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This study proposes an analytical solution for the torsional vibration of a floating pile in unsaturated soil, factoring in the influence of construction disturbance. The shear complex stiffness transfer model is introduced to simulate the radially inhomogeneous surrounding soil. Concurrently, a fictitious unsaturated soil pile model is implemented to consider the influence of pile end soil. On this basis, the governing equations for the torsional vibration of the pile-soil system are established, incorporating the effect of soil saturation degree on soil shear modulus. By solving the governing equations and utilizing the impedance function transfer method, an analytical solution for the floating pile embedded in radially inhomogeneous unsaturated soil is derived in the frequency domain. The validity of the obtained solution is confirmed through comparison with existing works. Subsequently, the effect of pile end soil thickness and shear modulus on the torsional vibration characteristics of the pile is parametrically examined under different saturation degrees and construction disturbance conditions. • A fictitious unsaturated soil pile model is developed to simulate unsaturated pile end soil. • The construction disturbance of unsaturated soil is simulated accurately. • The analytical solution for pile torsional vibration is established considering the pile end soil. • The influence of unsaturated pile end soil on pile torsional vibration is investigated under different conditions. [ABSTRACT FROM AUTHOR]

Existing study shows that small-strain shear modulus is a promising parameter for characterizing soil liquefaction resistance, while liquefaction resistance is liquefaction type dependent. In this study, firstly a revisit of laboratory tests on saturated sands was conducted to explore the relationship between liquefaction resistance CRR and small-strain shear modulus G max with emphasis on cyclic mobility type of liquefaction. The investigation indicates that in the stress-normalized space of cyclic resistance and small-strain shear modulus, the fitting curve of soil testing data does not always approach to the coordinate origin and there will be an intercept on the abscissa axis. Based on this finding, a more general form of the power function between liquefaction resistance and small-strain shear modulus is proposed. Then, undrained cyclic triaxial tests were conducted in conjunction with the data available from LEAP to establish the power function between CRR and G max for medium dense to dense Ottawa F-65 sand, which leads to an updated characterization model on the basis of Zhou-Chen model. Finally, centrifuge model tests of submerged gently sloping ground of Ottawa F-65 sand conducted at Zhejiang University (i.e., ZJU) for LEAP were used to compile liquefaction and non-liquefaction case histories with shear wave velocity measurement to investigate the validity of the updated model for evaluating the cyclic mobility type of liquefaction. The test results show that the updated model could classify the case history datasets produced by centrifuge model tests well. And the further consideration of initial shear stress acting on the slope could enhance the evaluation performance of this characterization model, which is worth of further research. • A new V s -based characterization model for liquefaction resistance of sand is proposed. • The model could classify the case history datasets in centrifuge experiments properly. • The consideration of initial shear stress improves the performance of the model. [ABSTRACT FROM AUTHOR]

In order to investigate the dynamic characteristics of frozen saline silty clay (studied saline soil) under reciprocating loading, a series of cyclic tri-axial experiments have been conducted for studied saline soil with 0.0, 0.5, 1.5, and 2.5 % of Na 2 SO 4 contents under confining pressures 0 MPa–18 MPa at −6 °C, respectively. The test results show that as the increase of number of cycle N , the accumulated axial strain ε a N continuously increases, and the relationship between ε a N and N can be described by an exponential function: ε a N = a N b ; As the number of cycle N increasing, dynamic shear modulus G dN and dynamic bulk modulus K dN increase firstly and then decrease slightly; Salt content and confining pressure have great influences on the ε a N , G dN and K dN. Within the same loading cycle, G dN and K dN decrease until reaching their minimums when the salt content is 0.5 %, and then G dN and K dN increase as the increase of salt content. With the change of salt content, ε a N presents an opposite change law to G dN and K dN. For the studied saline soil with same salt content, during the same loading cycle, ε a N and G dN increase until reaching their minimums, and then decrease as the increase of confining pressure, K dN increases with the increase of confining pressure. This study can be applied to evaluate the elasto-plastic properties of frozen soils and saline soils subjected to cyclic dynamic loading. • It is the first time to study the dynamic properties of frozen saline soil in the range of low to high confining pressures. • The effects of confining pressures on the dynamic properties are investigated. • The effects of salt content on the dynamic properties are investigated. [ABSTRACT FROM AUTHOR]

This study introduces a novel solution for seismic protection of structures based on resonant metamaterials, named Periodic Foundation Piles, which can be integrated with deformable soil deposits in order to filter shear waves in a specific frequency range. A Periodic Foundation Pile consists of an array of vertical periodic structural elements containing internal resonators suitably tuned to one or more natural frequencies of the soil deposit. The proposed system is equivalent to a discontinuous foundation pile and can be installed in the ground with approximately the same procedure for piles, thus making it suitable also for applications in existing structures. The performance of the Periodic Foundation Piles in reducing the amplitude of a seismic motion has been shown through non-linear site response analyses carried out using real acceleration records as input motion. A soil deposit with an increasing shear wave velocity profile has been considered; the nonlinear behaviour of the soil has been modelled through the Iwan model, calibrated using a normalized secant shear modulus curve accounting for the influence of the confining pressure on the stress-strain relationship. Numerical results, presented in terms of peak acceleration, horizontal displacement and shear deformation profiles, as well as in terms of Fourier amplitude and response spectra, indicate that Periodic Foundation Piles may noticeably reduce the amplitudes of seismic motion in a suitable frequency range, hence potentially representing an innovative strategy to mitigate the effects of earthquakes on structures. • This study introduces an innovative seismic protection system. • This system filters shear waves in deformable soil to a specific frequency range. • Ground installation like foundation piles, enabling use for existing structures. • Numerical analyses with non-linear model confirm efficacy to reduce seismic motion. [ABSTRACT FROM AUTHOR]

The effect of geotextile inclusion on the shear modulus and damping ratio of sands is evaluated in a wide range of shear strain amplitudes, from very small to fairly large, using the results of several resonant column and hollow cylinder torsional shear tests. The resonant column test results are utilized to characterize the reinforced soil behavior at the range of small to medium strains whereas the hollow cylinder torsional shear test results are exploited to assess the medium to large strain dynamic properties. The results demonstrate that the inclusion of geotextile sheets in the soil medium would increase both its shear stiffness and damping ratio in the whole range of shear strain amplitudes, thus rendering a perfect composite to resist dynamic forces applied on geo-structures in earthquake prone areas. Empirical equations are proposed to estimate the small strain and strain-dependent shear modulus and damping ratio of geotextile-reinforced sands. The effect of scaling is also accounted for by a simple analysis so that the results obtained in the current study in the element scale could be extended to the prototype scale in the field. Finally, the accuracy of the proposed scaling approach is verified against a finite element model of a geotextile-reinforced embankment. • Effect of geotextile inclusion on shear modulus and damping ratio of sands is evaluated at various shear strain amplitudes. • Dynamic properties are assessed through several resonant column and hollow cylinder torsional shear tests. • Empirical equations are proposed to estimate the dynamic properties of geotextile-reinforced sands. • Effect of scaling is accounted for by a simple analysis to generalize the results of this study to the field scale. • Accuracy of the proposed scaling approach is verified against a finite element model of a geotextile-reinforced embankment. [ABSTRACT FROM AUTHOR]

The prediction and evaluation of environmental vibrations generated by traffic loads have been playing more and more important role during the planning and designing of high-quality traffic system. From the traffic source to sensitive building, the subsoil is the one of key propagation media, so the determination of soil dynamic parameters is very crucial in studying the transmitting and attenuation of environmental vibration. Due to the spatial variability of natural soil layers, the soil dynamic parameters are actually not certain but probabilistic with stochastic characteristics. However, most current inversion methods of soil parameters cannot consider the uncertainty. In this paper, an efficient inversion method is proposed to obtain the random distribution of soil dynamic parameters based on the combination of field experiment, forward soil modelling, and Bayesian theory. Take the shear modulus and damping ratio of subsoil as the typical parameters, the experimental dispersion curve and spatial attenuation curve can be obtained by field experiment, while the corresponding theoretical ones can be calculated by the thin-layered soil model with perfectly matched layer. The combining of experimental and theoretical curves generates the likelihood function. A prior probability distribution model is firstly established, and subsequently the posterior probability distribution model is deduced by genetic algorithm, Monte Carlo-Markov chain algorithm, and Bayesian theory. In order to verify the proposed inversion method, an on-site experiment based on Multichannel Analysis of Surface Waves(MASW) was conducted in an open field in Beijing. The results show the mean values of inversed soil parameters were close to the determined parameters provided by geological exploration. Compared to the traditional determined inversion, the proposed stochastic inversion method can consider the variety of soil parameters within small depth by providing probability distribution, mean and root-mean-square error, which has greater applicability in the further probabilistic prediction of environmental vibration. • Bayesian theory and Monte Carlo Markov chain algorithm can be well applied to soil parameter inversion. • The proposed inversion method can efficiently reflect the random variation of soil parameters. • The Metropolis Hastings algorithm is introduced to improve the computational efficiency. • The method is based on non-intrusive data and has more significant engineering value than traditional geological survey. [ABSTRACT FROM AUTHOR]

Soil response analyses require that the soil strata involved be characterized in terms of their dynamic material properties. Two important material properties are the shear modulus and a measure of energy dissipation characteristics, usually expressed as the damping ratio. Both can be obtained from standard laboratory tests, most commonly resonant columns or cyclic triaxial devices which provide strain-dependent values. Alternative experimental procedures are now available to estimate shear moduli at very small strains from piezoelectric transducer tests (bender elements); procedures have also been put forth to obtain the energy dissipation properties from this test. In this paper, we present a modified version of the spectral-ratio method using the wavelet transform to measure the damping ratio at small strains from waveforms acquired from bender element tests. Synthetic bender element signals were first used to test the procedure and validate the approach. Then, we analyzed signals obtained from a large-size oedometer equipped with bender elements on very soft Texcoco Clays (near Mexico City), and the waveforms were propagated along different paths. Our results show that the range of values of D min obtained from bender element tests agrees well with those obtained from resonant column tests performed on very soft clayey soil specimens retrieved from the same area at different depths. • This research is aimed to study the damping ratio on very soft soil Texcoco Clays (near Mexico City) using a large-size oedometer equipped with piezoelectric transducers. • We propose a modified version of the spectral ratio method for assessing the damping ratio at very small strains (elastic behavior). • It is calculated synthetic waveforms which input data are similar to the soil deposits present in the area where the specimens were retrieved. • We compare the data obtained with the modified version of the spectral ratio concerning to resonant column tests. [ABSTRACT FROM AUTHOR]

The dynamic stability of offshore foundations in the marine environment is one of the major technical challenges. Millions of loading cycles from waves and winds act on the foundations and seabed in their entire service life. The mixing of adjacent soil layers due to naturally occurring sediment or the construction process raises more difficulties in the design. Previous studies have focused on the dynamic constitutive relations of idealized clean sand or clay under cyclic loading, while the cyclic characteristics of sand-clay mixtures are still unclear. In this study, the dynamic responses of sand-clay mixtures under a large number of shear cycles were investigated through 25 constant-volume cyclic direct simple shear tests on sand-clay mixtures with sand contents of 0 %, 25 %, 50 %, and 75 %. The results indicate that high sand contents and high cyclic stress ratios accelerate the reduction of effective stress in sand-clay mixtures, resulting in a more rapid increase in shear strain. As the sand content increases from 0 % to 75 %, the normalized shear modulus decreases by 35.9 % at a shear strain of 1 %. In contrast, the normalized dynamic shear strength is reduced from between 0.490 and 0.525 to between 0.181 and 0.325 after over 5000 loading cycles. • Higher sand content makes stress paths reach the CSL earlier and hysteresis loops dumpier. • Sand content increases the accumulation of plastic strain with increasing shear cycles. • Sand content accelerates the reduction of the cyclic shear modulus of sand-clay mixtures. • Sand content increases the damping ratio of sand-clay mixtures under cyclic shearing. • Sand content reduces the long-term cyclic shear strength of the sand-clay mixtures. [ABSTRACT FROM AUTHOR]

We present the outcomes derived from controlled laboratory experiments on utilizing gravel rubber mixtures (GRM) as a geotechnical seismic isolation (GSI) stratum beneath the foundational structure of the EuroProteas prototype. The study encompassed three distinct GRM compositions characterized by varying rubber proportions relative to the total mixture weight (0%, 10%, and 30%) employed as the foundation soil. These GSI-structure systems were subjected to external harmonic forces applied atop the structure of EuroProteas across a broad spectrum of frequencies and force magnitudes. Preceding the commencement of field experiments, resonant column and cyclic triaxial compression assessments were conducted on specimens featuring identical rubber fractions and mean grain size ratios. Our laboratory tests revealed that an increase in rubber content resulted in a reduction of the shear modulus (G o) and an augmentation of the damping ratio (D o) while concurrently inducing a more linear character in the G/G o -log γ -D profiles. The findings derived from the laboratory examinations align closely with those ascertained from field investigations. Expressly, it was confirmed that a GSI layer with a thickness of 0.50 meters, composed of a GRM incorporating 30% rubber content, exhibited a discernible reduction in the overall stiffness of the GSI-structure system, accompanied by a corresponding alteration in its fundamental vibrational frequency. The enhanced damping within the system manifested through observable reductions in acceleration recordings and diminished strain development at the base of the GRM layer with 30% rubber content, encompassing a wide range of frequencies. • Controlled laboratory tests on GRM having different percentiles of rubber • Large field tests GRM to investigate their geotechnical seismic isolation capacity • Increase rubber content to reduce the shear modulus and increase damping of the GRM • Findings from the laboratory tests align closely with those obtained from field tests • A GRM layer 0.5 m thick having 30% rubber per weight offers seismic isolation [ABSTRACT FROM AUTHOR]

This paper presents results from full-scale tests aimed at characterizing the seismic response of shallow foundations embedded in tire derived aggregate (TDA) with large particle size. The high shear strength, low shear modulus, and high damping ratio of TDA with large particle sizes make it ideally suited for low-cost Geotechnical Seismic Isolation (GSI) systems. Unidirectional shake table tests were performed on a single-degree-of-freedom superstructure connected to a 0.46 m-deep concrete strip footing embedded within a 1.89 m-thick TDA layer inside a laminar box. The TDA-footing system was subjected to a series of sine sweep motions with varying amplitudes and frequencies between 0.4 and 10 Hz. Substantial nonlinearity was observed in the moment-rocking response of the footing, where the specimen experienced rocking stiffness softening at moment demands slightly below its moment capacity. While the footing exhibited moderate transient settlement and uplift during dynamic oscillation, it demonstrated low residual settlement. The TDA layer offered the footing an effective recentering system with an average residual recentering ratio of 0.991. In addition to being low-cost, abundant, and recycled, the TDA layer had both favorable energy dissipation and recentering, with better seismic resilience than structural hinging and conventional foundation rocking systems in soil. • TDA is a low cost, abundant recycled material for geotechnical seismic isolation. • Substantial nonlinearity was observed in the moment-rocking response of the footing. • TDA specimen experienced rocking stiffness softening at increasing moment demands. • TDA has favorable energy dissipation and recentering. • TDA has better seismic resilience than other passive isolation systems. [ABSTRACT FROM AUTHOR]

The goal of this study is to determine the scope of the impact of pile driving construction vibration on surrounding residential houses and buildings during engineering construction. Firstly, introducing the gradient factor of unsaturated soil, proposed a model for non-uniform variation of pores with depth. Secondly, Consider the coupling between the model and soil skeleton density, relative fluid density, relative gas density, pore fluid, pore gas, and shear modulus. Finally, coupling the pile with the driving depth and propose a pile driving vibration model for non-uniform unsaturated soil. Proposed a new method for solving coupled equations using Hankel transform. Moreover, the analytical solution of this study was validated through on-site experiments. Results show that, deeper the pile is inserted into the soil, the greater the peak vertical velocity at different measuring points. The vibration of the pile is strongest at the last 1 m into the soil. When close to the vibration source, the amplitude values in the three directions are: maximum in vertical direction, followed by horizontal and radial direction, and minimum in horizontal and tangential direction. When pile driving construction is carried out outside the range of vibration influence, the seismic damage generated is equivalent to the seismic intensity below V (excluding V). The rate amplitude calculated by the model established in this study is closer to the measured value. Therefore, using the model established in this work can more accurately evaluate the impact of pile driving vibration during the construction process of highways and high-speed railways. • A pile driving vibration model for non-uniform unsaturated soil is established. • Gradient factor is introduced for uneven changes in porosity with depth. • The analytical solution of this study is validated through on-site experiments. • Variation pattern of vibration distance attenuation is analysed. • Results show significant improvement compared to uniform model. [ABSTRACT FROM AUTHOR]

The small-strain shear modulus G 0 is a fundamental parameter for characterizing the dynamic behavior of soils. In this study, bender element tests were performed to investigate how the effective confining stress σ' c , relative density D r , void ratio e , and a wide range of fines content FC (0%–100%) influence the G 0 of soil mixtures containing both fine and coarse grains. The results show that under the same e and σ' c , G 0 first decreases and then increases with increasing FC. Furthermore, as characteristic state parameters, the extreme void ratios (i.e., the maximum void ratio e max and the minimum void ratio e min) reflect comprehensively the particle size distribution and shape of fine–coarse-grained soil mixtures. Under the same σ' c , the lower limit of G 0 (G 0min) decreases with increasing e max and the upper limit (G 0max) decreases with increasing e min , and the extrapolated upper and lower limits of the normalized G 0 /(σ' c / P a) show a negative power-law relationship with e min and e max , respectively. Empirical formulas are established for the G 0max and G 0min of fine–coarse-grained soil mixtures, and G 0 under various D r can be interpolated according to G 0min (for D r = 0) and G 0max (for D r = 1). Finally, a G 0 prediction model that offers reasonable characterization of fine–coarse-grained soil mixtures with different FC is established based on e min and e max. • A further investigation on the effect of fines content FC(0%∼100%) on small-strain shear modulus G 0 of soil. • Under the same e and σ' c , the G 0 of mixtures first decreases and then increases with the increase of FC(0%–100%). • The extreme void ratios can comprehensively reflect the particle size distribution and shape of fine-coarse-grained soil mixtures. • A G 0 prediction model that characterizes different FC of mixtures is established based on the extreme void ratios. [ABSTRACT FROM AUTHOR]

The beneficial effects of geocells on improving the soils' characteristics have always drawn researchers' attention. However, due to the geocell's large scale, more accurate analyses, such as large-scale cyclic laboratory tests, are still needed to determine the soil-geocell system's actual mechanism. In the present research, a series of large-scale triaxial tests are carried out on poorly graded sand samples with 30 cm diameter and 60 cm height reinforced by geocell with heights of 0.6, 1.0, and 1.4 of the pocket diameter and placement depths of 0.05, 0.15, 0.25, and 0.35 of the samples' height under static and cyclic loading conditions. Contrary to common opinion, the results obtained for unreinforced sands showed that the maximum bulge, instead of the middle, occurred at 0.25 of the sample's height from the top surface. Changing the bulging from the middle to the upper part reflects the role of the direction of stress applied and the accumulation of the deformation due to plastic behavior near the load position. On the one hand, the results of static tests revealed that placing geocell at this depth delivers the best performance in controlling the bulging and reducing settlement values due to the predominant lateral support to the sand particles, reducing the localized stress concentrations, increasing internal friction and interlocking, and reducing the likelihood of shear failure. On the other hand, the geocell with moderate height had higher wall rigidity and stability against deformations compared to the geocell with lower and higher height values due to higher soil confinement potential and more resistance against buckling, respectively. Cyclic loading was also performed on geocell-reinforced soils under 110 cycles with cumulative strains ranging from 0.13 to 0.155 %. The cumulative strains for the unreinforced and reinforced soils were 0.196 % and in the range of 0.130–0.154 %, respectively. The best geocell placement depth under cyclic loading mode was at 0.05 of the sample's height, which had a cumulative strain of 0.13 % in 110 cycles and reduced the cumulative strain by about 34 % compared to the unreinforced sample. The presence of geocell in the soil generally led to an increase in the shear modulus and a decrease in the slope of the damping ratio. Further, the shear modulus was reduced by increasing the geocell placement depth. • Geocell's wall rigidity has a significant impact on confinement and buckling. • Maximum bulge for static and cyclic loadings occurs at 0.25 and 0.05 of the sample's height. • The cumulative settlement of geocell-reinforced sand reduced by about 34 %. • Geocell placement effect at shallow depth was more remarkable under cyclic loading. • Shear modulus was reduced by increasing the geocell placement depth. [ABSTRACT FROM AUTHOR]

The artificial ground freezing method (AGF) is becoming increasingly popular in the construction of subway stations surrounded by soft soil foundations. However, the freeze and thaw lead to the deterioration of the soil properties, causing a huge risk to the subway station subjected to earthquakes. Based on the dynamic triaxial test, the damping ratio and dynamic shear modulus of the soft clay before and after the process of freeze-thaw were obtained. Moreover, the finite element model was conducted to investigate the earthquake behavior of the station structure in the unfrozen and freeze-thaw clay fields. The research results illustrate that there exists a significant difference in the characteristics of the ground settlement and structural displacement between these two soft clay fields subjected to the seismic wave with the peak ground acceleration (PGA) of 0.3 g. Compared with the unfrozen clay field, the surface settlement induced by the earthquake in the freeze-thaw clay field is larger. The damage degree of the subway station is more severe in the freeze-thaw clay field. • Original recording of earthquake acceleration at ground surface was inverted. • Dynamic shear modulus and damping ratio of clay before and after freeze-thaw were studied. • Seismic behaviors of subway station in clay were compared with those in freeze-thaw clay. [ABSTRACT FROM AUTHOR]

The purpose of this study is to evaluate the influence of soil spatial variability (SSV) on the simulation of depth-varying multi-support seismic motions (DMSMs) at offshore sites. Firstly, the random field theory is used to quantify the extent of SSV, and a series of random field models with different characteristics are established for an offshore site by changing the coefficient of variation (COV) and correlation distance of soil parameters. Then, the simulation approach for random ground motion transfer functions (GMTFs) and DMSMs at offshore sites are introduced. The sensitivity of each uncertain soil parameter on the offshore seismic motions is explored using the single variable method. Finally, the effects of SSV on the GMTFs and DMSMs are investigated, in which the effects of COV and correlation distance are studied in detail. The results demonstrate that SSV has a remarkable influence on the GMTFs of offshore sites, which results in a large intensity variation of DMSMs. The sensitivity analysis indicates that the soil density and shear modulus are influential factors for the horizontal components of DMSMs; except these two parameters, the Poisson's ratio also significantly affects the vertical DMSMs. Moreover, both COV and correlation distance can lead to certain variability in the GMTFs and DMSMs, and the effect of COV is more prominent than the correlation distance. This study provides an effective approach for the simulation of DMSMs at random offshore sites, which is valuable for rational probabilistic seismic performance assessment of offshore engineering structures. • An approach for simulating depth-varying multi-support seismic motions at random offshore sites is proposed. • Influences of parameter uncertainties and spatial variability of soil properties are included in the simulation. • Ground motion transfer functions of offshore sites are considerably impacted by soil spatial variability. • COV and correlation distance can affect the transfer functions and seismic motion intensities of offshore sites. [ABSTRACT FROM AUTHOR]

The evaluation of dynamic soil characteristics is a crucial task in understanding the geotechnical engineering problems associated with dynamic loads. Most of the investigations concentrated on non-expansive materials, and there is a dearth of information on the dynamic performance of fibre reinforced expansive soil. This research paper presents the experimental soundings on unreinforced and reinforced expansive soil with randomly distributed polypropylene fibre with varying confining pressures under cyclic loading. Furthermore, to understand the micro structural behavior of the fibre reinforced soil, samples are examined under SEM analysis after being subjected to cyclic loading. Quantitative analysis of soil micro pores was done through image processing. In addition, the study also included the presentation of maximum shear modulus, a modulus reduction curve and a pore pressure variation curve. Experimental results indicate that, the addition of fibres caused an improvement in the dynamic shear modulus and damping ratio with a rise in confining pressure. Inclusion of fibres reduces the permanent strain. The change of dynamic shear modulus and damping ratio over shear strain amplitude and the dynamic shear stress–strain curves were analyzed under different confining pressures. From the SEM analysis, fibre reinforced soil has a fabric with large packets of soil particles. Moreover, the presence of fibres enhanced pore distribution and diminished considerable amount of voids. The results of image processing shown the area porosity of unreinforced soil is 25.3% and that for 1% of fibre reinforced soil is 6.9%. This shows the enhancement of the interface effect of soil reinforced with fibre, which strengthens the soil and integrity. • A scarcity of data on the dynamic performance of fiber-reinforced expansive soil. • Fibre reinforced soil is made of a fabric that contains large packets of soil particles. • The presence of fibres improved pore distribution and reduced the amount of voids significantly. • Image processing results show that the area porosity of unreinforced soil is 25.3% and 6.9% for fibre reinforced soil. • Improving the interface effect of soil reinforced with fibre, which strengthens the soil and its integrity. [ABSTRACT FROM AUTHOR]

For undisturbed loess with water sensitivity and dynamic vulnerability, which is often in a state of damage accumulation due to the influence of natural factors (the fluctuation of groundwater level, rainfall infiltration/evaporation, and seismic load), the impact of relevant engineering problems is significant, and the disaster-causing process is complex. Cyclic simple tests were used to illustrate the behaviour of the dynamic shear modulus of loess exposed to various factors of dry-wet(D-W) cycles and stress conditions (D-W cycles times N , lower limit water content w 1 , and consolidation stress σ v). Using scanning electron microscopy (SEM), we assessed the inherent damage mechanism under D-W cycles. The findings show that the D-W cycles considerably affect the dynamic shear modulus of undisturbed loess, with the strongest effect occurring during the first D-W cycles. Based on the Hardin hyperbolic model, the stress exponent n is a specific parameter of w 1. In addition, the relationship between N and G 0 / P a /(σ v / P a) n is a power function, and G 0 / P a /(σ v / P a) n drops as w 1 and N increase. The fitting parameters a of the dynamic shear modulus ratio normalization model are not sensitive to σ v / P a , D-W cycles times N , and lower limit water content w 1. Based on the dynamic shear modulus, a damage degree prediction method considering N , w 1 , and σ v is established. The results can provide a theoretical reference for earthquake disaster prediction in collapsible loess areas. [Display omitted] • Dry-wet cycles test, cyclic simple shear test, and SEM test were carried out. • The behavior of dynamic shear modulus under the coupled action of dry-wet cycles and dynamic load was investigated. • Method were proposed and verified to predict dynamic shear modulus under dry-wet cycles. • This study can provide reference for earthquake disaster prediction in loess area. [ABSTRACT FROM AUTHOR]

The seismic response of low plasticity medium-stiff soil deposits has been investigated through non-linear one-dimensional analyses carried out with reference to a set of 30 soil profiles, with bedrock depths varying in the range 20–60 m. More than 300 horizontal acceleration time histories recorded on almost flat rock outcropping sites have been used as input motions with amplitude, energy and frequency content varying in wide intervals, which should lead to outcomes of general validity. In the modelling of soil hysteretic behaviour, the backbone curve was described by a modified hyperbolic model calibrated against well-established stress-dependent relationships describing the variation of shear modulus and damping with the strain level. The analysis results show that the stratigraphic amplification factor is significantly influenced by the peak outcrop acceleration and bedrock depth while it is almost unaffected by magnitude sorting of the data; accordingly, original empirical predictive models have been proposed to estimate the stratigraphic amplification factor as a function of the peak outcrop acceleration and bedrock depth. Also, it has been demonstrated that, regardless of the amplitude of the input motion and whatever is the sorting of data with reference to magnitude and bedrock depth, a direct proportionality exists between the stratigraphic and the spectral amplification factors, implying an almost constant value of the spectral shape ratio. Finally, the relevance of using stress-dependent shear modulus and damping curves has been pointed out to allow a reliable evaluation of the stratigraphic and spectral amplifications. • Medium-stiff low-plasticity soil deposits on a complaint bedrock have been analysed. • Stratigraphic and spectral amplification factors have been examined via 1D analyses. • The seismic response analyses have been performed through a non-linear approach. • The effect of bedrock depth on the soil amplification factor has been investigated. • Equations for stratigraphic and spectral amplification factors have been proposed. [ABSTRACT FROM AUTHOR]

Fragility functions and demand hazard curves are important metrics for assessing the seismic damage and risk of an engineering system. This study aims at conducting seismic fragility and demand hazard analyses for earth slopes incorporating soil property variability. The soil parameters of cohesion, friction angle, and initial shear modulus are taken as random variables following a lognormal distribution. Based on a suite of 100 input motions selected, nonlinear dynamic analyses are conducted for a 10-m-high earth slope implemented in FLAC. The corrected cloud analysis is used to describe the relationship of ground-motion intensity measure and engineering demand parameter (EDP) of the slope. The response surface method in conjunction with Monte Carlo simulation is employed to efficiently develop fragility functions accounting for the variability of soil property parameters. The seismic demand hazard curves implemented by incorporating the soil property variability of the slope are subsequently developed. Comparative results indicate that: (1) considering the soil property variability would shift the median and increase the dispersion of the slope fragility functions; (2) neglecting the soil property variability would significantly underestimate the seismic demand hazard, especially for relatively high EDP levels; (3) increasing the variability of soil property parameters would increase the dispersion of fragility functions, inevitably escalating the seismic demand of the slope system. The proposed numerical-based approach provides an effective way of conducting the fragility and demand hazard analyses for earth slopes. • Α corrected cloud analysis is conducted to take failure cases into fragility analysis. • A RS combined with MCS method is used to evaluate the fragility functions. • Soil property variability shifts median and magnifies dispersion of fragility models. • Neglecting soil variability underestimates the seismic demand hazard of slopes. • The Newmark approach exaggerates the effect of soil variability on slope hazard. [ABSTRACT FROM AUTHOR]

This paper presents a fundamental study to explore the independent effects of grain size and shape on the pre-liquefaction, liquefaction, and post-liquefaction shearing behaviour of granular ensembles through a series of multi-stage constant volume simple shear tests. Three different granular materials (glass ballotini, river sand, and manufactured sand) of three different sizes (fine, medium, and coarse) with distinct shape descriptors were chosen for the study. Shape parameters of the granular materials, including roundness, sphericity, regularity, and angularity, and their grain level kinematic behaviour were determined from the microscopic images using image analysis algorithms. Experiments were carried out on reconstituted specimens prepared at different relative densities of 15, 30, and 45%, and the results were interpreted in the light of the critical state framework. Undrained monotonic shear tests showed that ensembles with similar grain shapes exhibit a unique critical state line (CSL) and also exhibit a unique phase transformation line (PTL), irrespective of the grain size. However, ensembles with different grain shapes exhibited different CSLs and different PTLs. Irrespective of grain shape, an increase in grain size increased the liquefaction resistance because of an increase in the tendency for dilation. Irrespective of grain size, an increase in particle angularity and irregularity increased the liquefaction resistance due to an increase in the interlocking tendency at grain contacts. Grain size and shape significantly affected the post-liquefaction shear strength of the granular ensembles. The post-liquefaction initial and secondary shear moduli were found to be highly dependent on the grain size and shape. • Shape descriptors of grains and their contact kinematics were assessed using image analysis. • Undrained monotonic shear behaviour of materials was analyzed in critical state framework. • Multi-stage constant volume simple shear tests were performed for liquefaction assessment. • Independent effects of grain size and shape on the liquefaction response were quantified. • Role of grain size and shape on the post-liquefaction behaviour was assessed. [ABSTRACT FROM AUTHOR]

Coral silt, a type of coral soil with more than 50% silt content, is formed during the process of land reclamation. Given the frequent action of waves, wind, earthquakes and other dynamic loads, the cyclic dynamic shear characteristics of coral silt are important for determining the seismic safety of reef infrastructures. A series of symmetrical and asymmetrical cyclic simple shear tests were performed to characterize the cyclic behavior of coral silt with particular consideration given to the static-cyclic shear stress coupling. Two empirical formulas for the undrained peak shear strength and critical state strength in monotonic simple shear tests are proposed. For both symmetrical and asymmetrical-loading cyclic simple shear tests, a CSR threshold value lying between 0.05 and 0.075 controls the final failure. The cyclic shear stress significantly influences the cyclic deformation, cyclic pore water pressure, cyclic strength, and cyclic shear modulus of coral silt. • The undrained shear strength of coral silt can be estimated by the empirical formula: S up = 0.1992 σ v 0 ′ and S uc = 0.1435 σ v 0 ′ , respectively. • There is a threshold value of CSR between 0.05 and 0.075 that controls whether the final failure. • There is an inflection point in the cyclic shear strain development curve of all ultimate failure tests. • The cyclic pore water pressure development model and cyclic shear modulus significantly depend on CSR. • The dynamic strength of coral silt increases as the α and σ ′ v0 increase. [ABSTRACT FROM AUTHOR]

The effect of gravel contents on the cyclic and post-cyclic monotonic simple shear behavior of gravelly soils during seismic events has significant implications for civil infrastructure. Large-scale cyclic simple shear tests and post-cyclic monotonic simple shear tests were performed on gravelly soils with different levels of gravel content (GC) and loading conditions. The test results indicated that the GC of a sand-gravel mixture (SGM) profoundly influences the mixture's cyclic simple shear characteristics. The SGM specimen with the lowest GC had the broadest hysteresis loops. The shear modulus of the SGM specimens differing in GC was found to increase with increasing cyclic number. The increase in shear modulus was more pronounced during the first 10 cycles. The damping ratio of the SGM decreased to some extent as the cyclic loadings increased. Overall, the results suggested a modified relationship between the damping ratio and shear modulus. The modified function accurately represented the relationship between the normalized damping ratio and the normalized secant shear modulus for SGMs varying in GC. Shear strain obviously decreased with the number of cycles during the initial cyclic loadings, when loading frequency was low. However, at a higher loading frequency, shear strain was less affected by the number of cycles. In general, the inclusion of gravel particles slightly reduced the post-cyclic monotonic shear resistance. • The SGM specimen with the lowest gravel content had the broadest hysteresis loops. • The increase in shear modulus with cyclic numbers was pronounced at first 10 cycles. • Proposed an improved function related the damping ratio and shear modulus. • The cyclic loading frequency has more effects on the initial hystersis loops. • Post-cyclic monotonic shear resistance slightly reduced with inclusion of gravels. [ABSTRACT FROM AUTHOR]

The current study investigated the extent to which the choice of the soil constitutive models can impact the predicted seismic performance of a 20-story reinforced concrete moment-resisting building with a mat foundation considering the Seismic Soil-Structure Interaction (SSSI). Since the soil, in general, is the weakest material, involved in the commonplace geotechnical engineering projects, a soil constitutive model would be able to rule the dynamic response of the system. In this research, the hardening plasticity-based soil constitutive model, named "hyperbolic hardening with hysteretic damping", in conjunction with the two simple, conventional soil models, namely, the isotropic elastic with hysteretic damping model, and elastic-perfectly plastic Mohr-Coulomb with hysteretic damping model, were invoked in the three-dimensional coupled soil-structure numerical simulations using FLAC3D software. The direct method of analysis was used for analyzing the soil-foundation-structure system in one single step without a need to separately analyze each part of the domain. The cherry-picked earthquake excitations, viz, the 1999 Chi-Chi (Taiwan), and 2011 Kohriyama (Japan), were scaled by means of the widely-used response spectrum matching method as per the design response spectrum of a strong rock. The plastic moment concept was employed so as to assign the elastic-perfectly plastic model to the superstructure and its foundation. Additionally, the strain-compatible shear modulus and damping dependency on the cyclic shear strain were considered via the programmed hysteretic damping algorithm. The numerical predictions included the response spectra at the seismic bedrock and ground surface, base shear forces, shear force distributions along the building height, maximum and permanent foundation displacements, and foundation rocking, plus the flooring lateral deflections and inter-story drifts. The life safety limits for the transient and residual total inter-story drift ratios were not met whilst considering the soil pre-failure plasticity. The concluded remarks herein on the significant effects of the soil hardening plasticity on the seismic performance of the adopted 20-story moment-resisting frame would be applicable to the other structures on a mat foundation, potentially experiencing the foundation rocking amidst the earthquakes. Schematic of numerical model concomitant with seismic analysis of soil-foundation-superstructure system, having adopted soil constitutive models, viz, isotropic Elastic with Hysteretic Damping (E-HD), elastic-perfectly plastic Mohr-Coulomb with Hysteretic Damping (MC-HD), and Hyperbolic Hardening with Hysteretic Damping (H2-HD), conducted in FLAC3D, subjected to scaled 1999 Chi-Chi earthquake and scaled 2011 Kohriyama earthquake, so as to investigate effects of soil pre-failure hardening plasticity on seismic performance of 20-story reinforced concrete moment-resisting building frame, supported on mat foundation, experiencing foundation rocking, using soil-structure interaction approach: fx1 • Hyperbolic hardening with hysteretic damping model was adopted for the Seismic Soil-Structure Interaction (SSSI) analysis. • Adopted soil model possessed the shear strain hardening, dilation hardening, and pressure-dependent stiffness. • Soil hardening plasticity dislocated the predicted seismic performance level of the adopted 20-story moment-resisting frame. • Excluding the soil plasticity would result in the life-threatening seismic design of a building with significant rocking. [ABSTRACT FROM AUTHOR]

Abstract Characterizing the small-strain shear modulus (G 0) of sand with fines is of importance in geotechnical applications since natural sand is usually not clean but contains a certain amount of fines. This paper presents an experimental study to investigate G 0 values of several sand-fines mixtures, formed by mixing clean quartz sands of different sizes with crushed silica fines of varying quantity. Focus of the study is on the possible interplay between the influence of particle size disparity and the influence of fines contents for which current understanding is not adequate. By defining the particle size disparity as D 50 / d 50 , where D 50 is the mean size of base sand and d 50 is the mean size of fines, a critical range of size disparity is found to be approximately between 4 and 7. When the size disparity is smaller than 4, the role of fines is manifested mainly by fines content; when the size disparity is beyond 7, the contribution of fines to the load transfer gradually becomes negligible because in this case fine grains tend to roll into the voids. A new concept, referred to as combined size disparity, is proposed to capture the influence of fines content and the influence of size disparity in a collective manner. By adopting this concept, an empirical relationship is proposed for estimating G 0 values of sand-fines mixtures. The predictive performance of the relationship is then examined using literature data and a reasonably good agreement between prediction and measurement is obtained. Highlights • The small-strain shear modulus (G 0) of sand-fines mixtures was studied. • A critical range of size disparity was found to be approximately between 4 and 7. • The influences of fines content and size disparity on G 0 are strongly interplayed. • A new concept, referred to as combined size disparity, was proposed. • By using this concept, an empirical relationship was proposed for estimating G 0. [ABSTRACT FROM AUTHOR]

The safe operation of offshore wind turbines (OWTs) is significantly influenced by the combined effect of wind, waves, and offshore earthquakes. However, limited seafloor ground motion data have been used to determine the dynamic characteristics and responses of OWTs subjected to offshore earthquakes. Hence, synthetic seafloor ground motions are particularly important for seismic analysis of OWTs. This paper proposes a new method to simulate seafloor ground motions. In the study, the dynamic shear modulus of the water-bearing soil layer and the damping effect of the soil–seawater layers were introduced to modify the simple Crouse and Quilter (C-Q) model in seawater and P-SV and SH transfer function models at offshore sites. Further, three-dimensional seismic waves were synthesized based on the modified transfer function models at a typical offshore site with bedrock–soil–seawater layers, and a fully coupled numerical analysis model of OWTs, including the rotor nacelle assembly, tower structure, and substructure with pile–soil interaction (PSI) under wind, wave, and seafloor ground motion, was established by incorporating the earthquake module and PSI module into the updated FAST v8 software. Moreover, based on the established coupled OWT model, the measured seafloor ground motion records and the seafloor ground motions synthesized using the proposed method were compared, and a coupled analysis of the OWT under wind, wave, and offshore earthquake loadings was carried out. Furthermore, the coupled mechanisms of the OWT under synthesized and recorded seafloor ground motions were determined. • The transfer function of SH, SV and P seafloor ground motions in the typical offshore sites were modified. • The fully coupled analysis model of offshore wind turbines with foundation flexibilities under offshore earthquakes was established. • The comparsions between the recorded and synthesized seafloor ground motions were carried out. [ABSTRACT FROM AUTHOR]

This study shows the modelling of the dynamic properties of sand-polyurethane composite materials through the Artificial Neural Network method (ANN). Such properties are relevant to assess the effectiveness of polyurethane injected into the foundation soil as Geotechnical Seismic Isolation (GSI) system. Three FeedForward Neural Network (FFN) models are developed for the prediction of the shear modulus decay, the normalised shear modulus decay and the damping ratio curve. Four inputs are considered, namely the dynamic properties of pure sand and pure polyurethane, the volumetric percentage of polyurethane and the isotropic confining stress. Each model is trained and tested on a database including previous experimental results of Resonant Column (RC) tests performed on layered sand-polyurethane specimens, with polyurethane volumetric percentages varying from 10% to 30%. In all cases, the network architecture is found to be optimal with a single hidden layer and the number of hidden neurons from 4 to 6 according to the complexity of the data to be fitted. By comparing the predicted properties with the experimental results, a good prediction quality of the models is shown both in terms of the coefficient of correlation R 2 and the Mean Squared Error MSE. A relative importance analysis finally reveals that polyurethane mainly affects the properties of the composite materials with its volumetric percentage, rather than its dynamic properties especially in terms of shear modulus. • Sand-PUR dynamic properties predicted through Artificial Neural Network method. • Fully-connected FeedForward Neural Networks trained on Resonant Column test results. • Four-input simplified FNN modelling for layered sand-polyurethane specimens. • FNN models to assess PUR-based GSI effectiveness in large-scale applications. • Connection Weights reveal sand-PUR dynamic properties affected by PUR percentage. [ABSTRACT FROM AUTHOR]

In offshore engineering, the dynamic properties of ultrasoft clay in the seabed could affect the stability of offshore construction under dynamic loading. The typical rheological response of ultrasoft clay is studied based on the test results from large amplitude oscillatory shear tests with a rheometer. The ultrasoft clay undergoes three phases: the solid phase, transition phase and liquid phase, under dynamic loading. Modulus overshoot is observed when a phase transition occurs. The shear modulus and damping ratio of ultrasoft clay are studied based on the relationship between rheological parameters and dynamic parameters. The results show that the maximum shear modulus of ultrasoft clay could be expressed as a function of water content. Compared with general clay, the normalized shear modulus of ultrasoft clay decreases, and the damping ratio rapidly increases with increasing shear strain. Models describing the change in the normalized shear modulus and damping ratio with the shear strain of ultrasoft clay are suggested based on our test results. This study could aid in the evaluation of the stability of submarine structures at the seabed level under dynamic loading. • Dynamic properties of ultrasoft clay were studied by large amplitude oscillatory shear tests with a rheometer. • The effect of water content on the rheological behavior of ultrasoft clay was investigated. • The phase transition of ultrasoft clay was studied based on the typical rheological response. [ABSTRACT FROM AUTHOR]

It is of great significance to study the seismic response of the shallowly buried subway station in the inhomogeneous site caused by the soil consolidation. The dynamic characteristics of Shanghai soft clay under different confining pressures were studied by a series of dynamic triaxial tests. The nonlinear analysis was used to investigate the influence of the inhomogeneous clay site on the seismic response of the shallowly buried subway station. The variations of dynamic shear modulus ratio and damping ratio under different buried depths were obtained. The research results indicate that the damage to subway stations is more serious in the inhomogeneous clay site under the same seismic wave. The inhomogeneity of the clay site has an amplification effect on the horizontal relative displacement between the ceiling and bottom slabs, as well as the vertical displacement of the ground surface. However, the effect of the inhomogeneous site on the acceleration of the slabs and the maximum horizontal relative displacement of the middle column is small. After the earthquake, the horizontal relative displacement of the middle column is strongly affected by the inhomogeneous site. The results can provide a reference to the earthquake prevention and disaster reduction in the soft clay area. • Variations of dynamic shear modulus and damping ratio with depths were considered. • Seismic response was analyzed with considering inhomogeneity of clay site. • Seismic response of inhomogeneous site was compared with that of homogeneous site. [ABSTRACT FROM AUTHOR]

Inherent fabric anisotropy has been widely recognized to have significant effects on the liquefaction behavior of sand. A discrete element method (DEM) study was conducted to investigate the liquefaction behavior of inherently anisotropic sand under cyclic simple shear conditions. In the DEM model, the under-compaction method was modified to generate uniform and inherently anisotropic specimens. A series of DEM simulations of undrained cyclic simple shear tests were performed to investigate the effects of bedding plane angles with a full spectrum ranging from −90° to +90°. The relative magnitudes of the three effective normal stress components were compared and analyzed. The internal structure evolution was quantified through a contact-normal-based fabric tensor that could describe the load-bearing structure of granular specimens. The simulation results show that the effect of bedding plane angle on the liquefaction resistance of anisotropic sand is not monotonic. For example, as the bedding plane angle of specimen increases from 0° to 90°, the liquefaction resistance first decreases and then increases, with the most detrimental scenario occurs at 45°. This could be explained by correlating the magnitudes of shear modulus with the discrepancy between the loading direction and the direction of fabric during each cycle. • 3D DEM simulations of undrained cyclic simple shear tests were conducted on inherently anisotropic specimens. • The three effective normal stress components for undrained cyclic simple shear conditions were compared and analyzed. • The internal structure evolution was quantified through a contact-normal-based fabric tensor. • The effect of bedding plane angle on liquefaction resistance was explained from microscopic mechanisms. [ABSTRACT FROM AUTHOR]

Un-utilized coal ash is commonly used as fill material for the construction of highway and railway embankment, which experiences different anisotropic stress conditions under different types of loading conditions. This study investigated the shear modulus of compacted coal ash under different anisotropic stress conditions simulating highway and railway embankment stress states. The small-strain shear modulus was obtained by performing the bender element tests under consolidation and shearing stages of consolidated undrained (CU) triaxial testing. The effect of different consolidation stress paths on the small-strain shear modulus of coal ash was evaluated using experimental data obtained from a bender element system affiliated with a stress-path controlled advanced triaxial setup. The small-strain shear modulus of coal ash at different ranges of mean effective stresses (at the end of consolidation) was also determined under various anisotropic stress conditions. The measured shear modulus (G max) of compacted coal ash under small-strain dynamic loading conditions was determined to be the function of mean effective stresses and deviatoric stress. At the later stage of shearing, the shear modulus was observed to attain a constant value subjected to large strain levels. • Bender element system to determine small strain shear modulus (G max). • G max increased with increasing anisotropy at end of consolidation. • For IC and K 0 condition, G max found to be more dependent on p ' than e. • For shearing, maximum value of G max obtained to be higher for K c = 1 than K c = 0.35 • During shear deformation, G max found to be directly proportional to p ' and σ d. [ABSTRACT FROM AUTHOR]

The dynamic impedance of saturated soil layer with a radially inhomogeneous boundary zone to horizontally vibrating pile is theoretically investigated. A continuous, radial variation for the soil properties is assumed, so that there are no wave reflections from the fictitious interface. For the purpose of analysis, the inhomogeneous boundary zone is subdivided into a series of concentric annular sub-zones with constant material properties. The impedances of soil are obtained by adopting transfer matrix method. To verify the solution obtained herein, the computed results are compared with those obtained from earlier solution. Then, a parameter study is performed to investigate the effect of parameters involved. It is found that variations in shear modulus and the width of boundary zone have significant influence on the soil impedances. [ABSTRACT FROM AUTHOR]

The present study reviews a series of cyclic triaxial tests to investigate the liquefaction characteristics of Babolsar sand reinforced with randomly distributed fibers using an energy-based approach. The effect of fiber content, fiber length, confining pressure, and relative density were studied. The test results revealed that the addition of fibers increased the number of cycles required to liquefaction, resulting in higher cumulative dissipated energy. This accounted for the higher cyclic shear resistance of reinforced sand compared to unreinforced sand. Capacity energy is defined as cumulative dissipated energy to onset of liquefaction. The test results showed that W liq was significantly affected by the fiber inclusion. Comparative studies demonstrated that energy-based method is a good way to evaluate liquefaction potential of fiber-reinforced sands. [ABSTRACT FROM AUTHOR]

A random effect regression model is used to formulate a unified equation and estimate shear wave velocity ( V s ). Standard penetration test ( SPT ) number, effective overburden pressure, plasticity index, and the fines content ( F c ) are used as input parameters. First, a fixed model regression is used to obtain the regression parameters. SPT number and shear wave velocity are measured at 2 m intervals up to a depth of 10 m, for 71 boreholes, distributed evenly in Urmia city. Plasticity index and fines content are evaluated from laboratory tests that were performed on 355 samples obtained from the 71 boreholes (i.e., 5 samples from each borehole). Statistical analysis performed on the fixed effect model showed the need for examining the random effects arising from variable SPT test conditions in each borehole. A mixed effect regression model is employed to investigate such effects. The distribution of residuals is found to satisfy the normality criteria for the mixed effect model. A strong fit for the model is obtained, and through statistical evidence, it is implied that the proposed model is practical. The model's most prominent feature is the capability of unifying different soil types via the incorporation of plasticity index and fines content as inputs. [ABSTRACT FROM AUTHOR]

Dynamic properties of soils at very small strains are of particular interest for geotechnical engineers for the characterization of the behaviour of earth structures subjected to a variety of static and dynamic stress states. This study reports on the small-strain dynamic properties of silty sand with particular emphasis on the effect of non-plastic fines content on the small-strain shear modulus ( G max ) and material damping ( D s , min ). Several clean sands with a wide range of grain size distribution and particle shape are mixed with different percentages of a silica non-plastic silt. The laboratory created samples are subjected to torsional resonant column tests with small-strain shear moduli and damping ratios measured along an isotropic stress path. It is shown that at low percentages of fines content, there is a significant difference between the dynamic properties of the various samples due to the different characteristics of the sand portion of the mixtures. However this variance diminishes as the fines content increases and the soil behaviour becomes mainly silt-dominant, rendering no significant influence of different sand properties on the small-strain shear modulus and damping ratio. Using the experimental results, new expressions for the prediction of small-strain shear modulus and small-strain damping ratio of non-plastic silty sands are developed accounting for the percentage of silt and the characteristics of the sand portion. [ABSTRACT FROM AUTHOR]

This paper presents a one dimensional nonlinear stress-strain model called ARCS ( A xis R otation and C ubic S pline) capable of reproducing any user-input modulus reduction and damping curve. Unlike many previous nonlinear models, the ARCS model does not utilize Masing's rules, nor does it require a specific functional form for the backbone curve such as a hyperbola. Rather, the model matches the desired modulus reduction curve by fitting cubic splines to the implied stress-strain curve, and matches the damping curve by utilizing a coordinate transformation technique in which one axis lies along the secant shear modulus line with the other axis in the orthogonal direction for a particular unload-reload cycle. Damping is easily controlled in the transformed coordinate space. An inverse coordinate transformation returns the desired stress. The integration algorithm is independent of strain step size, meaning that the returned stress for a large strain increment is identical to the stress that would be returned by subdividing the strain increment into smaller increments. Small-strain damping may be modeled hysteretically, avoiding the need for supplemental viscous damping. The model is shown to match the results of laboratory cyclic simple shear tests involving deliberately irregular stain histories. The performance of the model is illustrated in a set of ground response simulations where its predictions are compared with those of existing models. The ARCS model does not explicitly account for rate effects, cyclic degradation, or pore pressure generation. However, the equations can potentially be adapted in more advanced constitutive models to capture these effects. Such implementations are reserved for future publications. [ABSTRACT FROM AUTHOR]

As a type of artificial filling material, the shear modulus and damping ratio of expanded polystyrene (EPS) composite soil are two key parameters used to analyze the dynamic stability of an embankment. Nineteen combined axial–torsional tests are conducted on hollow cylinder specimens of EPS composite soil to study its dynamic characteristics under the complex stress path induced by the simulated traffic loadings. The characteristics of skeleton curve, dynamic shear modulus and damping ratio for EPS composite soil are analyzed. It is found that EPS composite soil is characterized by typical dynamic nonlinearity, which is influenced by the mixing ratio and the initial stress state. The increasing cement content can effectively improve the dynamic strength of EPS composite soil. EPS bead content has a slight influence on the initial shear modulus of EPS composite soil as well as the cyclic stress-strain curve in the linear elastic stage. However, the increasing EPS bead content obviously reduces the dynamic strength. The initial shear modulus increases with increasing initial minor principal stress for the isotropic and anisotropic consolidated specimens. The characteristics of modulus attenuation are significantly influenced by the initial minor principal stress, EPS bead content and initial rotation angle of the major principal stress axis. The “structural damping” effect induced by the weak interface formed between EPS beads and cemented soil is an important component of the damping mechanism for the EPS composite soil. Based on the experimental results, this paper provides the empirical models to describe the skeleton curve, modulus attenuation and damping growth characteristics for EPS composite soil. [ABSTRACT FROM AUTHOR]

A deep learning method consisting of the gated recurrent (GRU) neural network is proposed to predict the seismic responses of underground structures in single-layered soil and multi-layered soil. The proposed neural network employed ground motion as the input, and the acceleration time history of underground structure acquired by a finite element method (FEM) to be the output. The distribution of the normalized errors and the error of the peak value of the predicted acceleration time history are adopted to evaluate the prediction performance and extrapolating ability of the proposed GRU architecture. The GRU network showed better prediction performance in the seismic response of a tunnel in a homogeneous sand layer than in a clay layer, as sand has a higher shear modulus representing lower nonlinearity of the soil-structure system. The peak acceleration of a two-story three-span subway station in multi-layered soil exhibited similar prediction accuracy to the tunnel in single-layered clay. The proposed GRU neural network generally displayed satisfactory prediction performances on the acceleration responses of underground structures in various soil conditions. • Proposes a GRU-based model to predict seismic response of underground structures. • Model employes ground motion as input. • Exhibits better seismic response of tunnel in sand than in clay layer. • Obtains well acceleration responses of subway station in multi-layered soil. [ABSTRACT FROM AUTHOR]

Direct simple shear tests were conducted to investigate the cyclic behaviour, dynamic properties, and stress–dilatancy relationship of fine-grained silica sand for a wide range of constant vertical stresses, including low stresses. Multi-stage cyclic tests were conducted by increasing the shear strain amplitude from low to high values in subsequent loading stages. Test results show that the volumetric strain is related to the vertical stress and shear strain amplitude. The cyclic shear modulus decreases and the damping ratio increases with shear strain amplitude, and they are influenced by the low-amplitude cyclic loading history. The volume change is related to the cyclic stress–dilatancy relationship, which depends on the vertical stress, shear strain amplitude, number of cycles, and shearing direction. In some tests, the stress–dilatancy relationship can be represented by two parallel lines for unloading and reloading, except for the initial parts. The increase in density with cyclic loading reduces the contractive behaviour and increases the dilative response in the large-amplitude loading cases, which reduces the rate of volumetric compaction with the number of cycles. • Multistage cyclic tests were conducted using a direct simple shear apparatus that has been designed for relatively low-stress level tests. • Tests were conducted under constant vertical stress of 12.5–400 kPa to investigate normal stress effects on drained cyclic behaviour. • Test results show that stress–dilatancy of sand in cyclic loading is not unique but highly depends on normal stress, density, number of the loading cycles, shear strain amplitude and loading direction. • Unique linear or two almost parallel nonlinear lines of stress–dilatancy, as found in some previous studies, is valid only for certain normal stresses and shear strain amplitudes. [ABSTRACT FROM AUTHOR]

The soil small-strain shear modulus, G 0 , is necessary for static and dynamic soil analyses and is often correlated to other soil properties such as density and void ratio, on their turn depending on gradation. The paper first presents a concise literature review of parameters influencing G 0 in detail. Secondly, a particle shape analysis is performed. Silica sand is found much more spherical than calcareous sand, and calcareous sand becomes more spherical after crushing. Bender element test results indicate that not only uniformity coefficient (C u ) but also particle characteristics including particle shape and stiffness are very important to G 0 . G 0 of calcareous sand is found higher than that of silica sand. Indeed, with less sphericity and more angularity, the variety of particle shape in calcareous sand produces a better fabric for shear wave propagation. For calcareous sand, the test results show that particle shape is the main factor affecting G 0 . Less dynamic stiffness is found for particles owning more sphericity and less angularity. The increase of C u or finer particles (at low C u ) causes a decrease in G 0 . Finally, predictions of G 0 for the tested calcareous sands using empirical equations from previous studies give very high relative errors (16.7–30%). [ABSTRACT FROM AUTHOR]

Correlations between “dynamic” (small-strain) and “static” (large-strain) stiffness moduli for sand are examined. Such correlations are often used for a simplified estimation of the dynamic stiffness based on static test data. The small-strain shear modulus G dyn = G max and the small-strain constrained modulus M dyn = M max have been measured in resonant column (RC) tests with additional P-wave measurements. Oedometric compression tests were performed in order to determine the large-strain constrained modulus M stat = M oedo , while the large-strain Young's modulus E stat = E 50 was obtained from the initial stage of the stress-strain-curves measured in drained monotonic triaxial tests, evaluated as a secant stiffness between deviatoric stress q =0 and q = q max / 2 . Experimental data for 19 sands or gravels with specially mixed grain size distribution curves, having different non-plastic fines contents, mean grain sizes and uniformity coefficients, were analyzed. Based on the present data, it is demonstrated that a correlation between M max and M oedo proposed in the literature underestimates the dynamic stiffness of coarse and well-graded granular materials. Consequently, modified correlation diagrams for the relationship M max ↔ M oedo are proposed in the present paper. Furthermore, correlations between G max and M oedo or E 50 , respectively, have been also investigated. They enable a direct estimation of dynamic shear modulus based on static test data. In contrast to the correlation diagram currently in use, the range of applicability of the new correlations proposed in this paper is clearly defined. [ABSTRACT FROM AUTHOR]

A series of 1-g shaking table tests were performed on five reduced-scale soil-nailed wall models to investigate the influence of peak acceleration, loading duration, and nail length on seismic response of the soil-nailed walls in terms of the distribution of shear modulus (G) and damping ratio (D) in soil-nailed mass, the axial force distribution along the nails and the distribution of dynamic lateral earth pressure behind the surface. It was found that the seismic response of walls highly depends on the length of nails and input motion parameters. By introducing a new non-dimensional parameter (G global ) for soil-nailed walls, it was observed that the values of G , G/G 0 , and D are strongly dependent of confining pressure, L/H ratio, and shear strain levels, so that the variation trend of these parameters with γ is well expressed as an exponential equation with a high correlation coefficient. Additionally, a proper convergence was found between T max /H.γ s .S V .S H and L/H ratio at different levels of acceleration and duration, so that T max /H.γ s .S V .S H can be defined as a function of L/H ratio and seismic parameters for different rows of nail. Also, It was discovered that the values of predicated earth pressure by conventional methods in static and seismic conditions are too conservative and these methods predict the location of the resultant lateral earth pressure higher than the actual point. [ABSTRACT FROM AUTHOR]

In this paper, shear wave propagation in soils is examined in a stochastic context considering spatial variability of the shear modulus soil parameter. To this purpose, the recently established concept of dynamic mean and variability response functions (DMRF, DVRF) is reformulated in the framework of stochastic finite element analyses of shear wave propagation problems in order to efficiently calculate the response time history statistics of the soil surface. Similarly to the approximation formulas of classical VRFs, a fast Monte Carlo simulation procedure is implemented to numerically evaluate the above functions in the time domain. The main advantage of the proposed methodology lies on the independence of the DMRF and DVRF on the marginal probability density function and correlation structure of the stochastic system parameter, which in our case is assumed to be the inverse of the soil shear modulus 1 / G . By integrating the product of the spectral density of 1 / G with the DMRF and DVRF, the mean and variance of the ground response are obtained at each time step of the dynamic analysis. The method also allows for the estimation of time dependent but spectral and probability distribution free upper bounds of the response mean and variance. To illustrate the efficiency and applicability of the proposed approach, stochastic finite element analyses of wave propagation of a Ricker synthetic wavelet as well as a recorded earthquake motion in 1D and 2D soil domains are performed and a sensitivity analysis is carried out with respect to various correlation structures of the underlying random fields representing 1 / G . The accuracy of the proposed methodology is validated with comparison to direct Monte Carlo simulation. Useful conclusions regarding the sensitivity of the system response to the spectral characteristics of the underlying random fields representing 1 / G are drawn. [ABSTRACT FROM AUTHOR]

The recent significant development of technical infrastructures in Poland, along with the construction of tower blocks, roads, railways and underground rapid transit system, resulted in greater demands for investment projects as well as geotechnical data characterizing the variation of various soil parameters found in the subsoil. The most important parameter, which represents the stiffness of soil deposits, is the shear modulus G . Therefore, this study focused on determining the initial shear modulus of cohesive soils from the area of the capital of Poland. In this research, a set of the resonant column (RC) tests was performed and the influence of three selected factors, i.e. mean effective stress ( p’ ), void ratio ( e ) and plasticity index ( PI ), on the low-amplitude shear modulus ( G 0 ) was presented and discussed. The results obtained from laboratory tests indicated that the stress state plays an important role for the small-strain shear modulus values of the Polish Quaternary cohesive soils. In contrast, there was no clear trend observed for the significant effect of e or PI on G 0 for the studied soils. Based on the performed tests, the authors proposed the power-law relations for G 0 versus p ′ of the forms: G 0 =3.02p′ 0.68 and G 0 =0.82p′ 0.96 . [ABSTRACT FROM AUTHOR]

The dynamic properties of sands, including the small-strain shear modulus (G max ) and the small-to-medium strain shear modulus (G) and shear damping (D s ) have been examined extensively in the literature. However, most works published over the past decades have focused on the behavior of soils subjected to isotropic stress paths. In the present study, the dynamic properties of a biogenic sand with origin from Western Australia were examined in the laboratory using a resonant column of fixed-partly fixed boundary conditions. This configuration allows the study of the small-strain shear modulus, the strain-dependent modulus and shear damping of samples subjected to stress anisotropy, which stress conditions may represent more effectively the in-situ state of a soil. For this purpose, proper calibrations of the resonant column were carried out in order to capture the rotational inertia of the apparatus in a wide range of cyclic frequencies covering, in this way, typical resonant frequencies of real soil samples. Basic geotechnical characterization of the biogenic sand was carried out quantifying the shape of the grains and conducting a series of monotonic triaxial tests capturing the peak and critical state friction angles. The dynamic test results indicated a more pronounced effect of the stress anisotropy on G max of the biogenic sand in comparison to the corresponding effect on quartz sands reported in the literature. For the limited set of experiments conducted in the study, the effect of stress anisotropy was found less pronounced for the small-to-medium strain shear modulus and shear damping, even though the results indicated a marked drop of shear damping at small strains when the samples were subjected to a deviatoric compressive load. [ABSTRACT FROM AUTHOR]

Dynamic response in a saturated porous medium (i.e. two-phased medium) is significantly different from the commonly assumed single-phased elastic medium in vibration analyses. To investigate the ground vibration isolation by wave impeding block (WIB) in saturated layered soils under vertical loading, an improved three-dimensional (3D) boundary element model is established for analyzing the soil-foundation-WIB interaction problem. The equations of boundary element method (BEM) for saturated and layered soils were deduced using fundamental solution (Green's function) based on thin layer method (TLM), in order to account for the lamination characteristics of the ground. The vibration screening effectiveness of WIB with different thicknesses, equivalent diameters, shear module and embedded depths were systematically investigated and the results were compared with those in a single-phased elastic soil. The results show that the WIB can effectively reduce the vibration amplitude in the saturated ground and its effectiveness increases with increasing shear modulus, equivalent diameter, thickness, and decreasing embedded depth of the WIB. In addition, a significant amplification of the vibration is observed in the saturated soil when the dimensionless embedded depth is larger than or the dimensionless thickness is smaller than a threshold value. [ABSTRACT FROM AUTHOR]

High rockfill dams experience a wide range of shear strain amplitudes during earthquakes. To provide more reliable material property descriptions for earthquake response analysis of high rockfill dams, this study investigates the dynamic properties of rockfill materials in a wide strain range by large-scale cyclic triaxial testing with a high-sensitivity laser sensor. The results reveal the considerable increase of shear modulus and decrease of damping ratio with increasing confining pressure for a given initial stress ratio and the significant effect of the initial stress ratio on the small-strain shear modulus and normalized shear modulus. Previously proposed equations were found to imprecisely depict the variation of the dynamic shear modulus of rockfill materials for a wide strain range. Furthermore, the dynamic shear modulus is dependent on the Initial stress ratio in the anisotropic stress condition. Based on the existing hyperbolic model, a modified model for rockfill materials is suggested to accurately estimate the nonlinear behavior. The applicability of the modified model and previous studies for rockfill materials are assessed in the estimation of the normalized shear modulus. The results provide a reference for evaluating the accurate shear modulus in a wide strain range for strong earthquake motions. [ABSTRACT FROM AUTHOR]

Offshore wind turbine (OWT) foundations are subjected to a combination of cyclic and dynamic loading arising from wind, wave, 1P (rotor frequency) and 2P/3P (blade passing frequency) loads. Under cyclic/dynamic loading, most soils change their characteristics. Cyclic behaviour (in terms of change of shear modulus change and accumulation of strain) of a typical silica sand (RedHill 110) was investigated by a series of cyclic simple shear tests. The effects of application of 50000 cycles of shear loading having different shear strain amplitude, cyclic stress ratio (ratio of shear to vertical stress), and vertical stress were investigated. Test results were reported in terms of change in shear modulus against the number of loading cycles. The results correlated quite well with the observations from scaled model tests of different types of offshore wind turbine foundations and limited field observations. Specifically, the test results showed that; (a) Vertical and permanent strain (accumulated strain) is proportional to shear strain amplitude but inversely proportional to the vertical stress and relative density; (b) Shear modulus increases rapidly in the initial cycles of loading and then the rate of increase diminishes and the shear modulus remains below an asymptote. Discussion is carried out on the use of these results for long term performance prediction of OWT foundations. [ABSTRACT FROM AUTHOR]

Dynamic triaxial tests of lightweight soil were conducted to explore the dynamic characteristics of expanded polystyrene (EPS) particle lightweight soil under traffic load. The effects of different mixed ratios, confining pressure, frequency on the backbone curves, dynamic shear modulus, and damping ratio characteristics of lightweight soil were investigated. The maximum dynamic shear modulus formula and maximum damping ratio formula of lightweight soil were established. The results indicated that backbone curves of lightweight soil had typical nonlinear and strain-hardening characteristics. With an increase in dynamic shear strain, the dynamic shear modulus curves appeared as inverse "S-shaped". The dynamic shear modulus in the initial stage varied under different confining pressures. For γ d ＞10−4, the attenuation rate of the dynamic shear modulus increased with an increase in the dynamic shear strain, and for γ d ＞10−2, the relationship curve between the dynamic shear modulus and dynamic shear strain coincided gradually, and the attenuation process then stabilized. Owing to the special structure of lightweight soil, the damping ratio curves were "Bell-shaped" and "S-shaped." Both the confining pressure and compressive yield stress determined the change trends of the damping ratio curves of the lightweight soil. The specimens were in an over-consolidated state and the mixed soil was in the state of shear dilatancy under dynamic loads when the confining pressure was less than the compressive yield stress, resulting in "Bell-shaped" damping ratio curve. The specimens were in the normal consolidated state and the mixed soil was in the state of shear shrinkage under dynamic loads when the confining pressure was greater than the compressive yield stress, resulting in "S-shaped" damping ratio curves. The calculation methods of the relative structural degree k and generalized void ratio e ' of lightweight soil were defined to express the structural damage laws of lightweight soil having different mixed ratios under complex stress conditions using a unified formula. Based on Hardin's empirical formulas, the maximum dynamic shear modulus and maximum damping ratio formulas of lightweight soil were established by introducing the relative structural degree k and generalized void ratio e '. The formulas can quantitatively describe the dynamic responses of the special structure of lightweight soil under complex stress conditions. [Display omitted] • The backbone curves of lightweight soil have typical nonlinear and strain-hardening characteristics. • The dynamic shear modulus curves of lightweight soil appear as inverse "S-shaped" with an increase in the dynamic shear strain. • Owing to the special structure of lightweight soil, the damping ratio curves are "Bell-shaped" and "S-shaped.". • The maximum dynamic shear modulus and maximum damping ratio formulas of lightweight soil are established by introducing structural parameters. [ABSTRACT FROM AUTHOR]

The study of site-specific dynamic properties of soil holds vital importance in many geotechnical engineering problems for the region holding high active seismicity. The Sutlej River basin, a valley and high-risk seismic zone in the north-eastern part of the Punjab state, has been considered for the study. The site-specific shear modulus reduction curves and material damping ratio curves for a range of shear strain amplitudes have been developed under varying experimental conditions of confining pressure, relative density, and loading frequency using the resonant column (RC) tests and cyclic torsional shear (CTS) tests. The study addresses the usage of two testing approaches, i.e., resonant column test (RC) and cyclic torsional shear test (CTS), for the estimation of shear modulus and damping ratio values at varying shear strain amplitudes. The regression analysis has been performed for the two testing techniques viz. RC and CTS to study the sensitivity of shear modulus values and material damping ratio values towards varying experimental conditions. The shear modulus and damping ratio values determined from cyclic torsional shear tests were observed to have great dependency on the frequency of loading. The knowledge of site-specific dynamic properties will support practical interpretation for the geotechnical engineering problems in the region. • The resonant column and cyclic torsional shear testing of Sutlej river sand have been performed under varying experimental conditions to analyze the dynamic properties. • Site-specific shear modulus reduction and damping ratio curves have been developed under varying relative density, confining pressure, and loading frequency conditions. • The influence of frequency of cyclic torsional shear loading on shear modulus and damping ratio has been analyzed. • The modified hyperbolic model has been used to assess the non-linear dynamic behaviour of sand. [ABSTRACT FROM AUTHOR]

The use of rubber-sand mixture (RSM) cushion in geotechnical seismic isolation (GSI) systems is an emerging technique for protecting buildings in earthquake-prone areas. The advantage is that RSM with high shear resistance and low shear modulus improves the foundation soil, allowing seismic energy to be partially dissipated in the cushion before it is transmitted to the structure. However, the isolation effect of the RSM cushion considering site classification has not been recognized due to the complexity of the problem. In this paper, a simplified analysis model is established to study the seismic performance of the RSM cushion, in which 195 ground motion records are obtained from different site conditions according to the Code for Seismic Design of Buildings GB50011-2010, reflecting the influence of site classification. By using the developed theoretical analysis method, the seismic isolation effect of the RSM cushion under different site classes is investigated. The key influencing factors to be considered include the cushion thickness, base pressure and seismic excitation intensity. The results show that: 1) The isolation effect of the underlying RSM cushion on the superstructure is affected by site classification. The harder the site, or more specifically, the shorter the predominant period of the site, the better the isolation effect of the RSM cushion. 2) For the same site classification, the isolation effect increases with increasing cushion thickness, base pressure and seismic excitation intensity. In particular, the robustness of the seismic performance of the RSM cushion deteriorates upon reaching a cushion thickness of 500 mm, and this deterioration in robustness is independent of site classification. Overall, the present study is the first systematic analysis of the effects of ground motion on GSI systems with RSM as the core under different site classes, and the research findings are of great significance for the low-cost seismic design of residential houses in developing countries. • Seismic performance of rubber-sand mixture cushion considering site classification is studied. • Theoretical-based analysis model is established to identify the isolation effect of the cushion. • A damping-based hysteresis model is introduced to simulate the nonlinear site response. • Effects of cushion thickness, base pressure and seismic excitation intensity are evaluated. • Response spectrum reduction coefficient of the isolation system is quantified. [ABSTRACT FROM AUTHOR]