Finite element formulation for the analysis of interfaces, nonlinear and large displacement problems in geotechnical engineering

Ph.D.R. D. Barksdal

Advanced tools and techniques to add value to soil stabilization practice

The aim of this paper is to demonstrate the advanced tools and techniques used for adding value to the soil stabilization practice. The tools presented involve advanced laboratory tests and modeling using codes and soft computing to evaluate the mechanical behavior of stabilized soils with cement, ranging from short-term to long-term behavior. More precisely, these tools are able to: 1. Predict the mechanical behavior of the stabilized soils over time from data obtained in the early ages saving time in laboratory tests; 2. Predict the mechanical behavior of the stabilized soils over time based on basic parameters of soil type and binder using historical accurate data, avoiding mechanical laboratory tests. 3. Incorporate the serviceability limit state concept in a novel proposal to estimate the design modulus in function of the uniaxial compressive strength and the strain level, making more economic and sustainable geotechnical solutions.This work was supported by FCT—‘‘Fundação para a Ciência e a Tecnologia’’, within ISISE, project UID/ECI/04029/2013 and through the post doctoral Grant fellowship with reference SFRH/BPD/94792/2013. This work was also partly financed by FEDER funds through the Competitivity Factors Operational Programme—COMPETE and by national funds through FCT within the scope of the project POCI-01-0145-FEDER-007633.info:eu-repo/semantics/publishedVersio

A macro-element based practical model for seismic analysis of steel-concrete composite high-rise buildings

This is the post-print version of the final paper published in Engineering Structures. The published article is available from the link below. Changes resulting from the publishing process, such as peer review, editing, corrections, structural formatting, and other quality control mechanisms may not be reflected in this document. Changes may have been made to this work since it was submitted for publication. Copyright @ 2012 Elsevier B.V.Seismic behaviour of steel–concrete composite high-rise buildings, composed of external steel frames (SFs) and internal concrete tube (CT), with rectangular plan is investigated in this paper. A macro-element based model is established for seismic analysis of composite high-rise buildings aiming at predicting their global responses under earthquakes. By employing this macro-element based model, natural frequencies and vibration modes, storey and inter-storey drifts, overturning moments and storey shear forces of composite structures, induced by earthquakes, are able to be obtained with much less computation time and cost compared with using micro-element based analytical models. To validate its efficiency and reliability, the macro-element based model is employed to analyse a 1/20 scaled-down model of a 25-storey steel–concrete composite high-rise building subjected to simulated earthquakes with various intensities through a shaking table. Natural frequencies and storey drifts of the model structure are obtained from numerical analyses and compared with those from shaking table test results. It has been found that the calculated dynamic responses of the composite model structure subjected to minor, basic, major and super strong earthquakes agree reasonably well with those obtained from experiments, suggesting that the proposed macro-element based model is appropriate for inelastic time-history analyse for global responses of steel–concrete composite high-rise structures subjected to earthquakes with satisfactory precision and reliability. This research thus provides a practical model for elastic and inelastic deformation check of high-rise composite buildings under earthquakes.Ministry of Science and Technology of Chin

Large temporal variations of functional properties of outdoor equestrian arena surfaces and a new concept of evaluating reactivity with light weight deflectometer settlement curves

Sports physiological properties of ten sand or sand-mineral outdoor arenas, five with vertical drainage systems and five with an ebb and flow like system were assessed over a period of eight weeks. For each arena, the riding zone was spatially delineated, nine locations at medium to intensely used zones were selected by simple random sampling and used along the whole measurement period. A total of 72 values for the dynamic deflection modulus (Evd), attenuation (s/v), settlement (s) and moisture content (Vol %) were analyzed for each arena. A novel technique to analyze the settlement curves of the light weight deflectometer (LWD) to describe reactivity of the footing surface was introduced. Statistical testing was done by linear mixed models. Three of the five arenas with a vertical watering system were judged to be hard (Evd > 20 MN/m2), whereas all five arenas with an ebb and flow like watering systems were medium hard (Evd = 10-20 MN/m2) over the entire eight weeks. Significant (p<0.01) temporal differences in Evd, s/v and moisture were demonstrated for both watering systems; however, the spatial and temporal variations were much lower with the ebb-flow system. Temporal consistency in the parameters over the test weeks appeared to be a criterion for stability of the arena surface. The analysis of the settlement curves of the LWD showed that the slope symmetry has a large potential to describe the restoration of the energy of an equestrian surface than only the settlement, which requires further validation

Effective Width of Floor Systems for Application in Seismic Analysis

Effective width coefficients for floor systems have been developed for use in the analysis of frames subjected to lateral seismic loads. The results cover a wide range of the governing nondimensional parameters, and are applicable to floor slabs with supporting beams as well as to flat slabs. The effective width coefficients were derived from a parametric study of typical interior panels of floor systems using elastic finite element analysis. An example of the application of the use of the results in seismic analysis of low-rise building frames is presented.National Science Foundation Grants ENV 77-07190 and PFR 80-0258

Development of modified p-y curves for Winkler Analysis to characterize the lateral load behavior of a single pile embedded in improved soft clay

In the past decades, the behavior of pile foundations in liquefiable sands has been studied extensively; however, similar investigations of soft clays or static/seismic response of piles in improved soft clay soils are scarce. Despite the widespread presence of this soil type in high seismic regions and the frequent need to locate bridges and buildings in soft clay, only a few investigations have been carried out to guide engineers in evaluating the effectiveness of ground improvement techniques on increasing the lateral resistance of pile foundation embedded in soft clay, and no numerical models have been validated to evaluate this approach. Thus, the objective of this research was to develop modified p-y curves for Winkler analysis to characterize the lateral load behavior of a single pile embedded in a volume of improved clay surrounded by unimproved soft clays. A detailed literature review was completed in the study, aiming to gain knowledge on the development and fields of applications together with limitations of different ground improvement techniques. The ability of each available analysis method for lateral loaded piles was assessed for determining lateral responses of pile foundation in a volume of improved soil surrounded by unimproved soil. A method of developing p-y curve modification factors to account for the effect of the improved soil on enhancing the lateral load behavior of a single pile embedded in soft clay was developed by integrating the effectiveness of the improved soil into the procedures of constructing p-y curves for stiff clay recommended by Welch and Reese (1972). It was achieved by estimating the effective length for a infinitely long soil layer with soil improvement so that the fraction of the load resisted by the soil improved over a limited horizontal extent could be accounted for by taking the ratio between the soil resistance attenuation at actual length of the soil improvement and the effective length. The accuracy of the method was verified against the centrifuge test data from Liu et al. (2010) and the full scale field test from Fleming et al. (2010). The verifications using experimental data demonstrated that the Winkler analysis with proposed p-y modification factors is able to capture the full range of elastic and inelastic pile responses with slopes that correspond well with the results obtained from both centrifuge and field testing, the effectiveness of the soil improvement can be adequately evaluated. In addition, an analytical study on the effectiveness of the cement-deep-soil-mixing (CDSM) ground improvement technique on controlling the lateral displacement of pile foundations embedded in different clay soil conditions with and without ground improvement was carried out. A set of lateral load analyses was performed to establish permissible displacements for precast, prestressed concrete piles as well as open-ended steel pipe pile prior to reaching the curvature capacity of piles. The analysis results showed an average of 66% reduction on the permissible displacement limit by providing a volume of CDSM soil improvement around the prestressed precast concrete piles embedded in medium clay and soft clay. And an average of 79% reduction was observed on steel pipe pile embedded in CDSM improved medium clay and soft clay

Prediction of Ground Settlement Induced by Slurry Shield Tunnelling in Granular Soils

Underground structures play an important role in achieving the requirements of rapid urban development such as tunnels, parking garages, facilities, etc. To achieve what is needed, new transportation methods have been proposed to solve traffic congestion problems by using of high-speed railway and subway tunnels. One of the issues in urban spaces due to tunnel excavation is considerable surface settlements that also induce problems for surface structures. There are a variety of published relationships concerned with field measurements and theoretical approaches to evaluating the amount of the maximum surface settlement value due to tunneling. This paper studies the ground surface settlement caused by the Greater Cairo Metro – Line 3 - Phase-1. This project was constructed by a slurry shield Tunnel Boring Machine (TBM). Therefore, this work consists of two parts. The first part presents the details of the project and monitoring results field and laboratory geotechnical investigations in order to determine the soil properties. The second part is to the comparison between the field measurements and theoretical approaches for surface settlement due to tunneling construction. At the end of the works, the results show that the more convenient methods which approach the field measurements, and the major transverse settlement occurs within the area about 2.6 times the diameter of the tunnel excavation. Doi: 10.28991/cej-2020-03091617 Full Text: PD

A critical review on the performance of pile-supported rail embankments under cyclic loading: Numerical modeling approach

Searching for economical and practical solutions to increase any transport substructures protection and stability is critical for ensuring the long-term viability and adequate load-bearing capacity. Piles are increasingly being used as an economical and environmentally sustainable solution to enhance the strength of soft subgrade soils on which embankments are raised. As per the available literature, there are two main strategies used to explain railway embankments performance: experimental approaches and numerical simulations on a broad scale. The purpose of this study is to examine the state-of-the-art literature on numerical modeling methods adopted to assess the performance of pile-supported rail embankments subjected to cyclic loading. The paper addresses the main results from various numerical methods to explain the appropriate mechanisms associated with the load deformation response. It also presents the key issues and drawbacks of these numerical methods concerning rail embankment development while outlining the specific shortcomings and research gaps relevant to enhanced future design and analysis. (c) 2021 by the authors. Licensee MDPI, Basel, Switzerland

Staattisesti sivukuormitetun paaluryhmaän mallintaminen

Tässä diplomityössä käsitellään staattisesti sivukuormitetun paaluryhmän mallintamista siirtymäelementtimenetelmään pohjautuvilla laskentaohjelmilla. Esitys käsittelee kolmen erityyppisen paaluryhmän mallinnusohjelman laskentaprosessia sekä analysoi laskentatulosten luotettavuutta vertailukohteena käytettävän paaluryhmän kuormituskokeen mittaustuloksiin. Tutkimuksen perustaksi on kerätty aikaisempien sivukuormitettujen paaluryhmien kenttäkokeiden tuloksia sekä niiden perusteella annettuja suosituksia. Lisäksi esitykseen on koottu paalun sivuvastuksen huomioimiseksi johdettuja matemaattisia laskentamalleja, jotka perustuvat vahvasti edeltäviin kenttäkokeisiin sekä soveltuvat siirtymäelementtimenetelmää käyttäviin laskentaohjelmiin. Työssä käydään läpi yksittäisen sivukuormitetun paalun mallintaminen sekä sen eroavaisuudet paaluryhmässä olevan paalun mallintamiseen. Alustavassa laskentatekniikassa käydään läpi yksittäisen paalun lineaarisesti elastinen mallinnustapa, josta edetään epälineaarisen elastoplastisen paaluryhmän laskentaprosessiin. Esiteltyjä menetelmiä sovelletaan kenttäkokeen paaluryhmän mallintamiseen. Käytettyjen elastoplastista laskentamenetelmää noudattavien paaluryhmäohjelmien suurimpina eroina on niiden tapa mallintaa yksittäisen paalun siirtymien aiheuttamien jännityksien vaikutuksia ympäröivissä paaluissa. Yleisimmin käytetty ryhmävaikutuksen huomioiva tapa on vähentää paalun sivuvastusta erikseen määritettävällä kertoimella. Vaihtoehtoinen metodi analysoi paaluja ympäröivän maan elastisena massana, jossa paalun sivusiirtymät johtuvat jännityskenttänä ympäröiviin paaluihin. Tässä diplomityössä keskitytään paalun sivuttaisliikkeiden sekä taipumien, eikä niinkään aksiaalisten jännitysten tai geoteknisen kantavuuden selvittämiseen. Tarkoituksena ei ole vertailla mitoitusohjeisiin perustuvia laskentatapoja, vaan esittää menetelmiä paaluryhmän matemaattiseen mallintamiseen. Tarkoituksena ei myöskään ole esitellä miten mallinnusohjelma tulisi ohjelmoida, vaan lähinnä esitellä millaisia asioita mallinnusohjelman kokoamisessa pitäisi ottaa huomioon ja miten kyseisten asioiden huomioiminen siirtymäelementtimenetelmällä on mahdollista toteuttaa.This thesis explores the modeling of a pile group under static lateral loading with computer programs based on finite element method. This investigation discusses three various types of a pile group computation program and analyses the reliability of computation results with measurement results from a field test. Various results from previous field tests of laterally loaded pile groups are collected and also recommendations based on these tests are presented. In addition, mathematical calculation models for modeling the side resistance of a pile group are collected which are strongly based on previous results. The presented mathematical formulas are especially suitable for finite element modeling programs. This investigation introduces mathematical modeling of a laterally loaded single pile, the modeling of a laterally loaded pile group and presents the differences. In the basic mathematical modeling method of a single pile, the pile is modeled as a linearly elastic beam. From this simple model the research advances to elastoplastic modeling of a pile group. The presented modeling methods are applied to calculate a field load test of a pile group. The leading difference between the used elasto-plastic pile group computation programs is in the process of modeling the stress fields within a pile group formed by the lateral movement of a single pile. A more common method is to reduce the lateral soil resistance with a multiplier whereas an alternative method analyses the surrounding soil of a single pile as an elastic mass. This thesis focuses on lateral movement and bending of a pile and ignores the discussion of axial stresses within the pile and the geotechnical bearing capacity of surrounding soil. The intention of this thesis is to present methods to calculate an accurate mathematical model of a pile group under static lateral loading and does not incorporate the assessment of the different pile group designing methods. In addition the aim of this thesis is not to provide guidance or recommendation to programming techniques, but to present different features to take into consideration in a reliable modeling application