Dynamic Response Of Foundation Research Articles

A study on parameter setting for deformation characteristics in a dynamic ground response analysis

A study on parameter setting for deformation characteristics in a dynamic ground response analysis

Short-time frequency-domain method for truly nonlinear dynamic ground response analysis: The equivalent-nonlinear approach

Evaluating soil nonlinearity during cyclic loading is one of the most significant challenges in ground response analysis, especially when dealing with the inverse problem of deconvolution. Different schemes have already been developed for dynamic ground response analysis, both in the time and the frequency domain. The most accurate method to account for soil nonlinearity is the nonlinear dynamic analysis in the time domain. This approach is based on nonlinear constitutive models capable of accurately simulating highly nonlinear problems like soil liquefaction. However, the time-domain analysis is suitable only for the convolution analysis to define the ground motion at the free surface of a soil deposit from the bedrock motion. The frequency-domain analysis is the most common solution for the inverse problem called deconvolution, which is used to define the bedrock motion from the free surface ground motion. A well-known approach developed in the frequency domain for ground response analysis is the equivalent-linear method (EQL). This approach adopts an iterative procedure to define elastic shear modulus and damping ratio compatible with the induced strain level. Still, it presents some limitations, especially for highly nonlinear soil response, due to the use of strain-compatible but constant soil properties. This article presents a new scheme to conduct truly nonlinear dynamic analysis in the frequency domain based on the new concept of the short-time transfer function. Unlike the EQL method, which uses a constant transfer function, the proposed approach, called the “Equivalent-Nonlinear” method (EQNL), defines a soil transfer function evolving in time, depending on the shear stress and strain demands. The EQNL method approximates the response of a nonlinear system as an incrementally changing viscoelastic system and could represent a valuable tool for nonlinear deconvolution. This article shows the analytical formulation and the first set of validations of the EQNL approach, with detailed comparisons with the EQL and NL methods and vertical array data. These comparisons show the potentialities of the EQNL approach to reproduce the results of the nonlinear dynamic analysis. The EQNL approach has been implemented in MATLAB, and the source code is provided as supplementary material for this article. A more comprehensive validation is underway, aiming to better characterize the limitations and the capabilities of the method.

Ground vibration induced by high speed trains on an embankment with pile-board foundation: Modelling and validation with in situ tests

To investigate the train-induced ground vibration, an explicit time-domain, three dimensional (3D) finite element (FE) model is developed. The train, track, embankment, pile-board structure and nearby ground soils are all fully coupled in this model. The complex geometries involving the track components and pile-board structure are all modelled in detail, which makes the simulation of wave propagation more realistic from the train to the ground. The model is validated with in situ tests data collected in the Beijing-Shanghai high speed railway line. Good agreements have been achieved between the numerical results and experimental results both in time domain and frequency domain. The proposed model is thus capable of reproducing the dynamic ground response induced by a typical high speed train. Soil responses induced by different number of vehicles are compared. With more vehicles, the spectral peaks of soil responses are more prominent at the integral multiples of the vehicle passing frequency. Too few vehicles will not bring about such phenomenon, thus sufficient number of vehicles should be included in a train to properly model train-induced ground vibration. With the proposed model, the influence of the pile-board foundation on the ground vibration is investigated. It is found that the pile-board foundation can significantly attenuate the low frequency ground vibration. The attenuation of the ground vibration as a function of distance from the track is simulated and the influential factors to the local vibration amplification are investigated. It is found that soil Young’s modulus and soil impedance contrast are the two main factors influential to the local vibration amplification. The softer the natural soil, the larger the amplification. The larger soil impedance contrast makes the amplification more obvious. The soil stratification and geometric discontinuity at ground surface are not the main cause of the local vibration amplification in this work.

Dynamic Ground Response during Vibratory Sheet Pile Driving

AbstractVibratory sheet pile driving is a widely used foundation method. In order to investigate the effect of different operational parameters, such as vibration frequency and eccentric moment on ...

Analysis of Lateral Dynamic Response of Caisson Foundation in Layered Clayey Soils considering Scour-Hole Dimensions

As a cross-sea or river deep-water foundation, it is clear that the caisson foundation will be subjected to significant lateral dynamic loads due to winds or waves and suffer from scouring under its long-term effect. In order to obtain the scour effect on the dynamic response of the foundation, an analytical model describing the scour-hole effect in terms of scour depth, scour width, and slope angle was constructed. Combined with the nonlinear Winkler theory, a method for the dynamic response of the caisson foundation considering the scour-hole dimensions was proposed. Comparisons against the results from the dynamic FEM demonstrate the reliability of this method. The effects of the scour width, slope angle, and scour depth on the dynamic response of the caisson were discussed. The results show that the scour depth affects the dynamic displacement and resonant frequency of the foundation most, whereas the scour width does less and the slope angle does the least; the dynamic response of caisson can be approximated as the case of the slope angle 5° and the scour width 5B when the slope angle is less than 5° and the scour width is greater than 5B, respectively; the effects of scour width and slope angle on the dynamic response of caisson have the similar change pattern in the displacement and resonant frequency when the scour depth is different. However, the effect of amplitude on dynamic response shows a nonlinear increase trend when the scour depth is relatively large.

Nonlinear dynamic behavior of laterally loaded composite caisson-piles foundation under scour conditions

A simplified method for predicting the nonlinear dynamic response of composite caisson-piles foundation (CCPF) under scour conditions is proposed. The Hardin-Drnevich model is employed to represent the nonlinear soil reactions. Stress history is also considered to study the scour effect on the dynamic impedance of foundation. Then, harmonic vibration tests considering scour are conducted on a CCPF. It can be observed that the predicted trends of the CCPFs response agree with the experimental data, which verifies the reliability of the method. Then, a case study is investigated to evaluate the effects of stress history, scour depth and soil nonlinearity on the dynamic response of the foundation. The results show that soil nonlinearity has a close relationship with the lateral dynamic displacement of foundation, and it will result in a slight reduction in the resonant dimensionless frequency of the CCPFs. Additionally, with increasing scour depth, a remarkable decrease in the dynamic impedances is produced when soil nonlinearity is considered. Compared with soil nonlinearity, stress history is found to have greater influence on the displacement of the CCPFs, especially in the low frequency range. Finally, a discussion is conducted on the relationships between the resonant frequency of the CCPFs and the scour depth.

An analysis of influence of material damping on dynamic response of surface foundation under rotational motion

ABSTRACT Material damping arises due to the soil present beneath the foundation and controls the behaviour of the foundation under dynamic excitation. In the present study, an attempt has been taken to observe the effect of soil material damping on the dynamic response of foundation under rocking and torsional motion. A recent trend in present methods of dynamic analysis of foundation in the frequency domain is to find out the dynamic impedance functions, i.e. spring coefficient and damping coefficient. For foundation under rotational motion, i.e. rocking and torsion, the material damping is introduced using the Kelvin model and the results thus obtained are compared with those obtained by Hysteretic model and Voigt model. Parameter sensitivity analysis is carried out to determine the most influencing parameter. The study suggests that foundation under rocking motion is non-linearly influenced by the Poisson’s ratio of soil.

Dynamic response of ground supported rectangular water tanks to earthquake excitation

This study investigates an idealized ground supported reinforced concrete rectangular water tank under earthquake excitation. A linear three-dimensional finite element analysis and SAP2000 software have been used to predict tank response. The variable analysis parameters considered are the aspect ratio (tank height to length ratio) and tank water level, while the tank wall thickness is taken as a constant. The convective and impulsive masses are also represented by spring-mass model in the time history analysis for El-Centro earthquake ground motion record. Five tank models with a capacity of 216, 288, 360, 432 and 504 m3 were developed and analyzed for hydrodynamic and hydrostatic effects. In general the results show that, there is a smooth increase in the moment and displacement of both hydrostatic and hydrodynamic analysis with a decrease in aspect ratio. The top displacement and moment for the hydrodynamic effects are greater than the hydrostatic results and it is observed that the maximum hydrodynamic moment is 91.3% higher than the corresponding maximum hydrostatic moment. Likewise the displacement obtained from hydrodynamic analysis is 63.58% more than the corresponding hydrostatic value.Keywords: Hydrodynamic effect, Convective and Impulsive, Rectangular tanks, Finite Element Models, Time history, SAP2000, Ethiopia

Three‐dimensional dynamic response of ground with a poroviscoelastic interlayer to a harmonic moving rectangular load

SummaryStratification is a basic characteristic of ground. Due to the influence of ground water, saturated weak interlayers widely exist, particularly in soft soil area. An interlayer of high compressibility and low strength has a substantial effect on dynamic response of the ground, especially under high speed moving load. Thus, a comprehensive investigation in the influence of interlayer is essential and useful in geotechnical and transportation‐related engineering. This paper presents a three‐dimensional semi‐analytical approach to study the dynamic response of a layered ground with a soft saturated interlayer. The ground is modelled as a half‐space consisting of three parts: a viscoelastic upper layer, a saturated poroviscoelastic interlayer governed by Biot's theory and a viscoelastic half‐space. An ‘adapted stiffness matrix’ is proposed to obtain the semi‐analytical solution to the system. Comprehensive parametric study is conducted to investigate the influences of existence, geometrical and physical properties of the interlayer. Depth, thickness, hydraulic permeability of the interlayer, load speed and frequency significantly influence the dynamic response of the ground, among which the interlayer depth plays a dominant role. Resonant frequency exists, which is highly affected by the interlayer thickness, especially in low speed regime. Both hydraulic permeability and boundary conditions of the interlayer influence the characteristics of pore pressure distribution. Copyright © 2017 John Wiley & Sons, Ltd.

Parametric study of turbo generator foundation considering different types of beam column joint

In the current work, turbo generator foundation system is simulated in SAP: 2000 V17.1 software and dynamic response of foundation are analyzed. Parametric study of Strong Column Weak Beam (with and without haunches) and Weak Column Strong Beam has been carried out considering Winkler spring soil model, solid finite element modelling and dynamic analysis of Turbo machinery foundations. The comparison of frequency and time periods at various mode shapes has been performed. The effects of damping (0%, 3% and 5%) on the response spectra curve of the foundation top deck are investigated considering the dynamic machine load.It has been found that Strong Column Weak Beam remains more elastic during seismic action compared to Weak Column Strong Beam. Hence Strong Column Weak Beam is recommended while designing a turbo machine foundation as it can provide strength and stability to the entire structure. The presence of haunches did not show any influence on vertical stiffness, however, it showed the increase in lateral Stiffness of the frame thus enhancing the stability of the foundation.

Critical Velocity of High-speed Train Running on Soft Soil and Induced Dynamic Soil Response

The determining of the critical speed under train operation remains difficult due to the complex properties of the track, embankment and ground. In this paper, a dynamic analysis model comprising track, embankment and layered ground was proposed based on the two-and-half-dimensional (2.5D) finite elements combining with thin-layer elements to predict vibrations generated by train moving loads. The track structure is modeled as an Euler-Bernoulli beam resting on embankment. The train is treated as a series of moving axle loads; the embankment and ground are modeled by the 2.5D finite elements. The dynamic responses of the track structure and the ground under moving axle loads at various speeds are presented. The results show that the dynamic response of ground induced by moving constant loads is mostly dominated by train speed and the stiffness of the topsoil. The critical speed of a train moving on an embankment is higher than the Rayleigh wave velocity of the underlying soil, and softer soils results in lower overall critical speed of the system.

Effect of local soil conditions on dynamic ground response in the southern coast of Izmir Bay, Turkey

The city of Izmir, located at the western end of Turkey, has experienced many strong earthquakes throughout its history. The southern coast of Izmir Bay, one of the most densely populated areas of Izmir, is located on deep alluvial sediments. It is important to determine the effect of local soil conditions on dynamic ground response in the study area, where thick loose water-saturated alluvial sediments exist. A database including geotechnical and geological information on the study area is constructed. Majority of the site is classified as D and E according to NEHRP provisions. Dynamic site response analyses are performed with EERA by utilizing the field and laboratory test results and earthquake time histories of moderate-scale earthquakes such as 1977 Izmir (ML=5.3), 2003 Urla (Md=5.6), and 2005 Uzunkuyu-Urla (ML=5.9), which occurred in and nearby Izmir. In addition, a scenario ground motion generated by the Izmir Fault with a magnitude of 6.5, having an average distance of 10km to the study area, is also considered. The output data obtained from the dynamic site response analyses are evaluated, and maps displaying variation in dynamic parameters on ground surface are prepared for the southern coast of Izmir Bay, Turkey. Consequently, the dynamic analyses performed with the soil models constituted for the study area verified the damage occurred in a close distance event of 1977 Izmir earthquake. The scenario earthquake resulted in peak ground accelerations more than 0.6g at the eastern and western ends of the study area. However, long distance events resulted in spectral amplifications by up to 5 times. With this study, it is emphasized that local soil conditions should be evaluated individually in the area of interest. Generation of a site-specific design spectrum is recommended for the areas located on deep alluvial sediments.

Numerical analysis of soil vibrations due to trains moving at critical speed

High-speed train induced vibrations of track structure and underlying soils differ from that induced by low-speed train. Determining the critical speed of train operation remains difficult due to the complex properties of the track, embankment and ground. A dynamic analysis model comprising track, embankment and layered ground was presented based on the two-and-half-dimensional (2.5D) finite elements combining with thin-layer elements to predict vibrations generated by train moving loads. The track structure is modeled as an Euler–Bernoulli beam resting on embankment. The train is treated as a series of moving axle loads; the embankment and ground are modeled by the 2.5D finite elements. The dynamic responses of the track structure and the ground under constant and vibrating moving loads at various speeds are presented. The results show that the critical speed of a train moving on an embankment is higher than the Rayleigh wave velocity of the underlying soil, attributed to the presence of the track structure and the embankment. It is found that the dynamic response of ground induced by moving constant loads is mostly dominated by train speed. While for the moving load with vibration frequency, the ground response is mostly affected by the vibration frequency instead of train speed. Mach effect appears when the train speed exceeds the critical speed of the track–embankment–ground system.

Physical and Numerical Modeling of Seismic Soil-Structure Interaction in Layered Soils

The structural response of buildings subjected to seismic loads is affected by local site conditions and the interaction between the structure and the supporting soil media. Seismic centrifuge model tests were conducted on two layered clay soil profiles at 80 g field to investigate soil-structure interaction and dynamic response of foundation. Several earthquake-like shaking events were applied to the models using an electro-hydraulic shaking table to simulate linear and nonlinear soil behavior. Results showed that the foundation input motion was significantly amplified in both models, especially for weak earthquake motions. Seismic soil-structure interaction was found to have an important effect on structure response by increasing the amplification of foundation input motion. A 3D finite difference numerical model was also developed to simulate the response of centrifuge model tests and study the parameters that affect the characteristics of earthquake at the base of the structure. The results indicated that the stiffness and stratification of the soil profiles had a significant effect on modifying the foundation input motion.

Three‐dimensional finite element modeling of tire/ground interaction

SUMMARYTire/ground interaction has been an important issue in terramechanics, transportation and pavement engineering. Characterization of tire/ground interaction has been majorly investigated based on empirical approaches and field tests. So far very few dynamic tire/ground interaction models have been presented. This paper presents a three‐dimensional finite element model for tire/ground interaction. The rubber material is modeled as nearly incompressible finite strain hyperelasticity instead of being modeled as a rigid wheel. The tire is also modeled as bias type and steel rebars are embedded within the tire structure. The tire model is combined with the ground model to form a tire/ground interaction model. Both single tire/ground interaction and four‐tire vehicle/pavement interaction models are presented, which allow us to investigate a lot of issues easily and accurately, such as compaction, pavement response and pavement damage. Numerous simulations are carried out to demonstrate that the dynamic tire/terrain interaction model can be used to predict the dynamic ground response due to moving vehicle. Different tire rolling conditions can be easily incorporated into the tire/ground interaction model, which further substantiates the broad application of the model in transportation and pavement engineering. Copyright © 2011 John Wiley & Sons, Ltd.

Experimental Investigation of Effect of WIB Embedded Depth on Ground Vibration Isolation

In this paper, an exploration was presented to access the actual screening effectiveness of concrete wave impeding block (WIB) and the influence of WIB embedded depth on the vertical vibration isolation effect under the continuous vertical loading. Furthermore, the displacements of measuring points were simulated with a semi-analytical boundary element method (BEM) and validated by the measured records. It was found that a concrete WIB with a reasonable embedded depth was able to decrease the ground vibration greatly. It was also proved that decreasing the embedded depth was an efficient measure for WIB to reduce the dynamic response of ground. Besides, the good qualitative agreement between the calculation and the experiment proved the reliability of the numerical method.

Experimental evaluation of vertical response of rigid surface footing on layered soil

The study of the dynamic response of foundations is of significant importance in the machine foundation design and soil-foundation interaction problems, in general. This paper presents experimental investigations in the field studying the effect of layering of soil mass on the dynamic response of foundation under vertical mode of vibration. Model block vibration tests on a rigid surface footing were conducted on different layered soil systems. A concrete block of size 400×400×100 mm was used as the model block and a Lazan type mechanical oscillator was used for inducing vibration in vertical direction. In the investigation two different soils, namely, gravel and fly ash were used. In total 132 tests were conducted on different layered soil beds with different loading combinations. Dynamic response of foundation resting on layered soil system were also analyzed by two simple approximate methods namely, mass spring dashpot model and equivalent elastic half-space theory. Results obtained from the two methods were compared with that obtained from the experimental investigation. It was found from the comparisons that the simple mass-spring dashpot model was capable of predicting the resonance frequency and the resonance amplitude satisfactorily. Elastic half space theory with equivalent soil properties was found to underestimate the displacement amplitude.

Foundation Structure Design and Analysis for Offshore Wind Turbine

Offshore Wind Turbine (OWT) is a device to extract and convert offshore wind energy into useful electrical power. The typical concept design of monopile foundation structure for 1.5MW OWT is raised in this paper. The arrangement of the monopile and related accessorial facilities are especially considered during design. Mechanical characters of the foundation structure are emphatically analyzed, including static analysis, dynamic analysis, fatigue analysis and bucking analysis. The time domain approach is preferable for the dynamic response of foundation under the condition of earthquake and wave. Based on the analysis results, the reliability of the structure is proved to be satisfied with the requirements .The paper provides the reference for the design of OWT.

Spectral Analysis of Ground Acceleration-Based Testing

Spectral analysis of downhole acceleration data is used to identify changes in elastic properties of track substructure. The spectral analysis is based on the power spectral density (PSD) as an indicator of frequency content. This method was developed and tested at the Transportation Technology Center, Inc., in Pueblo, Colorado. The system provides an efficient means for monitoring track bed to predict settlement and deformation conditions that would require maintenance. The method relies on a triaxial piezoelectric accelerometer inserted into a permanently installed inclinometer casing installed into the subgrade. Periodic measurement of the dynamic ground response allows for the identification of changes in the small strain elastic properties of the substructure layers. The methodology uses conventional downhole seismic shear wave velocity testing. For the purpose of comparison, test sections were constructed with clean and fouled ballast. Shear wave velocities indicated the differences in material properties. PSDs of the signals were analyzed to determine variation resulting from differences in soil conditions. PSDs were calculated at different intervals of loading. With increased loading, settlement of the subtrack soils occurs. The densifi-cation can be seen as an increase in the predominant frequency of the PSD. The PSD from the section with the clean ballast had a higher predominant frequency than the PSD from the section with the fouled ballast. A decrease in predominant frequency over time would indicate the decrease in stiffness and the potential of increased fouling of the ballast with fines. Changes in the frequency content would indicate changes in elastic response.

Effect of Presence of Rigid Base within the Soil on the Dynamic Response of Rigid Surface Foundation

Abstract The present experimental investigations study the effect of presence of rigid base at any depth within the soil mass on the dynamic response of foundation under vertical mode of vibration. Model block vibration tests on rigid surface footing are conducted on a different soil layer of finite thicknesses underlain by a rigid base. A concrete block of size 400 × 400 × 100 mm is used as the model block, and a Lazan type mechanical oscillator is used for inducing vibration in vertical direction. The finite soil layers of different thicknesses are prepared in a pit at the bottom of which a massive concrete layer of 300 mm thick was cast to represent it as a rigid base. In the investigation two different soils, namely, local in situ soil and sand are used. In total 72 tests are conducted in different loading combinations and soil types, and several important observations are reported. Two different methods are proposed to analyze the dynamic response of a foundation resting on a finite layer underlain by a rigid layer. Finally, the experimental results are compared with the results that were obtained by the proposed method. A Mass-Spring-Dashpot (MSD) model with proper consideration of damping factor is found to provide reasonably accurate results. Elastic Half Space Theory (EHST) with equivalent soil properties is found to underestimate the displacement amplitude.