Abstract:

There was an unsupported underground tomb very close to the foundations of the bridge along Gushikawa By-Pass roadway. The effect of constructing bridge piles on the nearby underground tomb was a concern to the owner of the tomb. As a result, the authors were asked to check the effect of the construction on the tomb utilizing various non-destructive testing techniques and multi-parameter monitoring scheme. The authors describe an integrated study on the response of underground tomb undertaken before and during and after the construction of bridge piles. The authors describe the outcomes of laboratory test, in-situ explorations, rock mass evaluation, numerical analyses and multi-parameter monitoring undertaken in this study and discuss their implications. By virtue of this integrated study, it was possible to construct the bridge foundations without any harming effects on the underground tomb.

1 Introduction

The use of unsupported cavities as tombs was quite common in Okinawa Prefecture, Japan. Some of them are still used tombs and there was a case that an unsupported underground cave was very close to the foundations of the bridge along Gushikawa By-Pass roadway. The owner of the cavity was extremely worried for the stability of the cavity during the construction of the bridge piles having end-bearing on the phyllite formation below the Ryukyu limestone formation. The authors were asked to check the effect of the piles on the response and stability of the underground cavity, which was excavated about 400 years ago, during the construction process. Various laboratory on rock samples, in-situ explorations, seismic wave propagation studies and multi-parameter monitoring system to measure AE and displacement together with environmental monitoring and strong motion measurements were utilized to investigate the effect of pile construction on the nearby unsupported underground cavity. The new Rock Mass Quality Rating (RMQR) was utilized to characterize the surrounding rock mass. Furthermore, 2D elasto-plastic finite element simulation were also performed to check the stress changes and deformation response in relation to the construction stages. The authors will explain the outcomes of this unique integrated study on the response of unsupported undergound cavity to the nearby construction of piles of Gushikawa By-Pass Bridge. It will be also shown that various laboratory on rock samples, in-situ explorations, seismic wave propagation studies and multi-parameter monitoring system and strong motion measurements were quite effective to evaluate the effect of pile construction on the nearby unsupported underground cavity.

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