Latest Developments in Geotechnical Earthquake Engineering and Soil Dynamics

Seismic earth pressures computed using an elastodynamic Winkler solution that considers soil–structure interaction effects were recently developed by the authors using two different analysis approaches: a frequency-domain method in which ground motion time series are utilized to represent seismic demand and a single-frequency solution in which the ground motion is modeled using a single representative surface displacement and frequency. This paper provides guidance on selection of appropriate surface displacement and frequency for the single-frequency method to provide reasonable agreement with the frequency-domain solution. Suites of frequency-domains solutions are first performed, and peak seismic increment earth pressure resultants are computed. Single-frequency solutions are then performed by setting the frequency to the inverse of the mean period of the ground motion and selecting the surface displacement amplitude required to match the seismic increment resultant from the frequency-domain solution. Regression equations are provided to define the surface displacement amplitude as a function of peak ground velocity and mean frequency.

Earthquake-induced faulting may cause severe damage to adjacent underground structures such as pile foundations and tunnels. A reasonable distance to the free-field fault rupture outcrop is important for the safe design of pile foundations. Identifying the potential damage zone for a tunnel crossing a fault is also crucial. In this paper, three-dimensional centrifuge and numerical modeling of piles and tunnels subjected to normal faulting are reported and discussed. Propagation of fault rupture and induced pile displacements in centrifuge tests were captured and analyzed by the particle image velocimetry technique. The performance of a single pile, a pile group and a tunnel was monitored. A series of three-dimensional numerical back-analyses were performed using a strain-softening Mohr–Coulomb model in FLAC3D. Moreover, a numerical parametric study was conducted to examine the distance from the pile foundation to the free-field fault rupture outcrop. Furthermore, the effects of tunnel depth on the behavior of the tunnel were investigated by comparing two different tunnel depths. New insights from the centrifuge tests and numerical analyses are revealed and three characteristic zones namely safe, transition and translational can be identified.

Subsoil liquefaction caused by strong earthquakes is one of the big threats to urban environment. Engineering communities became concerned about this problem in 1960s and many mitigation measures have been developed since then. This paper reviews the historical development of this technology up to the present time and classifies them into several categories. Major trend nowadays is the emphasis on ground improvement under existing structures, which is still difficult or costly. More efforts are needed to develop a social framework by which liquefaction problem is mitigated at an acceptable cost.

Frequently, deep foundations extend through liquefiable sand layers and bear on more competent layers at depth. When liquefaction occurs, the skin friction in the liquefied layer would be expected to decrease to near zero; however, as pore pressure dissipates and the liquefied layer settles, negative skin friction can develop along the pile. This paper summarizes full-scale pile downdrag testing at four sites where liquefaction was induced by small explosive charges. Test were performed on driven piles, bored piles, augercast piles and micropiles. Despite the variation in pile type, observed performance was similar at all sites. Negative friction in the liquefied layers was between 40 and 55% of the positive friction before liquefaction as the sand reconsolidated. Negative friction in the non-liquefied layers was about the same as the original positive friction. Following liquefaction, the ground around the piles settled between 7.5 and 27 cm; however, pile settlement was typically small and was most dependent on the end-bearing resistance. Pile settlement and load in the pile were generally consistent with the neutral plane method. Steps necessary to estimate the neutral plane and pile settlement are summarized in the paper.

Understanding the mechanisms for the development of large deformation of sand within sloping ground due to liquefaction remains one of the most challenging topics in earthquake geotechnical engineering, due to its complexity and the large number of factors that may affect the liquefaction resistance (e.g., soil density, soil type and fabric, stress conditions, etc.). Very often the use of stress conditions different from simple shear and technical limitations of testing devices (i.e., inadequacy to reach large shear strain levels or prevent large extents of non-uniform deformation of the specimens at higher strain levels) has limited the possibility to entirely define the effects of sloping ground on the cyclic resistance of sands. The development of a state-of-the-art torsional shear testing device that is capable of reproducing the simple shear condition and achieving 100% double amplitude shear strain (γ_DA), however, has made it possible to obtain new insights on this challenging topic. This paper provides first an overview of this large-strain torsional testing apparatus and the ad hoc procedure employed to carry out high-quality experimental tests, including the correction for membrane resistance. Following, results of undrained cyclic torsional shear tests with initial static shear conducted on loose (D_r = 25–30%) and medium dense (D_r = 44–48%) Toyoura sand specimens are reported. Specifically, the post-liquefaction response is scrutinized in terms of observed failure modes, strain development characteristics and cyclic resistance up to 50% single amplitude shear strain. The occurrence of strain localization observed at strain levels higher than 20% is described in detail, and the role of key factors affecting its properties is discussed.

The subject of moving load has been studied analytically and numerically since the 1950s. The studies initially dealt with concentrated constant or harmonic loads over the surface of a homogeneous half-space. The accelerated development of high-speed railway lines since the 1990s, especially in regions with soft ground conditions, has attracted a considerable research into this subject, and a host of analytical and numerical solutions has been proposed for general soil conditions and for complex mitigation measures. This paper gives an overview of the developments in the subject and presents representative results for various analyses using an analytical model based on the Green’s functions in viscoelastic layered ground. The cases cover load speeds below and over the critical speed representing the sub-seismic and trans-seismic conditions. The same model and its variations, including coupling to piles, are used to investigate the changes in the pattern of the track/ground responses. To this end, the impact of different countermeasures such as soil replacement or improvement, use of stiff beams below the track and use of piles together with continuous girders under the track are demonstrated. It is shown that by placing the track on piles one can increase the critical speed and reduce the vibrations in soft soil sites.

Coir geotextile is a natural fiber derived from the husk of coconut, and its use as a reinforcement element has recently shown great potential for applications in geostructures. The biodegradable nature of the coir fibers makes coir geotextiles an environmentally friendly ground improvement alternative for use in various infrastructure projects. In the recent past, a number of laboratory investigations have been carried out on the behavior of coir geotextile reinforced soil during monotonic loading; however, only limited number of studies have been carried out on coir geotextile reinforced soil during cyclic loading. In this study, a robust finite element model has been developed to understand and investigate the behavior of coir geotextile reinforced soil during cyclic loading. It was observed that the inclusion of coir geotextiles increases the bearing capacity and reduces the settlement of soil during cyclic loading. The inclusion of coir geotextile in the soil creates a shear interface between the geotextile and soil, which helps in transferring the stress from the soil to the geotextile. The inclusion of coir geotextiles in the middle of the subbase layer yielded their optimum performance during cyclic loading.

This paper summarizes 12 cases of Holocene liquefaction in Pleistocene deposits reported in the literature and reviews nine proposed relationships for estimating the effect of aging on soil liquefaction resistance. The 12 cases are from Argentina, China, Israel, Lithuania, Republic of Karelia and the USA. The nine relationships for estimating the effect of aging are based on laboratory test results, laboratory and field test results, or field test results and ground behavior observations. Because aging processes in soil depend on many factors (e.g., grain size distribution, grain shape, mineral composition, groundwater chemistry, stress history), time is sometimes not a good predictor of the aging effect in liquefaction assessments for engineering projects. Combining small-strain shear wave velocity and larger-strain penetration resistance provides a more robust predictor of the aging or diagenesis effect than using time as the predictor variable.

The ground response to seismic waves is governed by the geometry and the mechanical properties of the site. A proper characterization of the soil behavior is thus a fundamental aspect, and it should account for the uncertainties associated with the model parameters. In particular, the quantification of the small-strain damping is a critical task, especially in low-to-moderate seismicity areas. In the present paper, the main issues related to the definition of the damping at small strains are firstly treated in the light of the biases affecting both laboratory and in situ tests. Higher values of damping are expected in field, where wave scattering phenomena take place. The influence of the parameter on the overall site response is subsequently assessed through a stochastic database of ground response analyses. The results highlight a reduction of the expected ground motion at the surface, especially for deep and soft sites when site-based small-strain damping is selected. Finally, the differences between site and laboratory values are analyzed regarding a specific case study. The influence of the damping at small strains resulted to be comparable or even higher with respect to the uncertainties related to the shear wave velocity profile and the modulus reduction and damping curves. Therefore, a proper evaluation of the uncertainties in the small-strain damping evaluation should not be neglected.

Realistic prediction of seismic landslides is critical for performance-based design in the seismically active regions. To date, analytical methods for estimating seismic landslides have been based on simplified models. Many gaps still remain in the scientific understanding of earthquake-induced landslides, especially the landslide triggering process and post-failure behavior. In this study, a strain-softening fully nonlinear dynamic soil model is formulated using the material point method (MPM) to simulate the soil slopes failure process under dynamic loading. The study demonstrated that MPM can capture entire slope failure process, including slide triggering, shear band formation, runoff and final deposition. The complicated interaction between sliding masses can also be captured. Numerical simulation also demonstrated that residual soil strength is an important factor in determining landslide runoff and deposition. The study demonstrated the great promise of MPM method in improving our understanding of the coseismic landslide process and these underlying influential factors.

For the same void ratio (e) and stress conditions, a systematic increase of non-plastic fines content (f_c, particle size ≤ 0.075 mm) in clean sands, generally, follows an increase in contractive tendency in their stress–strain behaviors. While keeping the same e, fines act as a filler between sand particles, reducing its force resisting skeleton structure up to threshold f_c (f_thr). Thus, for sand with a range of f_c, e loses its credibility as one of the state variables in the critical state soil mechanics (CSSM) framework. This can be avoided by −1) considering sand with each f_c as a separate soil to establish its CSSM framework which is not practical due to laborious effort for predefining critical state lines (CSLs) for a range of f_c, 2) correcting e to an equivalent granular void ratio (e*), considering relative interaction of fine particles in the matrix of sand particles. This state-of-art lecture presents the progressive development of the simplistic model for e* using experimental and discrete element method (DEM) data, which may coalesce CSLs for sand with a range of f_c to a single equivalent granular critical state line (EG-CSL). The advantage of the EG-CSL is that only a CSL for clean sand or sand with an f_c is required to define it, which applies to a range of f_c as a single framework. The substitution of e* for e modifies the concept state parameter (ψ) to equivalent granular state parameter (ψ*). The e* and ψ* capture the effect of fine particles in the characteristic features of drained and undrained behavior, including static and cyclic liquefaction. Again, the substitution of e* and ψ* for e and ψ into state-dependent constitutive models (e.g., SANISAND family of models) works very well for the prediction of static and cyclic liquefaction. The theories of e*, EG-CSL, ψ* and relevant constitutive modelling are defined here as the equivalent state theory (EST). The limitation and potential application of the EST are discussed with relevant literature.

The Central Sulawesi Province of Sulawesi Island of Indonesia was hit by a powerful earthquake of moment magnitude (Mw) 7.5 on September 28, 2018. The earthquake was triggered by the left lateral Palu–Koro fault at a shallow hypocentral depth of 20 km. The event resulted in major geotechnical failures and structural damages in Palu city and Sigi Regency, causing thousands of deaths and injuries to more. Areas such as Balaroa, Petobo, Jono Oge and Sibalaya suffered enormous damage due to long-distance flow-slides and mud flows. It was the first of its kind of a large-scale flow-slide event triggered by an earthquake, surprisingly on a very gently sloped ground, displacing ground to hundreds of meters. The objective of this paper is to provide a brief insight on the outcomes of the field investigations launched by teams of researchers from Japan, immediately after the earthquake to delineate the key factors responsible for triggering such intensive flow-slides. Findings from the field investigations performed by means of unmanned aerial vehicle (UAV), in situ testing using portable dynamic cone penetration test (PDCPT) and trench survey, are described here. In addition, subsequent data interpretation and some probable mechanism of the flow-slides are discussed.

Empirical prediction equations are developed for Fourier spectrum amplitudes at different natural periods using a database of 217 three components of strong motion accelerograms recorded in western Himalayan region. Prediction relations are also developed for the equivalent group velocity values due to various types of waves at each Fourier frequency using two horizontal components of a subset of 182 digital accelerograms. The group velocity values are then used to generate the Fourier phase spectra, which along with the predicted amplitude spectra are used to simulate site-specific design accelerograms by inverse Fourier transformation. The design accelerograms are also used to compute the design response spectra with different damping ratios. The design accelerograms and response spectra obtained are of site-specific nature in that they are able to include the effects of earthquake magnitude, source-to-site distance, local geological condition and site soil condition for any site in western Himalayan region of India.

Seismic risk map of the Indian subcontinent presented here places the tectonic ensemble of Westcentral Himalaya, Indo-Gangetic Foredeep, Bengal Basin, Darjeeling-Sikkim Himalaya to Northeast India including Bhutan in ‘High’ to ‘Severe’ Risk, thus rendering it a model case study for site-specific seismic hazard study based on an enriched surface and in-situ downhole geotechnical and geophysical database with a new regional fifth degree nonlinear power law polynomial combining shear wave velocity with geology, geomorphology, landform and topography, a set of new lithology-based depth-dependent SPT-N value derived/in-situ downhole seismic measurement yielded shear wave velocity categorizing the region into Site Classes E, D4, D3, D2, D1, C4, C3, C2, C1, B and A with spectral amplifications of 5.8, 4.8, 4.2, 3.9, 3.3, 2.58, 2.2, 1.87, 1.81, 1.3 and 1.0, respectively, at the predominant frequency varying between 1.41 and 8.5 Hz as envisaged through nonlinear soil–structure interaction modeling which is seen to influence the surface consistent PGA and PSA significantly with multifold enhanced design response spectra of the region and also brought in focus the issues of induced seismic catastrophe in terms of liquefaction hazard evidenced in the city of Amritsar, Agra, Kolkata, Dhaka, Guwahati, and landslide in Gangtok presented here. In order to understand the implications of this seismic hazard its impact is quantified through SELENA-based building damage and casualty assessment in the city of Amritsar, Kolkata, Dhaka, Gangtok and Guwahati, thus providing a unique seismic hazard–disaster model to be put in place for pre-disaster preparedness through updated urban bye-laws and post-disaster mitigation.

Low tensile strength of soils makes them unsuitable for constructions where soils are subjected to tensile loads. Earthquake loading on soils impose compression and tension loading cycles during which there is a high possibility of failure in geotechnical structures like embankments, slopes and retaining walls. Geosynthetics come to rescue in many such cases where the inclusion of tensile elements in the form of polymeric reinforcement not only reduce the seismic demand on the structures but also provide adequate support to the structures during cyclic loading conditions. This paper presents shaking table studies on unreinforced and reinforced soil retaining walls to demonstrate the beneficial effects of geosynthetic reinforcement under earthquake loading of these structures. Models of wraparound, rigid-faced, segmental and geocell retaining walls were built in a laminar box and tested on a shaking table at different accelerations and frequencies. Results from these tests show that geosynthetic reinforcement can significantly reduce the deformations in these structures and help in avoiding failures.

The paper presents the modeling considerations of dynamic compaction (DC) at enhanced gravities in a geotechnical centrifuge. An in-flight actuator is developed for this purpose, equipped with an automatized lifting and dropping mechanism. The actuator is robust and versatile in terms of accommodating varying tamper shapes, tamper diameter, mass and drop heights during centrifuge testing, thereby simulating both low-energy blows and high-energy DC processes adopted in the field. Additional measures are taken for minimizing Coriolis acceleration generated during flight. The results of centrifuge model tests conducted on dry and saturated loose granular deposits are discussed. All tests are conducted using the 4.5-m radius large beam centrifuge facility available at IIT Bombay, India. The instrumentation involved pore water pressure transducers and accelerometers, and GeoPIV analysis was additionally employed. The results are interpreted in terms of pore water pressure variations during blows, crater profiles, radial and vertical ground displacements, volumetric strains, peak ground accelerations (PGAs) and peak ground velocities (PGV) induced in soil at various stages of DC.

Most of the existing nuclear power plants (NPPs) in India were constructed on rock which may not have the requirement of seismic soil–structure interaction (SSI) analysis but Narora nuclear power plant and some of the new upcoming nuclear power plants are planned to be founded on the soft soil necessitating to consider SSI for analysis. Some of these will be founded on piled raft foundation. Therefore, analysis considering the recent research development is required. In this state of art of SSI for NPPs, a detailed literature review of different approaches based on FEM considering SSI, solution techniques, effect of nonlinearity and absorbing boundaries for nuclear power plants on soft soil is presented. None of the studies is found in which the nonlinearity of both soil and structural component is considered along with SSI of NPPs. However, the nonlinearity of soil is necessary to consider when subjected to strong excitation. Evaluation of performance of NPP structure during seismic loading is typically evaluated to make sure the safety and serviceability. Numerical finite element modeling in the direct method of SSI can be employed to such performance. Also, the finite element modeling is a best tool to evaluate the response of embedded foundation of NPP structure into the soil with nonlinearity and adequate modeling of boundary to represent the soil strata. Most of these finite element analyses are carried out for the vertically propagating shear waves. In the recent advancement of SSI for NPPs, researchers are using the simplified modeling of NPP structure by replacing the finite element modeling of soil with the spring–dashpot model so as to reduce the computation time. In this paper, a state-of-the-art review of different approaches considering SSI for nuclear power plants on alluvial soil is presented. A comparison of these approaches based on their assumptions and limitations is made.

In this paper, an attempt is made to capture the seismic stability of a finite slope reinforced with micropiles using the original pseudo-dynamic (OPD) approach. The stability of the slope is evaluated using the limit equilibrium method considering c-ϕ soil. The study is performed by assuming a circular slip surface passing through the toe of the slope. The effect of various parameters such as horizontal (k_h) and vertical (k_v) seismic acceleration coefficients, slope angle (i), angle of internal friction of the soil (ϕ), amplification factor (f_a) and angle of inclination of micropiles (θ_b) on the stability of the slope is explored in terms of the factor of safety (FOS). Under the seismic condition, the stability of a slope along with micropiles is found to be affected less compared to that of a slope without micropiles.

The railway embankments are always subjected to cyclic loads (loading and unloading cycles), and over the period, it leads to track deterioration. The maintenance cycles for ballast, sub-ballast and subgrade (worst-case scenario) become frequent. The availability of good material or substitute material is highly unlikely at the construction site. This paper deals with the evaluation of the height of embankments and design methodology adopted by the Indian Railways based on the stiffness of embankment. The parameter adopted for the existing study is deformation modulus which can be calculated using a cyclic plate load test with DIN18134 guidelines. A test program was devised to evaluate the deformation modulus for the different sections of the embankment based on adopted methodology by the Indian Railway. The study reveals that the height of the embankment can be reduced by more than 70% as compared to the height of the embankment calculated as per the current design methodology.

Soils under either road or railway embankments are subjected to tens of thousands of low-amplitude cyclic load. Such large number of small magnitude repeated loading can cause strain accumulation, and the subsequent dissipation of excess pore pressures with time changes the structural arrangement of soil. The load levels are not high enough to liquefy the soil, but results in the change in shear behavior of soil. Studies on large number of low amplitude stress are scarce. This study discusses the post-cyclic behavior of fine sand and low plastic silt samples, which were previously compressed at different levels of excess pore pressure ratios. In these laboratory tests, the excess pore pressures from the cyclic loading were permitted to dissipate before subjecting the samples to undrained monotonic compression. These findings show that post-cyclic recompression disturbed the soil's structure and changed the gradient of its original unloading–reloading line. The results imply that the post-cyclic recompressed strength and elastic moduli can be related to the excess pore pressures developed prior, during the cyclic loading.

Engineers use various soft computing techniques for solving different problems in geotechnical earthquake engineering. This paper will investigate the application of different soft computing techniques {artificial neural network (ANN), support vector machine (SVM), least square support vector machine (LSSVM), genetic programing (GP), relevance vector machine (RVM), multivariate adaptive regression spline (MARS), extreme learning machine (ELM), adaptive neurofuzzy inference system (ANFIS), minimax probability machine regression (MPMR), Gaussian process regression (GPR), adaptive neurofuzzy inference system (ANFIS)} in different fields of geotechnical earthquake engineering such as liquefaction, lateral spreading, seismic slope stability and reliability. The advantages of different soft computing techniques will be described.

The performance of a flexible pavement depends on its resilient response from the supporting structural layers, which include dense bitumen macadam, base and subbase layers. The use of reclaimed asphalt pavement (RAP) materials in pavement base course layer has proven alternative under the sustainability framework. Since the RAP is an inferior material, it needs to be stabilized with cementitious materials and ascertain their resilient behavior. In this present study, a high percentage of RAP stabilized with alkali-activated fly ash (FA) was considered as an alternative to 100% virgin aggregate (VA) and sustainable pavement base material. The proposed alkali activation is expected to enhance the reactivity of FA with time. The resilient modulus (M_r) and unconfined compressive strength (UCS) of various mixes were examined. The results show that the resilient behavior of RAP can be enhanced by about fourfold when an optimum stabilizer is adopted. A 12-fold increase in UCS is observed with an LAA ratio of 50:50. Based on the wide range of M_r test data, design charts were proposed to determine the stabilized reclaimed bases for flexible pavements.

Case studies of failures in cantilever retaining walls during earthquakes indicate the need for better prediction of the seismic displacements of these structures. The article presents a displacement-based design methodology for these walls using a double wedge model with due consideration to sliding and rotational failure modes. The present practice is to analyze these structures as gravity retaining walls by considering a vertical plane passing through the wall-heel and the soil mass above the heel as part of the wall. However, experimental evidence suggests the formation of v-shaped rupture planes in the backfill evolving from the heel. By simulating the v-shaped mechanism, an analytical double wedge model has been developed and validated through case studies for computing seismic sliding displacements. Plane strain FE analysis was carried out for several cases of cantilever retaining wall to understand its sliding as well as rotational deformations. By comparing the results of the FE analyses and the sliding displacement predictions from double wedge model, displacement factors have been proposed as a simple design methodology to obtain seismic displacements for design purpose. The seismic behavior of walls with shear key is expected to differ from those without shear key, yet the present practice ignores this aspect due to lack of sufficient knowledge. The proposed simplified method for these walls has been extended to walls with shear key by capturing the responsible mechanism. A case study has been discussed in detail, which shows the promise of the proposed method for estimating the seismic displacement of such walls.

Seismic microzonation plays an important role in city planning and assessing seismic design parameters for buildings. Further, seismic microzonation studies are useful for seismic vulnerability and risk studies. Aligning with Government of India’s vision, more projects for infrastructural development are under execution. Seismic microzonation of important cities, which are under above projects, can be very useful at this stage. This paper discusses important observations, made at various levels in a seismic microzonation study, which can affect the analysis and the overall outcomes of such study. These include identification of seismic source, methods of declustering of earthquake (EQ) catalogue, selection of ground motions for assessing local site effect, assessment of liquefaction potential and identification of liquefiable zones. It must be mentioned here that currently numerous seismic microzonation studies are ongoing. In such cases, observations made in this paper can be very useful to enhance the accuracy of ongoing studies and to provide very useful inputs for future seismic microzonation studies.

In the era of rising population and lack of space availability, soil improvement has evolved as an emerging research topic since even lands having problematic soils are sought out for construction purpose. Soils that are weak in sustaining different types of loading are stabilized and used for construction. In the current research, two such soils, soft clay and silty sands, are treated with two non-traditional soil additive, viz. nano-material (nano-silica) and biopolymer (agar), respectively. The treated and untreated soil samples are subjected to consolidated undrained strain-controlled cyclic loading and the effect of treatment on pore pressure response; secant shear modulus and damping ratio were explored. The treatment using biopolymer and nano-material was found to decrease the pore pressure buildup and increase the secant shear modulus for the selected soils. Therefore, they were found to be a prospective stabilizing agent in soils which may be subjected to dynamic loading.

The Stability of the superstructure of any building and its response against vibrations are completely dependent upon foundation systems adopted. The analysis and design of a foundation system with respect to ground motion and vibration relies on the dynamic properties of the soil. Therefore, the characterization of dynamic soil properties like shear modulus, damping ratio, and Poisson’s ratio is essential for the safe design of foundation systems. Dynamic characterization of geotechnical properties of lunar soil is essential for the design of rovers and other Space exploration vehicles apart from the in situ resource utilization (ISRU) on the Moon. The futuristic Moon colonization also needs to build different lunar infrastructure facilities on the Moon. The foundation systems of these lunar structures are expected to encounter various types of vibrations due to moonquakes. Therefore, it is imperative to evaluate the dynamic properties of the lunar soil against the moonquake induced vibrations. This paper explains the characterization of the dynamic properties of the lunar soil simulant (LSS-ISAC-1). The cyclic triaxial tests and bender element tests were performed to determine the shear modulus, damping ratio, and Poisson’s ratio of the lunar soil simulant

Offshore wind turbines (OWT) are constructed in the seismically active areas to meet the growing energy demand. Monopile are commonly used as a foundation for OWT due to simple construction techniques and cost-effectiveness. OWT is subjected to various operational loads, such as wind, wave and seismic load during its design life. This study examines the dynamic response of the monopile supported OWT installed in layered sand deposits under the combined effect of operational and seismic loads. A two-dimensional (2D) finite element (FE) model is developed using OpenSees. Monopile and tower are modeled as linear Euler–Bernoulli beam, and soil domain is modeled as a quadrilateral plane strain element with solid–fluid fully coupled material. Pile–soil interaction is modeled using nonlinear p-y springs. Various earthquake records collected from online resources are scaled and applied at the base of the soil column along with various operational loads. The effect of intensity and depth of liquefaction on the dynamic response of the OWT structure are studied. The implication in the design of OWT in liquefied soil is suggested.

The response of any structure depends on its regional seismicity, source mechanism, geology and local soil conditions. This paper reports the outcome of the one-dimensional nonlinear ground response analysis (GRA) conducted for a typical site of Amingaon, Guwahati, using scaled strong motions of various intensities. Soil profiles at the study region comprised mixtures of silts, sands and clays, with a sufficiently high water table. Responses at various soil layers indicate profound influence of the chosen strong motion and local site effects. Maximum and residual strain distributions indicate that there are possibilities of liquefaction at the softer pockets due to an extreme event.