Buried Structures Research Articles

Imaging the Mahout structure at the Oman desert with the aid of geophysical observations

Geophysical methods may provide crucial information for the characterization of buried impact structures. In this study, we report and comment on the results of the geophysical survey of an elliptical-shaped structure near Mahout at Oman’s central desert. Geophysical models describe the variation in the physical properties of this structure’s subsurface in terms of density, magnetic susceptibility, and electrical resistivity of the formations buried under the desert sand. For the two former physical properties, a 3D inversion scheme was utilized, while for the latter, the very-low-frequency electromagnetic (VLF-EM) method and 2D inversion were involved for the first time in a similar study. The resultant models are in good agreement for imaging a generally bowl-shaped structure buried under the desert sand with a low resistivity (<40 Ohmm), highly magnetic (magnetic susceptibility 0.03–0.08 SI), and mixed density center (2.2–3.2 g/cm3). The results of the integrated geophysical survey at Mahout enhance the information about the applicability of the specific geophysical techniques at structures buried by sandy formations with less than 1-km diameter, which, currently, mostly comes from large-scale impact craters (>100 km), and confirm that such a multi-geophysical approach can be successful for imaging similar structures.

The Effect of Protective Barriers on the Dynamic Response of Underground Structures

Engineers have dedicated considerable attention over the past ten years to studying the influences of dynamic loads caused by both intentional and unintentional events on infrastructures. As a result, determining how buried structures react to explosions and enhancing their security against blast loads have become crucial subjects in defensive engineering. To achieve this goal, constructing a protective barrier, which is known as a blast wall, in front of structures can be an effective measure. This research focused on examining the impact of a protective barrier on the response of a box-shaped tunnel located in Kobe, Japan, using a comprehensive numerical approach. The results revealed that incorporating a barrier with widths of either 1 m or 2 m resulted in a significant reduction in peak pressure. Specifically, the use of a 1 m wide barrier resulted in a 77% decrease, while a 2 m wide barrier achieved an even greater reduction of 84%. Additionally, it was observed that minimizing the distance between the barrier and the explosion point, as well as increasing the width of the barrier, resulted in reduced peak pressure throughout all sections of the tunnel.

Integration of satellite and aerial images with multichannel GPR surveys in the archaeological area of Augusta Bagiennorum for an improved description of the urban setting

The archaeological area of Augusta Bagiennorum (NW Italy) is a well-known archaeological site, extensively investigated since the end of the 19th century. Previous archaeological studies in the area allowed a preliminary definition of the urban setting through several direct soundings. However, the current knowledge of the site needs to be more complete due to the limited extension of previous archaeological surveys. To obtain a more complete description of the urban setting, we analysed aerial and satellite images and multichannel Ground Penetrating Radar (GPR) surveys, which are two remote-sensing technologies often used in this field. Aerial images showed vegetation cropmark patterns in different areas, depending on the time of the day, year, and camera acquisition setup. The GPR surveys locally confirmed the presence of buried structures in correspondence with the cropmarks, and provided a more detailed view of the underground features. The GPR was also helpful in adding Ground Control Points for georeferencing hot-air balloon images. The combined view of aerial and GPR images allowed us to confirm the overall extent of the archaeological area, as reported in past archaeological reports. However, some of the observed structures were located outside the previously known extent of the town. The orientation of some suggests that the streets of Augusta Bagiennorum are not always arranged in a perpendicular pattern, typical of the Roman orthogonal town planning. The adopted methodological approach could be a valuable tool in similar case studies, since it provides multiscale information composed of both overall views and detailed images.

3‐D Subsurface Geophysical Modeling of the Charity Shoal Structure: A Probable Late Proterozoic‐Early Paleozoic Simple Impact Structure in Eastern Lake Ontario

AbstractThe Charity Shoal structure is a circular, ∼1.2‐km‐diameter, bedrock‐rimmed shoal in eastern Lake Ontario with a ∼20‐m‐deep central basin. The structure has been proposed as a possible Middle Ordovician impact crater or volcanic intrusion. We conducted marine seismic and magnetic surveys (9‐km2) and 3‐D geophysical modeling to better resolve the Charity Shoal subsurface geology and possible origins. Three models were evaluated: (a) a buried (>450 m) impact structure in Mesoproterozoic basement, (b) a maar‐diatreme, (c) a cylindrical, zoned volcanic plug. Seismic profiles and multi‐beam bathymetry revealed >30 m of Quaternary sediments overlying Middle Ordovician (Trenton Group) carbonate bedrock and complex, 3‐dimensional folding and faulting of the structure rim. Magnetic surveys recorded an annular magnetic high (>600 nT) over the structure rim and a central magnetic low (∼500–600 nT) coincident with a ∼−1.7 mGal Bouguer gravity anomaly. The continuity of Trenton Group strata in seismic profiles rules out a previously proposed Mesozoic maar‐diatreme intruded into Paleozoic strata. The zoned volcanic plug model reproduced the annular magnetic anomaly but was incompatible with Bouguer gravity profiles. The magnetic anomaly was best reproduced by a simple impact structure seated in Mesoproterozoic basement at 450–500 m depth with a rim‐to‐rim diameter of ∼1.2 km and rim height of ∼10–20 m. A 100‐m wide and 50‐m‐deep channel in the Mesoproterozoic basement may record fluvial dissection of the southwestern rim. A buried (>450 m), simple impact crater is most compatible with all available geophysical data at Charity Shoal.

Seismic Response Characteristics of a Utility Tunnel Crossing a River Considering Hydrodynamic Pressure Effects

As a long lifeline system of buried structures, the utility tunnel (UT) is vulnerable to earthquake invasion. For utility tunnels with inverted siphon arrangements crossing rivers, the seismic response is more complex due to the basin effect of acceleration in the topography and the influence of fluctuating hydrodynamic pressure, but there is currently a gap in targeted seismic response analyses and references. Based on a UT project in Haikou, this paper studied seismic responses of a cast-in-place UT considering the coupled model of water–soil–tunnel structure on ABAQUS software. Herein, the dynamic fluctuation of hydrodynamic pressure is simulated using an acoustic–solid interaction model. A viscoelastic artificial boundary was used to simulate the soil boundary effect, and seismic loads were equivalent to nodal forces. Considering seismic invading direction and varying water elevation, this paper investigates the dynamic response characteristics and damage mechanisms of river-crossing utility tunnels. This study shows that the basin effect causes the soil acceleration around the UT to show variability in different sections, and the amplification factor of the peak acceleration at the central location is almost doubled. The damage and dynamic water pressure of the UT are intensified under bidirectional seismic excitation, and the damage location is concentrated at the junction of the horizontal section and the vertical section. Bending moments and axial forces are the main mechanical behaviors along the axial direction. Changes in river levels have a certain positive effect on the UT peak MISES, DAMAGEC, and SDEG, and it exhibits a certain degree of energy dissipation and seismic damping effect. For the aseismic design of cross-river cast-in-place utility tunnels, bidirectional seismic calculations should be performed, and the influence of river hydrodynamic pressure should not be neglected.

Hidden Archaeological Remains in Heterogeneous Vegetation: A Crop Marks Study in Fortified Settlements of Northwestern Iberian Peninsula

This study evaluates the effectiveness of multispectral imaging via Unmanned Aerial Systems (UAS), in combination with advanced digital image processing techniques, for the detection and mapping of archaeological sites within diverse landscapes. The research focuses on six case studies located in the northwest of the Iberian Peninsula, a region marked by complex vegetation patterns and varying topography. The primary objective is to assess the potential of these non-invasive remote sensing techniques in identifying crop marks associated with buried structures from ancient, fortified settlements. By means of Principal Component Analysis (PCA) and vegetation indices, the study aims to pinpoint areas of interest that may indicate the presence of archaeological features, while effectively distinguishing them from modern disturbances or natural terrain variations. The research encountered several challenges, including seasonal variations in crop conditions and recent land-use changes. The methodology successfully identified distinct archaeological features. In some instances, natural vegetation variability, typically seen as an obstacle, enhanced the visibility of crop marks, aiding in the detection of underlying structures. These results offer a cost-effective and scalable option for preliminary archaeological surveys, particularly in refining survey methodologies and guiding future excavation efforts aimed at uncovering and preserving ancient, fortified settlements in the region.

Calculation of seasonal soil freezing depth by engineering and numerical methods

Introduction. Provided by severe climatic conditions in the Russian Federation, seasonal soil freezing and emerging cryogenic processes cause frost heaving that negatively affect foundations and buried structures. As the magnitude of frost heaving forces significantly depends on the soil freezing depth, the assessment of soil freezing depth becomes very relevant.Aim. Calculation and estimation of the depth of seasonal soil freezing by engineering and numerical methods.Materials and methods. Calculations of soil freezing depth were performed for two sites composed of sandy loam and loam. Engineering calculations were performed according to four methods set forth in the normative documents, namely Recommendations on Thermal Engineering Calculations and Pipeline Laying in Areas with Deep Seasonal Soil Freezing, Handbook on Construction on Permafrost Soils, Recommendations on Accounting and Prevention of Deformations and Forces of Soil Frost Heaving, Recommendations on Forecasting the Thermal State of Permafrost Soils. Numerical calculations were performed in the Frost 3D and Borey 3D software systems. The experimental sites are located in the Tymovsky district of Sakhalin Oblast, where the Sakhalin-2 pipeline was laid.Results. The engineering methods for calculating the required depth of soil freezing give overestimated results when using a large range of climatic and soil parameters: air temperature, snow cover height and density, wind speed, convective heat transfer coefficients, total solar radiation, surface albedo, maximum elasticity of water vapor, etc. At the same time, the use of Stephan’s formula with a limited set of input parameters gives results close in values. The numerical methods showed close results among themselves, though 32–47 % more than the results of engineering calculations at bare ground surface.Conclusions. Research on the dynamics of soil freezing depth in field conditions is suggested to be carried out and compared with the results of engineering and numerical calculations to improve these methods.

Terahertz near-field imaging of buried structures.

We report a characterization of the spatial resolution of terahertz (THz) apertureless near-field imaging of metal lines deeply buried beneath a silicon dioxide layer. We find a good resolution for edge contrast, even in the case where the capping layer is considerably thicker than the tip radius. We find that contrast and resolution depend on demodulation frequency, thickness of the capping layer, and radius of the tip. Furthermore, we observe a distinct dependence of the contrast on the direction of the incoming radiation, in both experiments and simulations. Characterization of buried features can be a valuable tool in non-contact failure analysis of semiconductor devices.

LOADS ON SUBMERGED WALLS OF PROTECTIVE STRUCTURES

The intensification of military operations on the territory of Ukraine, which are accompanied by missile attacks and bombing of territories, requires the use of reliable protective structures. Modern codes require the provision of each new building with storage facilities that guarantee the safety of life and health of citizens, so the correct determination of all loads on the structural elements of protective structures is an urgent issue. Taking into acoount the fact that the previous codes were somewhat outdated and had limited access for a long time, a significant event was the adoption in 2023 of new codes for the design of protective structures of civil defence. The main requirements and recommendations of SBC B.2.2-5:20023 were taken into account when conducting research on determining the loads on buried walls of bomb shelters. Such structures, as we know, perceive a constant load from the lateral pressure of the soil, which during an explosion is supplemented by an episodic load from the action of an air wave. Modern specialized literature contains rather limited information on scientific research and development in the field of design of protective structures. An actual issue is also the study of the influence of determining factors on the intensity of the load on the walls of buried protective structures and the possibility of its adjustment in order to reduce it. Taking into account the nature of the distribution of loads on the underground walls of bomb shelters, a dependence was obtained to determine the resulting active pressure and quasi-static load caused by the action of an air wave. The pressures from the soil and the blast wave at different orientations of the contact wall and for different types of soil environment were studied. The loads in contact of a smooth and rough wall with sandy, sandy and loamy soils with different indicators of physical and mechanical characteristics were considered. The obtained results indicate a significant influence of the geometric parameters of the wall and the features of the contact soil on the resulting pressure, which can vary depending on the studied factors by 10-20%, which indicates the possibility of reducing the load on protective structures, operating with the considered indicators.

Laboratory characterisation of sand-tyre mix as bedding material for buried structures

Bedding material directly interacts with buried structures and supports to sustain external loadings such as traffic and overburden soil pressure. Therefore, soil-structure interaction plays an essential role in the stability and safety of buried structures. In particular focusing on underground pipelines, the annual rate of failures in Australia is around 19 % per 100 km of pipeline and can cost millions of Australian dollars in maintenance. Of these annual failures, ground vibrations from heavy traffic and construction activities are a major cause. In order to reduce such effects of ground vibrations on buried structures, this paper presents the possible application of sand-rubber mixes as a bedding material, where rubber is sourced from recycled tyres. The performance of sand-tyre mixes with regard to the potential for vibration reduction is assessed through this experimental study which comprises of particle size distribution, standard proctor compaction, permeability test, direct shear test, California Bearing Ratio and Repeated Load Test. From these tests, it was found that sand mixed with up to 20 % recycled tyre rubber was the most suitable mix for use as a bedding material.

Study on Ground Motion Amplification in Upper Arch Bridge Due to “W”-Type Deep Canyon Using Boundary-Integral and Peak Frequency Shift Methods

The study of the dynamic response characteristics of “W”-type deep canyon terrain to double-span concrete arch bridges under earthquake action holds great practical significance. In this research, a bridge in Sichuan Province is taken as the object of study. The boundary-integral equation method and peak frequency shift method are combined to apply an embedded linear time–history analysis algorithm to the finite element spatial dynamic calculation model of the entire bridge, resulting in an improved model. By comparing these two methods with model test results, the seismic response characteristics of the middle part of a “W” concrete arch bridge under different foundation depths and seismic intensities are examined. The boundary integral equation method was utilized to calculate ground motion response at any point on site, revealing a significant amplifying effect of increased seismic wave intensity on acceleration response at the top of the arch bridge. When input seismic wave intensity increased from 0.1 g to 0.3 g, maximum acceleration at buried depths of 3 m and 8 m in the middle of the arch bridge foundation increased by 102.63% and 79.16%, respectively, indicating that shallow buried depth structures are more sensitive to seismic wave intensity. Furthermore, using peak frequency shift rules for analyzing seismic wave propagation characteristics in “W”-type deep canyon topography confirms the sensitivity of shallow buried depth structures to seismic wave intensity and reveals the mechanism through which topography influences seismic wave propagation. This study provides a helpful method for understanding the propagation law and energy distribution characteristics of seismic waves in complex terrain. It was observed that the displacement at the top of the arch bridge increased significantly with an increase in seismic intensity. When subjected to 0.1 g, 0.2 g, and 0.3 g EI-Centro seismic waves, the maximum displacement at the top of the arch bridge model with a foundation buried depth of 3 m was 8 mm, 32 mm, and 142 mm, respectively. For arch bridge models with an 8-m foundation buried depth, these displacements were measured at 6.2 mm, 21 mm, and 68 mm, respectively. The results from model tests verified that increasing the depth of foundation burial effectively reduces the displacement at the top of the structure. Furthermore, by combining a boundary-integral equation method and peak-frequency shift method, this study accurately predicted significant influences on W-shaped double deep canyon topography from seismic response, and successfully captured stress concentration and seismic wave amplification/focusing effects on arch foot structures. The calculated results from both methods align well with model test data which confirm their effectiveness and complementarity when analyzing seismic responses under complex terrain conditions for bridge structures.

Novel Fast-X-Ray Reflectivity Setup for Studying Electrochemical Interfaces

A fundamental understanding of atomic scale processes occurring at electrochemical interfaces is crucial for advancing the development of energy-related electrochemical systems such as ion batteries or fuel cells. For this purpose, operando experiments are imperative. X-ray reflectivity (XRR) is a non-destructive technique that enables operando analysis of buried structures with atomic resolution [1,2]. However, the time-resolution of typical XRR setups of minutes per XRR scan is limited by diffractometer motor motion and detector read-out times; this resolution is in many cases too slow to observe interfacial electrochemical phenomena [1,2].To overcome these limitations, we developed a novel fast-XRR setup, which employs a fast quasi-continuous rotation stage in combination with a stationary, high frame rate area detector. With this setup, the sample can be rotated with a frequency of up to 10 Hz, yielding sub-second time resolution for an individual XRR scan. In contrast to complementary fast-XRR setups [3,4], the presented setup can easily be combined with complex sample environments, as typically required for the investigation of electrochemical interfaces.We present first fast-XRR results obtained at PETRA III beamline P08 at DESY using 18 keV and a Dectris Eiger1M detector. We reached a time resolution below one second for an incident angular range between 0° – 6° (≙ 0 – 2 Å-1, i.e., covering the Fresnel XRR range). We measured several multilayer samples (e.g., 2 nm Ti / 20 nm Au coating on a Si substrate) and benchmarked the results to “standard” XRR measurements, where the measurements took several minutes. We find good agreement and conclude, that our novel setup provides significant XRR data within less than one second, demonstrating its usability for operando XRR measurements.Literature:[1] C. Cao, H.-G. Steinrück, Encyclopedia of Solid-Liquid Interfaces, 391–416, Elsevier, 2024.[2] C. Cao, H.-G. Steinrück et al., Nano Letters, 16, 12, 7394–7401, 2016.[3] M. Lippmann et al. Review of Scientific Instruments, 87, 113904, 2016.[4] H. Jorres et al., Applied Physics Letters, 114, 081904, 2019.

Correlative Microscopy Analysis for Battery Materials

Lithium batteries (LB) are in high demand for a diverse range of applications, such as automotive industry, consumer electronics, wearable and medical devices, grid storage, etc. Each application demands a specific set of performance advantages, such as high capacity and/or energy density, long cycle life, superior electrochemical stability. Therefore, there is no one-size-fits-all for a LB chemistry and its form factor. Battery performance advantages rely on optimization of the battery components, including active materials, electrolyte, separator, binder system, and current collectors. For meaningful device optimization, electrochemical battery testing needs to be combined with a deep understanding of the material and device microstructure. Physical and chemical characterization on the material- and electrode-level is needed to establish root-cause relationships with battery performance. Properties of the interfaces between layers of the battery components often define the device characteristics. Critical information is usually buried beneath the surface of a material specimen or encapsulated in a closed-form device. Microstructural defect identification in the battery needs to be followed by a targeted defect study. Different battery form factors and chemistries make it hard to streamline root-cause analysis.Recently, a commercial focused-ion beam scanning electron microscope was developed with an integrated fs-laser mill attached to the load lock of the microscope, opening the door to new and more powerful analysis approaches in energy materials research. Applications include rapid access to deeply buried structures for high resolution imaging and analytics, large area cross-section preparation, and massive material ablation for sample preparation of structures; e.g. FIB-SEM tomography, TEM, APT, or X-ray nanoCT. Additionally, each of these methods may be correlatively guided by prior imaging, with techniques like 3D X-ray microscopy (XRM), to enable targeted analysis and preparation. The non-destructive nature of 3D XRM makes it an ideal tool for microstructural defect identification in LB. Laser mill allows researchers to combine non-destructive X-ray defect identification with electron microscopy methods for targeted defect characterization. This approach can be used for various battery types and form factors.By combining the laser mill with 3D X-ray microscopy, this platform enables comprehensive analysis of energy materials at the nanoscale. We illustrate these concepts with application examples, and use cases demonstrating the utility of the approach.

Gamma-Irradiation-Induced Electrical Characteristic Variations in MoS2 Field-Effect Transistors with Buried Local Back-Gate Structure.

The impact of radiation on MoS2-based devices is an important factor in the utilization of two-dimensional semiconductor-based technology in radiation-sensitive environments. In this study, the effects of gamma irradiation on the electrical variations in MoS2 field-effect transistors with buried local back-gate structures were investigated, and their related effects on Al2O3 gate dielectrics and MoS2/Al2O3 interfaces were also analyzed. The transfer and output characteristics were analyzed before and after irradiation. The current levels decreased by 15.7% under an exposure of 3 kGy. Additionally, positive shifts in the threshold voltages of 0.50, 0.99, and 1.15 V were observed under irradiations of 1, 2, and 3 kGy, respectively, compared to the non-irradiated devices. This behavior is attributable to the comprehensive effects of hole accumulation in the Al2O3 dielectric interface near the MoS2 side and the formation of electron trapping sites at the interface, which increased the electron tunneling at the MoS2 channel/dielectric interface.

Imaging buried anticlines in the Po Plain, northern Italy, based on HVSR frequency and amplitude analyses

The use of the HVSR (Horizontal-to-Vertical Spectral Ratio) method on single-station microtremor measurements is well documented in small alluvial plains for bedrock mapping. In large sedimentary basins, like the Po Plain, its application is still debated. To shed some light on this issue, we investigated two seismogenic structures buried below the Po Plain Quaternary deposits: the Mirandola and Casaglia anticlines. We acquired and analysed a dense distribution of HVSR data covering the two areas and mapped the frequency and amplitude values of the observed resonance peaks. The top of both anticlines is highlighted by high amplitude peaks picturing E-W elongated sectors with high-impedance contrast, where Quaternary deposits are reduced in thickness to about 60–130 m and directly overlay the Pliocene (Mirandola) and Miocene (Casaglia) marine units. In Mirandola, the high-amplitude peaks also correspond to higher resonance frequencies, while in Casaglia, the distribution of resonance frequencies is relatively uniform suggesting a flatter crestal region and the lateral continuity of the resonance surface. The combination of peak frequency and amplitude information on a dense grid of measurement points is thus confirmed to be useful for identifying and mapping buried geological structures such as structural highs. Further modelling is being carried out to estimate the depth of the surface responsible for the observed resonances, through calibration with borehole information.Graphical

Failure assessment of deteriorated steel light poles

Steel poles are extensively used as street light posts and various other applications within the power distribution network. For partially buried pole, the effect of corrosion below and at the ground level significantly controls the overall load capacity. In this study, number of in-service steel pole specimens extracted from field were assessed for the corrosion damage. The level of corrosion was estimated by remaining wall thickness measured using ultrasonic testing and the surface corrosion was estimated using 3D laser scanning to adopt an appropriate existing model for buried steel structures. A relationship between maximum and average corrosion pit depth and loss of embedment depth was then developed. Finally, the corrosion parameters, combined with uncertainty in loading and soil properties were employed to perform time-dependent reliability assessment for steel light poles which can be used to assist the asset maintenance team in planning the replacement or strengthening works for steel pole.

Detection of subsurface archaeological features using the GPR method with a 250 MHz antenna in Borsippa site, Babylon, Iraq

The GPR method was used to determine the depth and extent of the subsurface archaeological features at the archaeological site of Borsippa. The extensions of the archaeological walls were identified through the creation of three-dimensional maps. The LMX200 device conducted the survey using a 250 MHZ antenna. sixty parallel profiles were collected and processed by GPR Slice software. Several reflections of possible archaeological walls buried at different depths and extensions of 2, 4, 6, 11, and 20 m were identified. The 250 MHz antenna gave clear reflections of the archaeological walls, with a penetration depth of up to 4 meters. The time slice map identified a buried archaeological structure at 1–1.1 m deep, consisting of many rooms with thick walls up to 2-3 m.

Multichannel GPR and multi-depth electromagnetic surveys for the study of Villa Eucheria and Aquinum at Castrocielo (Frosinone, Central Italy)

The municipality of Castrocielo (Frosinone, Italy) is a historically significant center which includes several centers of great archaeological importance, including part of the archaeological site of the ancient Roman city of Aquinum. In this work, we show the results of geophysical surveys performed in two different areas: the first area is close to the Monacato of Santa Maria al Palazzolo, built on the foundation slab of a Roman villa dating back to the 1st-2nd century BCE; the second area is close to the charging station Casilina Est, where several burials, dating back to different periods from 4th century BCE to 4th century CE, were found. The aims of geophysical investigations is to identify structures linked to the ancient Roman villa (Villa Eucheria) in Area 1, and to identify the tombs of the necropolis in Area 2. The two areas were investigated in two different days, on 27th and 28 th March 2023 respectively, through a multi-channel georadar system (GPR). In the second area, an electro-magnetometric survey was also performed. This choise is to address the heavy rain developed during the night before the acquisition. Infact the GPR survey performed during the second day of the geophysical campaign did not provide good results.Based on the geophysical results, the archaeological excavation in Area 1 confirmed the detected anomalies, documenting a section of wall and other structures and elements brought to light over a length of approximately 9 m. The results obtained in Area 2 confirmed the cropmarks visible in the aerial photo, highlighting the traces of buried structures.

Plane SV-waves scattering by seawater convex surface topography and underlying lined tunnel in a saturated half-space

Analytical solutions of boundary-valued problems for aboveground topography and underground buried structures, especially for sites with overlying seawater, have always been challenging. Based on the region decomposition technique (RDT) and Hankel integral transform method (HITM), SV-waves scattering by the convex circular topography with seawater and underlying tunnel in a saturated half-space is solved. The primary problem is tackling additional scattered waves introduced by the water–soil interface and convex topography, while ensuring boundary conditions are all met. To this end, scattering wave potential functions in cylindrical coordinates are first transformed into the Hankel integral form in Cartesian coordinates. This greatly facilitates the straightforward application of free boundary conditions at the soil–seawater flat interface, rather than making a large circular arc approximate assumption, which, in turn, avoids the resultant accumulating errors. Secondly, scattering problem to be solved is mathematically and analytically formulated as solving a 5 × 5 linear equation system comprised of wave functions inside the convex topography and lining tunnel while satisfying all physical continuous boundary conditions. This is the main innovation and resulting consequence from the theoretical derivation process. Finally, validation of numerical examples between this paper, existing studies and theoretical analysis further demonstrates the reliability and general adaptability of solutions. Parametric studies of the incident SV waves are conducted to investigate the spatially varying seismic response. The effects of SV-waves incident angles and frequencies, tunnel burial depth, tunnel lining thickness, saturated soil porosity, and seawater depth are investigated and analyzed in detail. This study provides a feasible scheme of investigating the dynamic response of complex submarine sites, which is of great significance for both theoretical value and engineering purposes.

Evolution of Long-Term Load Reduction Using Borrowed Soil

AbstractThe effectiveness of load-reduction techniques often diminishes due to creep behavior observed in geomaterials, as loess backfill is used, the load reduction rate of high-filled cut-and-cover tunnels (HFCCTs) after creep will decrease by 10.83%, posing a threat to the long-term stability of deeply buried structures such as HFCCTs. Therefore, a geotechnical solution is crucial to ensuring sustained effectiveness in load-reduction strategies over time. This study utilizes a finite-difference method to examine three promising measures for mitigating creep effects. Our analysis focuses on the time-dependent changes in earth pressure atop the cut-and-cover tunnel (CCT) and the internal distribution of cross-sectional forces, including bending moment, shear force, axial force, and displacement. Results indicate that the creep behavior of load-reduction materials significantly influences the internal force distribution. Furthermore, sustained load reduction is achieved when utilizing low-creep materials like dry sandy gravel as backfill soil, which needs to be borrowed from other sites. Additionally, integrating concrete wedges with load-reduction techniques facilitates a more uniform stress distribution atop CCTs.