Layered Soil Medium Research Articles

Vibration mitigation using dual-open and infilled trenches in layered soil media: Field tests and numerical simulations

Ground-borne vibrations are increasing at a rapid rate due to the rise in urban expansion and industrial activities. The current solution to mitigate the unwanted vibrations is limited to the use of single trenches that require unrealistic depths. This paper presents the possibilities of using dual open and infilled trenches to mitigate the vibrations generated due to continuous harmonic motions. Full-scale field tests and comprehensive numerical studies were performed to systematically design dual trenches. The field vibration tests were performed under a wide range of frequencies using the Lazan-type mechanical oscillator. Similarly, numerical studies have been performed using finite element analysis software, PLAXIS 2D. Expanded polystyrene (EPS) geofoams of different densities, bentonite, ceramsite, concrete, and sand-rubber mixture were used as the infill materials. The normalized depths of 0.40 and 0.50 were observed as the optimal values to reach an average amplitude reduction ratio (average ARR) of 0.25 for the dual open and EPS15-infilled trenches, respectively. The isolation efficiency of EPS15-infilled trenches was observed to be 178 % higher compared to the EPS48-infilled trenches. The performance difference between EPS15 and ceramsite-filled dual trenches was observed to be only 4 % in terms of average ARR, the former being superior.

Double-gradient seismic metamaterials with zero-frequency bandgap characteristic in a layered soil medium

Seismic metamaterials (SMs) are an artificially composite material designed within the sub-wavelength range. To attenuate low-frequency seismic surface waves, a metamaterial structural unit composed of a lead core and an auxetic foam coating layer was proposed; the higher impedance ratio results in the creation of a zero-frequency bandgap under layered soil conditions. To broaden the attenuation zone (AZ), double-gradient seismic metamaterials (DGSMs) were designed. The frequency domain analysis indicates that the attenuation area covering the range of 0–10 Hz is 89.8%. Through displacement-field analysis, the attenuation mechanism of DGSM on specific frequency surface waves can be fully explained. Finally, Taft seismic wave excitation is input for time history analysis, and the acceleration amplitude within 0–2 Hz decreases by 58.6%, which verifies the effectiveness of DGSMs in attenuation of low-frequency seismic waves.

Seismic Response of Pile-raft Foundations of a Building on Layered Soil-based Design in South India

Abstract This study aims to assess the seismic effects of a mid-rise building on the layered soil medium and to estimate the dynamic impacts of pile raft performance that have been studied using PLAXIS 3D-based finite element analysis, optimization of BSDPT, and economical building design. Further, to understand the stiffness of the raft and the effect of the piles on the surface and inside an excavation. The geotechnical analysis of raft with piles PLAXIS 3D simulation, Poulos-Davis-Randolph (PDR), and Stress Distribution on Pile Top (BSDPT) optimization method indicate the displacements have been reduced by 60% based on superstructure design. The column reactions were estimated by Indian standard code using STAAD-Pro. The study reveals that when the building is as-built on the ground, piled-raft foundations have a considerable favourable influence on the seismic behaviours of the building structure, such as a 20% reduction in load and 2.36 cubic meters (m³) pile volume reduction. This study provides insight into the impacts of pile-raft foundations on the seismic response of pile-raft foundations of the superstructures, helping to fill a knowledge gap and better understanding the dynamic assessment of the layered soil settings.

Multistage-based evaluation of tunnelling effects on the skin friction of adjacent building piles in layered media

Pile skin friction performance has been recognized as a significant role in the stability of structures adjacent to underground tunnel constructions. Many previous studies paid attention to the ultimate bearing capacity of the pile when undergoing tunnel excavations, but the skin friction response to multistage tunnelling process is still far from clear. This paper conducted multistage-based modelling about the effect of tunnelling process on the pile-soil interaction in layered soil media, which aims at examining the skin friction performance of the single pile and pile group subject to both vertical building loads and adjacent shield tunnelling. Based on the multistage modelling of the tunnel excavation process, the distribution features and mobilization patterns of the skin friction on single piles were obtained as tunnel excavation continuously proceeded towards the single pile and away from it. In addition, the skin friction behaviours of the double piles and pile group adjacent to shield tunnelling in multi-stages were compared with that of the single pile under the same conditions. The research results show that adjacent tunnelling could cause stress release and additional settlement of the surrounding soils and thus change the distribution features of skin friction of building piles. For double piles, the isolation and dragging effects from the interaction between the front pile and the rear pile are presented and examined. The skin friction distribution on double piles during tunnelling process is primarily dependent on the distance of the pile from the tunnel centreline. For pile groups, the negative skin frictions are easy to appear on the side piles and the centre pile subjected to both vertical loading and adjacent tunnelling.

3D time‐domain nonlinear analysis of soil‐structure systems subjected to obliquely incident SV waves in layered soil media

AbstractNumerous experiments and prior analyses have confirmed that the angle of incidence of a seismic wave can significantly affect ground response and dynamic soil–structure interaction (SSI) behavior. Realistically, obliquely incident waves will be generated due to the soil heterogeneity and stratigraphy, which can lead into complex wave propagation and scattering patterns. In this study, we propose a novel methodology that (i) utilizes the wave potential theory to derive the 3D time‐domain analytical solutions for free‐field response under obliquely incident SV waves in layered soil media; (ii) makes use of high‐fidelity numerical tools—namely, the domain reduction method (DRM) and the perfectly matched layers (PMLs)—to inject the obliquely incident waves into the domain of interest and to absorb the outgoing scattered motions, respectively; (iii) enables nonlinear time‐domain site response and SSI analyses that feature an advanced constitutive model for soil. Finally, a 3D 20‐story steel building is modeled as a case study. The building rests on a two‐layer half‐space and is subjected to an obliquely incident seismic wave. The SV wave's angles of incidence are varied to investigate its effects on structural responses, such as horizontal, vertical, and rotational floor accelerations, as well as interstory drift ratios.

Considering SSI by an equivalent linear method for nonlinear analysis of concrete moment frames

This paper evaluates the effects of Soil-Structure Interaction (SSI) on the seismic response of multi-story concrete frames subjected to earthquake ground motions. To calculate the structural response, an iterative Wave-Propagation (WP) based method has been used. The exact solution of SSI problems, in addition to high computational costs, due to general complexity of finite element analysis, require an advanced computer system. According to the method proposed herein, buildings were modelled as an extension of the layered soil media by considering each story as a layer in the WP path. The motion in each layer could be determined from the motion in any other layer. This permitted to use an operation called deconvolution, which could be considered to investigate the effect of substructure soil layers on the structural response. One of the capabilities of WP method is to facilitate the computation of bedrock motion from a known free surface motion and consequently determination of correct foundation input motion. While most of the current methods assume constant values for basic parameters such as; stiffness and damping, in the present method in order to investigate the nonlinear behaviour, stiffness and damping are proportional to the displacement level of soil layers or structural floors. The computational speed and accuracy of the proposed method are also verified by a benchmark frame analysis. Also, based on the Park-Ang Damage Index, this paper evaluated the measures of damage (the relationship between earthquake characteristics (PGA) and damage level) which govern structural degradation and/or collapse obtained from different well-known destructive earthquakes.

Regional seismic ground‐motion simulation and observation with engineering applications

Regional seismic ground‐motion simulation and observation with engineering applications

Large-scale testing and finite-element simulation of twin square anchor plates embedded at shallow depth in layered soil media

The motivation and scope of the present work are to investigate the interaction phenomenon of two closely spaced square plate anchors through physical modelling and validating it with the help of finite-element modelling. In the present study, different sizes of plate anchors are considered for studying their uplift behaviour when they are laid as single as well as in a group of two symmetrical anchors. A large-scale model testing facility has been developed and fabricated in order to perform the physical modelling. In physical modelling, poorly graded, dry Quartzanium sand is utilized as the foundation material. PLAXIS3D, a finite-element software for geotechnical engineering, has been used to validate the experimental results obtained from the large-scale model testing facility. The effects of embedment depth and size of the anchor plate as well as layering in soil media are the parameters considered in order to determine the interaction factors with respect to the uplift capacity and displacement of anchors.

Deep cavity detection using propagation of seismic waves in homogenous half-space and layered soil media

Understanding of subsurface anomalies has always been of interest to the geotechnical and geological engineers. Identification of dimensions and the location of these anomalies are still controversial at deeper depths due to a reduction in the resolution and the accuracy of recorded data. In this paper, the propagation mechanisms of the longitudinal (P), Rayleigh (R) and shear (S) waves are compared to investigate the ability of P waves in cavity detection in half-space and layered soil media. The results obtained from the analysis of the propagated P waves from the cavity show that the location of the cavity can be revealed in homogeneous half-space media. Hence, filtering methods and large amplitude clipping of the direct P and R waves are used to detect diffracted waves and provide a more precise illustration of propagated waves, especially in 3D view. The diffracted waves from the cavity appear as a symmetrical arc in the wave-field in which the peak point indicates the location of the cavity. However, the shape (slope) of the three curved paths corresponding to the diffracted waves from the boundary between two layers is not symmetric and gradually turns to a linear form as the distance increases. Furthermore, it is difficult to detect deep cavity using Rayleigh waves in layered soil media. For this purpose, seismic sources with low frequencies or passive methods should be used.

Built-up structural steel sections as seismic metamaterials for surface wave attenuation with low frequency wide bandgap in layered soil medium

The purpose of this work is to investigate the propagation of surface waves through periodically arranged built-up steel section (resonator) in single and multiple layered soil medium (substrate) and to study the feasibility of surface waves attenuation by finite element technique. Two types of simple and small geometric size built-up sections are taken into consideration. Due to occurrence of local resonance between resonator and surface waves propagating on the surface of semi-infinite substrate, low frequency wide bandgaps are reported. Generation of local resonance is mainly governed by (i) impedance mismatch between the resonator and substrate (ii) coupling of longitudinal resonance modes of resonator with surface waves propagating on the surface of semi-infinite substrate. To have a more general and realistic study, surface wave propagation in single and six-layered soil medium is considered and the bandgaps are compared. Furthermore, with the variation in geometrical configuration of built-up section and change in material properties (soil profile), bandgap width and location changes. In the case of a layered soil medium, a relative bandwidth greater than 1.5 for both types of resonator is achieved. This implies that the proposed built-up sections are capable of attenuating surface waves in an extremely low frequency range. The position and width of bandgaps are further validated through finite unit cell based frequency response and time transient analyses. The findings substantiate the infinite unit cell model proposed here with the conclusion of more than 50% reduction in surface wave amplitude. The feasibility study manifests that the built-up structural steel sections can be applied as resonant barriers for mitigating seismic waves to protect important civil infrastructures from earthquake hazards.

Optimization Method for Irregular Piled Raft Foundation on Layered Soil Media

Important buildings such as nuclear power plants always require stricter control of differential settlement than ordinary buildings. Therefore, it is necessary to provide an optimized design for the piled raft foundations of important buildings. In this paper, a new optimization method (using different pile diameters and different pile spacing) was proposed for the design of piled raft foundations. This method adjusts the pile diameters and pile spacing according to the stress distribution at the pile top of the initial design to achieve a more uniform settlement of the raft and stress distribution on top of piles, which can solve the differential settlement problems caused by uneven loads of the superstructure. After optimized design, the differential settlement and integral bending moment of the raft decreased more than 64% and 52%, respectively, and the differential stress on top of piles decreased by at least 63%. The new method proposed in this paper could be applied to large‐scale piled raft foundations with complex superstructure loads.

An Efficient Algorithm for Calculating Rheological Parameters of Layered Soil Media Composed from Elastic-Creeping Materials

A method is proposed for calculating the average rheological characteristics of inhomogeneous soils consisting of layers of elastic-creeping materials. The "cores" of the creep equations describing the stress-strain behavior of "equal" quasi-homogeneous soil media with averaged parameters are suggested. The calculation of these parameters is reduced to determining the roots of the polynomials of degree equal to the total number of exponential functions that enter the creep cores obtained for soil layers. The proposed technique can be used to calculate slow creep displacements and the stress-strain state of layered rocks, as well as to statistically assess the characteristics of composite materials. An example is presented for calculating the effective coefficients of an elastic-creeping mountain massif consisting of two parallel layers alternating in pairs.

Effect of track defects on vibration from high speed train

The response of railway tracks and trackside vibration are strongly governed by the quality of the track. Defects or non-homogeneities in the track/substructure/ground can remarkably increase the responses in the system, leading to further deterioration of the track. This issue is more dramatic in high-speed lines. The objective of this paper is to study the impact of two types of non-homogeneities on the track response. In the first case, the effect of hanging sleepers is studied, and in the second case, the effect of locally deteriorated substructure is investigated. Two numerical solutions are used for the simulation of track-substructure-ground response. The first is the frequency-domain solution VibTrain that has been developed for efficient simulation of track/ground response under moving loads using a combination of beam elements for the track/substructure and Green’s functions for the layered soil medium. The second model is a FE model in COMSOL Multiphysics enhanced with the absorbing boundary PML (Perfectly Matched Layer) in the time domain. In addition to studying the effect of track defects on rail vibration, the results of the two solutions are compared and practical conclusions are drawn on the potential of using vibration data for detection of track defects.

Boundary reaction method for nonlinear analysis of soil–structure interaction under earthquake loads

This paper presents a boundary reaction method (BRM) for nonlinear time domain analysis of soil–structure interaction (SSI) under incident seismic waves. The BRM is a hybrid frequency–time domain method, but it removes global iterations between frequency and time domain analyses commonly required in the hybrid approach, so that it operates as a two-step uncoupled method. Specifically, the nonlinear SSI system is represented as a simple summation of two substructures as follows: (I) wave scattering substructure subjected to incident seismic waves to calculate boundary reaction forces on the fixed interface boundary between a finite nonlinear structure-soil body and an unbounded linear domain; and (II) wave radiation substructure subjected to the boundary reaction forces in which the nonlinearities can be considered. The nonlinear responses in the structure–soil body can be obtained by solving the radiation problem in the time domain using a general-purpose nonlinear finite element code that can simulate absorbing boundary conditions, while the boundary reaction forces can be easily calculated by solving the linear scattering problem by means of a standard frequency domain SSI code. The BRM is verified by comparing the numerical results obtained by the proposed BRM and the conventional frequency-domain SSI analysis for an equivalent linear SSI system. Finally, the BRM is applied to the nonlinear time-domain seismic analysis of a base-isolated nuclear power plant structure supported by a layered soil medium. The numerical results showed that the proposed method is very effective for nonlinear time-domain SSI analyses of nonlinear structure-soil system subjected to earthquake loadings.

Experimental investigation of free head model piles under lateral load in homogenous and layered sand

Model pile tests were carried out and subsequently the experimental study was supplemented by numerical study to determine coefficient of horizontal modulus of sub-grade reaction (ηh). Both short and long free headed piles were tested in homogeneous and layered soil media. Relative density of sand, slenderness ratio (SR), and embedment ratio of pile (thickness of top weaker layer) were varied. The numerical study was done by three-dimensional finite element method with the help of PLAXIS 3D Foundation version 2.1 software. Then, finite difference method was applied on the deflection profile along pile depth obtained from output of finite element analysis to determine ηh, the coefficient of horizontal modulus of sub-grade reaction. In finite element analysis, the test conditions were simulated and variables of the same soil–pile parameters were considered as in case of the experimental study. The numerical results were found to agree considerably well with the experimental ones for both long and short piles in homogeneous and layered sand media. Subsequently, variation of ηh was studied with the soil–pile parameters as mentioned. The variation of normalised form of ηh, defined as flexibility ratio with different soil–pile parameters, was also studied. At the outset, some behavioural changes were noted for long and short piles in both homogeneous and layered sand. In case of layered sand medium, ηh increased as the overlying weaker sand layer thickness decreased. However, in case of short piles and long piles, this variation was continuously linear. For short piles, ηh increased with increase in sand compactness and SR of pile, whereas in case of long piles, it increased with sand compactness and decreased with the SR of pile beyond SR of 40. This paper focuses on change on variation of different soil–pile parameters on ultimate lateral load as well as coefficient of horizontal modulus of sub-grade reaction (ηh), the principle stiffness parameter, which determines the ultimate lateral load of a single pile.

Effect of a forced harmonic vibration pile to its adjacent pile in layered elastic soil with double-shear model

A new model named double-shear model based on Pasternak foundation and Timoshenko beam theory is developed to evaluate the effect of a forced harmonic vibration pile to its adjacent pile in multilayered soil medium. The double-shear model takes into account the shear deformation and the rotational inertia of piles as well as the shear deformation of soil. The piles are simulated as Timoshenko beams, which are embedded in a layered Pasternak foundation. The differential equation of transverse vibration for a pile is solved by the initial parameter method. The dynamic interaction factors for the layered soil medium are obtained by the transfer matrix method. The formulation and the implementation have been verified by means of several examples. The individual shear effects of soil and piles on the interaction factors are evaluated through a parametric study. Compared to Winkler model with Euler beam, the present model gives much better results for the dynamic interaction of piles embedded in stiff soil with small slenderness ratios. Finally, the effect of a forced long pile to a short pile embedded in multilayered soil medium is studied in detail.

Prediction of nonlinear characteristics of soil-pile system under vertical vibration

In the present study an attempt was made to predict the complex nonlinear parameters of the soil-pile system subjected to the vertical vibration of rotating machines. A three dimensional (3D) finite element (FE) model was developed to predict the nonlinear dynamic response of full-scale pile foundation in a layered soil medium using ABAQUS/CAE. The frequency amplitude responses for different eccentric moments obtained from the FE analysis were compared with the vertical vibration test results of the full-scale single pile. It was found that the predicted resonant frequency and amplitude of pile obtained from 3D FE analysis were within a reasonable range of the vertical vibration test results. The variation of the soil-pile separation lengths were determined using FE analysis for different eccentric moments. The Novak's continuum approach was also used to predict the nonlinear behaviour of soil-pile system. The continuum approach was found to be useful for the prediction of the nonlinear frequency-amplitude response of full-scale pile after introducing the proper boundary zone parameters and soil-pile separation lengths.

Representation of Soil-Foundation Systems and Its Application to Shaking Table Tests by Constructing a Mechanical Interface

Experimental studies on the dynamic response of structures comprising soil-foundation systems require an appropriately constructed soil-foundation model below the superstructures in order to properly estimate structural responses. In most studies, applying a small scaling is necessary for constructing the entire structural system, since there is limited space on shaking tables. This constraint has been a hindrance in experimental studies. Thus this study proposes a mechanical interface (MI) that represents the impedance characteristics of a 3 × 5 pile group embedded in a layered soil medium. The MI is constructed on the basis of lumped parameter models with gyro-mass elements. This element is mechanically realized in the MI using a rotational mass in combination with coupling gears. The results show that the MI properly simulates the impedance functions with frequency-dependent oscillations, and shaking table tests using the MI for an inelastic structure are demonstrated.

Use of the laboratory tests of soil modulus in modelling pile behaviour

Abstract This article deals with the question of theoretical description of behaviour of a single pile rested in a layered soil medium. Particular attention is paid to soil modulus which is used in calculation method for pile load-settlement curve. A brief analysis of the results obtained by laboratory tests to assess soil modulus and its nonlinear variability has been presented. The results of tests have been used in triaxial apparatus and resonant column/torsional shear device. There have also been presented the results of load-settlement calculation for a single pile under axial load with implementation of different models of soil modulus degradation. On this basis, possibilities of using particular kinds of laboratory tests in calculation procedure of foundation settlement have been presented as well as further developments of them.

Closure to “A Parametric Study on Factors Affecting Ground Vibrations during Pile Driving through Finite Element Simulations” by Mo Zhang and Mingjiang Tao

Closure to “A Parametric Study on Factors Affecting Ground Vibrations during Pile Driving through Finite Element Simulations” by Mo Zhang and Mingjiang Tao