential role that such anomalies may impart on shear strength calculations in slope stability.

Enhanced boiling heat transfer on binary surfaces

A novel idea for the improvement of boiling heat transfer is that of a binary surface – where a non-boiling liquid coats sub-surface irregularities and aids in heat transfer to the primary working fluid. The threefold goal of this effort was to: (i) prepare durable, low-cost, scalable binary surfaces for boiling heat transfer enhancement, (ii) conduct pool boiling experiments on these surfaces, and (iii) derive the physical mechanisms perceived as responsible for the observed boiling enhancements. Accordingly, robust binary surfaces were prepared on copper using a facile, scalable bulk micro-manufacturing approach. These surfaces consist of numerous micro-/nano-cavities filled by a non-boiling liquid creating puddles around solid islands. Boiling experiments were carried out using a dielectric liquid, PF-5060, as the primary working fluid (the boiling liquid). It was observed that, compared to a smooth/plain copper surface, a binary copper surface, with water as the NBL, was able to simultaneously enhance the maximum heat flux limit by ∼2.2 times and the average heat transfer coefficient by ∼7.5 times. A maximum heat flux of 35.06W/cm2 was recorded, which is higher than the enhancements reported so far in literature for the pool boiling of PF-5060 on any enhanced surface. It was further found that decreasing the contact angle of the non-boiling liquid on the binary surface enhances both the heat transfer coefficient and the maximum heat flux limit.

Site - building resonance response in a complex geological setting: Ground motions recorded in the centre of Paleohora Basin and at a rock fractured outcrop site close to the basin edge (SW Crete, Greece)

Seismic site characterization is an important parameter in earthquake hazard assessment for risk mitigation studies, which are essential in engineering design practices and urban planning providing useful information to governmental or private civil protection authorities. Recent advances from site effect studies envisage for the future the importance of incorporating microzonation as a tool for determining resonance prone buildings especially for the most earthquake hazardous municipalities. This study aims to assess the frequencies of vibration of selected masonry and reinforced concrete buildings and to examine potential soil - building resonance in a complex geological setting of the small scale Paleohora Basin (southwest Crete). Ambient noise survey was performed in masonry and reinforced concrete buildings, on soil foundation and on soil at several distances from the base of the selected buildings. The selected public and private (masonry and RC) building constructions are located in the centre of the Basin which is characterized by heterogeneities induced by large scale E-W fault and at rock fractured (of complex orientation and opening of fractures and joints) outcrop site close to the margins of the Basin in the southeast bordered by an NNE-SSW fault. The spatial horizontal to vertical spectral ratio (HVSR) technique using ambient noise reveals that soil-building resonance phenomena could be inferred in the small scale alluvial Paleohora Basin.Two amplified peaks in the centre of the Basin and one amplified peak at the rock fractured outcrop site close to the Basin margins are observed from the data sets. In the centre of the Basin, the amplified peak at medium frequency (3.85–7.11 Hz) is related to the near subsurface irregularities locally induced by E-W faulting, while the low frequency (0.75 Hz) is related to the overlain Quaternary deposits. At the rock fractured outcrop site close to the margins of the Basin the one amplified peak at medium frequencies (2.5 Hz) is related to the fractured limestone outcrop. Weak motion earthquake data following the main earthquake event that occurred near to the southwest coast of Paleohora are recorded in the centre of the Basin (at the schoolyard) and on rock fractured outcrop close to the margins of the Basin. The HVSR of the weak motion earthquake data present in the center of the Basin two amplified peaks at low (0.75 Hz) and medium frequencies (6.56 Hz) and at the rock fractured outcrop site close to the Basin edge one amplified peak at medium frequencies (2.58 Hz). This study conducted in the complex small scale and dense populated Basin, highlights the necessity of incorporating the determination of prone resonance buildings into urban planning for risk mitigation studies, specifically in this earthquake hazardous municipality.

An indirect boundary element method to model the 3-D scattering of elastic waves in a fluid-saturated poroelastic half-space

The indirect boundary element method (IBEM) is extended to solve the scattering of elastic waves by three-dimensional (3-D) subsurface irregularities in a fluid-saturated poroelastic half-space. The Green׳s functions of inclined circular loads and fluid source in a poroelastic full space are deduced based on Biot’s theory. According to the single-layered potential theory, the scattered waves are constructed by using fictitious uniform loads and fluid source distributed on the boundary elements on the scatterer surface, and their magnitudes are determined by the continuity or traction-free boundary conditions. Accuracy verification illustrates that this proposed method can deal with 3-D wave scattering problems in an infinite poroelastic medium conveniently and accurately. Then, the scattering of plane waves by a 3-D canyon is investigated. Numerical results indicate that: the scattering of waves in a poroelastic half-space strongly depends on the incident frequency and incident angle; the 3-D amplification effects both on the displacement and pore pressure appear to be more significant than the corresponding 2-D case; medium porosity of the half space also plays a key role on the wave scattering, especially for obliquely incident waves at the critical angle, and the influence of drainage condition seems to be more considerable for high porosities.

Dynamic stress concentration for multiple multilayered inclusions embedded in an elastic half-space subjected to SH-waves

The dynamic stress concentration factor (DSCF) is evaluated along the interfaces of multiple multilayered inclusions embedded in a half-space when subjected to a plane harmonic SH-wave. A weak form of Helmholtz equation is utilized to derive a non-hypersingular boundary integral equations to compute the stresses. Eliminating the need to rely on hypersingular integrals, greatly simplifies the procedure. The numerical results obtained by the proposed method, are validated against analytical solutions.Various contributing factors that can influence the DSCF are investigated, including multiple scattering, layering, stiffness of the adjacent inclusions, and impedance contrast of the layers. The DSCF is found to be highly prone to these changes, particularly with the soft materials. Therefore, accurate analysis of stresses requires models that consider multiple scattering and layering. The presented result could be used for predicting the seismic failure of pipes and underground tunnels and for estimating the stress failure in strong ground motion seismology due to subsurface irregularities.

Damage characterization of surface and sub-surface defects in stitch-bonded biaxial carbon/epoxy composites

The scope of this work is to study the effects of manufacturing and installation defects on mechanical performance of polymer matrix composites appearing in civil infrastructure and aerospace applications. The objective of this study is to create a link between defects detected through nondestructive testing (NDT) and the mechanical performance of the composite structures using strain mapping technique. Monotonic tensile samples of polymer matrix stitch-bonded biaxial composite laminates [90,0]s are tested. Flash Thermography, a conventional NDT technique, is used to predict detectable pre-existing surface and sub-surface irregularities and defects. Attention is drawn to the homogenized mechanical behavior and to damage initiation and propagation. Damage onset and propagation are studied using time-dependent nonlinear regression of the strain field. Effects of the manufacturing and installation irregularities on damage initiation, propagation, and failure are monitored as the structure is subjected to load or studied at the end of the loading process.

Experiments on the dynamic correction of magnetotelluric and magnetovariational data

Pathways of further development of the dynamic correction technique suggested by E. Fainberg are discussed. This technique allows the correction of magnetotelluric (MT) and magnetovariational (MV) data distorted by subsurface irregularities within a broad range of frequencies beyond the static shift interval. This paper addresses new algorithms for the dynamic correction of tensor MT and MV response functions. Moreover, experiments on the dynamic correction of MT and MV data calculated for models containing heterogeneities in sedimentary cover and infinite or half-infinite conductive crustal prism are described. Model experiments show that the dynamic correction can ensure sufficient accuracy of the input data for the reliable solution of the inverse problem of magnetotellurics.

Thermal Behavior ofTiO2-xNxNanostructured Powder

Diffusion structural analysis (DSA), based on the measurement of the release of radon previously incorporated into the samples, was used to characterize thermal behavior of N-doped titania powder prepared by heat treatment of anatase in gaseous ammonia at575∘Cand the referenceTiO2powder prepared from the ST-01 anatase titania powder (Ishihara Ltd., Japan). The results of DSA, surface area and porosity measurements by nitrogen adsorption, SEM micrographs, XPS, and XRD are presented and discussed. The results of DSA are in agreement with the results of other methods and indicated the annealing of the subsurface structure irregularities of the samples. Transport properties of the samples were determined from the mobility of radon atoms released on sample heating in air. The decrease of radon permeability in the porous titania powders in the temperature range 850–1000∘Cdue to annealing of the subsurface structure irregularities, that served as radon diffusion paths in the samples, was evaluated from the DSA results.

Boundary Element Methods in Dynamic Analysis: Part II (1986-1996)

A review of boundary element methods for the numerical solution of elastodynamic problems covering the period 1986-1996 is presented. It is a continuation of a review article on the same subject by the same author which appeared previously in Applied Mechanics Reviews (AMR 40(1) 1-23 (Jan 1987) Reprint No AMR015). Integral formulations and their advanced numerical treatment in both frequency and time domains from the direct boundary element method viewpoint are described. They cover two - and three - dimensional cases as well as the anti-plane case of linear elastodynamics under harmonic or transient disturbances. Indirect formulations, boundary methods, T-matrix methods, symmetric formulations, dual reciprocity boundary element methods and hybrid schemes combining boundary with finite elements are also described. All these boundary element methodologies are applied to: i) wave propagation analysis including wave propagation due to external loads, wave diffraction by surface or subsurface irregularities and cracks and crack propagation; ii) dynamic analysis of structures including beams, membranes, plates and shells as well as two - and three - dimensional structures; iii) soil-structure interaction including foundation analysis, piles and underground structures; iv) fluid-structure interaction including structures inside fluids or containing fluids and dam-reservoir systems; and v) the special subjects of viscoelasticity, inhomogeneity, anisotropy, poroelasticity-thermoelasticity, large deformations, contact analysis, inverse scattering and optimum design and control. Finally, areas where further research is needed are identified. There are 1333 references.

Frequency Response Characteristics for Incident P-SV Waves in Multi-Layered Irregular Strata Including Water-Saturated Layers Using Discrete Wave Number Method.

It is important to investigate wave propagation characteristics taking into account the effects of pore-water in, e.g., soft sand layers with topographical and/or subsurface irregularities. To obtain information on the spatial variation of displacements, stresses and pore-water pressures, the authors have extended the Discrete Wave Number Method proposed by Aki and Larner (1970) to the P-SV wave incident problems in multi-layered media with topographical and/or subsurface irregularities including water-saturated layers. This paper first explains the analytical method and then verifies it using numerical examples incorporating spatial variation characteristics of frequency response functions of displacements, stresses and pore-water pressures. The effects of subsurface irregularities on the frequency response are discussed. The response characteristics of an elastic model and a water-saturated model are compared. It is thus confirmed that the Discrete Wave Number Method can be efficiently used to calculate amplifications of ground motions taking into account wavetype coupling and wavenumber coupling in a multi-layered alluvial deposit with subsurface irregularities and a very permeable water-saturated layer.

基礎加振による不整形地盤の振動特性に関する数値解析 : 油圧制御起振機による強制振動試験に関する研究(4)

Scattering of harmonic waves by subsurface irregularities is studied experimentally with the detailed measurements of a surface ground motion generated by forced vibration of a reinforced concrete model footing placed on a subsurface irregular ground. Observations indicate that the variations of measured velocity amplitude are most influenced by SH wave motion among various types of propagating waves and that they are highly frequency dependent. They also indicate that the measured velocity amplitudes do not always decay monotonously with increasing the source-receiver distance and that it is the measurement points of the filling ground in the vicinity of interface between the cutting ground and filling ground that surface ground motions are significantly amplified. The variations of measured velocity amplitudes have been modeled by a two-dimensional model of an arbitrarily-shaped soil deposit excited by forced vibration of a footing and it is analyzed by the indirect boundary integral equation. It is shown that the computed amplitude variations coincide qualitatively with the observed ones.

Ground motion amplification by cylindrical valleys embedded in a layered medium

AbstractThe phenomenon of localized amplification of seismic waves due to subsurface irregularities has attracted the attention of seismologists and engineers for many years. In this paper we present a hybrid numerical method to investigate the ground motion amplification due to sedimentary basins. This method combines the integral representation and the finite element to solve the scattering problem due to an arbitrary cylindrical scatterer. A study is done on two shapes of valleys to show the effect of the angle of incidence, the incident wave type and the layering on the amplification of the surface displacement components by different valleys.

The Effect of Sub-Surface Irregularities on the Strength of Multi-Year Ice

Abstract Presented in this paper is a simple two-dimensional model to examine the effects of sub-surface irregularities on the strength of multi-year ice. The irregularities cause bending moments which can lead to surface tensile stresses. When these tensile stresses are sufficiently high for crack nucleation to occur, a very brittle fracture of the entire ice sheet will ensue. The fracture is brittle because, for the large grain sizes in the natural ice cover, the stress required for crack nucleation is greater than that necessary to propagate a crack. The theory has been examined with experimental laboratory tests on columnar ice. The importance and significance of the results are that old thick multi-year ice in winter conditions may be substantially weaker than expected, and thus it is the limited strength of the multi-year ice that may dominate design ice forces on arctic structures rather than a limited driving force.

Transient Scattering of Elastic Waves by Dipping Layers of Arbitrary Shape Part 1: Antiplane Strain Model

AbstractScattering of elastic waves by two dimensional multilayered dipping sediments of arbitrary shape embedded in an elastic half‐sapce is investigated by using a bondary method. The displancement field is evaluated throughout the elastic media for both steady state and transient incident SH waves. The unknown scattered field is expressed in terms of wave functions which satisfy the equation of motion, traction‐free boundary condition and appropariate radiation conditions. The transient response is constructed from the steady state solution by using the fast Fourier transform technique.The numerical results presented demonstrate that scattering of waves by subsurface irregularities may cause locally very large amplification of surface ground motion. The motion can be affected greatly by the scattered surface waves in the sediments. The results clearly indicate that the surface ground motion depends upon a number of parameters present in the problem, such as frequency and the angle of incidence of the incoming wave, impedance contrast between the layers and location of the observation point.

Application of a hybrid method for scattering of P, SV, and Rayleigh waves by near-surface irregularities

Abstract Application of a hybrid method to problems of diffraction of plane harmonic P , SV , and Rayleigh waves by subsurface irregularities of arbitrary shape is investigated. Special emphasis is made to irregularities in the form of dipping layers of arbitrary shape. The method presented in this paper combines the finite element method with an indirect boundary integral equation approach. The accuracy and efficiency of the method are demonstrated through several numerical examples. The numerical results presented are in excellent agreement with the ones derived by other methods. It is found that the numerical efficiency of the hybrid method is superior in general to that of boundary integral equation methods.

Effects of surface and subsurface irregularities on the amplitudes of monochromatic waves

Abstract Measurements of surface ground motion generated by forced vibration of a nine-story reinforced concrete building at a distance of 2 to 5.5 km are described. Three components of the displacement field were measured at 13 points along a line traversing an elongated canyon underlain by a shallow and dipping alluvial layer. The variations of measured displacement amplitudes have been modeled by (a) a two dimensional surface topographic feature corresponding to the average cross section of the canyon and (b) by a two-dimensional model of an alluvium valley excited by a line source. Comparison of the observed and computed amplitude variations with distance suggests that for the geometry corresponding to this experiment the effect of the dipping layer of alluvium seems to play a considerably more important role than the canyon.