Study of Ground Treatment on Improvement of Pile Foundation Response in Liquefiable Soils
Résumé
In light of the disastrous the 2011 Tohoku Pacific Earthquake, the government of Japan has conducted studies to revise the seismic design code, and elevated peak ground accelerations have been adopted. Consequently, revisions on existing design to comply with the updated code are required for public projects that are still undergoing. The design safety needs to be reassessed, and implementation of strengthening measures is required if deemed necessary. For liquefaction countermeasures, ground treatment techniques that could increase the density of soils are often the preferable alternatives. The treatment usually increases the in-situ SPT-N or CPT-qc values, which in turn would increase the resistance of soil against liquefaction. For many public infrastructures in Japan supported by bored piles embedded partly or entirely in sandy soils, reevaluation of design safety against soil liquefaction would be required. In an assessment of possible retrofitting countermeasures for an infrastructure foundation, ground treatment has been considered. In this case study, effect of ground treatment on response of piles in liquefiable soils was investigated with numerical analyses using FLAC. Results provide insights into this ground treatment effect and useful information for consideration in future design or decision making. Introduction. The 2011 Great East Japan Earthquake, with a magnitude of Mw=9.0, occurred in the Pacific Ocean about 130 km off the northeast coast of Japan's main island on March 11, 2011. The hypocentral region of this quake was about 500 km in length and 200 km in width. The quake was followed by a huge tsunami that destroyed many cities and killed and injured many people along the Pacific Coast. The numbers of dead and missing persons as of July 11, 2012 were 15867 and 2909, respectively. The tsunami broke the emergency cooling system of a nuclear power plant in Fukushima Prefecture, and large areas of Japan have been plagued by radiation and a shortage of electricity ever since. In the geotechnical field, many houses and lifelines were damaged by soil liquefaction, landslides occurred, dams failed and river dikes settled not only in the Tohoku district of northeastern Japan, but also in the Kanto district, which surrounds Tokyo. Liquefaction occurred over a wide area of reclaimed lands along Tokyo Bay, although the epicentral distance was very large, about 380–400 km. During the 2011 off the Pacific Coast of Tohoku Earthquake, soil liquefaction caused extensive damage to residential lands and houses, as well as to infrastructures, such as roads, rivers, ports, and water supply/sewage systems, over a wide area along the Pacific Coast in Tohoku and in Kanto, including the Tokyo Bay area. Due to the large fault zone, the duration of the strong shaking was extremely long. According to Tokimatsu et al. [1], liquefaction induced damages in Urayasu City such as sand piping on ground surfaces and significant ground subsidence resulting in buildings settlement, tilt, and lateral movement from 3cm to 45cm, 2 to 3, and 1 cm to 20cm, respectively, were recorded.
Domaines
Sciences de l'environnement
Origine : Accord explicite pour ce dépôt
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