Soil Liquefaction and cyclic mobility for level ground during earthquakes
It is shown that the design engineer has two basic choices if he considers it appropriate to neglect the possible effects of drainage occurring during the period of cyclic stress applications: (1)To calculate the stresses induced in the ground by the design earthquake, and to compare these stresses with those required to cause cyclic mobility or liquefaction of representative samples in the laboratory. The main problem in this approach lies in correctly assessing the characteristics of the in-situ deposit from laboratory tests performed on even good quality undisturbed samples. (2)to be guided by the known field performance of sand deposits correlated with some measure of in-situ characteristics, such as the standard penetration test. In some cases it is desirable to evaluate the possible effects of pore pressure dissipation in different layers of a deposit during and following earthquake shaking. Methods of accomplishing this are reviewed and described.
Available from: Mohammad M. Ahmadi
- "For this modification, there are different relationships. Equation 5 is one of the most common methods provided bySeed et al. (1979), and is used in this study. "
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ABSTRACT: Several methods have been used for the evaluation of liquefaction potential, among which the simplified method is mostly used. In this method, which is mainly based on standard penetration test (SPT), cone penetration test (CPT) and shear wave velocity (Vs) measurement, a boundary curve is provided to separate the liquefiable and non-liquefiable soil zones. Vs measurement is a good alternative method of penetration-based methods (SPT and CPT). This is especially true in micro-zonation of liquefaction potential. Although relatively large studies have been carried out to establish the correlation between Vs and liquefaction resistance for sands; there are uncertainties about the effects of non-plastic fines on the correlation. The objective of this research is to study the effects of fines on the correlation of Vs and liquefaction resistance. In this regard, the cyclic triaxial and bender elements tests have been performed, and Vs and liquefaction resistance of a clean sand and four combinations of this sand with non-plastic fines up to 25% have been measured. A simple, semi-empirical, semi-analytical method is proposed to establish a correlation between Vs and liquefaction resistance. The effects of non-plastic fines on Vs and liquefaction resistance of silty sands have been examined in this study, and the effects of non-plastic fines on the correlations between these two parameters are considered. The results in this study show that an increase in the ratio of silt to sand will result in a decrease in Vs and liquefaction resistance. Based on these results, it is argued that the correlation between Vs and liquefaction resistance of various combinations of sand and non-plastic fines are soil specific. Also based on the results of this study, it is found that the existing methods of liquefaction potential evaluation which are based on Vs may underestimate or overestimate the liquefaction resistance of silty sands.
- "A historical soil liquefaction hazard, such as an upset and an uneven settlement of a reinforced concrete building, occurred during the Niigata earthquake in 1964 (Niigata Local Meteorological Office 2014; Japan Association for Earthquake Engineering 2009). The importance of the foundation and underground soil was recognized, and the research and development of countermeasures against soil liquefaction were promoted worldwide (Castro 1975, Castro andPoulos 1977;Seed 1979;Tokimatsu and Yoshimi 1984;Idriss and Boulanger 2008;Elgamal et al. 2009). To mitigate soil liquefaction hazard, many assessment methods were proposed in terms of soil liquefaction potential; the energybased intensity measure is one such useful assessment measure (Jafarian et al. 2014). "
Available from: Gabriele Chiaro
- "However, an alternative approach to use field data is to use laboratory data. In fact, the cyclic resistance from triaxial tests (CSR tx ) can be converted to field values using the following expression proposed by Seed (1979) "
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ABSTRACT: A site investigation program was undertaken in Chiba (Japan) to evaluate the undrained cyclic strength properties of two sandy soils (Holocene and landfill deposits), which is believed to have experienced liquefaction during the 2011 Off the Pacific Coast of Tohoku Earthquake. In this regards, the application of advanced sampling technology was crucial for obtaining high quality undisturbed samples, as soil fabric and ageing effects would be significant. This paper examines the quality of undisturbed samples which were taken by " Gel-push " (GP) sampling using comparisons between dynamic shear moduli directly evaluated in-situ (downhole) and those measured in the laboratory on undisturbed triaxial samples extracted by both GP and conventional triple-tube sampling (TB) techniques. Preliminary results are presented endorsing the ability of the GP sampler to achieve higher quality samples suitable for liquefaction strength testing compared to the TB sampler.
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