Κατά τον αντισεισμικό σχεδιασμό δύσκαμπτων και ογκωδών κατασκευών εδαφικής αντιστήριξης (π.χ. τοίχοι αντιστήριξης από σκυρόδεμα) οι δράσεις που λαμβάνονται υπόψη κατά τις αναλύσεις ευστάθειας περιλαμβάνουν την στατική και δυναμική εδαφική ώθηση καθώς και την αδρανειακή δύναμη του τοίχου. Οι τρέχουσες μέθοδοι σχεδιασμού (ψευδοστατική, μετακινήσεων) θεωρούν ότι οι δύο ανωτέρω δράσεις ενεργούν συγχρονισμένα, δηλαδή οι μέγιστες τιμές τους ασκούνται ταυτόχρονα στην κατασκευή αντιστήριξης. Εν τούτοις αποτελέσματα πρόσφατων πειραματικών και υπολογιστικών διερευνήσεων υποδεικνύουν ότι (τουλάχιστον στην περίπτωση των ευμετακίνητων κατασκευών αντιστήριξης) αναπτύσσεται σημαντική διαφορά φάσης μεταξύ των δύο δράσεων (ασύγχρονη δράση). Αυτό έχει ως αποτέλεσμα να προκύπτει ιδιαίτερα συντηρητικός σχεδιασμός της κατασκευής αντιστήριξης όταν γίνεται δεκτό ότι τα μέγιστα των δύο δράσεων συμπίπτουν χρονικά (σύγχρονη δράση). Στην παρούσα Διατριβή διερευνάται με παραμετρικές αριθμητικές αναλύσεις η ορθότητα της παραδοχής της σύγχρονης δράσης στην περίπτωση των ακλόνητων κατασκευών εδαφικής αντιστήριξης. Χρησιμοποιείται η μέθοδος των πεπερασμένων στοιχείων (χρήση κώδικα πεπερασμένων στοιχείων PLAXIS) για την προσομοίωση ακλόνητων τοίχων αντιστήριξης από σκυρόδεμα που συγκρατούν μη-συνεκτικό επίχωμα με ελαστοπλαστική σχέση τάσεων-παραμορφώσεων (και κριτήριο αστοχίας Mohr-Coulomb) και υποβάλλονται σε οριζόντια ταλάντωση (είτε αρμονική κίνηση είτε καταγεγραμμένη χρονοϊστορία σεισμικών γεγονότων). Οι παραμετρικές αναλύσεις περιλαμβάνουν τη μεταβολή: α) της σχετικής πυκνότητας του επιχώματος (χαλαρή, μετρίως πυκνή και πυκνή κατάσταση), β) της έντασης της επιβαλλόμενης οριζόντιας ταλάντωσης (0.05g έως 0.7g) και γ) του ύψους του τοίχου (4.0m και 7.5m). Τα αποτελέσματα των αναλύσεων χρησιμοποιούνται κατ’ αρχήν για τον προσδιορισμό της στατικής κατανομής και του μεγέθους των εδαφικών ωθήσεων στον τοίχο. Στη συνέχεια υπολογίζεται, η διαφορά φάσης μεταξύ της αδρανειακής δύναμης του τοίχου και της εδαφικής ώθησης, καθώς και του αντίστοιχου ποσοστού της μέγιστης τιμής της δυναμικής εδαφικής ώθησης που ασκείται κατά τη χρονική στιγμή της μεγιστοποίησης της αδρανειακής δύναμης του τοίχου. Οι αναλύσεις υποδεικνύουν ότι η στατική κατανομή των ωθήσεων είναι τριγωνική με τον συντελεστή πλευρικών ωθήσεων να προκύπτει, περίπου, ίσος με Κ0. Κάτω από συνθήκες δυναμικής φόρτισης το ποσοστό της δυναμικής ώθησης προκύπτει πολύ υψηλό (80% έως 90%) – κυρίως για μετρίως πυκνό και πυκνό εδαφικό επίχωμα – ανεξάρτητα από την ένταση της φόρτισης σε αντίθεση με τις πολύ χαμηλές τιμές (δηλαδή ασύγχρονη δράση) που έχουν προκύψει από αντίστοιχη διερεύνηση για την περίπτωση των ευμετακίνητων τοίχων αντιστήριξης. Ιδιαίτερα ενδιαφέρουσα είναι η παρατήρηση ότι για μικρές τιμές της έντασης της δυναμικής φόρτισης (≤ 0.2g) η συμπεριφορά του υψηλού τοίχου (7.5m) προκύπτει διαφοροποιημένη σε σχέση με αυτή του τοίχου των 4.0m: το ποσοστό της σεισμικής ώθησης είναι πολύ μειωμένο (20% έως 40%), ιδιαίτερα στην περίπτωση των πολύ χαλαρών επιχωμάτων. Παρατηρείται επίσης ικανοποιητική συμφωνία της προκύπτουσας τιμής της εδαφικής ώθησης με αυτή από τη σχέση του Wood(1973) και της αναλυτικής λύσης των Kloukinas et al.(2012). Ιδιαίτερο ενδιαφέρον παρουσιάζει η τροποποιημένη κατανομή των εδαφικών ωθήσεων καθ’ ύψος του τοίχου, οι οποίες προκύπτουν αυξημένες στο ανώτερο τμήμα του. Συμπεραίνεται ότι στην περίπτωση του σχεδιασμού των ακλόνητων τοίχων με μετρίως πυκνό και πυκνό επίχωμα η δράση της δυναμικής εδαφικής ώθησης είναι εύλογο και δικαιολογημένο να θεωρείται σύγχρονη με την αδρανειακή δύναμη του τοίχου. / --

The influence of yielding foundations on the mechanical behaviour of reinforced soil walls including wall deformations and loads (strains) in the reinforcement layers is very complex. Based on a review of the literature, there is a need to quantify and isolate the influence of foundation boundary type and magnitude of foundation stiffness on deformations and reinforcement loads in geosynthetic reinforced soil walls. This thesis presents the results of a series of 1/6-scale reinforced soil wall model tests that were carried out to examine the influence of horizontal and vertical toe compliance and vertical foundation compressibility on wall behaviour. The heavily instrumented walls were constructed in a strongbox that was 1.2 m high by 1.6 m wide and retained soil to a distance of 2.3 m behind the facing. The models were uniformly surcharged in stages following construction. The experimental program consisted of three groups of tests. Group 1 tests involved five walls. One wall was constructed with a very stiff horizontal restraint, and three walls were constructed with different horizontal toe stiffness using combinations of coiled springs. The remaining wall in this series was constructed without any horizontal toe restraint. Group 2 was comprised of three walls. One wall was a control wall with a rigid toe. The other two walls were constructed with different vertical toe stiffness support using different combinations of rubber blocks. Group 3 included a control wall with a rigid foundation and a companion wall constructed with a compressible foam and rubber layers below the backfill soil and the wall facing. The results demonstrate that the quantitative behaviour of the models was affected by the type and magnitude of foundation stiffness. For example, as horizontal toe stiffness increased a greater portion of the total horizontal earth load against the wall facing was carried by the toe. The data showed that the shape of facing lateral deformation profiles changed from rotation about the toe for the case of a very stiff horizontal toe to a more uniform profile for the unrestrained toe case. For the case of a rigid vertical footing support below the facing, vertical toe loads were greater than those computed from facing self-weight alone due to down-drag forces developed at the facing–reinforcement connections as the wall facing moved outward. As vertical toe support stiffness decreased with respect to foundation compressibility below the soil backfill, the magnitude of soil down-drag forces diminished resulting in a decrease in vertical toe load. / Thesis (Master, Civil Engineering) -- Queen's University, 2007-10-27 12:15:56.027

Thesis (Ph. D.)--University of Washington, 2007. / Vita. Includes bibliographical references (leaves 280-294).

Thesis (M.App.Sc.) - Carleton University, 2007. / Includes bibliographical references (p. 128-137). Also available in electronic format on the Internet.

Thesis (MScIng)--University of Stellenbosch, 2005. / Bibliography. Also available via the Internet.

Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Civil Engineering, 1982. / MICROFICHE COPY AVAILABLE IN ARCHIVES AND ENGINEERING / Bibliography: leaves 140-141. / by Chin Pang Wong. / M.S.

No description available.

The safety of gravity earth retaining structures is usually evaluated with regard to: (1) overturning about the toe, (2) sliding along the base and (3) bearing failure of the foundation. Conventional equilibrium methods are utilized in these analyses, which are performed using assumed earth loads based on simplified earth pressure theories. Recent finite element studies performed on gravity retaining walls founded on rock revealed that the use of conventional methods may lead to overly conservative results. The effects of soil-structure interaction result in a greater degree of wall stability than conventional approaches would indicate. This research examines the behavior of gravity earth retaining structures founded on soil. Two methods of analyses were used in these studies : (1) the Following Load method, which does net account for soil-structure interaction effects, and (2) the Backfill Placement method, which does account for soil-structure interaction effects. A procedure called the “Alpha Method” for 2D soil elements was developed for the purpose of improving the post-failure stress-strain behavior of the backfill and foundation soils and incorporated in the finite element program (SOILSTRUCT) utilized in the analyses. A series of analyses demonstrated the effectiveness of the Alpha Method in controlling overshoot and providing good estimates of collapse loads on wall-foundation systems. Following Load analyses indicated that walls on soil become unstable by bearing capacity rather than overturning or sliding. These results also provided the basis for modifications to Vesic’s bearing capacity theory, which extended the applicability of the theory to the conditions encountered in retaining wall problems. The Backfill Placement analyses showed that there are significant differences in behavior between walls founded on rock and walls founded on soil. These analyses also led to new insight into the factors that affect the shear forces within the backfill and which contributes to the stability of the wall. / Ph. D.

Experimental and analytic investigations were performed to examine the influences of wall height, backfill behavior, and compaction on the magnitudes of backfill loads on rigid retaining walls. Measurements of lateral and vertical backfill loads were made during tests using the Virginia Tech instrumented retaining wall facility. The tests were performed with two soils, moist Yatesville silty sand and dry Light Castle sand. Two hand-operated compactors, a vibrating plate compactor and a rammer compactor, were used to compact the backfill. The backfill height was 6.5 feet in all of the tests. Analyses of backfill loads were made using a compaction- induced lateral earth pressure theory and a vertical shear force theory. The compaction-induced lateral earth pressure theory was revised from a previous theory. The revisions improved the accuracy with which the theory models the hysteretic stress behavior of the backfill during compaction. The theory was also extended to include the pore pressure response of moist backfill in a rational manner. A vertical shear force theory was also developed during this research. The theory is based on consideration of backfill compressibility and mobilization of interface shear strength at the contact between the backfill and the wall. The theory provides a useful basis for understanding how wall height, backfill compressibility, wall-backfill interface behavior, and compaction-induced lateral pressures affect the vertical shear forces on rigid walls. Studies were also made to investigate the cause of erratic pressure cell readings. An important cause of drift in pressure cell readings was found to be moisture changes in the concrete in which the pressure cells were mounted. It was found that this problem could be mitigated by applying a water-seal treatment to the face of the wall. Both the vibrating plate compactor and the rammer compactor were instrumented to measure dynamic forces and energy transfer during compaction. The force applied by the vibrating plate compactor was about one-quarter of the manufacturer’s rated force. The force applied by the rammer compactor was about twice the manufacturer’s rated force. The transferred energy measurements provided a basis for relating laboratory and field compaction procedures. / Ph. D.

Previous laboratory and field experimental studies of earth pressures exerted on retaining structures and laboratory studies of the at-rest earth pressure coefficient are summarized. The current methods used to evaluate the earth pressures due to compaction are reviewed. The design features of a new instrumented oedometer developed to investigate the effect of number of load cycles on the at-rest earth-pressure coefficient are presented along with the results of a series of tests on Monterey sand #0/30. The Instrumented Retaining Wall Facility developed to provide a means of obtaining experimental measurements of the earth pressures exerted on retaining structures is described. The instrumented wall of the facility is seven feet high and ten feet long and is instrumented to measure horizontal and vertical forces, horizontal earth pressures, horizontal deformations, and temperature. A description of the microcomputer-based data-acquisition system and the software used to record the test results is included. The results of four tests where Yatesville silty sand was compacted in layers in the Instrumented Retaining Wall Facility are presented. The experimental results are compared with the results of similar studies by others and to an analytical method used to estimate compaction-induced earth pressures. / Ph. D.