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This paper investigates the possibility of the application of the HArdening State Parameter (HASP) constitutive model for numerical modelling of overconsolidated soft clay under embankment loading. The HASP constitutive model is a critical state soil model with a combined hardening rule that uses a state parameter to determine the dilatancy of overconsolidated clay. The model overcomes some shortcomings of the Modified Cam Clay (MCC) model in the prediction of overconsolidated clay’s behavior, while preserving the simplicity and the same set of five parameters. The HASP model was implemented in finite element software. In order to verify the applicability of the model in predicting the behavior of soft overconsolidated clay due to embankment loading, two examples reported in the literature are analyzed. The numerical predictions of the HASP model are compared with the field measurements of ground settlements and pore water pressures, and with the MCC model’s predictions. The results indicate that the HASP model predicts the development of the settlements of the overconsolidated soft clay deposits with a high accuracy from an engineering point of view. There are certain deviations from the field measurements in predicting the pore pressure development, which is often observed for other models as well. For the embankment settlement assessment, as important serviceability issue, the HASP model has an advantage over more complex models that require a large number of parameters. Since the parameters of the HASP model are obtained from standard laboratory tests, it can be easily applied for routine geotechnical analyses.

The mathematical formulation of the constitutive equations is expressed through a set of differential nonlinear equations. The incrementally-iterative procedures are mainly used for solving material nonlinear problems by the finite element method. It is necessary to calculate the current stresses based on the known deformations. The accuracy of stresses determination directly affects the accuracy of the results, which implies the importance of finding the most efficient methods for the numerical integration of the constitutive relations of the model. The first part of the paper describes several classes of algorithms that successfully solve the problem of stress integration for elastoplastic models, in the sense that they meet three basic requirements: consistency with constitutive relations, numerical stability and incremental condition of plastic consistency. The second part presents the original procedure for applying the implicit Governing Parameter Method for the Modified Cam Clay constitutive model, as well as an assessment of the accuracy of the method.

U radu je dat prikaz sanacionog rešenja temeljne konstrukcije jednog stambenog objekta u Zemunu. Do oštećenja objekta došlo je usled neravnomernog sleganja temeljnog tla lesoidnog porekla kao posledica havarije na vodovodnoj infrastrukturi. Sleganjem tla je bilo obuhvaćeno nekoliko objekata koji su pretrpeli znatna oštećenja. U radu je dat detaljan prikaz usvojene sanacione mere za objekat u Dobanovačkoj ulici broj 34d , koja se bazirala na primeni "Mega" šipova.

Ponašanje komunalnog otpada je nelinearno i veoma kompleksno usled izrazite heterogenosti materijala. Komponente od različitih vrsta materijala, biodegradacija organskih komponenti i veliko sekundarno sleganje usled mehaničkog puzanja nastalog od prepakivanja komponenti otpada zbog biodegradacijskih procesa, prouzrokuju poteškoće u matematičkom opisivanju ponašanja komunalnog otpada. Nelinearni elasto-plastični i viskozni konstitutivni modeli razvijeni za tlo mogu biti osnova konstitutivnog modela za komunalni otpad, ali se oni moraju modifikovati i prilagoditi ponašanju komunalnog otpada. Modifikacija se prvenstveno ogleda u uvođenju vremenski uslovljenih procesa koji se dešavaju u komunalnom otpadu: mehaničko puzanje i biodegradacija. U okviru ove disertacije formulisan je nelinearni elasto-plastični konstitutivni model za komunalni otpad – MSW (Municipal Solid Waste) model, baziran na teoriji kritičnog stanja i Modifikovanom Cam Clay modelu. MSW model u svojoj formulaciji sadrži priraštaj vremenski zavisnih zapreminskih deformacija usled mehaničkog puzanja i biodegradacije otpada. MSW model je implementiran u program ABAQUS/CAE, baziran na metodi konačnih elemenata, koristeći korisnički potprogram UMAT i Metodu vodećeg parametra za numeričku integraciju konstitutivnih relacija modela u kojoj je za vodeći parametar usvojen srednji efektivni napon. Validacija MSW modela je izvršena kroz poređenje sa publikovanim rezultatima edometarskih opita i dreniranih i nedreniranih triaksijalnih opita. Validacije su pokazale odlična poklapanja predviđanja MSW modela sa eksperimentalno dobijenim vrednostima. Mogućnost MSW modela da adekvatno predvidi ponašanje komunalnog otpada je ispitana kroz analizu konturnog problema metodom konačnih elemenata, gde je razmatran problem sleganja eksperimentalne deponije., Mechanical behaviour of municipal solid waste is nonlinear and very complex due to extreme material heterogeneity. Components of different types of materials, biodegradation of organic components and large secondary settlement due to mechanical creep caused by repackaging of waste components due to biodegradation processes, cause difficulties in mathematically describing the behaviour of municipal solid waste. Nonlinear elastic-plastic and viscous constitutive models developed for soil can be the basis of a constitutive model for municipal solid waste, but they must be modified and adapted to the behaviour of municipal solid waste. The modification is primarily reflected in the introduction of time-dependent processes that occur in municipal solid waste: mechanical creep and biodegradation. Within this thesis, a nonlinear elastic-plastic constitutive model for municipal solid waste - MSW model, based on the critical state theory and the Modified Cam Clay model, was formulated. The MSW model in its formulation contains the increment of time-dependent volumetric deformations due to mechanical creep and biodegradation of waste. The MSW model is implemented in the ABAQUS / CAE program, based on the finite element method, using the user subroutine UMAT and the Governing Parameter Method for the numerical integration of constitutive relations of the model in which the mean effective stress is adopted for the governing parameter. Validation of the MSW model was performed through comparison with published results of oedometer tests and drained and undrained triaxial tests. Validations showed excellent matches of the predictions of the MSW model with the experimentally obtained values. The ability of the MSW model to adequately predict the behaviour of municipal solid waste was tested through the analysis of the boundary value problem by the finite element method, where the problem of the experimental landfill settlement was analysed.

The process of preparation and parallel revisions of draft versions of the second-generation of Eurocodes is largely underway. The formal voting of new versions is scheduled for mid- 2024, which means that the first applications could begin immediately after the set-up of National Annexes, which is expected to happen around 2025-2026. For that reason, the authors which are otherwise, regular and active members of the commission U182 of the Serbian National Standardisation Body in the field of geotechnics, decided to, through this review paper, briefly present to the engineering community the novelties and changes brought by the second-generation of Eurocode 7.

U radu je dat pregled metoda za numeričku integraciju relacija elasto-plastičnih konstitutivnih modela za tlo. Prikazan je inkrementalno-iterativan postupak proračuna metodom konačnih elemenata, sa osvrtom na značajan uticaj algoritama za integraciju konstitutivnih relacija na tačnost određivanja naponsko-deformacijskih veličina definisanih modelom. Dat je pregled metoda integracije sa opštom podelom na implicitne i eksplicitne metode. Detaljnije je prikazan algoritam za tri odabrane metode koje se mogu primeniti na elasto-plastične modele za tlo sa ocenom ispunjenosti zahteva pouzdanosti, tačnosti i efikasnosti: metodu vodećeg parametra, metodu povratnog preslikavanja i “substepping“ metodu., A brief overview of methods for numerical integration of stress-strain relations of elastoplastic constitutive models for soil is presented. Firstly, incremental-iterative procedure for finite element method is described with emphasis on the importance of algorithms for numerical integration of constitutive relations. A review of explicit and implicit methods is given. A more detailed assessment of fulfillment of the requirements of reliability, accuracy and efficiency is given for three methods: governing parameter method, return mapping algorithm and substepping algorithm.

U radu je prikazan kratak pregled odredbi Evrokoda 7 za proračun aksijalne nosivosti šipova. Date su smernice i preporuke za proračun aksijalne nosivosti utisnutih MEGA šipova u skladu sa izabranim proračunskim pristupom prema nacionalnom prilogu za Evrokod 7 (Deo 1) u Srbiji i specifičnostima tehnologije izvođenja. Prikazana je uporedna analiza proračuna prognozne nosivosti MEGA šipova prema Evrokodu 7 i ranijem Pravilniku o tehničkim normativima za temeljenje građevinskih objekata, zasnovanom na teoriji dopuštenih napona, na primeru sanacije temelja stambene zgrade u Zemunu. Dobijeni rezultati potvrđuju adekvatnost izabranog proračunskog pristupa u nacionalnom prilogu i predloženih smernica za proračun nosivosti MEGA šipova., Short review of provisions of Eurocode 7 for determination of pile axial bearing capacity is given in this paper. Design guidelines and recommendations for determination of bearing capacity of jacked-in MEGA piles, according to pile installation technology and chosen design approach in National Annex for Eurocode 7 (Part 1) in Serbia are presented. A validation of proposed guidelines through comparison with previous concept of allowable pile force is presented on the example of the rehabilitation of the foundations of a residential building in Zemun, Serbia. Obtained results confirm the adequacy of chosen design approach and proposed guidelines for determination of bearing capacity of MEGA piles.

U radu je opisano rešenje fundiranja južne tribine stadiona FK "TSC" u Bačkoj Topoli. Razmatrana su varijantna rešenja plitkog fundiranja na temeljnim trakama i temeljnoj ploči, sa posebnim osvrtom na proračun sleganja temelja na deformabilnoj podlozi. Proračun sleganja je izvršen u iterativnom postupku, primenom sopstvenih računarskih programa i uz uzimanje u obzir interakcije tla i konstrukcije. Dobijeni rezultati proračuna su upoređeni sa rezultatima geodetskog osmatranja. Istaknuti su nedostaci Vinklerovog modela i date su preporuke za numeričku analizu sleganja plitkih temelja u inženjerskoj praksi., This paper describes the foundations solution of the south stand of the FC "TSC" stadium in Bačka Topola. Variant solutions (strip foundations and raft foundation) are considered, with special emphasis on the calculation of foundation settlements on a deformable base. The settlements calculation was performed in an iterative procedure, using own computer programs and considering the soil-structure interaction. The obtained results are compared with the results of geodetic monitoring of the structure. The shortcomings of the Winkler model are highlighted and recommendations for numerical analysis of the foundations' settlements in engineering practice are given

Foundations of wind turbines, bridges, offshore platforms, industrial chimneys, retaining structures, marine and harbor structures etc. can be loaded with significant horizontal loads from various sources. Appropriate assessment of the foundations capacity of these structures is necessary, especially when these structures are supported by pile groups. The horizontal loading on the pile group may have arbitrary direction. This paper addresses some important aspects of FEM numerical modeling of a bored pile group under arbitrary horizontal loading. Model parameters, validation and post-processing techniques are presented and discussed. The full 3D FEM model was found to be necessary for the correct problem solution.

U okviru koncepta granične površi formulisan je konstitutivni model koji uvodi stanje tla kao bitnu odrednicu mehaničkog ponašanja. Definisanjem zakona ojačanja u funkciji parametra stanja, kao i stepena prekonsolidacije, omogućeno je opisivanje brojnih elemenata mehaničkog ponašanja prekonsolidovanih glina u dreniranim i nedreniranim uslovima. Izvedena je jednačina putanje efektivnih napona u nedreniranim uslovima. Validacija modela je izvršena kroz poređenje sa publikovanim rezultatima nedreniranih triaksijalnih opita.

Konstrukcije vetroturbina, mostova, industrijskih dimnjaka, potpornih zidova i sl. mogu biti izložene značajnim horizontalnim opterećenjima iz različitih izvora. Ove konstrukcije su često fundirane na grupama šipova. Efekti interakcije šipova u grupi pri horizontalnim opterećenjima su bili predmet istraživanja u poslednjim decenijama, pri čemu je najčešće razmatran slučaj horizontalnog opterećenja u dva ortogonalna pravca (paralelno ivicama grupe šipova). Usled stohastičke prirode, horizontalno opterećenje na grupu šipova može biti proizvoljnog pravca, i broj istraživanja koji razmatra ovaj slučaj opterećenja je relativno mali. U ovom radu prikazani su rezultati istraživanja uticaja horizontalnog opterećenja proizvoljnog pravca na odgovor grupe šipova, u cilju poboljšanja trenutnog koncepta projektovanja ovakvih temelja. Razmatrani su bušeni šipovi fundirani u peskovitom tlu, kroz opsežnu numeričku analizu. Identifikovane su "kritične" pozicije šipova unutar standardnih konfiguracija, diskutovan je uticaj različitih uslova u tlu i date su preporuke za projektovanje ovakvih tipova temeljnih konstrukcija.

The analysis of pile groups subjected to horizontal loading in one of two orthogonal directions is a common problem in geotechnical engineering. However, the above analysis should sometimes be extended with the additional cases of horizontal loading, in arbitrary direction. Although the full scale experiments can provide the best insight into the above problem, they are expensive and therefore not feasible solution. Instead, numerical (i.e. finite element) analysis usually remains the ultimate tool for large scope studies. The main objective of this research is the improvement of the analysis methodology of pile group for the case of arbitrary static horizontal loading. Its influence is investigated numerically to check for the existence of the "critical" pile group configurations and soil conditions, that may lead to the failure of the foundation structure and superstructure itself. To reach the above objective, apriori sensitivity analysis of the considered problem and identification of the main problem parameters are conducted in the first phase. After that, series of complex 3D numerical models for laterally loaded pile group analysis have been generated using PLAXIS 3D. Model validation is done by the back-calculation of available experimental results. Parametric study of pile groups with various configurations under arbitrary horizontal loading is performed, with an emphasis on pile force distribution, bending response and pile group efficiency. Modelling and simulation processes and the optimization of the calculation time were improved using the originally developed codes in Python. The use of multiple computers was allowed by using the author’s scripts developed within the thesis. The above research resulted in thousands of numerical simulations, whose findings provided the improved design methodology of pile groups under arbitrary static horizontal loading., Analiza ˇsipova u grupi izloˇzenoj horizontalnom optere´cenju u nekom od dva ortogonalna pravca je uobiˇcajen problem u geotehnici. Medjutim, navedena analiza ponekad se mora proˇsiriti dodatnim sluˇcajevima horizontalnog optere´cenja, u proizvoljnom pravcu. Iako eksperimenti na realnim konstrukcijama mogu pruˇziti najbolji uvid u navedeni problem, oni predstavljaju skupo (i samim tim neizvodljivo) reˇsenje. Umesto toga, numeriˇcka analiza (npr. primenom metoda konaˇcnih elemenata) obiˇcno postaje primarni alat za studije velikog obima. Glavni cilj ovog istraˇzivanja je poboljˇsanje metodologije za analizu grupe ˇsipova za sluˇcaj proizvoljnog statiˇckog horizontalnog optere´cenja. Njegov uticaj je razmatran numeriˇcki kako bi se utvrdilo postojanje "kritiˇcne" konfiguracije ˇsipova u grupi i uslova tla, koja moˇze dovesti do loma temeljne konstrukcije i samog objekta. Radi ostvarenja gore navedenog cilja, u prvoj fazi sprovedena je uvodna analiza osetljivosti razmatranog problema i identifikacija glavnih parametara problema. Nakon toga, generisane su serije sloˇzenih 3D numeriˇckih modela za analizu boˇcno optere´cenih grupa ˇsipova u PLAXIS 3D. Validacija modela izvrˇsena je povratnim proraˇcunom na osnovu dostupnih eksperimentalnih rezultata. Sprovedena je parametarska studija boˇcno optere´cenih grupa ˇsipova razliˇcitih konfiguracija, sa akcentom na raspodelu sila u ˇsipu, odgovor ˇsipa pri savijanju i efikasnost grupe ˇsipova. Postupci modeliranja i simulacije, kao i optimizacija vremena proraˇcuna, poboljˇsani su primenom originalnih programa u Python-u. Upotreba viˇse raˇcunara za proraˇcun omogu´cena je primenom autorovih programa razvijenih u okviru ove teze. Navedeno istraˇzivanje rezultovalo je u hiljadama numeriˇckih simulacija, ˇciji su rezultati doveli do poboljˇsanja metodologije proraˇcuna ˇsipova u grupi usled proizvoljnog statiˇckog horizontalnog optere´cenja.

Special-purpose river port sediment was investigated for its potential use as a road construction material. Sediment samples were extracted from three locations in three small river ports, and detailed laboratory research was conducted to determine its basic mechanical properties and characteristics that can potentially have an adverse influence in a roadside environment. The results of the research conducted indicate that there is a need for systematic monitoring of the quality and quantity of sediment in special-purpose river ports of the Danube River Basin to maintain its mobility and prevent flooding. The basic engineering characteristics (Proctor elements, Atterberg limits, California bearing ratio, and unconfined compressive strength) determined represent the good potential of the sediment samples tested herein for use in road construction. In addition, the chemical characteristics tested indicate the need for detailed analyses of the potential environmental risk before application in civil engineering structures

Marine and harbor structures, wind turbines, bridges, offshore platforms, industrial chimneys, retaining structures etc. can be subjected to significant lateral loads from various sources. Appropriate assessment of the foundations capacity of these structures is thus necessary, especially when these structures are supported by pile groups. The pile group interaction effects under lateral loading have been investigated intensively in past decades, and the most of the conducted studies have considered lateral loading that acts along one of the two orthogonal directions, parallel to the edge of pile group. However, because of the stochastic nature of its source, the horizontal loading on the pile group may have arbitrary direction. The number of studies dealing with the pile groups under arbitrary loading is very limited. The aim of this paper is to investigate the influence of the arbitrary lateral loading on the pile group response, in order to improve (extend) the current design approach for laterally loaded pile groups. Free head, flexible bored piles in sand were analyzed through the extensive numerical study. The main hypothesis of the research is that some critical pile group configurations, loading directions, and soil conditions exist, which can lead to the unsafe structural design. Critical pile positions inside the commonly used pile group configurations are identified with respect to loading directions. The influence of different soil conditions was discussed.

Major infrastructure projects require significant amount of natural materials, often followed by the soft soil stabilization using hydraulic binders. This paper presents the results of a laboratory study of alternative waste materials (fly ash and slag) that can be used for earthworks. Results of high plasticity clay stabilization using fly ash from Serbian power plants are presented in the first part. In the second part of the paper, engineering properties of ash and ash-slag mixtures are discussed with the emphasis on the application in road subgrade and embankment construction. Physical and mechanical properties were determined via following laboratory tests: Specific gravity, grain size distribution, the moisture–density relationship (Proctor compaction test), unconfined compressive strength (UCS), oedometer and swell tests, direct shear and the California bearing ratio (CBR). The results indicate the positive effects of the clay stabilization using fly ash, in terms of increasing strength and stiffness and reducing expansivity. Fly ashes and ash-slag mixtures have also comparable mechanical properties with sands, which in combination with multiple other benefits (lower energy consumption and CO2 emission, saving of natural materials and smaller waste landfill areas), make them suitable fill materials for embankments, especially considering the necessity for sustainable development.