Soil-structure Interaction Research Articles

Fatigue analysis of offshore wind turbines with soil-structure interaction and various pile types

Monopile offshore wind turbines (OWTs) are susceptible to fatigue damage, and time domain fatigue analysis is time-consuming and unsuitable for simulating various loading conditions. In this study, frequency domain fatigue analysis of OWTs with soil-structure interaction (SSI) and different monopile designs (the conventional monopile, monopiles with an extension, a wheel, and four spoiler ribs) is conducted. First, detailed 3D finite element models of OWTs are developed. The tower, monopile, and soil are modelled using solid elements, and SSI is accounted for using the Mohr-Coulomb failure criterion and surface-to-surface contact. Next, the power spectral densities of wind and wave loads on the tower and monopile are derived. Subsequently, the fatigue damages of the OWTs are evaluated under individual and combined wind and wave loads. The results show that damage increases with wave height, peaking at the rated wind speed and wave frequency close to the first frequency of the OWTs. Wind-induced damage is significantly greater than wave-induced damage, and the combined wind and wave loads produce more damage than the sum of the individual loads. Additionally, alternative monopile designs, particularly the monopile with a wheel, can reduce fatigue damage, though stress concentration effects on the wheel and ribs require careful consideration.

Influence of Foundation–Soil–Foundation Interaction on the Dynamic Response of Offshore Wind Turbine Jackets Founded on Buckets

This study investigates the impact of soil–structure interaction (SSI) and foundation–soil–foundation interaction (FSFI) on the dynamic behaviour of jacket substructures founded on buckets for offshore wind turbines. A parametric analysis was conducted, focusing on critical load cases for conservative foundation design. Different load configurations were examined: collinear wind and wave (fluid–structure interaction) loads, along with misaligned configurations at 45° and 90°, to assess the impact of different loading directions. The dynamic response was evaluated through key structural parameters, including axial forces, shear forces, bending moments, and stresses on the jacket. Simulations employed the National Renewable Energy Laboratory (NREL) 5MW offshore wind turbine mounted on the OC4 project jacket founded on suction buckets. An additional optimised jacket design was also studied for comparison. An OpenFAST model incorporating SSI and FSFI considering a homogeneous soil profile was employed for the dynamic analysis. The results highlight the significant role of the FSFI on the dynamic behaviour of multi-supported jacket substructure, affecting the natural frequency, acceleration responses, and internal forces.

Case study of adjacent integral bridges supported on continuous secant piled walls

Integral bridges are often the preferred way of construction for short and medium span bridges in the UK. However, the behaviour of integral bridges is influenced by complex soil-structure interaction behaviour that may be cumbersome to predict and analyse when dealing with unusual structural arrangements. This paper presents a case study for the design of two single span bridges carrying a roundabout over a dual carriageway, supported on continuous secant piled walls. One of the bridges is fully integral while the adjacent structure is articulated at one end due to its skew. An alternative detail for the articulated end is proposed, to eliminate soil pressures and settlements at the back of the abutments as well as reduce the risk of water ingress to the bearings. The complex nature of the structural arrangement presented analytical challenges, that were solved by developing an advanced modelling approach, exploring two proposals. The first is to evaluate the geotechnical model for a range of imposed top of abutment displacements from the onset. The second, using unique non-linear springs and derived P-Y curves describes the more realistic variable nature of soil-structure interaction over the length of the walls leading to reduced soil pressures enhancing design feasibility.

An accurate and ready-to-use approach for the estimation of impedance functions of regular pile groups for offshore wind turbine foundations. Vertical and rocking components

The interaction factor superposition method in the determination of the vertical and rocking impedances of pile groups for jacket-supported Offshore Wind Turbines is studied. The vertical and rocking group dynamic impedances obtained by this method are compared with those computed by a previously developed continuum model. The influence of the main parameters that define the problem is also studied. In order to propose an alternative calculation solution, some expressions dependent of these parameters are fitted from an extensive selection of jacket pile group configurations. These expressions allow to estimate the vertical flexibility of the source pile and the interaction factor between a pair of piles. Subsequently, applying elastic superposition, the group impedance functions are determined. Results show that the interaction factor superposition method correctly reproduces the vertical and rocking group dynamic impedances. Therefore, for these regular pile groups with large spacing ratios, the assumption of only considering the direct interaction between pile pairs leads to accurate results. Results obtained with the proposed fitted expressions generally conduct to a good estimation, properly reproducing the variation produced by the influence of the different parameters. Thus, this superposition method and the proposed expressions can be employed to quickly and simply reproduce the vertical soil–structure interaction of this type of structures.

Seismic Design of Underground Structures’ Vulnerability – Review.

This article examines the vulnerability of underground structures to seismic activity, with a particular focus on design and mitigation strategies. Underground buildings are essential to the development of modern infrastructure and must include tunnels, subway stations, and storage facilities. Because of its deep location, seismic design and earthquake performance are both more challenging. In this study of seismic susceptibility, topics such as ground motion characterization, soil-structure interaction, structural reaction, and failure mechanisms specific to underground structures are discussed. According to the paper, their susceptibility can be affected by geotechnical conditions, the kind of structures they have, and the construction methods that are used. The seismic stability design and analysis process involves measuring the dynamic response of subsurface structures to seismic loads. The goal is to keep earthquake and seismic forces from toppling structures in any way that is possible. Advanced analytical and numerical approaches are used in seismic stability design. Some examples of these methods are finite element analysis (FEA), discrete element modeling (DEM), and the boundary element method (BEM). In addition to that, it investigates contemporary methodologies for assessing seismic vulnerability as well as international design standards. In addition, seismic retrofitting and design advances for underground structures are analyzed and discussed in this paper. This document compiles and evaluates previous research to gain an understanding of the seismic susceptibility of subsurface structures and to promote more seismic engineering research on this extremely important topic.

Numerical assessment of ship anchor penetration depth in Baltic Sea Sand: Implications for subsea cable burial

As renewable energy demand increases, protecting subsea cables from ship anchor damage has become essential. This research comprises numerical simulations of the anchor penetration process in Baltic Sea sand (for an AC-14, a Hall and a Spek anchor). We apply a coupled Eulerian–Lagrangian (CEL) framework and a hypoplasticity constitutive model to analyze the influence of different anchor characteristics on penetration depth and seabed stress distributions. We conducted investigations under high velocities (v≥1m/s) with focus on inertial effects only. Furthermore, this study introduces stress circles to visualize a simplified anchor-induced spatial stress distribution in the seabed. Findings show that heavier anchors and slower drag velocities generally result in deeper anchor penetrations. Fluke geometry significantly affects penetration depth, with pointed designs penetrating more deeply. The observed trends align with previous results from centrifuge tests and numerical modeling of ship anchors. This research improves understanding of soil–structure interaction in maritime environments, offering insights for the protection of subsea installations in the Baltic Sea and similar regions.

Application research on nonlinear partitioned analysis of soil-structure interaction method of seismic response for seawater-seabed-structure

The analysis of seismic response in marine engineering structures is pivotal for guaranteeing their seismic safety. Such analyses are intricate due to the complexity of fluid–structure and soil-structure interactions. This paper introduces a unified computational framework for wave motion within a water-saturated seabed-bedrock system, employing the Davidenkov model and a modified Massing rule to characterize the nonlinear properties of the saturated seabed. A comparative analysis is conducted between the nonlinear responses of marine sites subjected to linear and nonlinear free-field inputs, with a specific focus on the seismic response of bridges under seawater-seabed-structure interaction. The study demonstrates that the modulus of a nonlinear saturated seabed diminishes, leading to a decrease in the wave impedance ratio between the saturated seabed and bedrock. Consequently, the reflection and transmission coefficients from the bedrock to the saturated seabed increase, amplifying the seismic response. For deepwater bridges, under harder site conditions, the abutment’s bottom response is largely insensitive to increasing water depth, whereas the shear at the abutment’s base diminishes with increasing water depth. The proposed method is validated through two case studies, with an examination of the impact of saturated sites on the analysis results.

Advanced nonlinear soil-structure interaction model for the seismic analysis of safety-related nuclear structures

AbstractThis article proposes an advanced nonlinear soil-structure interaction methodology, for the seismic analysis of a nuclear structure. To do so, a study is performed on a nuclear reinforced concrete structure considering the effects of the nonlinearity due to the sliding and rocking at the soil-structure interface, under a Beyond Design Basis Earthquake. A tridimensional numerical model based on the Finite Element Method is developed for the structure and the soil. The model of the structure considers composite materials to describe all the structural members, taking full advantage of the modelling capabilities of the finite element method. The soil layers are modelled assuming their degraded properties due to the propagation of the seismic ground motion. An innovative approach to achieve spectral matching at the surface of the FEM soil model after propagation from the bedrock has been successfully implemented. The seismic analysis on the structure has been performed by considering three hypotheses for the contact between soil and structure: fixed-base, fixed contact and sliding-rocking contact. Insights are provided after comparing floor spectra for the contact approaches assessed in this research, calculated at the systems and components’ locations at the nuclear structure. Finally, a statistical approach for the soil properties allows to study the effects of these uncertainties on the structural response.

Experimental study on the seismic behavior of tunnels with distinct surface roughness in liquefiable soils

Earthquake-induced liquefaction poses grave safety risks to the underground structures. In this study, 1-g shaking table tests were conducted to investigate the uplift behaviors and soil-structure interaction (SSI) of a two-part tunnel located in liquefiable soils, with special attention paid to the influence of structural surface roughness. Two parallel tests, including a free-field test and a soil-tunnel test, were carried out to investigate the field responses and the effect of SSI during liquefaction induced by various input motions. The test results indicate that the ground partially liquefied during the first shaking event, and then experienced full liquefaction in the subsequent events with higher loading amplitude and longer loading duration. The excess pore pressure and horizontal acceleration responses around the tunnel were significantly altered due to the presence of the tunnel, which also led to different patterns of acceleration amplification and strain development in its vicinity. While structural surface roughness influenced the aforementioned responses to some extent, it played a more dominant role in the uplift behavior of the tunnel. The segment with lower surface roughness experienced significantly greater uplift compared to the rougher counterpart. Furthermore, it was found that the structural uplift behavior can be divided into distinct stages that feature different patterns of pore pressure development, and such behavior was notably different under varied loading conditions. The findings in this research emphasize the importance of incorporating the considerations of surface roughness in future numerical or experimental studies so that the structural uplift can be better captured.

Dynamic model identification of the medieval bell tower of Casertavecchia (Italy)

The structural safeguard of tangible cultural heritage, monuments in particular, needs a multi-disciplinary approach involving historical–critical analysis, survey, in-situ and laboratory testing to provide a comprehensive knowledge on the object under investigation and build a structural model representative of the current state of the monument. In this paper, this approach is applied to the case study of the bell tower of San Michele Arcangelo cathedral in Casertavecchia (Italy). The historical–critical analysis was fundamental to understand the evolution of the tower over the centuries. Material tests were complemented with ambient vibration testing (AVT) which allowed for a complete characterisation of frequencies and mode shapes for the bell tower. A further model identification procedure was carried out to exploit the amount of information gathered within the documental and experimental activities and set up a reasonably accurate numerical model. The activities described in this paper highlight (a) the importance of correctly representing all substructures present in the monument, possibly hidden and built in different historical periods; (b) the possibility offered by model identification procedures to separate identifiable from less significant parameters, as well as selecting the best model in terms of representation complexity; (c) the effect of soil-structure and structure-structure interaction on the modal behaviour of the monument. In particular, the identification analyses without considering the inner reinforced concrete frame are consistently characterised by higher values of frequency and modal shape discrepancies compared to the analogous analyses in which all substructures were included. The best fit with the dynamic data is obtained by introducing deformable structure-soil connection while the effect of lateral constraints cannot be captured by the utilised setup.

The significance of soil–structure interaction in the response of buildings to ground-borne vibration from underground railways

The response of buildings to ground-borne vibration is governed by many physical phenomena. Not least of these is the dynamic soil–structure interaction (SSI) that exists between the various components of the system. The majority of existing models assume that the interaction between a railway tunnel and a building’s foundation is negligible, with the two sub-systems behaving as though they are uncoupled; other components of SSI associated with the foundation and building are accounted for to varying degrees, often with little justification. This paper aims to further our understanding of the SSI between an underground railway tunnel and a nearby building. The response of a typical multi-storey building founded on piles is considered, over the frequency range typically associated with perceptible vibration. A comprehensive numerical model is used to capture the fully-coupled, three-dimensional behaviour of the tunnel–foundation–building system, to investigate the relative significance of four fundamental components of SSI when predicting the overall vibration levels within the building. The effects of building location, relative to the tunnel, pile length and foundation configuration are investigated. Three further building models, of varying complexity, are used to explore the extent to which simplified models can capture the fundamental SSI of the system. The conclusions appear promising for the development of simplified models, particularly those aimed at making overall or relative predictions of building vibration levels to guide the design of mitigation measures.

Investigating Calcareous and Silica Sand Behavior at Material Interfaces: A Comprehensive Study

Abstract This study centers on the crucial determination of the mobilized friction angle between soil and various materials, including steel and concrete, to enhance the modeling of soil-structure interaction. The primary objective of the current investigation was to assess the interfacial friction between calcareous and silica sands when interacting with concrete or steel surfaces. To achieve this, direct shear tests were conducted to examine the impacts of relative density (Dr), surface roughness (Rn), and shearing direction. The test results reveal that the shear strength of calcareous sand surpasses that of silica sand when considering a specific Rn. Furthermore, the interface friction of both sand types escalates with an increase in normal stress and Rn, with higher values observed in interactions with steel plates. Notably, the friction angle ratio (the interaction friction angle over the pure sand friction angle) demonstrates minimal dependence on the sand type. The most pronounced divergence in the friction angle ratio is evident at the maximum Rn value, which increases alongside Rn values for both calcareous and siliceous sands. With increasing Rn values, the maximum shear strength, contingent on normal stress and relative density, also rises. The influence of relative density on the interaction friction angle diminishes with escalating surface roughness.

Modeling ground vibration excited by a high-speed train running along a viaduct railway using a new structure-soil interaction method

Ground vibrations generated by high-speed trains running along railways either at grade or on viaduct bridges, are greatly concerned by the railway industry. Considering the train-track-bridge-abutment-pile-soil interactions involved, modeling the problem in an analytical manner is almost impossible, while conventional numerical methods struggle to accurately simulate the dynamic properties of infinitely large soils. Therefore, this study introduces a new substructure methodology for train-track-bridge-abutment-pile-soil interactions that leverages an ingenious combination of the 2.5-dimensional finite element-boundary element method (2.5D FE-BE) for dynamics of infinitely long periodic structures, and a local 3-dimensional finite element model for pile-soil interaction. This innovative method allows for the consideration of detailed pile-soil coupling using a local finite element model, all while retaining the ability to account for the infinite size of the soil structure using the 2.5-dimensional finite element-boundary elements. After a comparison between model prediction and field measurement, the model is employed to explore the environmental vibration characteristics of on-viaduct high-speed railways and analyze the vibration reduction effects of various measures, including rail fasteners, track slab pads, and bridge bearings.

Three-Dimensional Numerical Analysis of Seismic Response of Steel Frame–Core Wall Structure with Basement Considering Soil–Structure Interaction Effects

In recent years, numerous studies highlighted the crucial role of the soil–structure interaction (SSI) in the seismic performance of basement structures. However, there remains a limited understanding of how this interaction affects buildings with basement structures under varying site conditions. Based on the three-dimensional (3D) numerical analysis method, the influence of the SSI on the seismic response of high-rise steel frame–core wall (SFCW) structures situated on shallow-box foundations were investigated in this study. To further investigate the effects of the SSI and site conditions, three types of soil profiles—soft, medium, and hard—were considered, along with a fixed-foundation model. The results were compared in terms of the maximum lateral displacement, inter-story drift ratio (IDR), acceleration amplification coefficient, and tensile damage for the SFCW structure under different site conditions, with both fixed-base and shallow-box foundation configurations. The findings highlight that the site conditions significantly affected the seismic performance of the SFCW structure, particularly in the soft soil, which increased the lateral deflection and inter-story drift. Moreover, compared with non-pulse-like ground motion, pulse-like ground motion resulted in a higher acceleration amplification coefficient and greater structural response in the SFCW structure. The RC core wall–basement slab junction was a critical region of stress concentration that exhibited a high sensitivity to the site conditions. Additionally, the maximum IDRs showed a more significant variation at incidence angles between 20 and 30 degrees, with a more pronounced effect at a seismic input intensity of 0.3 g than at 0.2 g.

Dynamic analysis of a pedestrian bridge using monitoring and computational techniques

Soil-structure interaction (SSI) represents an important parameter when analyzing the dynamic behavior of bridges, considering the combined effects of soil, foundation, and structure to ensure an adequate structural representation. This paper applied a computational modeling strategy associated with soil-structure interaction methodology to represent the dynamic behavior of a timber-concrete pedestrian bridge of the Polytechnic School of the University of São Paulo. The computational models were validated and calibrated using monitoring results from an extensive structural health monitoring campaign. The bridge monitoring program was characterized using embedded sensors and remote monitoring technology: ground-based radar interferometry and video motion amplification. The instrumentation results were compared to establish the capabilities and advantages of this novel remote monitoring technique. The experimental results obtained from free and forced vibrations in the asset served as a basis for validating the developed computational model and allowed the evaluation of the asset behavior in service for different loading conditions. This paper emphasizes the importance of considering an SSI approach to represent the bridge dynamic behavior more accurately, enabling the use of more reliable numerical models to assess the bridge structural responses throughout its life-cycle.

Attenuation of bulk waves using locally resonant soil-coupled metabarriers

Abstract Low frequency ground-borne vibrations generated by transport infrastructure are one of the most serious causes of disturbance to the general population. One possibility to reduce this problem is to use the wave filtering properties of elastic metamaterials. However, their integration in the soil complicates the prediction of their response, and the influence of soil-structure interaction needs to be correctly evaluated for an efficient design. The aim of this work is to experimentally evaluate the efficiency of metamaterial trench barriers set in soil in attenuating vibrations, using low-frequency local resonance mechanisms. A lab scale model is proposed comprising different resonating structures and a cylindrical encasement is adopted to couple the structure to the soil. The influence of various parameters is evaluated, such as metamaterial structure, geometrical characteristics of the resonator, and constituent materials. Finite Element simulations are used to develop a suitable design, analysing mode shapes and resonance frequencies of structures with and without the surrounding encasement. Experimental modal analysis is then performed on the corresponding fabricated samples, providing both model validation and out-of-soil mechanical characterization. Finally, vibration transmission loss measurements are performed in a setup in which different resonant metamaterial barriers are embedded into the soil sample, allowing the evaluation of barrier performance. Results indicate that the metamaterial structures provide good attenuation of vibrations in selected intervals in the low to high frequency range (1–5 kHz), demonstrating the feasibility of the approach in a scaled sample. Preliminary data regarding the structures providing preferable design characteristics is also obtained. These results can be useful for the design of trench barriers scaled to large dimensions in more realistic applicative settings.

Laboratory Study of Interface Friction between Sand and Steel Surfaces

Abstract In this study, results have been reported from a series of laboratory tests to determine the interface friction angle of steel surfaces with sand through modified direct shear testing. For completion, steel surfaces with different surface geometry to replicate the roughness have been slid against various sands compacted at different relative densities under both dry and wet conditions. The standard square shape direct shear box has been modified into circular and rectangular boxes to sufficiently enhance the contact area and to subsequently quantify its effect on interface friction angle. A mild steel interface of smooth and rough texture with a groove depth of 0.2 mm and tipping at an angle of 90° has been used in this study. The analysis of results revealed that the interface friction angles obtained from the standard direct shear box agree closely with those obtained from both modified rectangular and circular shear boxes. However, the ratio of the interface friction angle from the modified apparatus and soil’s angle of internal friction significantly depends upon the roughness of the surface in contact with the sand, its median particle size, and is independent of the effects of box size, soil’s relative density, and dry or wet condition. A comparison between existing well-accepted guidelines and current observations has been presented for use by the practicing engineers dealing with soil-structure interaction.

A 4D Soil-Structure Interaction Model Testing Apparatus

Abstract A new three-axis loading frame has been developed to enable real-time visualization of in-situ soil and rock structure interactions via X-ray tomography during small-scale model testing. The constructed frame is capable of performing a wide range of small-scale 1g tests and can accommodate monotonic and cyclic actuation under both load and displacement control. The compact size of the system enables remote multi-axis operation from within an X-ray cone-beam scanning bay, a capability which is owed to a comprehensive design process. Design and fabrication involved a blend of physical and numerical experiments to assess suitable construction materials and performance. In this scope, the new equipment is discussed and its capability is showcased.

Centrifuge tests study on settlement and damage modes of bridge approaches using deep-seated slab

The issue of bridge end bumps is a critical concern in the failure of bridge and bridge approaches. A series of novel centrifuge tests utilizing a ring model box were conducted to investigate settlement and its induced damages at the bridge approach. A new mitigation method, the deep-seated slab, for bridge end bumps was modeled in the test. This study analyzed the decisive role of pavement stiffness, soil modulus, and load cycles on deformation from the perspective of structure-soil interaction under standard traffic load conditions. The test results show that when deep-seated slabs are used, the deformation of the bridge approach follows an exponential decay pattern, eventually stabilizing after approximately one slab length. Furthermore, the upper and lower bridges exhibit distinct damage modes, i.e., the bridge damage by wheel collision at the upper bridge and the pavement damage by wheel impact at the lower bridge. The damage zone on the pavement is approximately 1.7 times the wheel width and the damage zone on the bridge 2.6 times. Finally, a predictive model for the deformation of bridge approaches was proposed, considering the effect of pavement stiffness, subgrade soil modulus, and load cycles. The relationship between the deformation and the three normalized variables conforms to the quadratic polynomial function in matrix form.

Comparative Study of Semi-Active Control Effectiveness of Structures on Soft Soil Using MR Damper: Shaking Table Investigation

The effect of soil-structure interaction (SSI) cannot be neglected in semi-active vibration control of structures located on soft soil. To investigate the mitigating effect of magnetorheological (MR) damper on the semi-active control of structures considering the SSI, shaking table tests were conducted to evaluate the performance of the MR damper-based semi-active control system for structures on soft soil. In addition to a novel fuzzy control method based on online learning deep neural network (OL-DFNN), various control strategies, including passive OFF, passive ON, ON–OFF and deep neural network fuzzy control (DFNN) were systematically evaluated. The test results showed that the OL-DFNN control method exhibited superior adaptability to varying ground motion and structural dynamic characteristics compared to the other control methods. In particular, the OL-DFNN controller effectively mitigated the peak displacement and root mean square displacement, outperforming the passive OFF, passive ON, ON–OFF and DFNN control strategies. The test results highlight the effectiveness of the OL-DFNN control method in addressing the challenges posed by dynamic and time-varying characteristics in structural vibration control systems considering SSI.