Dynamic active thrust from c–ϕ soil backfills

This technical note presents an analytical derivation of the expression for the total dynamic active thrust on a retaining wall from the c–? soil backfill considering both horizontal and vertical seismic coefficients. The derivation is based on the Coulomb sliding wedge concept, and it considers tension cracks, wall adhesion, and surcharge in order to make the expression useful for practical applications. It is found that the special cases of the general expression result in the expressions for total static and dynamic active thrusts presented by earlier researchers for different field conditions of soil backfills with and without seismic loadings.     

Dynamic soil–structure interaction of monopile supported wind turbines in cohesive soil

Offshore wind turbines supported on monopile foundations are dynamically sensitive because the overall natural frequencies of these structures are close to the different forcing frequencies imposed upon them. The structures are designed for an intended life of 25 to 30 years, but little is known about their long term behaviour. To study their long term behaviour, a series of laboratory tests were conducted in which a scaled model wind turbine supported on a monopile in kaolin clay was subjected to between 32,000 and 172,000 cycles of horizontal loading and the changes in natural frequency and damping of the model were monitored. The experimental results are presented using a non-dimensional framework based on an interpretation of the governing mechanics. The change in natural frequency was found to be strongly dependent on the shear strain level in the soil next to the pile. Practical guidance for choosing the diameter of monopile is suggested based on element test results using the concept of volumetric threshold shear strain.     

Dynamic responses of structure–soil–structure systems with an extension of the equivalent linear soil modeling

A three-dimensional problem of cross interaction of adjacent structures through the underlying soil under seismic ground motion is investigated. The story shears and lateral relative displacements (drifts) are the targets of the computations. These are calculated using a detailed modeling of soil, the foundations and the two adjacent structures. An equivalent linear behavior is assumed for the soil by introducing reduced mechanical properties consistent with the level of ground shaking for the free-field soil. Then a distinctive soil zone (the near-field soil) is recognized in the vicinity of the foundations where the peak shear strain under the combined effect of a severe earthquake and the presence of structures is much larger than the strain threshold up to which the soil can be modeled as an equivalent linear medium. It is shown that it is still possible to use an equivalent linear behavior for the near-field soil if its shear modulus is further reduced with a factor depending on the dynamic properties of the adjacent structures, the near-field soil, and the design earthquake. Variations of the dynamic responses of different adjacent structures with their clear distances are also discussed.     

Dynamic response of structures subjected to pounding and structure–soil–structure interaction

During strong earthquakes, adjacent structures with non-sufficient clear distances collide with each other. In addition to such a pounding, cross interaction of adjacent structures through soil can exchange the vibration energy between buildings and make the problem even more complex. In this paper, effects of both of the mentioned phenomena on the inelastic response of selected steel structures are studied. Number of stories varied between 3 and 12 and different clear distances up to the seismic codes prescribed value are considered. The pounding element is modeled within Opensees. A coupled model of springs and dashpots is utilized for through-the-soil interaction of the adjacent structures, for two types of soft soils. The pounding force, relative displacements of stories, story shears, and plastic hinge rotations are compared for different conditions as the maximum responses averaged between seven consistent earthquakes. As a result, simultaneous effects of pounding and structure–soil–structure interaction are discussed.     

Dynamic analysis of offshore wind turbine in clay considering soil–monopile–tower interaction

A comprehensive study is performed on the dynamic behavior of offshore wind turbine (OWT) structure supported on monopile foundation in clay. The system is modeled using a beam on nonlinear Winkler foundation model. Soil resistance is modeled using American Petroleum Institute based cyclic p–y and t–z curves. Dynamic analysis is carried out in time domain using finite element method considering wind and wave loads. Several parameters, such as soil–monopile–tower interaction, rotor and wave frequencies, wind and wave loading parameters, and length, diameter and thickness of monopile affecting the dynamic characteristics of OWT system and the responses are investigated. The study shows soil–monopile–tower interaction increases response of tower and monopile. Soil nonlinearity increases the system response at higher wind speed. Rotor frequency is found to have dominant role than blade passing frequency and wave frequency. Magnitude of wave load is important for design rather than resonance from wave frequency.     

Dynamic soil–structure interaction analysis of a telescope at the Javalambre Astrophysical Observatory

This paper presents the dynamic soil–structure analysis of the main telescope T250 of the Observatorio Astrofísico de Javalambre (OAJ, Javalambre Astrophysical Observatory) on the Pico del Buitre. Vibration control has been of prime concern in the design, since astrophysical observations may be hindered by mechanical vibration of optical equipment due to wind loading. The telescope manufacturer therefore has imposed a minimal natural frequency of 10 Hz for the supporting telescope pier. Dynamic soil–structure interaction may significantly influence the lowest natural frequency of a massive construction as a telescope pier. The structure clamped at its base has a resonance frequency of 14.3 Hz. A coupled finite element–boundary element (FE–BE) model of the telescope pier that accounts for the dynamic interaction of the piled foundation and the soil predicts a resonance frequency of 11.2 Hz, demonstrating the significant effect of dynamic soil–structure interaction. It is further investigated to what extent the coupled FE–BE model can be simplified in order to reduce computation time. The assumption of a rigid pile cap allows us to account for dynamic soil–structure interaction in a simplified way. A coupled FE–BE analysis with a rigid pile cap predicts a resonance frequency of 11.7 Hz, demonstrating a minor effect of the pile cap flexibility on the resonance frequency of the telescope pier. The use of an analytical model for the pile group results in an overestimation of the dynamic soil stiffness. This error is due to the large difference between the actual geometry and the square pile cap model for which the parameters have been tuned.     

Dynamic structure–soil–structure interaction between nearby piled buildings under seismic excitation by BEM–FEM model

The dynamic through–soil interaction between nearby pile supported structures in a viscoelastic half-space, under incident S and Rayleigh waves, is numerically studied. To this end, a three-dimensional viscoelastic BEM–FEM formulation for the dynamic analysis of piles and pile groups in the frequency domain is used, where soil is modelled by BEM and piles are simulated by one-dimensional finite elements as Bernoulli beams. This formulation has been enhanced to include the presence of linear superstructures founded on pile groups, so that structure–soil–structure interaction (SSSI) can be investigated making use of a direct methodology with an affordable number of degrees of freedom. The influence of SSSI on lateral spectral deformation, vertical and rotational response, and shear forces at pile heads, for several configurations of shear one-storey buildings, is addressed. Maximum response spectra are also presented. SSSI effects on groups of structures with similar dynamic characteristics have been found to be important. The system response can be either amplified or attenuated according to the distance between adjacent buildings, which has been related to dynamic properties of the overall system.     

Solution of moving-load-induced soil vibrations based on the Betti–Rayleigh Dynamic Reciprocal Theorem

Based on the Betti–Rayleigh Dynamic Reciprocal Theorem, the reciprocal property of the Green's functions is demonstrated, on the basis of which the analytical solution of soil vibration subjected to moving loads is derived. By application of the Betti–Rayleigh Dynamic Reciprocal Theorem, the moving source problem is converted to the fixed source problem with receiver point moving in opposite direction, which greatly simplifies the complex analytical solution of soil/ground vibration induced by a moving load. A computer code for solving the ground responses subjected to the moving constant load and harmonic load is developed via MATLAB and is employed to perform a case study. The analyzed results show that the ground vibration induced by moving constant load is of typical low-frequency feature; the frequency range of ground vibration is controlled by the Rayleigh's wave velocity of the top layer soil; when the receiver nears the source path, the R-wave contributes to the ground vibration more than the P-wave and the S-wave; while when the receiver is far from the source path, the contribution of the P-wave is more obvious.     

Seismic soil–pile interaction in liquefiable soil

Numerical analysis of seismic soil–pile interaction was considered in order to investigate the influence of flow mechanisms. Two models were employed—a simplified model, where the pore pressure at any depth is that of the free field, and a more complete model in which the pore pressure is associated with three-dimensional flow. The soil behavior was modeled by a nonlinear, quasi-hysteretic constitutive relation. A parametric study was carried out, varying the superstructure mass and soil permeability. It was found that there is a pore pressure threshold below which both models yield similar results, but that this threshold cannot be quantified a priori, as it depends strongly on soil–pile interaction.     

Methane efflux from marine sediments in passive and active margins: Estimations from bioenergetic reaction–transport simulations

A simplified version of a kinetic–bioenergetic reaction model for anaerobic oxidation of methane (AOM) in marine sediments [Dale, A.W., Regnier, P., Van Cappellen, P., 2006. Bioenergetic controls on anaerobic oxidation of methane (AOM) in coastal marine sediments: a theoretical analysis. Am. J. Sci. 306, 246–294.] is used to assess the impact of transport processes on biomass distributions, AOM rates and methane release fluxes from the sea floor. The model explicitly represents the functional microbial groups and the kinetic and bioenergetic limitations of the microbial metabolic pathways involved in AOM. Model simulations illustrate the dominant control exerted by the transport regime on the activity and abundance of AOM communities. Upward fluid flow at active seep systems restricts AOM to a narrow subsurface reaction zone and sustains high rates of methane oxidation. In contrast, pore-water transport dominated by molecular diffusion leads to deeper and broader zones of AOM, characterized by much lower rates and biomasses. Under steady-state conditions, less than 1% of the upward dissolved methane flux reaches the water column, irrespective of the transport regime. However, a sudden increase in the advective flux of dissolved methane, for example as a result of the destabilization of methane hydrates, causes a transient efflux of methane from the sediment. The benthic efflux of dissolved methane is due to the slow growth kinetics of the AOM community and lasts on the order of 60 years. This time window is likely too short to allow for a significant escape of pore-water methane following a large scale gas hydrate dissolution event such as the one that may have accompanied the Paleocene/Eocene Thermal Maximum (PETM).     

Dynamic analysis of flexible cantilever wall retaining elastic soil by a modified Vlasov–Leontiev model

Dynamic response of a flexible cantilever wall retaining elastic soil to harmonic transverse seismic excitations is determined with the aid of a modified Vlasov–Leontiev foundation model and on the assumption of vanishing vertical displacement of the soil medium. The soil–wall interaction is taken into consideration in the presented model. The governing equations and boundary conditions of the two unknown coupled functions in the model are derived in terms of Hamilton׳s principle. Solutions of the two unknown functions are obtained on the basis of an iterative algorithm. The present method is verified by comparing its results with those of the existing analytical solution. Moreover, a mechanical model is proposed to evaluate the presented method physically. A parametric study is performed to investigate the effects of the soil–wall system properties and the excitations on the dynamic response of the wall.     

Anti-plane foundationless soil–structure interaction

This paper presents a closed-form wave function analytic solution of two-dimensional scattering and diffraction of anti-plane SH-waves by a two-dimensional foundationless structure that corresponds to a shear wall on an elastic half-space. A wave-function expansion method is used to solve this model by first prescribing a set of wave functions with undetermined coefficients and then assembling them together based on the stress and displacement boundary conditions on the surface between the structure and half space. This results in a set of infinite equations to be solved by truncating to a finite set. The amplitudes and residuals of the displacement and stress distributions around the structure and nearby ground surface will be discussed carefully. While the solution is analytical, the computation of the numerical results involves the evaluation of complicated integrals. This analytic solution will be helpful to the understanding of propagation of seismic or other stress waves within the superstructure(s) undergoing earthquakes or other blast loads.     

Structure–soil–structure interaction: Literature review

The concept of structure–soil–structure dynamic interaction was introduced, and the research methods were discussed. Based on several documents, a systematic summary of the history and status of the structure–soil–structure dynamic interaction research that considers adjacent structures was proposed as a reference for researchers. This study is in the initial stage, given its complexity and excessive simplification of the model for soil and structures, and should be carried forward for its significance. An attempt was made to summarize the common major computer programs in this area of study. Furthermore, the advantages, disadvantages, and applicability of such programs were discussed. The existing problems and the future research trend in this field were also examined.     

Blind identification of soil–structure systems

Surrounding soil can drastically influence the dynamic response of buildings during strong ground shaking. Soil’s flexibility decreases the natural frequencies of the system; and in most cases, soil provides additional damping due to material hysteresis and radiation. The additional damping forces, which are in non-classical form, render the mode shapes of the soil–structure system complex-valued. The response of a soil-foundation system can be compactly represented through impedance functions that have real and imaginary parts representing the stiffness and damping of the system, respectively. These impedance functions are frequency-dependent, and their determination for different configurations been the subject of a considerable number of analytical, numerical, and experimental studies. In this paper, we first develop a new identification technique that is capable of extracting complex mode shapes from the recorded free or ambient vibrations of a system. This technique is an extension of the second-order blind identification (SOBI) method, which is fairly well established in a number of other areas including sound separation, image processing, and mechanical system identification. The relative ease of implementation of this output-only identification technique has been the primary source of its appeal. We assess the accuracy and the utility of this extended SOBI technique by applying it to both synthetic and experimental data. We also present a secondary procedure, through which the frequency-dependent soil-foundation impedance functions can be easily extracted. The said procedure has a practical appeal as it uses only free or ambient responses of the structure to extract the foundation impedance functions, whereas current techniques require expensive and time-consuming forced-vibration tests.     

Early history of soil–structure interaction

Soil–structure interaction is an interdisciplinary field of endeavor which lies at the intersection of soil and structural mechanics, soil and structural dynamics, earthquake engineering, geophysics and geomechanics, material science, computational and numerical methods, and diverse other technical disciplines. Its origins trace back to the late 19th century, evolved and matured gradually in the ensuing decades and during the first half of the 20th century, and progressed rapidly in the second half stimulated mainly by the needs of the nuclear power and offshore industries, by the debut of powerful computers and simulation tools such as finite elements, and by the needs for improvements in seismic safety. The pages that follow provide a concise review of some of the leading developments that paved the way for the state of the art as it is known today. Inasmuch as static foundation stiffnesses are also widely used in engineering analyses and code formulas for SSI effects, this work includes a brief survey of such static solutions.     

Effects of soil cracking on the seismic response of soil–structure systems

A numerical study on the influence that cracks and discontinuities (closed cracks) can have on the seismic response of a hypothetical soil–structure system is presented and discussed. A 2-D finite-difference model of the soil was developed, considering a bilinear failure surface using a Mohr–Coulomb model. The cracks are simulated with interface elements. The soil stiffness is used to characterize the contact force that is generated when the crack closes. For the cases studied herein, it was considered that the crack does not propagate during the dynamic event. Both cases, open and closed cracks, are considered. The nonlinear behavior was accounted for approximately using equivalent linear properties calibrated against several 1-D wave propagation analyses of selected soil columns with variable depth to account for changes in depth to bed rock. Free field boundaries were used at the edges of the 2-D finite-difference model to allow for energy dissipation of the reflected waves. The effect of cracking on the seismic response was evaluated by comparing the results of site response analysis with and without crack, for several lengths and orientations. The changes in the response obtained for a single crack and a family of cracks were also evaluated. Finally, the impact that a crack may have on the structural response of nearby structures was investigated by solving the seismic-soil–structure interaction of two structures, one flexible and one rigid to bracket the response. From the results of this investigation, insight was gained regarding the effect that discontinuities may have both on the seismic response of soil deposits and on nearby soil–structure systems.     

BIFoR FACE: Water–soil–vegetation–atmosphere data from a temperate deciduous forest catchment,including under elevated CO2

The ecosystem services provided by forests modulate runoff generation processes, nutrient cycling and water and energy exchange between soils, vegetation and atmosphere. Increasing atmospheric CO₂ affects many linked aspects of forest and catchment function in ways we do not adequately understand. Global levels of atmospheric CO₂ will be around 40% higher in 2050 than current levels, yet estimates of how water and solute fluxes in forested catchments will respond to increased CO₂ are highly uncertain. The Free Air CO₂ Enrichment (FACE) facility of the University of Birmingham's Institute of Forest Research (BIFoR) is the only FACE in mature deciduous forest. The site specializes in fundamental studies of the response of whole ecosystem patches of mature, deciduous, temperate woodland to elevated CO₂ (eCO₂). Here, we describe a dataset of hydrological parameters – seven weather parameters at each of three heights and four locations, shallow soil moisture and temperature, stream hydrology and CO₂ enrichment – retrieved at high frequency from the BIFoR FACE catchment.     

Tree root systems competing for soil moisture in a 3D soil–plant model

Competition for water among multiple tree rooting systems is investigated using a soil–plant model that accounts for soil moisture dynamics and root water uptake (RWU), whole plant transpiration, and leaf-level photosynthesis. The model is based on a numerical solution to the 3D Richards equation modified to account for a 3D RWU, trunk xylem, and stomatal conductances. The stomatal conductance is determined by combining a conventional biochemical demand formulation for photosynthesis with an optimization hypothesis that selects stomatal aperture so as to maximize carbon gain for a given water loss. Model results compare well with measurements of soil moisture throughout the rooting zone, of total sap flow in the trunk xylem, as well as of leaf water potential collected in a Loblolly pine forest. The model is then used to diagnose plant responses to water stress in the presence of competing rooting systems. Unsurprisingly, the overlap between rooting zones is shown to enhance soil drying. However, the 3D spatial model yielded transpiration-bulk root-zone soil moisture relations that do not deviate appreciably from their proto-typical form commonly assumed in lumped eco-hydrological models. The increased overlap among rooting systems primarily alters the timing at which the point of incipient soil moisture stress is reached by the entire soil–plant system.     

Energy dissipation by nonlinear soil strains during soil–structure interaction excited by SH pulse

Three variants of a two-dimensional (2-D) model of a building supported by a rectangular, flexible foundation embedded in nonlinear soil are analyzed. The building, the foundation, and soil have different physical properties. The building is assumed to be linear, but the foundation and the soil can experience nonlinear deformations. It is shown that the work spent for the development of nonlinear strains in the soil can consume a significant part of the input wave energy, and thus less energy is available for excitation of the building. The results help explain why the damage, during the 1994 Northridge earthquake in California, to residential buildings in the areas that experienced large strains in the soil was absent or reduced.     

Simplified seismic analysis of soil–well–pier system for bridges

Seismic analysis of soil–well–pier system was carried out using three different approaches to evaluate their comparative performance and associated complexities. These approaches were (a) two-dimensional nonlinear (2D-NL), (b) two-dimensional equivalent-linear (2D-EqL), and (c) one-dimensional spring–dashpot (1D). Soil was modeled as 2D plane-strain elements in the 2D-NL and 2D-EqL approaches, and as springs and dashpots in the 1D approach. Nonlinear behavior of soil was captured rigorously in the 2D-NL approach and approximately in the remaining two approaches. Results of the two approximate analyses (i.e., 2D-EqL and 1D) were compared with those of the 2D-NL analysis with the objective to assess suitability of approximate analysis for practical purposes. In the 1D approach, several combinations of Novak's and Veletsos' springs were used to come up with a simplified 1D model using three types of spring–dashpots. The proposed model estimates the displacement and force resultants relatively better than the other 1D models available in literature.