Numerično modeliranje jet-grouting (JG) slopov za zaščito gradbenih jam : magistrsko delo

Bratina, Nick (author), Pulko, Boštjan (mentor)

Magistrska naloga obravnava numerično modeliranje opornih konstrukcij za zaščito gradbenih jam iz slopov, izdelanih po tehnologiji injektiranja pod visokimi pritiski – jet-grouting (JG). Namen dela je prikazati vpliv prerazporeditve napetosti in redukcije upogibne togosti v razpokanih JG slopih. Naloga se osredotoča predvsem na upogiben odziv razpokanih slopov. Najprej so opisani uveljavljeni postopki injektiranja in pripadajoči kontrolni parametri izvedbe. V nadaljevanju so predstavljene pričakovane materialne lastnosti JG kompozita in empirični izrazi za njihovo oceno. Predstavljeni so različni elasto-plastični materialni modeli, ki so v uporabi za oceno materialnega obnašanja JG kompozita. Predstavljen je napredni Concrete konstitutivni model, ki je zaradi implementacije deformacijskega utrjevanja in mehčanja primeren za modeliranje betonov. Izpeljani so matematični izrazi za določitev računske geometrije JG opornih konstrukcij, ki so primerni za numerično reševanje problemov ravninskega deformacijskega stanja za analizo po metodi končnih elementov (Plaxis 2D). Izpeljani so analitični izrazi za določitev mejne nosilnosti in upogibne togosti armiranih in nearmiranih JG prerezov. Mejna nosilnost prereza je določena po pristopu nemškega standarda DIN 4093:2005-11, ki je edini standard na področju projektiranja JG konstrukcij skladen z Evrokodi. Raziskovalni del naloge temelji na uspešno izvedenem projektu A-Tower v Ljubljani. Prvotna JG oporna konstrukcija je bila izdatno dimenzionirana, zato smo za analizo vpliva razpokanja slopov zasnovo varovanja gradbene jame modificirali. Materialni parametri JG kompozita so določeni na podlagi rezultatov standardnega enoosnega tlačnega preizkusa in preizkusa natezne trdnosti na dveh, iz slopov odvzetih vzorcih. Primerjali smo upogiben odziv slopov pri uporabi različnih konstitutivnih modelov in pristopov pri modeliranju slopov. Prikazane in razložene so razlike, med različnimi načini izračuna notranjih statičnih količin. Preučili smo vpliv privzete vrednosti Youngovega elastičnega modula JG kompozita na odziv slopa. Preverilo se je vpliv modeliranja armature v primeru armiranih slopov ter vpliv trenja po plašču pri uporabi različnih kontaktnih elementov. V analiziranih prečnih profilih smo, v skladu z veljavnim standardom, izvedli dimenzioniranje armiranih in nearmiranih JG slopov v kritičnih prerezih.

• Language: Slovenian
• Keywords: jet-grouting, gradbena jama, numerično modeliranje, PLAXIS 2D, konstitutivni modeli, materialno mehčanje, upogibna togost, natezna trdnost
• Work type: Master's thesis/paper
• Organization: FGG - Faculty of Civil and Geodetic Engineering
• Year: 2022
• PID: 20.500.12556/RUL-140084
• COBISS.SI-ID: 125846019
• Publication date in RUL: 10.09.2022

Secondary language

• Language: English
• Title: Numerical modelling of jet-grouting (JG) columns for deep excavation support : master's thesis

Abstract

This master thesis deals with numerical modelling of jet-grouting (JG) columns for deep excavation support. The purpose of work is to demonstrate the effect of redistribution of stresses and reduction of flexural stiffness in cracked JG columns. The thesis focuses mainly on the flexural response of cracked JG columns. First, the established jet-grouting proccedures and the associated quality control parameters are described. Then, the expected material properties of JG composite and empirical correlations for their evaluation are presented. Different elasto-plastic material models used to assess the material behaviour of JG composite are briefly described and the advanced Concrete constitutive model, suitable for modelling of cast concrete due to implementation of strain hardening and softening, is presented. Appropriate mathematical expressions are derived to determine the computational geometry of JG retaining structures for use in plane strain numerical analyses using finite element method (Plaxis 2D). The analytical expressions for the load-bearing capacity and flexural stiffness of reinforced and unreinforced JG column cross sections are derived and presented. The ultimate capacity is determined according to the German standard DIN 4093:2005-11, which is the only standard in the field of JG design complying with Eurocodes. The computational part of the thesis is based on the successfully executed A-Tower project in Ljubljana. The implemented JG retaining structure was designed with high margin of safety, so the initial design was numerically modified in order to analyse the effect of JG cracking on the structural behaviour. The material parameters of JG composite were determined based on two standard uniaxial compression and tensile strength tests results on specimens taken at the construction site. The flexural responses of JG columns were compared using different constitutive models and different approaches regarding structural modelling. The differences due to different approaches for calculating bending moments are shown and discussed. The influence of adopted value of Young's modulus on the behavior of the JG columns was also analysed, as well as the influence of steel bars reinforcement and JG shaft friction when using different interface elements. In the analysed transverse profiles, the dimensioning of reinforced and unreinforced JG columns in the critical cross-sections was also carried out according to valid standards.

• Keywords: jet-grouting, deep excavation, numerical modeling, PLAXIS 2D, constitutive models, strain softening, flexural stiffness, tensile strength