1A.Research on Seismic Disaster Prevention and Restoration

Background and Objectives

  • To counter large-scale disasters including Nankai megathrust earthquakes and earthquakes in the greater Tokyo area, the following countermeasures are required: securing trunk line cargo transportation soon after an earthquake and quickly securing the transportation of key emergency supplies for recovery and reconstruction hubs. In addition, the interaction of earthquakes, tsunamis, and high waves with the ground might cause coastal disasters, so it is necessary to reduce such risks.
     
  • Therefore, the themes of this research cover research and development which simultaneously achieves the two goals of improving quake resistance and reducing construction costs. These two goals can be achieved through diagnosis and performance verification of earthquake-resistance which address the properties of long-period and long-duration earthquake ground motion, which is expected to occur during a subduction- zone large-scale earthquake, as well as the properties of earthquake ground motion caused by local ground characteristics. Research and development are being conducted mainly on methods for investigating and diagnosing earthquake resistance as well as construction methods that improve the resistance, while using existing facilities with limited design life erected during the era of rapid economic growth.

Research topics

 Research and development comprises the following three subthemes:

  1. Development of techniques for predicting strong ground motions and damage which may occur in the case of the greatest earthquakes
     Subduction-zone megathrust earthquakes may cause the greatest and long-duration earthquake motions, so we will develop techniques for predicting such motions. Also, we will develop techniques for predicting liquefaction and structural damage caused by such motions.
     
  2. Research on damage-reduction techniques against the greatest earthquakes
     We will suggest the most effective countermeasures under given limitations to effectively promote seismic strengthening of existing structures. In doing so, we will actively utilize damage reduction and strengthening techniques that use novel materials, structures, and construction methods. Especially, as quake-resistance countermeasures for industrial complexes, we will consider maintaining the functions while reducing costs for overall plants, and then develop investigation, diagnosis and countermeasure techniques which minimize usage limitations. In addition, we will develop testing methods to rapidly evaluate damage levels on site immediately after a disaster as well as emergency restoration techniques.
     
  3. Research on the interaction of earthquakes, tsunamis,and high waves with ground dynamics
     We will conduct research on the interactions of earthquakes and ocean waves with the ground dynamics, including seabed liquefaction at the time of earthquakes and due to wave actions; the mechanism of the instability of breakwater foundation at the time of a tsunami; and other interactions. Also, we will use numerical simulation models, model experiments (including a centrifuge equipped with a tsunami generator and a large-scale wave tank), and other methods to investigate ground dynamics regarding earthquake-induced submarine-landslide development and the resulting tsunami phenomena, as well as geodynamics under the influence of tsunami and high waves. The research will include the analysis of deformation and destruction mechanisms as well as their countermeasures.

Activities in FY 2016

  • We obtained 2488 strong motion earthquake records during the period from January to December 2015.
    We organized and analyzed these records and published the data as a Technical Note of the Port and Airport Research Institute data.
     
  • Regarding the Kumamoto earthquake in April 2016, we dispatched investigation teams to Kumamoto Port, Kumamoto Airport, Beppu Port, and Yatsuhiro Port to study the damage situations and causes, and then we used the information for technical assistance including restoration activities. In addition, we devised countermeasures against large-scale disaster factors for sheet pile-type quay walls in the 2011 Great East Japan Earthquake.
     
  • In response to the Kumamoto earthquake in April 2017, we estimated the rupture processes of the earthquake source faults, analyzed strong-motion earthquake records near an earthquake source, and developed an earthquake source model to estimate earthquake motions of ports and airports where such records were not obtained.
     
  • We conducted various experiments and analyses regarding liquefaction under combined earthquake motions and summarized the liquefaction characteristics and mechanisms, as well as their prediction and evaluation. We developed a generalized liquefaction prediction and assessment method that is capable of simultaneously considering the irregularity of the waveforms and durations of earthquakes and that can be applied to various simplified methods used overseas, thereby facilitating more rational liquefaction prediction and assessment worldwide.
     
  • We studied whether pier structures can survive after deformation due to an earthquake in terms of general stability, and then organized data for evaluating the aseismic capacity of existing piers. For example, we suggested a model to quantify changes in the plate thickness and yield strength of steel pipes.
     
  • We used E-Defense, a large shake table owned by the National Research Institute for Earth Science and Disaster Resilience (NIED), to conduct a model vibration-table test of 1/8-scale oil tanks, piers, and revetment in an industrial complex. In the test, we created two models, cross sections with or without earthquake countermeasures, and then conducted a comparative study.
     
  • We validated the results predictions by the proposed model regarding the process of development of submarine landslides and gravity flows in light of the latest event of submarine mass movement induced by seabed liquefaction. In addition, we elucidated the mechanism of destabilization of breakwaters, rubble mounds, and foundation caused by the coupling effect of overflow and seepage under a tsunami. We also established a method for evaluating the stability of breakwater foundations under tsunami-induced seepage.

 

Peak slip velocity distribution on the fault plane during the 2016 Kumamoto earthquake (unit: m/s)
Red areas represent areas with greater slip velocity
(i.e., areas where especially strong earthquake waves were generated).
★ represents destruction initiation and arrow marks represents destruction order.

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