New horizons in practical liquefaction prediction and mitigation measures for existing structures
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REVIEW
New horizons in practical liquefaction prediction and mitigation measures for existing structures Shinji Sassa1 Received: 27 May 2020 / Accepted: 19 June 2020 © Springer Nature Switzerland AG 2020
Abstract The paper presents some recent research advances on practical liquefaction prediction and mitigation measures for existing structures. A new simplified generalized liquefaction prediction and assessment method that is capable of considering the influence of the waveforms and durations of earthquakes has been developed. The validity of this method adopting the effective number of waves concept has been comprehensively verified using the case histories of past major earthquakes for the cases of liquefaction and no liquefaction. A unique feature of the new simplified method is its universality, allowing it to be applied to all types of liquefaction charts based on SPT N-values, CPT q-values, and shear-wave velocities. The paper also presents a new compaction grouting that can reduce the ground upheaval quantity, which has remained an issue for more than 50 years, by 80–90%. The new compaction grouting, up-and-down method, has substantially higher efficiency of upheaval/ uplift control and higher efficacy as liquefaction countermeasures around existing structures. Keywords Liquefaction · Prediction · Compaction grouting · Earthquake · Structures
Introduction Liquefaction prediction and assessment is a vital part of the earthquake-resistant design of structures on/around liquefiable soils. Liquefaction can not only cause major damages to facilities that include underground structures but also give rise to concurrent phenomena such as landslides and tsunamis. Indeed, in the 2018 Indonesia Sulawesi earthquake and tsunami disasters, the cascading mechanisms of liquefaction, landslides, and tsunamis resulted in more than 4000 fatalities [1, 2]. Liquefaction prediction and assessment charts, originally developed by Seed and Idriss [3], have been widely used for such design in practice, as well as for disaster prevention and mitigation. The liquefaction charts commonly represent the relationships between the severity of earthquake loading defined in terms of the cyclic stress ratio versus the soil liquefaction resistance represented by the field measured values such as the SPT N-values from standard penetration tests * Shinji Sassa [email protected] 1
Port and Airport Research Institute, National Institute of Maritime, Port and Aviation Technology, 3‑1‑1 Nagase, Yokosuka 239‑0826, Japan
[4–9], the CPT q-values from cone penetration tests [9–12], and the shear-wave velocities Vs [12–14]. All these charts shear the basic principle and important characteristics and have been calibrated for cases of liquefaction and no liquefaction at given sites. Earthquake motions at given sites generally have different waveforms and durations that vary considerably in space and time. This stems from the fact that earthquake motions depend strongly on the characteristics of the sites, the seismic-wave propagation routes, and
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