The quest for clean, renewable energy resources has given a global rise in offshore wind turbine (OWT) construction. As OWTs are more exposed to harsh environmental conditions, the dynamic behavior of OWTs with jacket support structures under critical loading scenarios is crucial yet least understood, which becomes more convoluted with the consideration of soil-structure interaction (SSI) effects. In addition, the seismic characteristics of such systems heavily depend on the excitation characteristics like frequency content, a feature that is still ambiguous. This research aims to examine the influence of seismic frequency contents on the dynamic characteristics and damage modes of jacket-supported OWT systems including SSI effects. The numerical model is established and validated based on a previous study, which ensures the accuracy of the numerical modeling framework. Upon validation, extensive numerical analyses are performed under earthquakes with varying frequency contents. Results reveal the relationship among the ground motion frequency, SSI, and the dynamic and damage behavior of jacket-supported OWTs, offering important insights for the improved seismic design and analysis of jacket-supported OWTs.

The underestimated risk of contact erosion failure in railway substructures poses a significant threat to railway safety, particularly at the interface between the ballast/subballast and subgrade. The larger constriction size at this interface exacerbates the potential for long-term erosion, necessitating attention to safeguard railway integrity. This study introduces a novel laboratory erosion testing apparatus to evaluate contact erosion at the subballast-subgrade interface under cyclic loading. Subgrade soils with varying fines contents are tested, and the effect of pressure head on erosion is investigated in detail. The results indicate that sandy soil with higher internal stability exhibits a higher critical pressure head for contact erosion. Cyclic loading induces oscillations in pore water pressure within the subballast layer, with higher pressure heads leading to larger amplitudes. Excess pore water pressure is generated in the sandy soil layer during cyclic loading and gradually dissipates over time. Fine eroded particles migrate into the subballast layer, forming mud, while coarse eroded particles accumulate at the base, creating low-permeability interlayers. Notably, the geometric conditions alone may not guarantee effective prevention of contact erosion in railway substructures. The hydraulic conditions for contact erosion are more easily achieved under cyclic loading compared to static loading. These distinctive features of contact erosion in railway substructures, different from those observed in hydraulic structures, provide some insights for the development of remediation strategies and improvements in railway substructure design.

This study investigates the mechanical enhancement of sandy soils through cement stabilization modified with Consoil, targeting improved pavement substructure performance. Unconfined compressive strength (UCS) tests were conducted on samples with varying cement contents (3%, 6%, 9%), Consoil dosages (0%, 5%, 10%, 15%, 20% by cement weight), and curing periods (3, 7, 28, 90 days). Field Emission Scanning Electron Microscopy and X-Ray Diffraction analyses complemented mechanical testing to understand strengthening mechanisms. Results demonstrated that 15% Consoil consistently optimized strength development across all cement contents, with 9% cement and 15% Consoil achieving peak 90-day UCS of 17.74 MPa, representing a 67% increase over control samples. Microstructural analysis revealed progressive matrix refinement with increasing Consoil content, while XRD indicated enhanced pozzolanic activity through calcium hydroxide consumption. The study introduces Consoil as an effective stabilization additive, establishing optimal dosage rates and demonstrating significant strength improvements through synergistic cement-Consoil interactions. The findings provide new insights into strength enhancement mechanisms in Consoil-modified cement-stabilized soils, offering practical guidelines for designing high-performance pavement substructures. The research contributes to sustainable construction practices by optimizing cement usage through Consoil incorporation.

The structural soundness of a conventional track is often assessed by a single parameter called track modulus. Track modulus is a measure of the vertical deflection of the track's components beneath the rail. However, defining the track substructure's condition based only on track modulus can be misleading, as combinations of different ballast and subgrade conditions might yield the same track modulus measurement. For railroaders to be able to make an informed decision on the right maintenance strategy when a low track modulus is present, identification of the defective component between ballast or soil is critical. The railroad industry, therefore, needs an inspection technique that independently highlights the condition of the ballast and the subgrade. Addressing this challenge, our research has devised a system that helps identify the ballast and subgrade condition without disrupting normal train operations. The proposed system is a significant advancement over conventionally employed inspection methods. This new system, called the Smartgrid, uses sensors and strain gauges embedded in a geogrid sheet placed in the ballast-subgrade interface to record data on the stress-strain relationship at this plane. This data is then analyzed using supervised machine-learning techniques such as Logistic Regression and the Support Vector Machine. The ultimate objective of the proposed Smartgrid system is to arm the railroader with the right information on the condition of the two major components of the substructure and facilitate efficient maintenance. The Smartgrid, which has been tested under various conditions, promises a substantial improvement in inspection of the rail substructure.

The jacket substructure is a critical component of the offshore wind turbine (OWT) that is the interface between the transition piece at the top and the grouted connection. This paper presents a comprehensive study on the optimization of a jacket substructure to achieve greater cost efficiency while maintain acceptable structural performance. A fast parametric finite element modelling (FEM) approach for jacket substructures was firstly proposed. The generated models took into account realistic loading conditions, including self-weight, wind load and sectiondependent wave load, and soil-pile interaction. Parametric studies were conducted afterwards to investigate the trends of the mass and response of the jacket substructure with respect to the variation of geometric and sectional parameters. Optimizations of the jacket substructure were carried out using parametric optimization and numerical genetic algorithm (GA) optimization under three different optimization strategies corresponding to three groups of objective and constraint functions. The trends obtained by parametric analysis were used to guide the parameter selection in parametric optimization, while a rank-based mutation GA was established with the proposed efficient FEM embedded in as the solver to the optimization objective and constraint functions. Parametric optimization gained its advantage in computational efficiency, and the mass reduction were 6.2%, 10% and 14.8% for the three strategies respectively. GA optimization was more aggressive as the mass reductions were 16.8%, 22.3% and 34.3% for the three strategies, but was relatively more computational intense. The two proposed optimization methods and the three optimization strategies are both expected to be applied in practical engineering design of OWT jacket substructure with good optimization output and high computational efficiency.

Evaluating the bearing capacity of bridge substructures is very important for bridge maintenance and management. However, existing studies that rely on static load tests (SLTs) or transient response methods (TRMs) have limitations that are difficult to apply to operational bridges or require knowledge of the relationship between static stiffness and dynamic stiffness. This paper proposed a novel Bayesian system identification framework for rapid assessment of the vertical condition of bridge substructures. In the first step, a simplified analytical model was formulated to interpret the vertical dynamics of the soil-foundation-bridge pier system with lumped parameters. A Bayesian joint-input-parameter-state procedure was introduced to simultaneously identify unknown input and structural parameters, including stiffness and damping coefficients. After that, the proposed framework was numerically demonstrated, and the influence of extensive random initial errors was methodically examined. Finally, a full-scale in situ test involving TRM and SLT was conducted to further test the engineering compatibility of the methodology. The achieved results indicated that the simultaneous identification framework is effective and robust for estimating the vertical stiffness of piers and foundations, structural states, and unknown excitation using output-only measurements. The proposed framework can be effectively employed to assess the vertical condition of bridge substructures during construction or operation, particularly for rapid damage assessment of bridge structures after natural disasters.

In recent years, strong earthquakes have caused a lot of damage around the world. In order to prevent such damage, proper evaluation of the seismic performance of buildings is absolutely necessary. However, the current analysis procedure in seismic design assumes fixed boundary conditions for the foundation and neglects the influence of the substructure on the superstructure. Previous studies have shown that the type of foundation affects structural responses during earthquakes. However, most of these studies have focused on single-degree-of-freedom (SDOF) structures and have not considered variations in response according to different substructure types. This study aims to investigate the effects of different substructures on ground motion and corresponding responses of the superstructure. Centrifugal simulations were conducted on a multi-degree-of-freedom (MDOF) superstructure, including a Half-embedded with Pile foundation, a fixed deep basement, and a Shallow foundation. The experimental results indicate that in the case of a half-substructure with a pile foundation, there was no significant difference between free field motion and foundation motion due to the pile foundation. However, in the case of a fixed deep basement, the embedment effect was most pronounced, especially in the short period range of 0.1 s to 0.5 s in the response spectrum. This resulted in a notable reduction in the spectrum. The analysis of the response spectra of foundation motion and free field motion revealed that the reduction effect was absent in the half-embedded with a pile foundation, but it was prominent in the fixed deep basement. Notably, the ratio of response spectrum increased in the fundamental period of the substructure. In the case of a shallow foundation, it was observed that foundation motion experienced larger amplification compared to free field motion. Shallow foundations have a relatively low stiffness of the substructure and are influenced by the inertial forces of the superstructure. Additionally, this tendency is believed to be more prominent due to the imperfectly fixed boundary conditions of shallow foundations to the ground. However, apart from the increase in foundation motion, the response of the superstructure was not proportional to it. These results contribute to a better understanding of the changes in seismic load and the response of multi-degree-of-freedom superstructures according to the type of substructure. The seismic design of the superstructure is safer and more reasonable when considering the effects of the type of substructure.

Climate change might increase the frequency of events such as heat waves, freeze-thaw cycles (FTC), and flooding, and more specifically in permafrost rich regions. These climate hazards are expected to have an impact on railway track performance. There is little publicly available data on their quantitative impacts on railway operations. Such quantitative data is essential for determining when, where, and to what extent climate adaptation measures are needed. Freeze and thaw cycle results in frost heave and thaw softening in track foundation (substructure). Both frost heave and thaw softening may lead to unsafe operating conditions especially for rail transit and passenger rail systems as their high operating speed makes them much less tolerant to deviations in track geometry parameters. In order to investigate the effects of a freeze-thaw cycles on an active railway, a structural and geotechnical monitoring system was designed and installed on a of VIA's track in Ontario. The instruments measure various track parameters such as pore water pressure, heave, and deformation at different depth within track foundation, track temperature, strain in the rail, and track surface deformation during freeze-thaw cycles. The data logging system relays static data and high speed data that are triggered by train passages. We show that the selection of instruments and design of the data logging system provide relevant geotechnical data in a manner that could be applied to northern regions and introduce recommendations for future installations. Moreover, we discuss the installation methods appropriate for cold climates because some instruments are temperature-sensitive. Since such systems typically need to be self-sufficient special considerations have to be taken to account for the relatively high power requirements of dynamic monitoring. The suggested system is shown to be useful for track monitoring projects in permafrost-rich regions where freeze-thaw cycles are a concern.