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Sun, Hong ; Miyajima, Masakatsu ; Qiao, Lei
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Setiawan, Hendra ; Serikawa, Yuko ; Sugita, Wataru ; Kawasaki, Hajime ; Miyajima, Masakatsu ; 宮島, 昌克
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金沢大学理工研究域地球社会基盤学系<br />BackgroundEarthquakes in liquefaction-prone areas are frequently followed by the settlement of su
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rface structures due to subsoil liquefaction. This paper aims to study the influence of geosynthetics along with gravel usage to reduce the vertical soil displacement caused by liquefaction using a shake table equipment. This influence is analyzed by means of measuring soil acceleration, pore water pressures and vertical soil deformation due to the shaking process.ResultsResults of a series of 1-g shaking table tests which have been conducted in different initial relative densities which are 50% (loose sand conditions) and 90% (dense sand conditions) to evaluate the performance of proposed mitigation against settlement problem are presented. It is found that ground settlement reduced around 11.4 mm for loose sand conditions, from 20.9 mm in the case with no countermeasure (Case 1) to 9.5 mm in the Case reinforced with gravel and geosynthetics Type II (Case 4). Correspondingly, for dense sand states, the settlement decreased by about 1.8 mm, from 5.6 mm in the Case 1 to 3.8 mm in Case 4. Moreover, a differential settlement between loose sand and dense sand conditions decreased as well, around 9.6 mm, from 15.3 mm in the Case 1 to 5.7 mm in Case 4.ConclusionsBy conducted a series of shake table tests, it is confirmed that the vertical ground displacement decreased by the use of geosynthetics and gravel up to 54% and 32% for loose sand and dense sand states, respectively. Furthermore, test results also show that there is a decrease in the differential settlement between loose sand and dense sand conditions, around 62%.
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Serikawa, Yuko ; Miyajima, Masakatsu ; Yoshida, Masaho ; Matsuno, Kenji ; 宮島, 昌克
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金沢大学理工研究域地球社会基盤学系<br />BackgroundOn September 6th, 2018, at 3:07 local time, a strong earthquake of magnitude Mw = 6.6 s
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truck the east Iburi region in Hokkaido, Japan. Many serious damages such as landslide, liquefaction and collapse of houses occurred from this earthquake. Liquefaction caused road deformation and inclination of houses in Sapporo city, Hokkaido. In order to understand the damage caused by the earthquake, and find a solution to mitigate the liquefaction-induced damage in Sapporo city, a preliminary investigation of the 2018 Hokkaido Iburi-tobu earthquake was conducted from 18 to 20 September 2018.ResultsThe damages to the houses at Satozuka town and Utsukushigaoka town in Sapporo city are focused on. The damage at Satozuka was so enormous that the residents could not continue to live in their houses. Although the inclination of houses can be seen by visual inspection at Satozuka, there were few houses where the inclination can be judged visually at Utsukushigaoka. Therefore we did a field survey of inclined houses by using a digital angle meter at Utsukushigaoka.ConclusionsThe inclination of 57 houses at Utsukushigaoka was measured, and the maximum value and direction of inclination are shown on the map. The houses located at the reclaimed land of the former river and former valley plain were inclined. Therefore, the old terrain greatly affected to the inclination of houses. These liquefaction-induced damage occurred in the same area where liquefaction occurred during the 2003 Tokachi-oki earthquake.
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Setiawan, Hendra ; Serikawa, Yuko ; Nakamura, Mitsuru ; Miyajima, Masakatsu ; Yoshida, Masaho ; 宮島, 昌克
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金沢大学理工研究域地球社会基盤学系<br />BackgroundIn April 2016, Kumamoto City, Japan, and its surroundings were hit by a sequence of str
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ong and devastating earthquakes including two significant events, one on April 14th, 2016, at 21:26 JST (Mw6.2) and the other on April 16th, 2016, at 01:25 JST (Mw7.0). These disasters caused 120 fatalities (including indirect fatalities), 2337 people injured and 177,914 residential houses were damaged. This paper aims to ascertain the damage to residential houses and buildings caused by liquefaction during this earthquake and suggests possible mitigation methods.ResultsField reconnaissance was conducted in the target area on May 27th–30th, 2016. The post-earthquake inclination angle and the tilt direction of 68 affected houses and buildings in the liquefied sites in Kumamoto City were measured by using a laser rangefinder (Leica DISTO D 510). Ground structure and condition were also determined from topographic maps, bore data and the calculated liquefaction resistance factor, FL.ConclusionsBased on this investigation, the inclination angle of the houses in the target area seems to be related to the type of building structure and their foundation as well to the local ground composition. The tilt direction has a tendency to be associated with the location of the nearby river. The results presented could be useful to develop future liquefaction mitigation measures for detached residential houses.
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橋本, 隆雄 ; 宮島, 昌克 ; Hashimoto, Takao ; Miyajima, Masakatsu
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金沢大学理工研究域地球社会基盤学系<br />兵庫県南部地震により宅地擁壁・のり面に甚大な被害を生じたことから、地震直後に被災建物危険度判定士が行う建築物の判定に対し、宅地擁壁・のり面を含む宅地地盤の危険度を判定する被災宅地危険度判定士制度
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ができた。この判定士がはじめて2000年10月の鳥取県西部地震で活躍し、被災宅地の判定を行い十分な貢献をした.しかし,この被災度判定には宅地地盤の被害についての検討が十分になされていなかっため、竹内工業団地を対象にして、被災宅地診断結果と実際の地盤被害状況を比較検討し,今後の宅地地盤被害の判定指標に役立つ知見を明らかにした.<br />第38回地盤工学研究発表会 The 38th Japan National Conference on Geotechnical Engineering
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宮島, 昌克 ; Miyajima, Masakatsu
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金沢大学工学部<br />まず,ライフラインの地震被害の重要な要因の1つである液状化のモニタリングについて検討した.すなわち,液状化地盤と非液状化地盤で観測された強震記録を収集し,液状化地盤における強震記録の特徴について考察した.振幅特性に
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注目し,上下成分と水平成分の比(以下,上下/水平比と記す)の経時変化を求めたところ,非液状化地盤においては水平加速度が最大値を示した後に上下/水平比が小さくなるのに対して,液状化地盤においては大きな値を示すことが明らかとなった.また,周波数特性としてランニングスペクトルに注目し,ランニングスペクトルの全体の体積に占める低振動数領域の体積の比や,卓越振動数の時間変化を評価することにより、液状化地盤の強震記録と非液状化地盤のそれとを区別することが出来た.そこで,これらの3つの指標を組み合わせることにより強震記録を用いた液状化判定方法を提案した.つぎに,液状化センサーなどによって数点での液状化の発生の有無が明らかになったときに,観測点以外の地域の液状化領域の推定方法について検討した.地盤統計学手法の一つであるクリギング法を援用して新潟地震の際の新潟市,日本海中部地震の際の能代市,兵庫県南部地震の際の神戸市臨海部を対象に液状化領域の推定を行い,推定精度の検証を行った.さらに,ライフライン施設の最適モニタリング位置に関して考察を行った.地震時のクリティカルポイントとなりうる箇所の抽出を,地震被害発生時における管路の流量解析を通して明らかにした後に,地震後の緊急対応などを考慮したライフラインネットワークの重要度を評価する手法を提案した.本研究では,各地区の人口のほかに総合病院,指定避難所,特別消防区域などを重要度評価の要因として考慮している.また,本手法を用いて金沢市上水道ネットワークを対象にケーススタディを行った.<br />This study deals with development of hybrid monitoring system of ground motion and lifeline facilities for early detection of their earthquake damage. First, the monitoring of ground failure, especially soil liquefaction was studied because liquefaction was one of the most crucial geotechnical hazards during an earthquake. In this study, strong ground motion records were used for detection of liquefaction. Amplitude characteristics of strong ground motion records were investigated. The time histories of the ratio of vertical ground acceleration to horizontal one was calculated from the strong ground motion records in liquefied and non-liquefied areas. As the ratio increased after the liquefaction occurred, the ratio seems to be one of the indices of detection of liquefaction. Frequency characteristics of the strong ground motion records were also studied. The running spectra and time histories of the predominant fequency of the strong ground motion records in liquefied and non-liquefie d areas were calculated. The decrease rate of the predominant frequency is the one of indices of detection of liquefaction.Next, the methodology for estimation of spatial liquefaction potential was proposed. The method was a geostatistical procedure which was called as Kriging technique using semi-variogram. This method was applied to estimation of liquefied sites by using the data obtained from boreholes at limited sites in Niigata, Noshiro and Kobe cities. The areas where the liquefaction occurred during the 1964 Niigata, 1983 Nihonkai Chubu and 1995 Hyogoken Nambu earthquakes, respectively, could be predicted relatively well.Furthermore, the optimum monitoring sites for lifeline facilities were investigated by case study of Kanazawa city. The critical points of pipeline network were clarified by the flow analysis after an earthquake, then the important sites for monitoring were determined in considering the crucial bases after an earthquake such as a general hospital, shelter, and so on.<br />研究課題/領域番号:08650545, 研究期間(年度):1996-1997<br />出典：「ライフラインの地震被害早期把握のためのハイブリッドモニタリングシステムの構築」研究成果報告書 課題番号08650545(KAKEN：科学研究費助成事業データベース（国立情報学研究所）) 本文データは著者版報告書より作成
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