Usability Assessment of Different Contact Models for Modelling the Failure Behaviour of Sedimentary Rocks Under Unconfined Stress Conditions

Year 2022, , 61 - 75, 29.03.2022

Enes Zengin

https://doi.org/10.17824/yerbilimleri.1030332

Abstract

The methods applied in rock material and rock mass studies related to rock mechanics have begun to differentiate with computational and software technology development in recent years. Particle Flow Code software, which is based on the discrete element method, is used in many studies on rock mechanics. With Particle Flow Code, rocks can be modeled in both two and three dimensions, and the behavior of rocks under different conditions can be analyzed. Rocks can be formed using disks in two dimensions and spherical particles in three dimensions. These particles are bonded to each other by contact models with different micro-mechanical properties. The failure of the model occurs as a result of the fracturing with the rupture of these bonds. Using parameters such as density, strength, deformation, which can be defined as the mathematical expression of the natural properties of rock samples, studies can be carried out for different stress conditions through models created after multi-stage calibration steps. In order to have a calibrated and representative model, chosen contact models should be mimic the failure of the rock material. For this purpose, a calibrated model was created for both PBM (Parallel-bonded model) and FJC (Flat-jointed model) using the results of the unconfined compressive strength test of Hawkesbury sandstone. In the calibration phase, the results obtained from the models were matched from the laboratory experiments by using elasticity modulus, uniaxial compressive strength, tensile strength, and Poisson ratio parameters. Results were evaluated by considering the displacement vectors, force chains, and crack resolution parameters. PBM and FJM were similar in terms of displacement vectors and force chains. However, in terms of fracture resolution, FJM stands out as it can be used to analyze failure behavior and modeling studies for sedimentary rocks by providing data up to four times that of PBM.

Keywords

Hawkesbury sandstone, failure behavior, parallel-bond model, flat-joint model, Particle Flow Code

Supporting Institution

Kutahya Dumlupınar University Scientific Research Projects Coordination Office

Project Number

2020-09

Thanks

This research has been supported by Kutahya Dumlupınar University Scientific Research Projects Coordination Office under grant number 2020-09. The author would like to thank Dr. David Potyondy and Dr. Sacha Emam from Itasca Consulting Group, Inc. for their theoretical and practical support regarding the software used in this study and Dr. Erik Eberhardt for his allowance to use Geological Engineering Advance Computing Laboratory of The University of British Columbia, Faculty of Science, Department of Earth, Ocean and Atmospheric Science.

Sedimanter Kayaçların Tek Eksenli Yükleme Koşullarında Yenilme Davranışlarının Modellenmesi için Farklı Temas Modellerinin Kullanılabilirliklerinin Değerlendirmesi

Abstract

Kaya mekaniği ile ilgili hem kaya malzemesi hem de kaya kütlesi ölçeğinde yapılan çalışmalarda uygulanan yöntemler son yıllarda gelişen hesaplama ve yazılım teknoloji ile birlikte farklılaşmaya başlamıştır. Ayrık elemanlar yöntemini temel alan Particle Flow Code yazılımı kaya mekaniği ile ilgili birçok çalışmada kullanılmaktadır. Particle Flow Code ile kayalar hem iki hem de üç boyutlu olarak modellenebilir ve farklı koşullar altında kayaların davranışları analiz edilebilir. Kayalar iki boyutta diskler, üç boyutta ise küresel tanecikler kullanılarak oluşturulurlar. Bu tanecikler ise birbirlerine farklı mikro mekanik özelliklere sahip olan temas modelleri ile bağlanırlar. Oluşturulan bu bağların kopması ile meydana gelen çatlakların sonucu olarak modelde yenilme meydana gelir. Kaya örneklerinin doğal özelliklerinin sayısal ifadesi olarak tanımlanabilecek yoğunluk, dayanım, deformasyon gibi parametreler kullanılarak çok aşamalı kalibrasyon adımlarının ardından oluşturulan modeller aracılığı ile farklı gerilim koşullarına yönelik çalışmalar yapılabilmektedir. Kalibre edilmiş ve temsil edici bir modele sahip olabilmek için seçilen bağ modelinin kaya malzemesinin yenilme davranışını tam olarak yansıtması gerekmektedir. Bu amaç doğrultusunda Hawkesbury kumtaşına ait olan tek eksenli sıkışma dayanımı deneyi sonuçları kullanılarak kalibre edilmiş bir model hem PBM hem de FJCM için oluşturulmuştur. Kablirasyon aşamasında elastisite modülü, tek eksenli sıkışma dayanımı, çekme dayanımı ve Poisson ratio parametreleri kullanılarak modellerden elde edilen sonuçlar laboratuvar deneylerinden elde edilen sonuçlarla eşleştirilmiştir. Sonuçlar yer değiştirme vektörleri, kuvvet zincirleri ve çatlak çözünürlükleri parametreleri dikkate alınarak değerlendirilmiştir. PBM ve FJM yer değiştirme vektörleri ve kuvvet zincirleri açısından benzerlik göstermiştir. Bununla birlikte çatlak çözünürlüğü açısından FJM, PBM’e göre dört kata varan veri sunarak yenilme davranışının analiz edilmesinde ve sedimanter kayalara yönelik modelleme çalışmalarında kullanılabilirlik açısından öne çıkmaktadır.

Keywords

Hawkesbury kumtaşı, yenilme davranışı, parallel-bond model, flat-joint model, Particle Flow Code

Project Number

2020-09

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