Abstract

In recent decades due to the development and diversification of construction technologies, soil improvement procedures became a competitive and cost-effective alternative to increase the load-bearing capacity of the subsoil, while reducing deformations of the structure. Attributed to urbanization, lands with insufficient soil bearing capacity are becoming construction sites, for which it is essential to influence or increase the bearing capacity of the subsoil for the safety and compatibility of structures. Soil reinforcement with concrete elements is used in more and more construction project in Hungary. The structural behavior of traditional pile foundation is well known, and adequate standards are available during the planning process. On the other hand, soil improvement procedures, in our case for the design of rigid inclusion foundation no standards are available only guidelines and recommendations.Because of that in almost all cases, the design phase includes numerical modelling, which is used to prove the efficiency of the system and receive a more accurate picture of the real structural behavior.

15004-1989 [16] allowed for the use of a so-called "permissible bearing pressure" for preliminary dimensioning, and for foundation design in case of buildings with low importance. With this method, the central, vertical limit load of strip foundations and column footings with a given geometry could be obtained by applying the permissible bearing pressure along with shape and depth factors. In the light of the popularity of this method, and given that EC7 allows for employing design methods based on prescriptive measures, the authors have developed a new calculation method which conforms to the principles of EC7 and which is similar to the former method.

The construction monitoring of Ráckóczi square metro station of Budapest Metro Line 4 offered a great opportunity to back analyse the braced deep excavation in the building period. Building movements, strut forces and wall displacement measurements have been compared to numerical results derived by PLAXIS using HSsmall soil model. Considering the influence of small strain stiffness of plastic soils, good fit of the measured and calculated movements could be observed and the strut forces could be calculated reasonable. Curve characteristic of surface settlements was explored, as well. Analysis were carried out to observe influence of the following inputs on the numerical results: soil material model; consolidation effects, boundary conditions. A detailed evaluation is given about the results of parametric analysis.

Design and modelling of raft foundations and selecting the value of coefficient of vertical subgrade reaction are still actively discussed topics in geotechnical and structural engineering. In everyday practice, soil-structure interaction is mostly taken into account by using the theory of 'beam on elastic foundation', in which the soil is substituted by a certain set of coefficients of subgrade reaction. In this study, finite element analysis of a building was performed using a geotechnical software (Plaxis 3D), which is capable of modelling the subsoil as a continuum, and a structural software (Axis VM), which uses the concept of 'beam on elastic foundation'. The evaluation of the results and recommendations for everyday engineering practice are introduced in this paper. IzvlečekNačrtovanje in modeliranje temeljenja na plošči kot tudi primerna selekcija koeficientov za vertikalne reakcije temeljev so zelo aktualne teme, ki so predmet skupnega interesa geotehniških in gradbenih inženirjev. V vsakodnevni praksi je problem interakcije konstrukcije in tal pogosto obravnavan kot problem ˝nosilec (preklada) na elastičnem temelju˝, pri čemer so tla zamenjana s skupino vertikalnih reakcij temeljev. V član-ku je prikazana statična analiza skeletne konstrukcije z uporabo metode končnih elementov s pomočjo geotehniškega programa Plaxis 3D, ki omogoča modeliranje temeljnih tal kot kontinuuma in tudi z uporabo programa za statične izračune (Axis VM), v katerem je uveljavljen koncept ˝nosilec (preklada) na elastičnem temelju˝. Prispevek podaja oceno rezultatov primerjalne analize in zaključke oziroma uporabna priporočila za vsakodnevno inženirsko prakso.Ključne besede: temeljenje na plošči, posedanje, metoda končnih elementov, vertikalne reakcije temeljev

This article presents the results of in‐situ and triaxial testing of tertiary soils (Pannonian sand and Oligocene clay) performed for two major Hungarian projects. The shear strength of these formations varies greatly. Just interpreting the shear strength of tertiary soils poses a number of questions, which definitely exceeds the scope of existing standards. Since extracting multiple samples from the overconsolidated, high‐density samples was not possible, the necessary parameters had to be determined from one larger specimen. Through short examples, it is demonstrated how the test results can be described using soil models and transferred into geotechnical design, highlighting the limits of numerical modelling (in case of these soils).

In this paper, the numerical back analyses of four, typical, monitored deep excavations completed in Budapest are presented. The typical excavation solution in Budapest city center, down to 15–18 m excavation depth, is a diaphragm wall embedded in the clay bedrock and supported by prestressed anchors embedded in the sedimentary soils above the clay. In these case studies this solution is analyzed with traditional Winkler type and more complex PLAXIS 2D and 3D finite element models. The focus of the study was to compare the measured wall deformations with the calculated ones derived by the listed methods. As the clay bedrock is a deterministic layer for the wall behavior, several different FEM models were prepared to analyze the appropriateness of the potential constitutive models for its proper characterization. As a conclusion, practical proposals were made for practitioners for future excavations.

Mély munkatérhatárolások témakörével foglalkozó doktori kutatási projektünk keretében Budapesten megvalósult munkagödrök mozgásmérési eredményeit rendszereztük és elemeztük. Vizsgálatunk eredményeit jelen publikációban ismertetjük. Bevezetésként összefoglaljuk a munkatárhatárolások deformációinak számítási lehetőségeit és összegezzük a nemzetközi szakirodalmak releváns, mozgásmérési tapasztalatait, ajánlásait. Bemutatjuk azt az adatbázist, amely az utóbbi 15 évben Budapesten, annak jellegzetes belvárosi talajkörnyezetében megvalósult 9 db mereven (támaszfödémes és/vagy csőtámaszos) vagy rugalmasan, talajhorgonyokkal megtámasztott mély munkatárhatárolás megvalósítása során mért deformációkat tartalmazza. Végezetül ismertetjük a faldeformációk és felszínsüllyedések a munkagödörmélység és megtámasztási mód függvényében azonosított tendenciáit és az azokból levonható következtetéseket.