Impact of Economic Crisis on Passenger Transportation – Case of Travelling to the Greek Mainland from Crete

The Greek economic crisis of 2009 onwards has affected all aspects of social and economic life of the country, including transportation. The present study focuses on the impact of economic crisis on the long distance transportation between the island of Crete in Greece, the largest Greek island and one of the largest in the Mediterranean Sea, and the Greek mainland. A questionnaire survey was used to investigate the opinions of the Cretans on the way the economic crisis influenced their transportation to the Greek mainland. The results of the survey show that the frequency of the Cretans’ travels was significantly limited, owing to the increased direct or indirect associated cost, due to the economic crisis. Especially for those who struggled to make ends meet, the transportation to the mainland dropped to the bare essentials. Furthermore, the respondents deemed that the&nbsp;deregulation of the Greek maritime and airline markets was also to blame for the high fares, thus they favoured a regulated public transport sector and were against privatization. Inevitably, financially vulnerable individuals were the most preoccupied with these issues. A feeling of isolation and exclusion was revealed by the sample on occasions when the scheduled trips were cancelled by the operators due to exogenous parameters.</p

The Mechanical Response of a Silty Sand Stabilized with Colloidal Silica

This paper presents a laboratory investigation into the mechanical response of a silty sand, with a fines content of 10%, stabilized with colloidal silica (CS). To this end, a series of unconfined compression tests as well as monotonic and cyclic triaxial tests was performed on a silty sand, comprising a mixture of a clean sand and a silty sand, stabilized with two concentrations of CS. The effect of various parameters on the behaviour of the stabilized silty sand was studied, such as CS concentration, soil density, and the presence of fines. The test results were compared with the corresponding of the untreated silty sand as well as the parent clean sand. It is shown that stabilization, even at the lowest CS = 6% concentration studied, significantly improves the undrained shear strength as well as the liquefaction resistance of the stabilized silty sand. Both the monotonic and cyclic response of the stabilized soil are only slightly affected by density. Furthermore, cyclic straining up to at least 5% of double-amplitude axial strain does not influence the undrained shear strength of the stabilized silty sand

Laboratory investigation into the behaviour of improved liquefiable soils under monotonic and cyclic loading

Liquefaction is a phenomenon in which saturated granular soils exhibit a significant loss of their shear strength and stiffness, as a result of increased deformation, due to static (monotonic), dynamic or cyclic loading, under undrained conditions. Excess pore water pressure development under undrained conditions, is the principal characteristic of all liquefaction cases. At a project site prior to construction, mitigation of liquefaction risk for granular soils may be achieved by a number of soil improvement techniques, based on densification, grouting, or excess pore water pressure dissipation. However, in cases where improvement of soil under existing structures is required, implementation of typical improvement methods is difficult, if not impossible, without the obstruction of operation or the development of structural failures, during the application of dynamic or vibrating techniques. Passive stabilization is a relatively new, non-desruptive soil improvement technique for the mitigation of liquefaction risk at existing developed sites. According to this technique, a stabilizer is slowly injected at the upgradient side of a developed site, by means of gradual or augmented groundwater flow. The stabilizing material has initially low viscosity, which increases rapidly after delivery at the target location at a controlled time. Thus, soil improvement by this technique applies to the whole structure area of interest, without causing obstructions to its normal operation. The enrichment of the pore fluid with the stabilizer alters the mechanical response of the soil skeleton - pore fluid system, making it less vulnerable to liquefaction. Passive stabilization with the use of colloidal silica as the stabilizing material, was first studied by Gallagher (2000). More recently (DeJong et al., 2013 among others), stabilization of granular soils with the use of bio-materials and bacteria was investigated in order to form cementation bonds among soil particles, thus creating artificially weakly cemented sandy soils. The effectiveness control of soil improvement techniques for the mitigation of liquefaction risk, requires the investigation of the mechanical behavior of improved liquefiable soils, under monotonic and cyclic loading conditions, as well as the determination of their maximum shear modulus. In this particular research, an extensive laboratory test programme was performed, consisting mainly of monotonic and cyclic triaxial tests, as well as bender element tests, executed at the Cyclic Triaxial Apparatus of the Laboratory of Soil Mechanics, Foundations and Geotechnical Earthquake Engineering (L.S.M.G.E.E.) of A.U.TH. The objective of the present thesis is the investigation of the mechanical response of improved sandy soils. To this extend, the behaviour under monotonic and cyclic loading, as well as the maximum shear modulus of untreated clean and silty sands, stabilized clean and silty sands with colloidal silica, as well as weakly cemented clean and silty sands, is thoroughly investigated. The effectiveness of the aforementioned studied improvement techniques is examined, by comparing test results of the treated and untreated soils.Η ρευστοποίηση είναι το φαινόμενο εκείνο κατά το οποίο κορεσμένα κοκκώδη εδάφη υφίστανται σημαντική απομείωση της διατμητικής αντοχής και της ακαμψίας τους, ως αποτέλεσμα της παραμόρφωσης, που προκαλείται κατά τη στατική (μονοτονική), δυναμική ή ανακυκλική φόρτισή τους υπό αστράγγιστες συνθήκες. Κατά το σχεδιασμό των τεχνικών έργων, πολλές φορές απαιτείται βελτίωση της μηχανικής συμπεριφοράς των ρευστοποιήσιμων εδαφών. Σε θέσεις νέων κατασκευών, η αποτροπή του κινδύνου ρευστοποίησης κοκκωδών εδαφών δεν παρουσιάζει τεχνικά προβλήματα και γίνεται επιλέγοντας από μια σειρά καθιερωμένες μεθοδολογίες που στηρίζονται στη συμπύκνωση, τη σταθεροποίηση ή την αποτόνωση των υπερπιέσεων του ύδατος των πόρων. Ωστόσο, σε πολλές περιπτώσεις απαιτείται η βελτίωση εδάφους έναντι ρευστοποίησης υφιστάμενων κατασκευών. Σε αυτή την περίπτωση, οι συνήθεις τεχνικές βελτίωσης είναι δύσκολο ή αδύνατον να χρησιμοποιηθούν χωρίς συνέπειες στη λειτουργικότητά τους ή την πιθανότητα εμφάνισης δομικών αστοχιών κατά την εφαρμογή δυναμικών ή δονητικών τεχνικών. Η παθητική σταθεροποίηση αποτελεί μία νέα μη καταστροφική μέθοδο βελτίωσης του εδάφους θεμελίωσης υφιστάμενων κατασκευών για την αποτροπή του κινδύνου ρευστοποίησης, σύμφωνα με τη οποία εισάγεται ένας σταθεροποιητής μέσω διήθησης με χαμηλή υδραυλική κλίση στο ρευστοποιήσιμο έδαφος θεμελίωσης μιας υφιστάμενης κατασκευής. Ο σταθεροποιητής διαθέτει αρχικά χαμηλό ιξώδες, το οποίο μετά την πάροδο ελεγχόμενου χρόνου αυξάνεται ραγδαία, ώστε να σταθεροποιηθεί όταν έχει ολοκληρωθεί η διήθηση. Με αυτό τον τρόπο η βελτίωση του εδάφους δεν έχει τοπικό χαρακτήρα, ενώ ταυτόχρονα δεν οδηγεί σε όχληση της λειτουργίας της υπάρχουσας κατασκευής. Ο εμπλουτισμός του ύδατος των πόρων του ρευστοποιήσιμου εδάφους με τον σταθεροποιητή έχει ως αποτέλεσμα την αλλαγή της μηχανικής συμπεριφοράς του συστήματος εδαφικού σκελετού - ύδατος των πόρων του εδάφους, καθιστώντας το περισσότερο ανθεκτικό στη ρευστοποίηση. Η συγκεκριμένη μέθοδος μελετήθηκε πρώτη φορά από την Gallagher (2000) με τη χρήση κολλοειδούς οξειδίου του πυριτίου ως σταθεροποιητή. Πιο πρόσφατα ακόμη (DeJong et al., 2013 κ.α.), μελετήθηκε η σταθεροποίηση κοκκωδών εδαφών με χρήση βιοϋλικών και μικροβίων, με σκοπό τη δημιουργία δεσμών τσιμεντοποίησης μεταξύ των εδαφικών κόκκων και κατά συνέπεια τη διαμόρφωση τεχνητώς ελαφρώς τσιμεντοποιημένων αμμωδών εδαφών. Ο έλεγχος της αποτελεσματικότητας των τεχνικών βελτίωσης του εδάφους για την αποτροπή του κινδύνου ρευστοποίησης απαιτεί τη μελέτη της μηχανικής συμπεριφοράς των βελτιωμένων ρευστοποιήσιμων εδαφών υπό συνθήκες μονοτονικής και ανακυκλικής φόρτισης, καθώς και τον προσδιορισμό του μέγιστου μέτρου διάτμησής τους. Στα πλαίσια της παρούσας έρευνας, εφαρμόστηκε ένα εκτεταμένο πρόγραμμα εργαστηριακών δοκιμών, που αποτελείται κατά κύριο λόγο από τριαξονικές δοκιμές μονοτονικής και ανακυκλικής φόρτισης, καθώς και δοκιμές πιεζοηλεκτρικών στοιχείων, οι οποίες εκτελέστηκαν στην Τριαξονική Συσκευή Ανακυκλικής Φόρτισης του Εργαστηρίου Εδαφομηχανικής Θεμελιώσεων και Γεωτεχνικής Σεισμικής Μηχανικής (Ε.Ε.Θ.Γ.Σ.Μ.) του Αριστοτέλειου Πανεπιστημίου Θεσσαλονίκης. Σκοπός της παρούσας διατριβής είναι η διερεύνηση της μηχανικής συμπεριφοράς βελτιωμένων αμμωδών εδαφών. Για το λόγο αυτό, μελετάται η συμπεριφορά μη βελτιωμένων καθαρών και ιλυωδών άμμων, σταθεροποιημένων καθαρών και ιλυωδών άμμων με κολλοειδή πυριτία, καθώς και τσιμεντοποιημένων καθαρών και ιλυωδών άμμων, υπό μονοτονική και ανακυκλική φόρτιση και προσδιορίζεται το μέγιστο μέτρο διάτμησης των παραπάνω εδαφών. Η αποτελεσματικότητα των μελετηθέντων τεχνικών βελτίωσης εξετάζεται με σύγκριση των αποτελεσμάτων των βελτιωμένων και μη εδαφών

The Mechanical Response of a Silty Sand Stabilized with Colloidal Silica

This paper presents a laboratory investigation into the mechanical response of a silty sand, with a fines content of 10%, stabilized with colloidal silica (CS). To this end, a series of unconfined compression tests as well as monotonic and cyclic triaxial tests was performed on a silty sand, comprising a mixture of a clean sand and a silty sand, stabilized with two concentrations of CS. The effect of various parameters on the behaviour of the stabilized silty sand was studied, such as CS concentration, soil density, and the presence of fines. The test results were compared with the corresponding of the untreated silty sand as well as the parent clean sand. It is shown that stabilization, even at the lowest CS = 6% concentration studied, significantly improves the undrained shear strength as well as the liquefaction resistance of the stabilized silty sand. Both the monotonic and cyclic response of the stabilized soil are only slightly affected by density. Furthermore, cyclic straining up to at least 5% of double-amplitude axial strain does not influence the undrained shear strength of the stabilized silty sand

Behaviour of a building foundation on unsaturated expansive soil

The paper presents a case study of the behaviour of a building foundation on expansive unsaturated clay. The load-bearing masonry building started exhibiting severe cracking in its superstructure, immediately after its completion around 1950. Despite the interventions, the problems continued to exist sixty years later. In the context of identifying the causes of these problems, the paper presents the results of the laboratory tests conducted on the expansive clay in order to estimate its swelling pressure and also understand its behaviour. It is shown that the seasonal variation of the water content of the foundation soil, combined with the intrusion of the root system of the nearby trees at the level of the foundation, subjected the soil to wetting-drying cycles, resulting in its corresponding swelling-shrinking and consequently the settlement of the building. Finally, the proposed countermeasures for the solution of problems are presented, which aimed mainly in minimizing the variation of the moisture of the soil around and at the foundation of the building

Behaviour of a building foundation on unsaturated expansive soil

The paper presents a case study of the behaviour of a building foundation on expansive unsaturated clay. The load-bearing masonry building started exhibiting severe cracking in its superstructure, immediately after its completion around 1950. Despite the interventions, the problems continued to exist sixty years later. In the context of identifying the causes of these problems, the paper presents the results of the laboratory tests conducted on the expansive clay in order to estimate its swelling pressure and also understand its behaviour. It is shown that the seasonal variation of the water content of the foundation soil, combined with the intrusion of the root system of the nearby trees at the level of the foundation, subjected the soil to wetting-drying cycles, resulting in its corresponding swelling-shrinking and consequently the settlement of the building. Finally, the proposed countermeasures for the solution of problems are presented, which aimed mainly in minimizing the variation of the moisture of the soil around and at the foundation of the building