Showing papers on "Soil structure interaction published in 1987"

Axial and lateral response of pile groups embedded in nonhomogeneous soils

Abstract: A numerical method of analysis based on elasticity theory is presented for the analysis of axially and laterally loaded pile groups embedded in nonhomogeneous soils. The problem is decomposed into two systems, namely the group piles acted upon by external applied loads and pile-soil interaction forces, and a layered soil continuum acted upon by a system of pile-soil interaction forces at the imaginary positions of the piles. The group piles are discretized into discrete elements while the nonhomogeneous soil behaviour is determined from an economically viable finite element procedure. The load-deformation relationship of the pile group system is then determined by considering the equilibrium of the pile-soil interaction forces, and the compatibility of the pile and soil displacements. The influence of soil nonlinearity can be studied by limiting the soil forces at the pile-soil interface, and redistributing the "excess forces" by an "initial stress" process popular in elasto-plastic finite element analysis. The solutions from this approach are compared with some available published solutions for single piles and pile groups in homogeneous and nonhomogeneous soils. A limited number of field tests on pile groups are studied, and show that, in general, the computed response compares favourably with the field measurements. (Author/TRRL)

Response of circular foundation to spatially random ground motion

Abstract: A method to obtain the response of a rigid circular foundation resting on a uniform elastic half‐space and subjected to a spatially random ground motion is presented. The solution of the resulting mixed boundary‐value problem is based on the use of an integral representation of the response of the foundation in terms of the free‐field ground motion and of the contact tractions between the foundation and the soil obtained in the course of calculating the dynamic compliance functions for the foundation. The results obtained indicate that the effects of the spatial randomness of the ground motion on the response of the foundation are qualitatively similar to deterministic wave passage effects. Both effects involve a reduction of the translational components of the response at high frequencies and the creation of rotational response components.

Simulation of soil-concrete interfaces with nonlocal constitutive models

Abstract: This investigation explores a method for predicting deformation in the vicinity of interfaces of dissimilar materials. Instead of using a slide‐line algorithm or interface elements, a new nonlocal approach for simulating the response near soil‐concrete interfaces is proposed. It is assumed that the stress field is a function of both strain and strain gradients, and that no slip occurs at the contact surface between soil and concrete. Different response features for the region of localized shear strain adjacent to the interface can be obtained by adjusting material parameters. Numerical results for static and dynamic cases show that softening and localization are handled in a stable manner independent of mesh size.

Strong ground motion seismology

Abstract: Section 1: Earthquake Source.- Strong Motion Seismology.- Earthquake Source Mechanisms: Case Studies.- Source Parameters of Some Friuli Earthquakes (1976-1977) From Strong Motion Data.- The Seismic Inverse Problem For a Flat Structure.- Section 2: Prediction of Strong Ground Motion.- The Prediction of Strong Ground Motion.- A Theoretical Study of the Dependence of the Peak Ground Acceleration on Source and Structure Parameters.- Numerical Simulation of Earthquake Ground Motion.- High Frequency Earthquake Strong Ground Motion in Laterally Varying Media: The Effect of a Fault Zone.- Physical Mechanisms Contributing to Seismic Attenuation in the Crust.- Section 3: Acquisition and Interpretation of Strong Motion Data (Including Case Histories).- Data Acquisition and Processing in Strong Motion Seismology.- Strong Ground Motions in Italy: Accelerogram Spectral Properties and Prediction of Peak Values.- Analysis of Strong-Motion Data From the New Hampshire Earthquake of 18 January 1982.- Seismic Intensity and its Applications to Engineering: A Study in Japan.- Seismic Intensity and its Applications to Engineering: A Study in Turkey.- Section 4: Hazard Assessment.- Probabilistic Models for Assessment of Strong Ground Motion.- Seismic Source Regionalization.- Section 5: Site Response and Engineering Application.- Site Response Analysis.- Constitutive Relationships for Soil Dynamics.- Source and Local Site Effects-Preliminary Results Based on the Friuli Earthquake Sequence 1976.- Soil Structure Interaction Effects on Strong Ground Motion.- Engineering Uses of Strong Motion Data.

The elastic stability of shallow buried tubes

Abstract: Theoretical solutions exist for buried tube buckling, but the influence of the depth of burial on the critical hoop forces is not well understood. Consequently a study of shallow buried tube buckling is carried out using both analytical and numerical methods. If the ground surrounding a shallow buried tube is approximated by a circular cylinder of soil which extends to the ground surface, then it is possible to develop analytical solutions for the hoop forces which elastically destabilize the structure. Three such solutions are examined, based on both subgrade and elastic continuum representations of the soil material. A finite element solution is also examined, which yields a solution for more realistic ground support conditions. That solution is used to undertake a parametric study of the problem, where the effects of ground and structural stiffness, burial depth and distribution of hoop forces around the tube circumference are examined. A procedure is also developed which permits the straightforward es...

Boundary element method applied to linear soil-structure interaction on a heterogeneous soil

Abstract: An extension of the boundary element method to heterogeneous domains composed of horizontal layers is here proposed. It includes a numerical computation of the corresponding Green's functions, thanks to an inverse Hankel transform of the closed form solutions obtained in the spectral domain with suitable variables derived from displacements and stress vectors to obtain the decoupling between P–SV and SH waves. Transmission and reflection operators are introduced to avoid the problem of overflowing exponentials met with in Thomson–Haskell matrices. Applications are given in the soil–structure interaction field to compute the impedances of surface and embedded circular foundations resting on a viscoelastic halfspace.

Elasto-Plastic Seismic Response of 3-D Earth Dams: Application

Abstract: The procedure outlined in the companion paper is applied to compute the nonlinear response of an earth dam to a 3-D input strong motion with recorded maximum acceleration of 1.2 Hg (in the upstream-downstream direction). Special features of the nonlinear seismic response due to the highly strong shaking are explored. Because of the modal expansion concept utilized in the procedure, insight is gained into the contribution of different modes to the response of the dam at different locations. Finally, comprehensive comparisons are made with results obtained through a more elaborate nonlinear, 3-D, finite element analysis of the dam. The comparison indicates that the proposed simplified analysis method can be used to reliably estimate the entire time history of all response quantities and the resulting permanent deformations of earth dams subject to earthquakes. In addition, it is found that the computed results agree reasonably well with those of the finite element analysis; further, the “modal” nonlinear procedure is found to be reasonably accurate and extremely efficient computationally.

Soil-Structure Interaction in Mexico City During the 1985 Earthquakes

Abstract: The effects of the flexibility of the soil and the foundation on the seismic response of structures, by opposition to clear foundation failures, cannot be easily identified from a simple observation of buildings after an earthquake, requiring either records of the motions (both translational and rotational components) at the base (and other levels), or detailed analytical studies. Although neither of these are available at this time, it is still possible, using relatively simple models, to make preliminary estimates of the types and magnitudes of the effects in Mexico City for different types of buildings and foundations. This paper presents a basic discussion of the nature of soil structure interaction effects and their possible importance in Mexico City, identifying some of the key aspects that should be taken into account, and recommends various topics where further research would be desirable.

The Mexico Earthquakes-1985: Factors Involved and Lessons Learned

Abstract: This publication reports initial results of study of the 1985 Mexico earthquake, one year after the event. The findings present sufficient depth of analysis to provide an understanding of the causes and effects of earthshaking within Mexico City that resulted in extensive damage to some buildings and structures. Also reported are the assessment of damage caused by the earthquake and emergency response including recovery operations. Buildings of different construction types and materials were subject to the earthquake. Performance of their response is analyzed and evaluated. Topics presented include seismicity associated with the Mexico earthquake of 1985. General engineering topics include dynamic soil response, foundation failure, performance of structures and analysis of building failure, analysis of lifelines performance, and emergency response including building code regulations. Specific practical problems addressed include: modeling of soil motion, modeling of structural behavior, analysis of drift in frame structures, structural pounding, structural stiffness softening due to long duration motion, soil-structure interaction, influence of local soil conditions on building performance, dam behavior, and repair and strengthening of buildings.

Nailed-soil retaining structures: design and practice

Abstract: Soil nailing is an in situ soil reinforcement technique that has been used during the last two decades, mainly in France and Germany, to retain excavations or stabilize slopes. The fundamental concept of soil nailing is the reinforcement of the ground by passive inclusions, closely spaced, to increase the overall shear strength of the in situ soil, to restrain its displacements, and to limit its decompression during and after excavation. The technology, construction process, design methods, and fundamental aspects of behavior and soil-nail interaction in nailed-soil retaining structures are discussed.

Generalized method for non‐linear seismic response analysis of a three dimensional soil–structure interaction system

Abstract: Previous achievements using the dynamic non-linear analysis of an interaction system are reviewed briefly, after which a three dimensional (3D) model of the stress redistribution of soil based on the Mohr–Coulomb failure law is presented to evaluate the unbalanced tensor at every iteration in the load transfer method. A 3D, full non-linear analysis was used to examine the validity and accuracy of results obtained by 2D analysis by combining the model of redistributed stresses proposed here with the joint element model. Based on the numerical solution reported here, we concluded that both the 3D and 2D models of stress redistribution work well and reflect the yielding pattern of soil during excitation, but the former is more realistic. The failure area in the structural zone obtained by 3D analysis is slightly larger but similar to that obtained by 2D analysis. The ratio of maximum strain to yield strain and non-linear time ratio, βs, for the soil elements in the structural zone are also a little larger. In contrast, the maximum separation values for the joint elements are much smaller and the separation pattern for the x-side wall interface is the reverse of that found by 2D analysis. These values, however, affect only responses in the short period range and the regions close to the interface. In general, the tendencies shown by 2D analysis for the effects of non-linear behaviour on structural responses are confirmed for the parameters investigated.

Structural design of buried corrugated polyethylene pipes

Abstract: Test sections of corrugated polyethylene pipe (CPEP) were buried, as in typical drainage installation, in competent, compacted, granular backfill. Both dead load (soil cover) and surface live load (truck dual wheels) were applied. The objectives of the tests were to (a) observe performance of the pipes under load, (b) identify performance limits, (c) resolve some of the questions unanswered by present design methods, and (d) propose improved methods for the structural design of buried CPEP. The objectives were achieved. Experimenters agreed that tests confirmed the complementary interaction of pipe and backfill. Minimum soil cover was investigated under multiple passes of live loads. Conditions for structural stability of the pipe were identified. An analytical procedure was developed for predicting the minimum height of soil cover to assure ring stability under multiple passes of live loads. Maximum soil cover tests confirmed the ring compression analysis as the primary basis for design but also revealed a need to include the effects of ring deflection. An observable performance limit was identified, and a method of design was developed that combined the effect of ring deflection and ring compression on the performance limits of CPEP buried under maximum height of soil cover.

Combined Finite Difference/Finite Element Analysis for Soil Structure Interaction

Abstract: A method for the analysis of buried structures subjected to stress transients is presented. The method combines the finite difference and finite element techniques to provide the analyst with the capability to model the complete effects of soil-structure interaction, including material and geometric nonlinearities. The method and its computer implementation are briefly described and the results of two example analyses are presented.

Two‐dimensional effective stress analysis of liquefaction of irregular ground including soil–structure interaction

Abstract: An effective stress method is presented for analysis of seismic response and liquefaction of irregular ground including soil–structure interaction, based on an implicit–explicit finite element method. A pore water pressure is computed with iteration from the total stress considering an undrained condition. The simulated pore water pressure is in reasonably good agreement with the experimental data. The proposed method of analysis is compared with other well-known methods for a one-dimensional model, which is in good agreement. The present effective stress method is also applied to liquefaction problems involving a two-dimensional soil–structure model. The structure is modelled by not only a rigid model but also as a multi-degree-of-freedom system with bi-linear springs. The numerical results are considered to be significant from the viewpoint of earthquake engineering.

Seismic Response of Dam with Soil‐Structure Interaction

Abstract: An analytical solution to the response of a long trapezoidal‐section dam on a foundation consisting of an elastic half‐space and subjected to simulated earthquake morion is developed. An optimum seismic design is achieved when the cross section of the dam is triangular. The effect of soil structure interaction is to lower the strain occurring in the dam.

Soil Structure Interaction Effects on Strong Ground Motion

Abstract: Dynamic interaction of soils and structures during dynamic excitation or earthquakes are of concern for the design of structures and foundations and also for the proper interpretation of the strong motion data recorded on the ground floor or basements of structures. In this paper a three-degree-of-freedom (3-D.O.F.) model for the soil-structure interaction problem will be studied on the basis of the sub-structure approach and the results will be applied to obtain the transfer function between the free field ground and structure-ground level motions during an earthquake.

Significance of foundation-soil separation in dynamic soil-structure interaction

Abstract: THe dynamic response of flexible surface strip-foundations allowed to uplift is numerically obtained for externally applied forces of a transient time variation The soil medium is represented by an isotropic, homogeneous and linear half-space The soil is treated by a time domain boundary element method, while the flexible foundation is treated by the finite element method It was concluded that intermediate relative stiffness leads to moderate deformations when uplift is permitted Very flexible footings produce higher deformations in unilateral contact compared to bilateral contact, and thus should be considered in their design Unilateral contact does not significantly increase deformations for stiff footings subjected to concentrated central loading However, relatively large deformation differences occur when the loading is eccentric, necessitating consideration of uplift in their design

Numerical Stimulation Model for Dynamic Response of Foundation Medium

Abstract: A simple mechanical model is developed for the dynamic response analysis of a layered soil medium. Each layer in the medium is idealized as a system of one-dimensional vertical elastic columns interconnected by the shear springs distributed along the column. The model is applied to formulate the dynamic response of the ground and beams lying on the ground. The obtained formulation is very efficient for computation. Numerical examples are provided to demonstrate the present approach. It is found that the present model can adequately reproduce the dynamic behavior of a continuous foundation medium.

Partial Loss Of Support And Frame-Soil Interaction

Abstract: An interaction analysis has been conducted to study the effects of a local loss of support beneath the beam footing of a two-bay plane frame. The results of the study indicate that the magnitude of increase in the bending moment and axial force in the structure due to the presence of a void are dependent, not only on the extent of support loss, but also on the relative stiffnesses between foundation beam and soil, and between superstructure and soil. The increase in bending moment even for a void span of 1/12 of the foundation beam length can become so significant as to exceed the safety provisions. The study shows that the effect of a void on the superstructure moments can be greatly minimized by a combination of rigid foundation and flexible superstructure.

Elastic‐Creep Analysis of Laterally Loaded Piles

Abstract: A simple one‐dimensional finite element procedure is used to analyze lateral piles in clayey soils. The analysis included a creep law for the soil based on a probabilistic model and allows for stress‐dependent creep. A field problem is analyzed taking into account the variation in the soil properties with depth. The numerical predictions are compared with field pile load test data and the creep deflections are found to increase nonlinearly with the applied loads. The depth variation of the soil properties is found to be important in the prediction of deflections of a pile‐soil system.

Dynamic and static behaviour of driven piles

Abstract: The rapidly increased use of pile foundations and the appearance of new driving techniques, as well as stress wave measurement equipment have led researchers to look for better understanding of the dynamic and static behaviour of the hammer-pile-soil system and to develop more reliable methods of pile analysis. The reliability of the pile driving analysis is primarily a function of the accuracy of the soil parameters and the rheological model of the soil. The scope of this study is an attempt to find a new soil model and a new computer program for pile driving analysis. The investigation has been focused on the derivation of soil parameters from conventional soil mechanics and soil dynamics. The solution of the stress equation is based on Smith's approach. After remarks on different existing soil models, a new soil model for pile driving analysis is proposed in this research work. The soil parameters can be determined directly from the shear modulus of the soil, material densities, Poisson's ratio, damping ratio and pile dimensions. Influences from installation of the pile, soil inertia, interparticle shear stress, mass of pile, soil type, number of blows count, etc, can be considered in the evaluation of soil stiffness, hysteretic damping, radiation damping and quake. The established guiding computer program SVIDYN can be run in a microcomputer using either the new soil model or smith's soil model. The program can be used to study the bearing capacity and driveability of piles. The program is tested with results from different field tests and parameter studies and compared with capwap analysis and shows the reliability of the new approach for pile driving analysis. The bearing capacity of the piles, force history, velocity history, permanent set, number of blow count and simulation of static load tests can be obtained with the SVIDYN computer program. (Author/TRRL)