地盤と地盤環境に関するアジアジョイントシンポジウムに参加して発表-地盤工学問題に関する研究・実務へのより理解を得るための相互意見交換を行う工学研究科 生産システム工学専攻・社会環境デザイン工学科 博士後期・２（派遣期間：平成 24 年 11 月 01 日～平成 24 年 11 月 04 日）高陽

I attended the International Joint Symposium on Urban Geotechnics for Sustainable Development(JS-Seoul 2012) in November 2~3. This symposium promoted the skills of researchers andengineers in the field of geotechnical engineering, and I had a good opportunities to exchange new
information and ideas related to the fields of geotechnical engineering.
１．国際会議の概要
The Symposium was organized by International Committee of Korean Geotechnical Society,Sungkyunkwan University, and Kyushu Branch of Japan Geotechnical Society. The theme of thesymposium is "Urban Geotechnics for Sustainable Development". An intellectually scientifictechnical program will be prepared in consistent with the theme of the symposium. A series of joint
symposiums have been held by Asian countries together with Kyushu branch of JGS: the 1st inShanghai 1997, the 2nd in Hong Kong 1999, the 3rd in Hanoi 2004, the 4th in Dalian 2006 and the5th in Fukuoka 2009. The 6th international joint symposium was held in Seoul.

２．発表内容と成果
道路トンネルにおいて，近年では，供用されているトンネルの長寿命化をはかることが，社会基盤整備において重要な課題となっている．トンネルの長寿命化をはかるためには，適切な時期に適切な対策を施すことが必要であり，その結果，ＬＣＣ（ライフサイクルコスト）やＴＣ（トータルコスト）を低79減することができる．道路トンネルにおいても，供用開始後数十年経過しているものも多く，これらのトンネルにおいては，ひび割れが多く発生している場合が多い．そのため，トンネルの健全度を評価することを目的として，覆工コンクリート表面の状態の変化（例えば，ひび割れ・浮き・剥離等）や漏水などの視覚的評価を主体とする方法が一般的に実施されている．本研究では，常時微動測定に基ずく覆工コンクリートの面的な健全性を評価する手法の開発が進められておりました．まず最初に、波形に対してフーリエスペクトル解析を行った．卓越振動数が健全度の高いスパンほど高い値となっており増した．それから，平均パワースペクトル密度を算出して，その平均値 P によって微動特性を評価した．各測定方向での微動特性を比較するため，それぞれの PSD の平均値 P を算出し，その割合 PD1/PD2 をRPSDD1/D2 と定義した．半径方向において，空洞のスパンの PSD が高くなる傾向が示された．ひび割れの伸張方向において，スパンの PSD が高くなる傾向が示された．今回の研究において，各測定方向および測定箇所の平均 PSD の比をとって相対的に評価することで，覆工コンクリートの健全度との関係性をある程度確認することができた．しかし，覆工コンクリートの健全度を正確に評価するためには，さらに多くのトンネルに対して常時微動測定を行うことにより，その評価確度を高めていくことが必要である．

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Frequency (Hz)80100(a) Sensor C1 in span S1VerticalHorizontalAxial

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Frequency (Hz)80100(c) Sensor C1 in span S3

Figure 1 The normalized PSD analyses (sensor C1)(English abstract) Many tunnels in Japan have been used for several decades, which require
effective inspection methods to assess their health conditions. The lining concrete of tunnels is
usually investigated through visual inspection, which could hardly provide sufficient
information about the inner state of the lining concrete, such as the existence of cracks andcavities. Given that the microtremor characteristics of a concrete structure change with its
damage degree, it may also be used to assess the health condition of lining concrete oftunnels. In this study, microtremors were measured on a tunnel lining in which cracks orcavities exist, and Power Spectra Density (PSD) at the frequency domain and short-time
Fourier transform (STFT) of the acceleration waveforms were calculated and analyzed. The
measurements were carried out on a span with both cavities and cracks (S1), a span only withcracks (S2), and a healthy span without cavities and cracks (S3). The results show that therelation of average amplitude of S1, S2 and S3 is S1<S2<S3, while the predominantfrequency is on the contrary (S1> S2>S3). Therefore, as an initial step, this study gives clear
evidence that the mocrotremor characteristics have the strong relation with the health80

condition of lining concrete, which has the potential to be used for the evaluation of the lining
concrete state in engineering practices.
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Figure 2 RPSD values

３．今後の展望と感想
As a preliminary study, the influences of different types of damages (e.g., cavities andcracks) on the PSD spectrum and vibration intensity were analyzed and were compared fromthe frequency domain and vibration intensity domain. However, it is still difficult toquantitatively evaluate the damage degree based on the current method based on the finite
field measurement. Future studies will focus on estimating the quantitative relation between
the parameters RPSD with the damage degree of the lining concrete. More fieldmeasurements and numerical simulations will also be required to improve this method forengineering practices.

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