Showing papers on "Soil structure interaction published in 2005"

Load Transfer Mechanisms between Underground Structure and Surrounding Ground: Evaluation of the Failure of the Daikai Station

Abstract: The Daikai Station, a cut and cover structure in the subway system in Kobe, collapsed during the Hyogoken-Nambu earthquake of January 17, 1995 in Japan. The Daikai Station is the first well-documented underground structure not crossing an active fault that has completely collapsed during an earthquake without liquefaction of the surrounding soil. What makes this case even more interesting is that tunnel sections adjacent to the station, with similar structural characteristics and analogous soil conditions, did not collapse. Dynamic numerical analyses have been conducted to investigate the load transfer mechanisms between the underground structure and the surrounding soil and to identify the causes for different behavior of similar sections of the station subjected to the same seismic loading. A hysteretic nonlinear soil model has been used for the analysis. The model captures well the soil's shear modulus degradation and the increase of damping with strain. The results from the analyses show that, for a given earthquake, there are two key factors that determine the response of an underground structure: the relative stiffness between the structure and the degraded surrounding ground, and the frictional characteristics of the interface. A stiff structure has small deformations; because the adjacent soil movement is restricted by the structure, the shear modulus degradation of the soil is limited which contributes to reduce further deformation of the soil and thus decreases the displacement demand on the structure. A strong interface is capable of transmitting larger shear to the structure but in turn increases the confinement of the soil surrounding the structure which limits the soil's shear modulus degradation. The model predicts larger deformations in the section that collapsed because this section had a smaller stiffness, and thus triggered drifts in critical structural elements which were larger than at other sections of the station which remained stable.

Estimation of building damage due to excavation-induced ground movements

Abstract: Building damage due to excavation-induced ground movement is evaluated using a damage criterion based on the average state of strain in the distorting portion of the structure, and by considering the effect of building shear stiffness on the distortions imposed by the ground settlement profile. Physical model tests and numerical simulations, correlated with case studies of building distortion and damage, have been used to evaluate these relationships for masonry bearing wall structures. The distinct element method was used to numerically model each masonry unit as a block, with the contacts between blocks having the stiffness and strength characteristics of mortar. In-plane displacements at the corners of the wall sections permitted determination of the average state of strain, and the components of rigid body tilt, angular distortion, lateral strain at the base, and the contribution of bending strain to the lateral strain in the upper portion of the wall. The increase in angular distortion with increase in the ratio of ground/structure shear stiffness (decrease in building shear stiffness) was examined for both elastic and cracked building walls. Cracking significantly reduced effective wall stiffness making the wall more conformable to the ground settlement profile, which increased angular distortion, causing it to approach the distortion (change in ground slope) that would occur in the absence of the structure.

A generic approach to soil-structure interaction considering the effects of soil heterogeneity

Abstract: The longitudinal variation of soil properties has a major influence for many types of structure, including pavements, buried pipes, raft foundations and railways, as it induces stresses and/or displacements that cannot be predicted when assuming soil homogeneity. A set of simple numerical models has been developed to describe how soil–structure interaction can be influenced by soil variability. These models include: (a) a description of the soil spatial variability, within the frame of geostatistics, where the correlation length of soil properties is the main parameter; and (b) a mechanical description of the soil–structure interaction, which depends on the structure resting on the ground. There are some differences between a (more or less) rigid raft on piles, a set of buried pipes with (more or less) flexible connections and a hyperstatic beam, but the basic principles of mechanics are similar in all these cases. Several very general conclusion are drawn. (a) Soil heterogeneity induces effects (differen...

Lateral Pipe–Soil Interaction in Sand with Reference to Scale Effect

Abstract: This paper investigates the pipe.soil interaction for pipes buried in cohesionless soil when subjected to lateral ground movement. A review and reappraisal of the literature is conducted to identify some inconsistencies and shortcomings of previous studies. The effects of model scale, stress level (via burial depth), burial depth ratio, and soil properties are systematically addressed through finite element analyses. The study concludes that the effects of pipe size and burial depth must be taken into account to properly estimate the maximum pipe.soil interaction forces induced by lateral ground movement. A unique equation considering scale and the effect of burial depth is proposed to determine the maximum pipe-soil interaction forces at various burial depth ratios.

Prediction of Field Behavior of Reinforced Soil Wall using Advanced Constitutive Model

Abstract: A geosynthetic-reinforced soil retaining wall using full-height concrete wall facing panel was constructed at Tanque Verde Road site for grade-separated interchanges in Tucson, Ariz. Numerical simulation of this wall was performed using a finite element code called DSC-SST-2D. The program allows for plane strain, plane stress, and axisymmetric idealizations including simulation of construction sequences. The wall was modeled as a plane strain, two-dimensional problem. Material parameters used in the analysis were obtained from experimental results from conventional triaxial compression tests for backfill soils and cyclic multidegree-of-freedom shear tests for interfaces. The soils and interfaces were modeled using the disturbed state concept and hierarchical single surface plasticity models, and the geogrid reinforcement was simulated by a linear elastic model. The interfaces between the reinforcement layers and soil were modeled using the thin layer element. The results of the finite element analysis were in good agreement with the measured field behavior of the wall. Comparison involved vertical and lateral stress transferred to reinforcements and wall face movements. It was found that the use of the unified constitutive model in a nonlinear finite element method provided satisfactory predictions for the field performance of the Tensar geogrid reinforced soil wall.

Nonlinear Interaction of Soil--Pile in Horizontal Vibration

Abstract: This paper presents a new model for analyzing a nonlinear soil–pile interaction subject to horizontal shaking of a vertical circular pile embedded in a soil layer of finite thickness. The pile rests on bedrock with either a pinned or a clamped support. The soil mass is assumed composing of a “semi-nonlinear” inner soil zone around the pile and a linear viscoelastic soil zone outside the inner zone. When the inner soil behaves linearly, the present solutions are identical to those obtained by Nogami and Novak in 1977. Numerical results show that soil resistance of less slender piles developed against the vibration is larger than that of more slender piles. Soil resistance depends more strongly on the size of the nonlinear inner zone when the pile is vibrating at a frequency higher than the natural frequency of the soil. Soil nonlinearity, in general, results in a smaller damping and stiffness of the soil–pile system, except at high frequency. At higher vibration frequency, the situation can be very complic...

Numerical modeling of pipe-soil interaction under oblique loading

Abstract: This paper studies pipe-soil interaction for pipelines subjected to combined horizontal and vertical (upward) movements in the oblique direction. An associative, hardening elasto-plasticity model is proposed in the horizontal-vertical sp-qd load space for pipes buried in clay. The failure surface is proposed based on experimental observations. Involving seven parameters that can be determined either experimentally or based on the recommendations of ASCE guidelines, the proposed approach reproduces the key features of force-displacement responses obtained from continuum finite element analyses for pipes of different sizes and various burial depth ratios.

Implications of the Observed Seismic Performance of a Pile-Supported Wharf for Numerical Modeling

Abstract: The seismic response and performance of pile-supported wharves on sloping ground is not well documented due to an historical lack of instrumentation on port structures. Although general surface observations have been made at numerous ports following recent earthquakes, much more specific soil foundation-structure-interaction data could have been obtained with the more widespread employment of instrumentation. This paper presents the results of empirical and numerical analyses of recorded strong-motion data (SMD) from an array of instruments located on a pile-supported wharf and in the adjacent free field. Data were recorded with an instrumentation array at Berth 24∕25 at the Port of Oakland, California, during the M7.0 Loma Prieta earthquake. The primary objectives of this project were to evaluate the SMD and identify the limitations inherent in capturing the complete dynamic character, including soil structure interaction, of a pier or wharf with a structural model. The project is expected to se...

Determination of Multidirectional p-y Curves for Soft Clays

Abstract: The evaluation of performance of soil-pile-structure systems under seismic loading is one of the most complex problems in earthquake engineering. In the most common methodology, force-displacement curves are used to describe the nonlinear response of discrete soil springs connecting the piles to the “free-field” soil column using the concept of beam on nonlinear Winkler foundation. Although there is a great interest and on-going research to characterize the multi-directional “free-field” soil response, there is a lack of information and experimental data to formulate p-y curves in multi-directional loading conditions. A new testing device was designed and constructed to obtain high quality data to calibrate numerical tools used to evaluate the seismic performance of structures supported on deep foundations in soft clay. A suite of different ground displacement path scenarios observed during recent earthquakes was simulated to assess the effect of displacement history on measured p-y response.

Influence of soil heterogeneity on load redistribution and settlement of a hyperstatic three-support frame

Abstract: Spatial and geometrical variability of mechanical soil properties can induce differential settlements and load redistribution in hyperstatic structures. Therefore damage prevention requires specific attention to be paid to the global mechanisms of soil–structure interaction. A reduced-scale model of a hyperstatic three-support frame (scale 1:100) is installed on the CEA-CESTA centrifuge, up to 100g. Various configurations are studied, with different loadings, different structural stiffnesses, and different geometries of the soil layer. Strain gauges are fixed at various points so as to enable the retro-analysis of all components of forces at free ends. Displacements are recorded at several points on the structure and on the free surface. A numerical model of the frame (based on beam theory with elastic supports) is calibrated, first to determine an equivalent support stiffness, and second to quantify the effect of variations of the structural stiffness/soil modulus ratio on the structural response. A prob...

Energy and variational principles for piles in dissipative soil

Abstract: Energy and variational principles have provided a valuable tool to analyse the behaviour of elastic structures for quite a long time. They have also been used infrequently to study soil–pile interaction problems, following the traditional methods that were developed for elastic structures. One of the possible reasons for the gap in applications is that soil is not a non-dissipative elastic medium. This paper presents an alternative energy-based variational approach that does account for the inelastic dissipative nature of soils. Other than theoretical advantages, the new approach seems very promising for practical reasons. This approach allows the recovery of an inherent set of differential equations, which in particular cases of proportional monotonic loading conditions may become identical to the previous equations obtained from the ‘elasticity’ methods. The new method also allows modelling of the kinematic hardening nature of the soil during cyclic loading events.

Numerical modeling of dynamic soil-pile-structure interaction

Abstract: By Surendran Balendra, M.S. Washington State University December 2005 Chair: Adrian Rodriguez-Marek The analysis of structures subject to earthquake ground motions must properly account for the interaction between the foundation and the superstructure. The passage of seismic waves through the foundation affects the ground motion at the base of the structure and generates stresses on foundation elements. This effect is termed kinematic interaction and its effects on the ground motion are described by a function termed the transfer function. On the other hand, the response of a structure is a function of the foundation compliance, and, in turn, inertial forces resulting from structural response affect the stresses on foundation elements. This interaction is termed inertial interaction and is captured by representing the foundation through an impedance function. In this study, numerical models using ABAQUS were developed to study both inertial and kinematic effects. The focus of this study was to perform parametric studies on the various variables that affect kinematic transfer functions and inertial impedance functions of pile foundations. The independent variables of this parametric study were material nonlinearity, soil-pile separation, pile diameter, intensity of the input motion, and the

A practical method for estimating dynamic soil stiffness on surface of multi‐layered soil

Abstract: It is important to estimate the influence of layered soil in soil-structure interaction analyses. Although a great number of investigations have been carried out on this subject, there are very few practical methods that do not require complex calculations. In this paper, a simple and practical method for estimating the horizontal dynamic stiffness of a rigid foundation on the surface of multi-layered soil is proposed. In this method, waves propagating in the soil are traced using the conception of the cone model, and the impulse response function can be calculated directly and easily in the time domain with a good degree of accuracy. The characteristics of the impedance, that is the transformed value to the frequency domain of the obtained impulse response, are studied using two- to four-layered soil models. The cause of the fluctuation of impedance is expressed clearly from its relation to reflected waves from the lower layer boundary in the model.

Mechanism of rupture of shaft linings in coal mine areas buried by thick over-soils in East China

Abstract: Non-mining ruptures of shaft linings in coal mines, which have repeatedly occurred in coal mine areas of East China in recent years, are a new kind of geological disaster. In this paper the characteristics of non-mining ruptures of the shaft linings are presented. The engineering geology conditions of the ruptures are analysed. A method for testing the interaction between soil and shaft wall by high-pressure direct shear apparatus and triaxial servo test system has been presented. The shear stress– displacement curves, coefficient of unit stiffness and strength parameters of the interaction between soil and shaft wall are obtained. Combining with the test results, the deformation characteristics of the interaction between soils and shaft wall during deep soil compression due to water loss are analysed: they are elastic in the shallow and bottom parts and plastic in the deep part. An elastic perfectly plastic analysis model of the interaction between soil and shaft wall has been set up. Some analytic formu...

Near-field effects on seismically excited highway bridge equipped with nonlinear viscous dampers

Abstract: Near-field ground motions cause significant damage to highway bridges because of high peak ground accelerations and high peak ground velocities of long period pulses. To quantitatively assess the influence of near-field ground motions on seismically excited highway bridges, a ground motion model consisting of both pulse-type low frequency (near-field) and broadband frequency (far-field) components is proposed. In this model, the effects of the local site condition and the seismic source are taken into consideration by varying relative contributions of near-field pulse-type and far-field broadband random ground motion components in the synthetic ground motion. Extensive numerical simulations are carried out to quantify effects of pulse-type component and soil-structure interaction through a parametric study. Simulation results demonstrate that pulse-type components in ground motions amplify the response quantities of the highway bridge significantly over those by the broadband component. Nonlinear viscous ...

Development of a model jack-up unit for the study of soil-structure interaction on clay

Abstract: The behaviour of spudcan footings under combined vertical, moment and horizontal loading is a critical aspect of the site-specific assessment of offshore jack-up platforms. In recent years, experim...

Seismic Behavior of Micropiles

Abstract: Micropiles are grouted and small diameter piles that are traditionally used in foundation retrofit. Experimental evidence has indicated that micropiles behave well under seismic loading due to their high flexibility. Moreover, observations in the 1995 Kobe Earthquake indicate a good performance of friction piles under seismic loading. However, the seismic behavior of micropiles is not fully understood due to the limited number of full- and model-scale tests, as well as the limited amount of numerical modeling studies for micropiles. This project focuses on Finite Element modeling (FEM) of single micropile and micropile groups under both static and dynamic loading. Initially, dynamic FE soil models were developed to conduct site response analyses. The lateral vertical boundaries of the soil were set up in such a way that the reflection of the arrival waves at the boundaries was avoided. The results of the site response analyses were verified against the well-validated code, SHAKE. Subsequently, FE models for micropiles were developed with two constitutive soil models, i.e. a linear elastic and a bounding surface plasticity model. The micropile/soil interface was modeled either with perfect bonding or with frictional interface elements. For dynamic loading cases, a single degree-of-freedom (SDOF) superstructure was placed on top of the micropiles. Parametric studies were performed for various independent variables including load intensity, non-linearity of soil, and soil stiffness for the static case; and soil non-linearity, input motion intensity, frequency contents of input motion, and the natural period of the superstructure for the dynamic case. The static and dynamic behavior of micropiles was studied via the effects of aforementioned independent variables on the deflections and bending moments along the micropile length.

Evaluation of base isolation and soil structure interaction effects on the seismic response of bridges

Abstract: Evaluation of Base Isolation and Soil Structure Interaction Effects on Seismic Response of Bridges. (August 2005) Wentao Dai, B. En., Tongji University, China; M.S., Tongji University, China Chair of Advisory Committee: Dr. Jose M. Roësset A continuous formulation to calculate the dynamic stiffness matrix of structural members with distributed masses is presented in detail and verified with some simple examples. The dynamic model of a specific bridge (the Marga-Marga bridge in Chile) was developed using this formulation, and the model was then used to obtain the transfer functions of the motions at different points of the bridge due to seismic excitation. The model included rubber pads, used for base isolation, as additional members. The transfer functions were obtained with and without rubber pads to investigate their effect. The dynamic stiffness of complete pile foundations was calculated by a semi-analytical solution with Poulos’ assumption. General observations on group effects under various conditions were obtained from the result of these studies. The dynamic stiffness of the pile foundations for the Marga-Marga bridge was then obtained and used to study the soil structure interaction effects on the seismic response of the bridge. Records obtained during a real earthquake were examined and interpreted in light of the results from all these analyses. Finally, conclusions and recommendations on future studies are presented.

Finite element analysis of bridge approach slabs considering soil – structure interaction

Abstract: The objective of this paper is to present results of a study employed to identify the probable causes and location of cracking in bridge approach and transition slabs and the factors influencing the crack development. A finite element (FE) model has been developed to study the cracking phenomenon in bridge approach and transition slabs under vehicular live load and soil settlement. A field survey was conducted to determine the extent and probable causes of crack development in these slabs at various bridge sites in the State of New Jersey, USA. The data collected from field observations were compared with those predicted by the FE model to determine its reliability and consistency. The FE model was employed in conducting a parametric study to evaluate the effect of various designs as well as soil parameters on the cracking behavior of the slabs. The results from the parametric study showed that increasing the slab thickness would significantly increase the cracking load carrying capacity of the approach s...

Factors Contributing to Bridge--Embankment Interaction

Abstract: Seismic analyses typically neglect four important phenomena that contribute to the complex interaction between bridges and approach embankments: three-dimensional embankment response, nonlinear soil behavior, soil-structure interaction, and embankment scattering. To identify the importance of each phenomena, a modeling approach was adopted that can be implemented with commonly available soil and structure properties, and whose computational demands are sufficiently low to perform numerous dynamic analyses. The accuracy of the methodology was established by comparing measured and computed abutment acceleration response histories, response spectra, structural periods, damping ratios, and abutment stiffnesses for several bridges. Parametric studies indicated that, to maintain accuracy over a range of earthquake intensities, it is important to consider three-dimensional embankment effects and to specify soil properties accurately. In contrast, the computed response was nearly insensitive to the effects of embankment scattering and changes in embankment geometry, including the embankment height.

A kinematic interaction model for a large-diameter shaft foundation. An application to seismic demand assessment of a bridge subject to coupled swaying-rocking excitation.

Abstract: The aim of this paper is to illustrate an analytical model for the assessment of kinematic interaction of large-diameter shaft foundations. The model is derived using recently obtained solutions of soil structure interaction problems of rigid walls and fixed base cylinders subjected to a dynamic excitation. The proposed model constitutes an extension to a deformable base of the elastodynamic solution of a rigid fixed-base cylinder imbedded in a homogeneous or inhomogeneous soil stratum with different lateral boundary conditions. The analytical model has been validated by means of a finite elements code and it has been implemented in a consistent seismic soil-structure-interaction analysis procedure. An application of the model to a long, multispan continuous prestressed concrete viaduct with tall piers has been carried out focusing on the importance of kinematic interaction. The main result is that the foundation input motion is characterised not only by a translational horizontal component which is usually of a reduced amplitude if compared with the free-field ground motion, but also by a rotation component that is responsible for a large seismic demand in the superstructure. The proposed model represents an effective tool to be used in the engineering practice to assess both the seismic actions induced by the ground shaking on the foundation system and the effective input motion of a superstructure founded on massive and large diameter shafts

Design of ribbed concrete approach slab based on interaction with the embankment

Abstract: To alleviate the "bump" problem at bridge ends, a ribbed concrete approach slab (similar to slab-on-beam bridge decks) was proposed in place of the pile-column-supported approach span or flat slab system. The effect of given embankment settlement on the structural performance of a ribbed concrete approach slab with a span length of 60 ft and a width of 40 ft was investigated. The approach slab was modeled as a ribbed slab with a beam spacing of 32, 16, and 12 ft. A three-dimensional finite element analysis was conducted to model the interaction between the approach slab and the embankment soil. Finite element modeling techniques that simulate the separation of the slab and soil provide information on the effect of the embankment settlement on structural performance and beam design. The predicted internal forces provide design engineers with a scientific basis to design the approach slab properly, considering different levels of embankment settlements. Current AASHTO code specifications do not provide guid...

Seismic response analysis of shielded subway tunnels

Abstract: The complex response method was used to analyze the seismic response of subway tunnels shielded with a stiff liner as a function of factors such as the distance between the twin tunnels and the elastic modulus and thickness of the lining. The numerical results show that the seismic response of closely spaced twin tunnels is significantly different from that of a single tunnel. The elastic modulus of the lining has little effect on the seismic response. The lining thickness has little influence on the seismic deformation response, but great influences the internal force response. The peak ground displacement relative to the bedrock is a more effective design parameter of ground motion than the ground motion acceleration for evaluating the seismic response of underground structures.