Prijenos sila kroz zrnati materijal na pragu cikličke posmične deformacije

doctoral thesis

• Author: Vedran Pavlić
• Mentor: Tomislav Ivšić (mentor)
• Committee member: Mario Bačić (predsjednik povjerenstva)
• Committee member: Meho-Saša Kovačević (član povjerenstva)
• Committee member: Leo Matešić (član povjerenstva)
• Granter: University of Zagreb; Faculty of Civil Engineering; (Geotechnical Engineering); Zagreb
• Defense date and country: 2025-01-10, Croatia
• Scientific / art field, discipline and subdiscipline: TECHNICAL SCIENCES; Civil Engineering; Geotechnology
• Universal decimal classification (UDC): 624/625 - Civil and structural engineering. Civil engineering of land transport. Railway engineering. Highway engineering

Abstract

Zrnati materijal podvrgnut cikličkom opterećenju karakteriziraju promjene modula posmika, pornih tlakova i volumena. Do promjene dolazi kada amplituda cikličke posmične deformacije prijeđe određenu vrijednost tzv. prag cikličke posmične deformacije. Posljedice prelaska praga se odražavaju kao ciklički fenomeni: slijeganja, nagomilavanja pornih tlakova, ojačanja i degradacije čvrstoće.
Kako bi se istražili ciklički fenomeni potrebno je modelirati prijenos sila u sustavu zrna i šupljina, pijesku... More ovisno o amplitudi deformacije. Osnovni alat istraživanja je numerička metoda diskretnih elemenata. Pomoću trodimenzionalnog numeričkog modela simulira se laboratorijski pokus jednostavni direktni posmik. Numerički model sastoji se od velikog broja zrna (574 507 zrna), a kalibriran je na osnovu tri krivulje (krivulja redukcije, krivulja nagomilavanja pornih pritisaka vode, histerezna krivulja).
Izvlačenje i analiza podataka iz numeričkog modela odvija se na nekoliko razina. Na mikro razini dan je primjer određivanja stabilnosti jednoga lanca sile, definirani su pozadinski mehanizmi (kompresija, ekstenzija i fleksija), a određen je i dominantan kontrolni mehanizam (postepena translacija zrna). Na mezo razini provjereni su kriteriji za definiranje lanaca sile (srednja sila, kut između kontaktnih sila, duljina lanca sile, grananje lanca sile).
Lanci sile imaju ključnu ulogu kao mehanizam prijenosa sile u zrnatom materijalu i određuju mehanička svojstva materijala: stabilnost, elastičnost i protočnost. Više lanaca sile čini jaku mrežu, čija stabilnost, a time i stabilnost sustava je određena na osnovu promjene: broja lanaca sile, mehaničkog koordinatnog broja i raspodjele veličina kontaktnih sila. Način širenja poremećaja sustavom je određen grafičkom analizom konfiguracije lanaca sile ovisno o amplitudi i ciklusu. Za opis cikličkog ponašanja zrnatog materijala na makro razini predlažu se dva praga. Prag akumulacije γt = 4∙10-5 i prag stabilnosti γt = 3∙10-4. Less

Abstract (english)

Granular material subjected to cyclic loading is characterized by the change of shear modulus, pore water pressure and volume. The change occurs when the amplitude of the cyclic shear strain exceeds a certain value, i.e. the cyclic threshold shear strain. The consequences of exceeding the threshold are reflected as cyclic phenomena: settlement, pore water pressure build-up, stiffening and degradation of stiffness.
In order to investigate cyclic phenomena, it is necessary to model the force... More transmission in the system of grains and voids (sand), depending on the strain amplitude. The basic research tool is the numerical discrete element method. Using a three-dimensional numerical model, the laboratory simple shear test was simulated. The numerical model consists of a large number of grains (574,507 grains), and is calibrated on the basis of three curves (reduction curve, pore water pressure accumulation, hysteresis loop).
Extraction and analysis of data from the numerical model takes place on several levels. At the micro level, an example of determining the stability of a single force chain is given, the underpinning mechanisms (compression, extension and flexion) are defined, and the dominant control mechanism (gradual grain translation) is also defined. At the meso level, the criteria for defining force chains were verified (mean force, angle between contact forces, length of force chain, branching of force chain).
Force chains play the key role as a force transfer mechanism in granular material and they determine the mechanical properties of the material: stability, elasticity and flow. Several force chains form a strong network, the stability of which, and thus the stability of the system, is determined based on changes in: the number of force chains, the mechanical coordinate number and the distribution of contact force sizes. The propagation mode of disturbances in the system is determined by graphical analysis of the configuration of force chains depending on the strain amplitude. Two thresholds are proposed to describe the cyclic behaviour of granular material at the macro level. Accumulation threshold γt = 4∙10-5 and stability threshold γt = 3∙10-4. Less

• Keywords: Geotehnika; mehanika tla
• Keywords (english): Geotechnics; soil mechanics
• Language: croatian
• URN:NBN: urn:nbn:hr:237:541559
• Promotion: 2025
• Study programme: Title: Postgraduate doctoral study of the Faculty of Civil Engineering; Study programme type: university; Study level: postgraduate; Academic / professional title: doktor/doktorica znanosti, područje tehničkih znanosti, polje građevinarstvo (doktor/doktorica znanosti, područje tehničkih znanosti, polje građevinarstvo)
• Type of resource: Text
• File origin: Born digital
• Access conditions: Open access
• Created on: 2025-02-03 11:34:35