Fundamental Research

Fundamental Research in FY 2014

 We are actively working to clarify the principles and phenomena related to tsunamis, beaches, ground, earthquakes,environment, etc. while focusing on fundamental research which yields various knowledge and innovations.

1 Observation of strong motions in port areas and airports followed by compilation and analysis of data
2 Earthquake disaster investigations
3 Development of methods for forecasting strong motions including huge subduction earthquakes considering the non-linear behavior of large ground areas
4 Research on the mechanism and evaluation prediction of liquefaction due to the coupling effect of seismic ground motion
5 Proposal of methods for evaluating the earthquake resistance of pile-type foundation structures and methods of reinforcing them
6 Development of technology for predicting damage to tsunami disaster prevention facilities caused by earthquakes and tsunamis
7 Development of an ocean-earth connection tsunami model
8 Creating databases that link the integrated processing and analysis of oceanographic measurement data to estimated values
9 Investigation, experiment, and analysis for the establishment of a method of measuring the emission and removal of carbon dioxide, and the amount of carbon sequestered in coastal areas
10 Investigation of the wind, high wave, and wave characteristics of catastrophic typhoons in inner bays in Japan
11 Surveys and experiments on the importance of the form and behavior of organisms in the structure of the coastal food webs
12 Full-time continuous monitoring of the environment of closed inner bays followed by statistical analysis
13 Study on settling process of suspended fine particles in estuaries and their modeling
14 Development of methods to predict changes in beach topography taking changes in nearshore currents into account
15 Proposal of testing methods for the strength and compressive properties of cohesive soil in designing port and airport facilities
16 Research on the dynamics of seabed flow and evaluation of the stability of breakwaters and seawalls
17 Research on technologies for improving the ground around existing facilities
18 Research on the durability of steel slag from rotating furnaces for marine use
19 Research on quantifying the improvement of soil properties by classification
20 Evaluation of the long-term durability of concrete, steel,and other materials through exposure tests
21 Improvement of the cathodic protection design of offshore steel structures considering soil properties

Examples of Fundamental Research

Improvement of the cathodic protection design of offshore steel structures considering soil properties

  • The amount of current that flows in the portion of steel structures with cathodic protection under the seabed is difficult to investigate, and therefore has not yet been clarified. To enhance the cathodic protection design, this study measured the amount of current that flows in the portion under the seabed as well as the electric potential of steel members regarding the single pile part of the taxiway for Runway D of Haneda Airport, which has a very deep embedment,and investigated the cathodic protection characteristics of the portion under the seabed (Figure 1.1.2.1).
  • The protective current density in the part under the seabed was far below the design value (Initial value: 20 mA/m2,steady-state value: 10 mA/m2) (Figure 1.1.2.2).
  • The time required to reach the protection state (protective potential of -800 mV) depends on the depth under the seabed.The greater the depth, the longer the time required.However, it was confirmed that the electric potential had reached -800 mV (the protection state had been achieved) in approx. 120 days even at the depth of up to approx. 60 m.
  • We studied the mechanism of cathodic protection under the seabed by an electrochemical technique and confirmed that steel members can be protected even with a protective current lower than the design value due to passivation following the reduction of dissolved oxygen concentration and the rise of pH on the surfaces of steel members over time by constantly supplying protection current, even if it is low.

Figure 1.1.2.1 Piles subject to investigation and positions of measurement

Figure 1.1.2.2 Measured value and analysis value of the distribution of protective current density under the seabed

Ear thquake disaster investigations

  • In surveys of the damage to wharfs due to the Great East Japan Earthquake, depression of the back ground was confirmed even at the wharfs where rock debris was used as back reclamation material and that were considered not to have liquefied. The generation of excess pore water pressure in rock debris during an earthquake has been studied, but the volume change due to an earthquake has not. Therefore,we studied the behavior of wharfs using rock debris as back reclamation material and evaluated the behavior
  • We created a 1/20 scale model of a caisson type wharf and conducted vibration tests using an underwater vibration table. For a wharf using loose rock debris as back reclamation material, the model well reproduced the actual residual deformation. The experiments revealed that the density of rock debris did not significantly influence the caisson horizontal displacement but greatly influenced the amount of depression of the back ground and that the difference was caused by the volume shrinkage characteristics of the rock debris during an earthquake. We also confirmed that excess pore water pressure was hardly generated during an earthquake regardless of the density of rock debris.
  • We tried to reproduce the behavior of wharfs using rock debris as back reclamation material in a model vibration test by numerical analysis (FLIP). We also confirmed the behavior of rock debris during repeated dynamic shearing by separate experiments using a shear soil tank and determined analysis parameters so that the results can be expressed.Using the parameters, we carried out a numerical analysis of the results of model tests for wharfs using rock debris as back reclamation material.The increasing tendency was well reproduced not only for the caisson horizontal displacement but also the depression of the back ground rock debris as well as the non-occurrence of excess pore water pressure.

 

Figure 1.1.2.3 Scene of a model vibration test using an underwater vibration table and comparison of experiment and numerical analysis results

Research on technologies for improving the ground around existing facilities

  • As measures for enhancing earthquake resistance and preventing liquefaction are increasingly applied to port and airport facilities, there is growing demand to apply such measures to existing facilities.To prevent liquefaction, static compaction grouting is frequently applied to the areas just below and around existing facilities. Since such grouting influences peripheral ground, the rate and area of improvement are often restricted due to the existence of objects buried near the target ground, existing structures including floating foundations,and so on. Therefore, the improvement rate is set to a low value and the area of improvement is kept at a distance from existing facilities. However, it is not clear to what extent the improvement rate can be lowered while sufficiently preventing liquefaction and how far the area of improvement should be kept from existing facilities.Thus, this research investigated the relation between the improvement rate of static compaction grouting and the range of influence on the peripheral ground as well as the liquefaction suppression effect.
  • In FY 2014, we investigated the relation between the improvement rate and the effect of improvement by the centrifugal model test method studied in FY 2013. As a result, we confirmed that the rise of excess pore water pressure was suppressed with an overburden pressure of 7 to 8 m even if the improvement rate was lowered to approx. 5% (Figure 1.1.2.4). Therefore,liquefaction can be somewhat suppressed at the depth even with an improvement rate of 5%. Meanwhile, in the case of an improvement rate of 5%, the earth pressure coefficient K lowered even at the depth under the same excitation (Figure 1.1.2.5). Thus, the improvement effect is considered to deteriorate in case of a disaster due to an unexpected earthquake even if there are no signs of significant liquefaction. Since the confining pressure is an important factor in the expression of the improvement effect of static compaction grouting, it is considered necessary to check the confining pressure in case of an unexpected earthquake.

 

Figure 1.1.2.4 Improvement rate and liquefaction suppression effect (400 Gal sine wave × 50)

Figure 1.1.2.5 Change of K value due to excitation (400 Gal sine wave × 50)

Study on settling process of suspended fine particles in estuaries and their modeling

  • It is important to grasp the behavior of muddy sediment in inner bays
    for the maintenance of port facilities, including taking measures against
    sedimentation in waterways and anchorage areas and also for preserving
    the sediment environment. Particularly in inner bays, the quantities
    of sedimentation and accumulation of suspended particles are
    difficult to evaluate because of the variety of sources (earth and sand
    carried by rivers, resuspension of sediments red tide plankton, etc.),
    and the influence of flocculation (condensation of fine particles) under
    the water. This research focuses on such sedimentation of suspended
    particles in inner bays and at the mouths of rivers in order to elucidate
    and model the main phenomena based on on-site observations.
  • In FY 2014, we analyzed the observation data obtained at Niigata West
    Port (the mouth of the Shinano River) to investigate the characteristics
    of sedimentation and accumulation of high-concentration turbid water
    at the mouth of the river at the time of a flood, and then confirmed that
    the fluid mud which moves just above the seabed from the upstream
    accumulated in the dredging area at the mouth of the river. Furthermore,
    we conducted laboratory experiment with circulating flume in
    order to reproduce this phenomenon occurring at the mouth of a river.

 

Figure 1.1.2.6 Fluid mud observed at Niigata West Port after a flood (vertical distribution of the wet density of muddy sediment in the vicinity of the seabed at Stn. B in the figure above (lower left) and a sample of fluid mud (lower right))

 

Photograph 1.1.2.1 Water tank experiment for studying the behavior of turbid water at the mouth of a river

Surveys and experiments on the importance of the form and behavior of organisms in the structure of the coastal food webs

  • It is important to correctly understand the structure and dynamics of food webs for the environmental management, improvement, preservation, and restoration of coastal ecosystems. The purpose of this research is to obtain knowledge to help create good habitats for the environmental management, improvement, preservation,and restoration of coastal ecosystems (including the enhancement of planning and designing techniques) through empirical studies (on-site surveys and experiments) focusing on the influence of the forms and behavior of organisms belonging to coastal ecosystems on the structure and dynamics of food webs.The empirical study is intended to elucidate the factors that determine the structure and dynamics of food webs in coastal areas such as tidal flats and seaweed beds from the viewpoint of ecological dynamics. The output of this research will be used to explicitly formulate the relation between the behavior (feeding and moving) as well as forms (weights and organ sizes) and the feeding habits of such organisms.
  • We collected data on the forms, behavior, and prey organisms of predators through multilateral approaches including sampling, temporarily capturing,photographing, and observing organisms in tidal flats and wetlands in Japan and abroad. We also investigated the environmental conditions such as water and sediment environments, analyzed the forms and feeding behavior from captured images, and conducted rearing experiments concerning the prey selection of birds and the influence on the whole food web.

  

Photograph 1.1.2.2 Scene of a bird-rearing experiment in a tidal flat experiment facility (left) and a photomicrograph of the biofilm on the surface of tidal flat mud, which is a key food source for birds (right)

Creating databases that link the integrated processing and analysis of oceanographic measurement data to estimated values

  • To contribute to port business, the Ports and Harbours Bureau of the Ministry of Land, Infrastructure, Transport and Tourism (the Ministry of Transport before January 2001) established the Nationwide Ocean Wave Information Network for Ports and Harbours (NOWPHAS) with other organizations in 1970, and has observed waves throughout Japan since then (there are 77 points of NOWPHAS wave observation as of March 2015). PARI conducts centralized processing and analysis of oceanographic observation data obtained through NOWPHAS and issues an annual report as a "Technical Note of the Port and Airport Research Institute."
  • In this research, we summarized the oceanographic observation data obtained through NOWPHAS from January to December 2013 (Figure 1), and in FY 2014, started high-precision directional spectrum calculation using observation data of multilayer flow velocity measured with a wave meter (directional wave meter) as well as onsite oceanographic observation using a new type of GPS-mounted wave buoy in the context of joint research with private companies.

 

Figure 1.1.2.7 Example of summarized NOWPHAS oceanographic observation data

 

 

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