Estimation of the methods to reduce the level difference generated in backfill of abutment using model tests


Earthquakes have frequently occurred in Japan. As a result, level difference was generated by the ground subsidence in backfill of abutment. That is an obstacle to rescue the victims and to transport the relief supplies during disasters. Although the concrete approach cushion is superior for preventing the level difference, continuous ground settlement due to consolidation and occurrence of liquefaction have been concerned because of its weight.
Therefore, objective of the present study is to propose a new approach cushion which overcome weakness of the existing method. Moreover, several countermeasures against level difference were compared considering ground subsidence and passage of traffic in the model tests of 1/20 scale.
°»Cross Wave°…, which is precast product with light weight, flexible and easy construction, has been chosen as the material for new method. Young°«s modulus was estimated as 1011 kN/m2 from the bending test using the Cross Wave. For the model test, urethane of yellow color whose Young°«s modulus is 61 kN/m2 was chosen considering similarity rule of 1/20 scale. Urethane of black color whose Young°«s modulus is 116 kN/m2 was also used for comparison in the model test.
The results of the model test describe that the concrete approach cushion was most effective to reduce the level difference. However, the Cross Wave was also effective as compared with the ground without countermeasures. The passage ability of traffic was estimated using the settlement of prototype scale. According to the reports of the Chuetsu and Chuetu-oki earthquakes, the level difference of abutment was mostly about 50 cm. From the results of the model test, the traffic can pass the road with the countermeasures using urethane of yellow color under even 60 cm settlement conditions. The passage ability was expanded by using urethane of black color, which have twice Young°«s modulus of yellow urethane.
As described above, the results of the model test have led to the conclusion that the Cross Wave is practically effective for the countermeasures against level difference of abutment.

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