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Discrete element modelling has been used to capture the essential mechanical features of railway ballast and gain a better understanding of the mechanical behaviour and mechanisms of degradation under monotonic and cyclic loading. A simple procedure has been developed to generate clumps which resemble real ballast particles. The influence of clump shape on the heterogeneous stresses within an aggregate was investigated in box test simulations. More angular clumps lead to greater homogeneity and the interlocking provides a much more realistic load-deformation response. A simple two-ball clump was used with two additional small balls (asperities) bonded at the surface, to represent a single particle; it is shown that particle abrasion gives the correct settlement response. A clump formed from ten balls in a tetrahedral shape was used in monotonic and cyclic triaxial test simulations and found to produce the correct response. The interlocking and breaking of very small asperities which find their way into the voids and carry no load was modelled using weak parallel bonds. The interlocking and fracture of larger asperities was modelled by bonding eight small balls to the ten-ball clump. Monotonic tests were performed on triaxial samples under different confining pressures and the results compared with existing experimental data. Tests were also simulated using uncrushable clumps to highlight the important role of asperity abrasion. Cyclic triaxial tests were then simulated on the same aggregates under a range of stress conditions and the results compared to existing experimental data for the same simulated ballast. The clumps are able to capture the behaviour of ballast under different conditions, and asperity abrasion plays an important role in governing strength and volumetric strain under monotonic loading, and on permanent strains under cyclic loading. The contribution of this thesis is therefore to show that it is possible to model a real granular material under static and cyclic conditions, providing much micro mechanical insight.

It is important to have consistent ballast testing methods that provide results reflecting the performance of different ballast materials in the railway trackbed. In this research, extensive laboratory tests were conducted to investigate the correlation between simple ballast index tests, and box tests simulating ballast field loading conditions in a simplified and controlled manner. In the box test, a sleeper load of 40kN was applied to a simulated sleeper on the top of a sample of ballast in a box of dimensions 700x300x450mm. The ballast was tamped using a Kango hammer which caused particles to rearrange as the level of the sleeper was raised. The ballast tests investigated in this project are those ballast tests specified in the Railtrack Line Specification (RT/CE/S/006 Issue 3, 2000), in addition to single particle crushing tests, oedometer tests, petrographic analysis, and box tests. It was found that there was some correlation between the single particle crushing tests, oedometer tests, box tests and petrographic analysis. One of the current ballast tests, namely the Aggregate Crushing Value (ACV) test, which is analogous to the oedometer test, is not appropriate because the ACV test uses 10-14mm ballast particles, and there is a size effect on the strength of ballast and different ballasts have different size effects. However, if an oedometer test is used on track ballast, the results correlate better with ballast field performance as simulated in the box tests. Six ballasts were tested: A, B, C, D, E and F (mineralogy of these ballasts can be found in the appendix). The aim was to examine the relative performance of these ballasts and to establish which index tests were most indicative of performance in the box test. Simple index tests were performed on each of the ballasts, whilst box tests were only performed on ballasts A, B, C and D. The box tests were generally performed wet by adding a known volume of water at each tamp. For ballast A, controlled tests were also performed on dry ballast, and tests involving traffic loading only and tamping only were also conducted. A box test on 10-14mm ballast A was also conducted to investigate the size effect on ballast behaviour in the box. The Wet Attrition Value (WAV), Los Angeles Abrasion (LAA), and Micro-Deval Attrition (MDA) seem to be suitable parameters to indicate ballast performance in the box test. However, this is considered to be due to the rearrangement of particles in the box test caused by the simulated tamping. In addition to the laboratory tests, the application of discrete element program PFC3D (Itasca Consulting Group, Inc., 1999) in simulating ballast behaviour was also investigated. Single particle crushing test was simulated to produce crushable agglomerates with a distribution of strengths of ballast A. These agglomerates were then used to simulate the oedometer test. The resulting normal compression line was compared with that for real oedometer tests: discrepancies can be attributed to the simplified geometry of the agglomerates. Due to the high computational time in simulating a box test with crushable agglomerates, uncrushable spherical balls and uncrushable angular agglomerates were used to represent individual ballast particles in the box. Important aspects of ballast behaviour under repeated loading, namely resilient and permanent deformation, were studied. It was found that the box test on uncrushable angular agglomerates give less permanent deformation compared with the test on spherical balls, because of the additional resistance provided by the irregular shape of the agglomerates.

Since it is difficult to conduct railway ballast testing in-situ, it is important to simulate the conditions experienced in the real track environment and study their influences on ballast in a controlled experimental manner. In this research, extensive laboratory tests were performed on three types of ballast, namely granites A and B and limestone. The grading of the tested ballast conforms to the grading specification in The Railway Specification RT/CE/S/006 Issue 3 (2000). The major laboratory tests in this research were used to simulate the traffic loading and tamping maintenance undertaken by the newly developed Railway Test Facility (RTF) and large-scale triaxial test facility. The Railway Test Facility is a railway research facility that is housed in a 2.1 m (width) x 4.1 m (length) x 1.9 m (depth) concrete pit and comprises subgrade material, ballast, and three sleepers. The sleepers are loaded with out of phase sinusoidal loading to simulate traffic loading. The ballast in the facility can also be tamped by a tamping bank which is a modified real Plasser tamping machine. Ballast breakage in the RTF was quantified by placing columns of painted ballast beneath a pair of the tamping tines, in the location where the other pair of tamping tines squeeze, and under the rail seating. The painted ballast was collected by hand and sieved after each test. It was found from the RTF tests that the amount of breakage generated from the tests was not comparable to the fouling in the real track environment. This is because the external input (such as wagon spillage and airborne dirt) which is the major source of fouling material was not included in the tests. Furthermore, plunging of the tamping tines caused more damage to the ballast than squeezing. The tested ballast was also subjected to Los Angeles Abrasion (LAA) and Micro-Deval Attrition (MDA) tests. It was found that the LAA and MDA values correlated well with the ballast damage from tamping and could indicate the durability of ballast. The large-scale triaxial test machine was specially manufactured for testing a cylindrical ballast sample with 300-mm diameter and 450-mm height and can perform both cyclic and monotonic tests with constant confining stress. Instead of using on-sample instrumentations to measure the radial movement of the sample, it measures sample volume change by measuring a head difference between the level of water that surrounds the sample and a fixed reference water level with a differential pressure transducer. The test results from cyclic tests were related to the simulated traffic loading test in the RTF by an elastic computer model. Even with some deficiencies, the model could relate the stress condition in the RTF to cyclic triaxial test with different confining stresses and q/p' stress ratios.

Στη παρακάτω διπλωματική εργασία, δύναται να περιγραφούν τα τεχνικο-γεωλογικά χαρακτηριστικά που μπορούν να ταξινομήσουν και να πιστοποιήσουν βραχώδη υλικά, κατόπιν εργαστηριακών δοκιμών, ως κατάλληλα (ή μη κατάλληλα), για συγκεκριμένες χρήσεις ως αδρανή υλικά. Η συγκεκριμένη εργασία, αναφέρεται για χρήσεις αδρανών υλικών σε έρμα σιδηροδρομικών γραμμών. Επίσης, γίνεται εκτεταμένη θεωρητική αναφορά στις φυσικές- μηχανικές, χημικές, γεωμετρικές και άλλες ιδιότητες, που παρουσιάζουν τα υλικά που μπορούν να χρησιμοποιηθούν ως αδρανή, καθώς και περιγραφή των εργαστηριακών δοκιμών, όπως προβλέπονται από τους Ευρωπαϊκούς Κανονισμούς (ΕΝ)περί καταλληλότητας αδρανών υλικών και που βρίσκονται σε συνάφεια με τις νομοθεσίες του Ελληνικού Κράτους για το θέμα αυτό. Μια άλλη πτυχή του θέματος που περιγράφεται, είναι οι λατομικές ζώνες (λατομεία), όπου είναι ο χώρος που γίνεται μαζική λήψη υλικού, απευθείας από το υγιές τμήμα της βραχόμαζας, που προορίζεται για χρήση αδρανών υλικών και εξετάζονται οι περιορισμοί που προκύπτουν βάσει της Ελληνικής νομοθεσίας στο θέμα αυτό, που αφορούν άμεσα αστικές και κατοικημένες περιοχές, καθώς και περιβαλλοντικές πτυχές του όλο θέματος. Εργαστηριακά, η παρακάτω διπλωματική εργασία, βασίζεται στην λήψη δείγματος από βραχώδες υπερβασικό υλικό (διαβασικά πετρώματα), το οποίο εξετάστηκε πετρογραφικά και εργαστηριακά βάσει των πιο πάνω Ευρωπαϊκών Κανονισμών και στην συνέχεια συγκρίνονται με τα προβλεπόμενα όρια της κάθε εργαστηριακής δοκιμής που αναφέρονται ως εργαστηριακά όρια χρήσης αδρανών υλικών σε έρμα σιδηροδρομικών γραμμών. Αυτή η διαδικασία πραγματοποιείται, ώστε να γίνει δυνατή η πιστοποίηση του συγκεκριμένου υλικού ως κατάλληλο ή ακατάλληλο για την συγκεκριμένη χρήση. Όλες οι διαδικασίες και εργαστηριακές δοκιμές, πραγματοποιήθηκαν στο χώρο του εργαστηρίου Τεχνικής Γεωλογίας ,στο τμήμα Γεωλογίας του Πανεπιστημίου Πατρών. Συγκεκριμένα πάρθηκαν 4 δείγματα όμοιου υλικού(διαβασικό) από κοινή πηγή (Πολύκαστρο- Κιλκίς) βάρους: ΔΕΙΓΜΑ (7)=17.775KG, ΔΕΙΓΜΑ (8)=16.345KG, ΔΕΙΓΜΑ (9)=19,490KG και ΔΕΙΓΜΑ (10)=17.231ΚG. Έπειτα, πραγματοποιήθηκαν οι πιο κάτω εργαστηριακές δοκιμές, στο εργαστήριο Τεχνικής Γεωλογίας του τμήματος Γεωλογίας του Πανεπιστήμιου Πατρών. (α)Κοκκομετρική Ανάλυση (β)Δείκτης Μορφής (γ)Δείκτης Πλακοειδούς (δ)Δείκτης Los Angeles (ε)Δείκτης micro- Deval Tα αποτελέσματα που πρόεκυψαν, εμφανίζονται στη διπλωματική εργασία στα Παραρτήματα 1, 2, 3, 4, 5. Γίνετε επίσης σύγκριση των εργαστηριακών αποτελεσμάτων με τα αντίστοιχα κατάλληλα όρια και το αποτέλεσμα εμφανίζεται στην ενότητα ‘’Συμπεράσματα’’ της εργασίας. Τέλος γίνεται γεωμορφολογική και γεωλογική αναφορά της περιοχής(Ν.Κιλκίς), από όπου πάρθηκαν τα δείγματα και περιγράφεται συνοπτικά η γεωτεκτονική ζώνη όπου ανήκει. / -