Two aspects of seismically-induced liquefaction are discussed which are of vital engineering significance: the triggering condition and the consequences of liquefaction. The triggering condition is examined with respect to liquefaction analysis, note being taken of the onset condition which is governed by cyclic strength. Consequences of liquefaction are discussed with respect to post-seismic stability analysis, in which the residual strength plays a major role. Procedures used for liquefaction analysis based on the results of in situ sounding tests are introduced, and the applicability of this method for estimating associated ground settlements is discussed. The evaluation of residual strength requires a better understanding of undrained sand behaviour. Results of extensive laboratory rests on Japanese standard sand are examined and new index parameters are proposed to quantify undrained sand behaviour better. The results of laboratory tests on silty sands are examined in the same way. AH the results are presented in terms of whether sand behaviour is contractive or diltative. The laboratory-established criterion for contractive or diltative behaviour is expressed in terms of field parameters such as N value from the SPT or qc value from the CPT. This correlation permits in situ deposits to be classified as being either able or not able to develop flow slide. The laboratory-established relationships between the normalized residual strength and the field parameters are presented. These correlations are shown to be consistent with many cases of flow failure observed in recent large earthquakes. The relationship between cyclic strength and residual strength is clarified. L'article étudie deux des aspects de la liquéfaction sismiquement induite qui sont d'une importance vitale pour les ingénieurs: les conditions de déclenchement et les conséquences de la liquéfaction. Les conditions de déclenchement sont examinées au travers d'une analyse de la liquéfaction pour laquelle les toutes premières conditions, régies par la résistance cyclique, sont prises en compte. Les conséquences de la liquéfaction sont étudiées à l'aide d'une analyse de stabilité post-sismique pour laquelle la résistance résiduelle joue une rôle primordial. L'on présente les méthodes utilisées pour l'analyse de la liquéfaction fondées sur les résultats d'essais in-situ. L'applicabilité de cette méthode à l'estimation des tassements associés est également discutée. L'évaluation de la résistance résiduelle demande une meilleure compréhension du comportement des sables non-drainés. Les résultats d'essais extensifs de laboratoire sur des sables japonais standards sont étudiés et de nouveaux paramètres sont proposés pour améliorer la quantification du comportement des sables non-drainés. Les résultats obtenus pour des sables argileux sont étudiés de la même façon. Tous ces résultats sont présentés différemment selon que le comportement du sable est contractant ou dilatant. Le critère établi en laboratoire pour des comportements dilatant ou contractant peut s'exprimer en terme de paramètres de chantier tels que N valeurs issues du SPT ou qc valeurs issues du CPT. CPT. Cette corrélation permet de classer les dépôts in-situ comme étant capables ou non de développer un glissement par écoulement. L'article présente également les relations établies en laboratoire entre la résistance résiduelle normalisée et les paramètres de chantier-tels que SPT ou CPT. Ces corrélations sont en accord avec de nombreux cas de rupture par écoulement observés lors de grands séismes récents. La relation existant entre résistance cyclique et résistance résiduelle est clarifiée.
Following disastrous earthquakes in Alaska and in Niigata, Japan in 1964, Professors H. B. Seed and I. M. Idriss developed and published a methodology termed the ''simplified procedure'' for evaluating liquefaction resistance of soils. This procedure has become a standard of practice throughout North America and much of the world. The methodology which is largely empirical, has evolved over years, primarily through summary papers by H. B. Seed and his colleagues. No general review or update of the procedure has occurred, however, since 1985, the time of the last major paper by Professor Seed and a report from a National Research Council workshop on liquefaction of soils. In 1996 a workshop sponsored by the National Center for Earthquake Engineering Research (NCEER) was convened by Professors T. L. Youd and I. M. Idriss with 20 experts to review developments over the previous 10 years. The purpose was to gain consensus on updates and augmentations to the simplified procedure. The following topics were reviewed and recommendations developed: (1) criteria based on standard penetration tests; (2) criteria based on cone penetration tests; (3) criteria based on shear-wave velocity measurements; (4) use of the Becker penetration test for gravelly soil; (4) magnitude scaling factors; (5) correction factors for overburden pressures and sloping ground; and (6) input values for earthquake magnitude and peak acceleration. Probabilistic and seismic energy analyses were reviewed but no recommendations were formulated.
The development of resistance to chemotherapy is a major obstacle for lasting effective treatment of cancer. Here, we demonstrate that endogenous mesenchymal stem cells (MSCs) become activated during treatment with platinum analogs and secrete factors that protect tumor cells against a range of chemotherapeutics. Through a metabolomics approach, we identified two distinct platinum-induced polyunsaturated fatty acids (PIFAs), 12-oxo-5,8,10-heptadecatrienoic acid (KHT) and hexadeca-4,7,10,13-tetraenoic acid (16:4(n-3)), that in minute quantities induce resistance to a broad spectrum of chemotherapeutic agents. Interestingly, blocking central enzymes involved in the production of these PIFAs (cyclooxygenase-1 and thromboxane synthase) prevents MSC-induced resistance. Our findings show that MSCs are potent mediators of resistance to chemotherapy and reveal targets to enhance chemotherapy efficacy in patients.
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