Seismic vulnerability of pile–supported wharves considering recurrent liquefaction–induced damage

To develop damage state–dependent seismic fragility functions for pile wharves supported on liquefiable soil. Seaports in seismically active regions may often undergo strong aftershocks following a mainshock event. Due to the short time interval between events in such a seismic sequence, retrofit interventions are often impossible; as a result, the aftershock acts in already damaged structures. Pile–supported wharves are particularly vulnerable to such seismic sequences with the main cause of damage being the liquefaction of soft underlying soils and/or hydraulic backfills

System response of liquefiable deposits : insights from advanced analyses of case-histories from the 2010-2011 Canterbury earthquakes.

Advanced seismic effective-stress analysis is used to scrutinize the liquefaction performance of 55 well-documented case-history sites from Christchurch. The performance of these sites during the 2010-2011 Canterbury earthquake sequence varied significantly, from no liquefaction manifestation at the ground surface (in any of the major events) to severe liquefaction manifestation in multiple events. For the majority of the 55 sites, the simplified liquefaction evaluation procedures, which are conventionally used in engineering practice, could not explain these dramatic differences in the manifestation. Detailed geotechnical characterization and subsequent examination of the soil profile characteristics of the 55 sites identified some similarities but also important differences between sites that manifested liquefaction in the two major events of the sequence (YY-sites) and sites that did not manifest liquefaction in either event (NN-sites). In particular, while the YY-sites and NN-sites are shown to have practically identical critical layer characteristics, they have significant differences with regard to their deposit characteristics including the thickness and vertical continuity of their critical zones and liquefiable materials. A CPT-based effective stress analysis procedure is developed and implemented for the analyses of the 55 case history sites. Key features of this procedure are that, on the one hand, it can be fully automated in a programming environment and, on the other hand, it is directly equivalent (in the definition of cyclic resistance and required input data) to the CPT-based simplified liquefaction evaluation procedures. These features facilitate significantly the application of effective-stress analysis for simple 1D free-field soil-column problems and also provide a basis for rigorous comparisons of the outcomes of effective-stress analyses and simplified procedures. Input motions for the analyses are derived using selected (reference) recordings from the two major events of the 2010-2011 Canterbury earthquake sequence. A step-by-step procedure for the selection of representative reference motions for each site and their subsequent treatment (i.e. deconvolution and scaling) is presented. The focus of the proposed procedure is to address key aspects of spatial variability of ground motion in the near-source region of an earthquake including extended-source effects, path effects, and variation in the deeper regional geology

System Response of Liquefiable Deposits

Results from a series of 1D seismic effective stress analyses of natural soil deposits from Christchurch are summarized. The analysed soil columns include sites whose performance during the 2010-2011 Canterbury earthquakes varied significantly, from no liquefaction manifestation at the ground surface to very severe liquefaction, in which case a large area of the site was covered by thick soil ejecta. Key soil profile characteristics and response mechanisms affecting the severity of surface liquefaction manifestation and subsequent damage are explored. The influence of shaking intensity on the triggering and contribution of these mechanisms is also discussed. Careful examination of the results highlights the importance of considering the deposit as a whole, i.e. a system of layers, including interactions between layers in the dynamic response and through pore water pressure redistribution and water flow

A CPT-based effective stress analysis procedure for liquefaction assessment

There is a growing awareness of the need for the earthquake engineering practice to incorporate in addition to empirical approaches in evaluation of liquefaction hazards advanced methods which can more realistically represent soil behaviour during earthquakes. Currently, this implementation is hindered by a number of challenges mainly associated with the amount of data and user-experience required for such advanced methods. In this study, we present key steps of an advanced seismic effective-stress analysis procedure, which on the one hand can be fully automated and, on the other hand, requires no additional input (at least for preliminary applications) compared to simplified cone penetration test (CPT)-based liquefaction procedures. In this way, effective-stress analysis can be routinely applied for quick, yet more robust estimations of liquefaction hazards, in a similar fashion to the simplified procedures. Important insights regarding the dynamic interactions in liquefying soils and the actual system response of a deposit can be gained from such analyses, as illustrated with the application to two sites from Christchurch, New Zealand

Liquefaction Evaluation in Stratified Soils

The Canterbury Earthquake Sequence 2010-2011 (CES) induced widespread liquefaction in many parts of Christchurch city. Liquefaction was more commonly observed in the eastern suburbs and along the Avon River where the soils were characterised by thick sandy deposits with a shallow water table. On the other hand, suburbs to the north, west and south of the CBD (e.g. Riccarton, Papanui) exhibited less severe to no liquefaction. These soils were more commonly characterised by inter-layered liquefiable and non-liquefiable deposits. As part of a related large-scale study of the performance of Christchurch soils during the CES, detailed borehole data including CPT, Vs and Vp have been collected for 55 sites in Christchurch. For this subset of Christchurch sites, predictions of liquefaction triggering using the simplified method (Boulanger & Idriss, 2014) indicated that liquefaction was over-predicted for 94% of sites that did not manifest liquefaction during the CES, and under-predicted for 50% of sites that did manifest liquefaction. The focus of this study was to investigate these discrepancies between prediction and observation. To assess if these discrepancies were due to soil-layer interaction and to determine the effect that soil stratification has on the develop-ment of liquefaction and the system response of soil deposits

Inelastic Response of Embedded Foundations

210 σ.Στην παρούσα εργασία παρουσιάζονται αποτελέσματα από τρισδιάστατες αναλύσεις πεπερασμένων στοιχείων με σκοπό τη διερεύνηση της ανελαστικής απόκρισης εγκιβωτισμένων θεμελιώσεων υπό μονοτονική και ανακυκλική εγκάρσια φόρτιση. Συγκεκριμένα, μελετάται η απόκριση θεμελιώσεων τετραγωνικής κάτοψης, βαθμού εγκιβωτισμού D/B = 0, 0.2, 0.5 και 1 επί ομοιογενούς στιφρού αργιλικού εδάφους, υπό αστράγγιστες συνθήκες φόρτισης. Ειδικότερα, η εργασία χωρίζεται σε δύο μέρη. Στο πρώτο μέρος εξετάζεται η φέρουσα ικανότητα του συστήματος εδάφους–θεμελίωσης υπό συνδυασμένη μονοτονική φόρτιση αξονικής (Ν), τέμνουσας δύναμης (Q) και ροπής ανατροπής (M), και παράγονται οι περιβάλλουσες αστοχίας σε χαρακτηριστικές τομές του τρισδιάστατου MQN χώρου φόρτισης. Αποδεικνύεται ότι η επίδραση του εγκιβωτισμού της θεμελίωσης είναι καταλυτική τόσο ως προς το μέγεθος όσο και ως προς το σχήμα των περιβαλλουσών επιφανειών αστοχίας. Επιπλέον, παρατηρείται ότι η απόκριση της θεμελίωσης είναι ιδιαίτερα ευαίσθητη στα χαρακτηριστικά της διεπιφάνειας θεμελίου–εδάφους. Στο δεύτερο μέρος προσομοιώνεται το σύνολο του συστήματος εδάφους–θεμελίου–ανωδομής, όπου η ανωδομή αναπαρίσταται από ένα απλό άκαμπτο στοιχείο δοκού με συγκεντρωμένη μάζα στην κορυφή του. Οι εξεταζόμενοι συνδυασμοί φόρτισης περιορίζονται τώρα από το λόγο λυγηρότητας της ανωδομής και εν προκειμένω εξετάζονται δύο χαρακτηριστικές τιμές αυτού : H/B = 1 και 3. Το σύστημα υποβάλλεται σε μονοτονική και ανακυκλική οριζόντια φόρτιση στο επίπεδο της συγκεντρωμένης μάζας της ανωδομής, ενώ λαμβάνονται υπόψη τα φαινόμενα P-δ. Πέρα από τη φέρουσα ικανότητα, μελετάται επιπλέον και η μεταπλαστική φάση της απόκρισης του συστήματος, ενώ έμφαση δίνεται στην ανακυκλική συμπεριφορά, τους μηχανισμούς αστοχίας και τις παραμένουσες παραμορφώσεις. Παρατηρείται μια σαφής διάκριση της απόκρισης μεταξύ ρηχά και σχετικά βαθιά εγκιβωτισμένων θεμελιώσεων.The inelastic response of embedded foundations under monotonic and cyclic lateral loading is investigated using 3D finite element analyses. The study has focused in particular on the undrained response of square foundations of various embedment ratios (0 ≤ D/B ≤ 1) on stiff clay. More specifically, the study is divided into two parts. In the first part, the bearing capacity of the soil–foundation system is examined under combined monotonic MQN loading and failure envelopes are predicted in typical sections of the three-dimensional load space. It is shown that both the size and the shape of the failure envelopes are highly dependent on the foundation embedment ratio. Moreover, it is observed that the system response is extremely sensitive to the soil–foundation interface characteristics. In the second part, the entire soil–foundation–superstructure system is simulated, where the superstructure is represented by a rigid beam element with a lumped mass at its top. The system is subjected to monotonic and cyclic horizontal loading applied at the level of the lumped mass. The load combinations are now restricted by the slenderness of the superstructure (i.e. the beam length). The metaplastic system response is investigated, as P-δ effects are taken into account. Emphasis is placed on the cyclic behavior, the failure mechanisms and the residual deformations. A significant difference is observed between the response of shallow and relatively deeply embedded foundations.Νικόλαος Α. Ντρίτσο

Liquefaction Performance & Characterisation of 55 Chrictchurch Sites

To identify key ground characteristics that led to different liquefaction manifestations during the Canterbury earthquake

Rotationplasty outcomes assessed by gait analysis following resection of lower extremity bone neoplasms: a systematic review and meta-analysis

Aims: The standard of surgical treatment for lower limb neoplasms had been characterized by highly interventional techniques, leading to severe kinetic impairment of the patients and incidences of phantom pain. Rotationplasty had arisen as a potent limb salvage treatment option for young cancer patients with lower limb bone tumours, but its impact on the gait through comparative studies still remains unclear several years after the introduction of the procedure. The aim of this study is to assess the effect of rotationplasty on gait parameters measured by gait analysis compared to healthy individuals. Methods: The MEDLINE, Scopus, and Cochrane databases were systematically searched without time restriction until 10 January 2022 for eligible studies. Gait parameters measured by gait analysis were the outcomes of interest. Results: Three studies were eligible for analyses. Compared to healthy individuals, rotationplasty significantly decreased gait velocity (-1.45 cm/sec; 95% confidence interval (CI) -1.98 to -0.93; p < 0.001), stride length (-1.20 cm; 95% CI -2.31 to -0.09; p < 0.001), cadence (-0.83 stride/min; 95% (CI -1.29 to -0.36; p < 0.001), and non-significantly increased cycle time (0.54 sec; 95% CI -0.42 to 1.51; p = 0.184). Conclusion: Rotationplasty is a valid option for the management of lower limb bone tumours in young cancer patients. Larger studies, with high patient accrual, refined surgical techniques, and well planned rehabilitation strategies, are required to further improve the reported outcomes of this procedure. Cite this article: Bone Jt Open 2023;4(11):817–824

Effects of partial saturation on the liquefaction resistance of sand and silty sand from Christchurch

The liquefaction resistance of partially saturated soil was experimentally investigated for one clean sand and one silty sand collected from a site in Christchurch, in an area severely affected by liquefaction in the 2010–2011 Canterbury earthquakes. A series of cyclic undrained tests were performed on fully and partially saturated sand and silty sand specimens, in conjunction with evaluation of saturation conditions in situ based on comprehensive field measurements of P-wave velocity (Vp) in Christchurch deposits. The Skempton’s B-value and P-wave velocity were comparatively used as measures for partial saturation in the laboratory. B-value - Vp relationships from the test results indicate that Vp steadily increases with the B-value until a threshold B-value is reached beyond which Vp remains unchanged at values indicating full saturation, i.e. Vp ;≥ ;1600 ;m/s. In general, the liquefaction resistance of tested sand and silty sand increases with a decrease in the B-value or Vp, i.e. with a reduction in the degree of saturation. Furthermore, test results suggest existence of threshold B-values and Vp for tested soils beyond which no significant increase in the liquefaction resistance was observed. This threshold B-values and Vp were found to be dependent on soil type and applied confining stress. The effects of partial saturation on liquefaction strength are different for the sand and silty sand when using Vp as a measure for the degree of saturation. While a gradual rate of increase in liquefaction strength with decreasing Vp is observed for the tested sand, the liquefaction strength of silty sand shows similar gradual increase with a decrease in Vp up to about 800 ;m/s, which is then followed by an abrupt increase in the liquefaction strength for Vp ;< ;800 ;m/s. Generally good agreement between liquefaction strength of tested soils and published data was observed, with a clear distinctive feature in the behaviour of the silty sand as compared to clean sands