関口 徹

Static load increment analyses were carried out for the investigation of the cause that the damage of piles occurred in Chiba prefecture during the 2011 off the Pacific Coast of Tohoku Earthquake. <br>Results similar to the real damage was obtained, using an analysis models considering the nonlinearity of piles, pile head connections and soil springs and assuming progress of graded destruction and distribution of axial loads.

 The objective of this study is to examine the concrete filled effect in the hollow part of SC pile in order to improve the deformation performance of pile. In the pile foundation structure, the improvement is prompted, assuming secondary seismic design. But, Study on the deformation capacity of precast concrete pile is not sufficiently advanced. The bending tests of plie are carried out on a daily basis for performance assessment. The purposes of the test is the confirmation of the flexural strength. Therefore, the test data accumulation is not enough to discuss the deformation performance of pile.<br> This study focuses on the SC pile in precast concrete pile. The SC pile is a cylindrically shaped member manufactured by centrifugal casting with concrete placed in the hollow section of a steel pipe. The SC pile is a composite pile that utilizes the merits of concrete with good resistance against compressive forces and steel shell with good resistance to tensile forces. Concrete prevents local buckling of the steel pipe, while the steel pipe constrains concrete; therefore, the SC pile has excellent flexural bearing capacity and deformation capacity.<br> This study examined effects of some parameters for deformation performance of the SC pile by the simple beam bending test. Four parameters are set for the test. The parameters are 1) Loading method, 2) Steel pipe thickness, 3) Axial force, 4) Infilled material. We observed the failure conditions, relations between the load and the displacement, and relations between the bending moment and the curvature.<br> The knowledge obtained from this study are shown below.<br><br> 1) Reinforced by infilling the hollow part of the pile with material, the following effects can be expected: prevention of depression of the steel pipe, prevention of flaking or crush of the pile body concrete, and improvement of the bending deformation performance of the pile. It is more effective to use infilled material with high Compressive strength and high Elastic modulus.<br><br> 2) The results of bending tests of piles, maximum flexural strength and maximum curvature, are influenced by loading method. The results obtained by the one-way cyclic loading are greater than those obtained by the peak-to-peak alternate cyclic loading. Test value obtained by the one-way cyclic loading is on dangerous side as the evaluation of the deformation performance of the pile. Therefore, it is desirable to adopt the peak-to-peak alternate cyclic loading for appropriate evaluation of the deformation performance of the pile.<br><br> 3) It is effective to increase the thickness of the steel pipe for the improvement of the flexural strength of the pile. But, it is not effective to increase the thickness of the steel pipe for the improvement of the deformation performance of the pile.<br><br> 4) With respect to the maximum value of curvature, the test value of the standard specimens is not more than the analysis value. The test value of the test specimen that was reinforced with soil cement is about equivalent to the analysis value. The test value of the test specimen that was reinforced with concrete is greater than or equal to the analysis value.

2011年東北地方太平洋沖地震により，東京湾岸に位置する千葉県浦安市では液状化現象で戸建住宅などの建築物やライフライン等に甚大な被害が発生した。浦安市内の被害が大きかったエリアにおいて，地震後にボーリング，サウンディング等の地盤調査を実施して，土質構成および土質特性を詳細に把握した。その結果，埋立砂質土層および沖積砂質土層の一部で土砂の噴出を伴う液状化が生じ，建築物やライフライン等が被災したことを確認した。本稿では，これらの液状化被害が生じた地盤の情報をできるだけ詳細に記述するとともに，表層地盤の土質特性および埋め立て時の排砂管吐出口の位置と建築物や下水道施設の液状化被害との関係を考察した。また、繰返し非排水三軸試験から得られた液状化抵抗比を求めた結果，原位置試験と土の物理特性から得られる液状化抵抗比と良く整合した。

In 2011 the Great East Japan Earthquake, many buildings prevented continued use by damage of foundation in spite of minor damage of superstructure. For continued use of buildings, seismic performance of foundation is important, not just seismic performance of superstructure. In this paper, I will report a case assumed that pile damage is caused by complicated dynamic characteristics of superstructure, and a study of the case used microtremor measurement, ARX model, and multi-degree-of-freedom system.

本研究では千葉県内の自然斜面及び、切土施工によって表面の軟弱な地盤を切り取った切土斜面を対象とし、それぞれの震動特性の評価を行った。斜面の法肩部と台地上の平坦な部分に地震計を設置し地震観測を行ったところ、自然斜面法肩部で地震動が大きく増幅していることが確認できた。そこで、地盤調査の結果に基づき地盤構造をモデル化し、2次元FEMを用いた動的解析による伝達関数の計算を行った。その結果、1次元解析では再現できない自然斜面法肩部での増幅特性を2次元解析で再現でき、斜面形状だけでなく台地端部表層の軟弱層が地震動を大きく増幅させることを確かめた。

著者らは、既存杭の活用も考慮した杭頭応力低減方法として、杭頭と基礎底面を完全に切り離した「杭頭絶縁基礎」という新しい基礎工法を提案しており、1/10スケールの構造物模型による実地盤での地震観測を行っている。本報告では、一連の現場模型実験から得られた地震記録を基に三次元有限要素法によるシミュレーション解析を行い、杭頭絶縁基礎の地震時応答特性を評価した。その結果、杭頭絶縁基礎は杭頭応力のみならず、直接基礎および杭基礎と比べて構造物の応答を抑制する効果があることが確認できた。

大規模に宅地造成が行われた千葉市おゆみ野地区、八王子市多摩ニュータウンの一部の地区を対象に、微動単点観測と表面波探査を行った。さらにおゆみ野地区については多数のボーリングデータをもとに25mメッシュ単位での表層地盤モデルを作成し地震応答解析を行い、微動や地震観測記録と比較するなどにより同地区の地盤震動特性の検討を行った。その結果、盛土地盤における微動H/Vスペクトルの卓越周期は、造成前の谷地形に軟弱層が堆積していない場合は盛土厚と高い相関が見られた。一方、谷津のような腐植土等の軟弱層が谷地形に堆積している場合は、軟弱層の影響を大きく受けるため微動H/Vスペクトルの卓越周期と盛土厚との相関は低かった。よって、宅地造成された地盤での地震動特性には、造成前の地盤種別や地形分類が大きく影響すると考えられる。

 The authors carried out static analyses using a foundation structure model in order to simulate the process leading to distinctive damage of pile foundations during the 2011 off the Pacific coast of Tohoku earthquake. Remarkable points of the proposed method were evaluation of nonlinear load-deformation characteristics of pile element and rotational stiffness at pile head depended on axial force and formulation of nonlinear behaviors of soil spring including group pile effect. Results obtained from the analysis in two stages to the process to failure of piles for each loading direction explain fairly well the actual damage of pile foundations. The proposed method can be considered as a practical seismic design method of foundations for severe earthquakes.

The 2011 moment magnitude (M-w) 9.0 Tohoku-Oki Japan earthquake occurred in a region where giant megathrust earthquakes were not expected. This earthquake proved the difficulty in assessing seismic hazard by relying mainly on information from historical and instrumental seismicity. To help improve the seismic-hazard assessment for such rare events, we propose a methodology to estimate the slip distribution of future megathrust earthquakes based on a model of interseismic coupling distribution in subduction margins, as well as information of historical earthquakes, and apply the method to the central Peru region, Lima. The slip model obtained from geodetic data represents the large scale features of asperities within the megathrust, which is appropriate for simulation of long-period waves and tsunami modeling. For the simulation of a broadband strong ground motion, we add small scale heterogeneities to the source slip to be able to simulate high frequencies. To achieve this purpose, we propose broadband source models constructed by adding short-wavelength slip distributions obtained from a Von Karman power spectral density function, to the slip model inferred from interseismic geodetic data. Using these slip models and assuming several hypocenter locations, we calculate a set of strong ground motions for Lima and incorporate site effects obtained from microtremors surveys and geotechnical data. Our simulated average pseudospectral accelerations (period 0.3 s) are above 1.5g for wide areas in Lima, which may be critical in terms of damage of low-to midrise masonry and reinforced concrete buildings, which characterize the majority of buildings in Lima.

We estimate several scenarios for source models of megathrust earthquakes likely to occur on the Nazca- South American plates interface in southern Peru. To do so, we use a methodology for estimating the slip distribution of megathrust earthquakes based on an interseismic coupling (ISC) distribution model in subduction margins and on information about historical earthquakes. The slip model obtained from geodetic data represents large-scale features of asperities within the megathrust that are appropriate for simulating long-period waves and tsunami modelling. To simulate broadband frequency strong ground motions, we add small scale heterogeneities to the geodetic slip by using spatially correlated random noise distributions. Using these slip models and assuming several hypocenter locations, we calculate a set of strong ground motions for southern Peru and incorporate site effects obtained from microtremors array surveys in Tacna, the southernmost city in Peru.

A currently populated slope in the northeast part of the city of Lima was selected as the target area of this study, with the aim of analyzing the influence of topography on its seismic response. A finite element model was constructed using soil information obtained by microtremor arraymeasurements conducted in flat and sloping areas, and solved for plain strain conditions in the time domain using an input motion developed for the most critical slip model of a simulation for megathrust earthquakes. Results showed that for this typical rocky slope, topographic effects do not have a significant influence on its seismic response, except for areas close to the foot of the slope where, even if soil vibration is restricted, an amplification of the seismic motion is still expected for short period structures.

During the last fifty years, the city of Lima has experienced an immigration process that has led to the urbanization of the Andean foothills surrounding the capital. With the aim of analyzing the dynamic response of these new populated places, a target area in a district called Independencia is chosen. Seven microtremor array measurements are carried out at different points on the flat level and along the slope in order to evaluate the variation in the depth of the bedrock. In addition, a seismometer is installed on the slope with the objective of determining if amplification due to topography exists in the area of study.

In order to evaluate effects of soil structure interaction on characteristics of traffic vibration propagation to buildings with different foundation type, vibration test was conducted to existing buildings with spread foundation and pile foundation from outside. Based on the results, simple evaluation technique for response of building foundation by ground surface point excitation using thin layer method supposing that traffic vibration derives from surface point excitation. It was shown that effect of soil structure interaction of pile foundation is more predominant than that of spread foundation at low frequency range.

This study investigates the possibility of acceleration of finite element method (FEM) using graphics processing unit (GPU). GPU is a cluster of processors specialized for image processing. In recent years, GPU’s computing power for simple calculation becomes higher than CPU’s. The use of GPU is quite common in finite difference analysis. Application of GPU to FEM, however, is considered difficult from the viewpoint of large amount of memory access. In this study, an attempt is made to introduce GPU computing to FEM in terms of frequency response analysis of two-dimensional wave propagation problem.

In order to create a soil amplification map for Lima, Peru, parameters that correlate best with amplification are examined. Shallow shear wave velocity profiles estimated from MASW measurements at 105 sites were used to provide amplification factor AvTF. AVs10 seems to be the best value for estimating amplification in Lima from the data available. We have attempted to create AVs10 map correlating three parameters - elevation, H/V peak period, and soil type. From this AVs10 map, we have estimated an amplification map for Lima.

The estimation of the shear-wave velocity profile in Lima, Peru, was originally performed through surface wave observation in microtremor arrays. In the observation of these surface waves, a low signal problem for long periods was identified that resulted in a poorly done correlation between signals recorded by sensors and, consequently, in difficulty obtaining deep velocity profiles with good resolution. As an alternative, surface wave observation from seismic records was proposed. To confirm the feasibility of this methodology, seismometers were installed in an approximately circular configuration on the campus of the National University of Engineering in Lima. The procedures used to carry out analysis are similar to those used when analyzing microtremor arrays, with the exception that only the coda of seismic records is used for analysis. Results show that the dispersion curve obtained from seismometer arrays agree well with dispersion curve obtained from microtremor arrays and are predominant in a large period range. Finally, the estimated profile is verified using the observed H/V spectrum.

東北地方太平洋沖地震による千葉市美浜区での液状化被害の分布には著しい偏りが見られた。本研究では，被害の不均一性を明らかにするため，表層地盤モデルの構築，地震応答解析，埋立造成履歴調査，常時微動観測，および，地盤調査を行った。その結果，全域が埋立地である美浜区の表層地盤構造は非常に複雑であり，地点ごとに土層中の砂質土層のせん断ひずみが大きく異なることが液状化被害分布の不均一性の主たる要因であることが分かった。また，狭い範囲で地盤構造が大きく変化するのは，埋立造成時のサンドポンプ工法の排砂管とその噴出口の位置が大きく影響している可能性があることを示した。<br>

東北地方太平洋沖地震で千葉市美浜区において生じた液状化被害への表層地盤構造とその地震動増幅特性の影響を検討するため、微動・地震観測を行った。そして多数のボーリング資料に基づき同区をメッシュ状に分割した表層地盤S波速度構造のモデルを作成した。推定されたS波速度構造は既往のPS検層の結果と調和的な結果となり、モデルから得られる地盤の固有周期は観測記録の微動H/Vスペクトルの卓越周期と良い相関が得られた。区内で観測された本震記録から工学的基盤波を求め、地盤モデルに対して等価線形解析を行った。その結果噴砂の被害分布と解析から得られた砂質土層の最大せん断ひずみの分布は調和的な結果となった。

長周期地震動は時として長大構造物に深刻な影響を及ぼす。地震動は、地盤構造に依存するいわゆるサイト特性が大きく関係するため、特にS波速度構造の詳細な把握は重要課題の一つとなっている。本研究では、千葉市を対象に、多数の地震計を用いたアレイ観測および微動アレイ観測により、主として深部の地盤構造を明らかにすることを目的としている。本報では、東北地方太平洋沖地震およびその余震を含む複数の地震記録を用いた観測結果、および、異なるサイズの微動アレイ観測から位相速度分散曲線を求め、これらが無理なく連続することを確認した上で逆解析を実施し、対象地域におけるS波速度構造の推定を行った。得られた結果は既往の研究結果とおおむね整合するものとなったが、一部深度において既往のS波速度をやや上回る可能性が示唆された。

南関東地域において微動の長期連続観測を実施し, 地震波干渉法に基づくデータ処理によって２観測点間のグリーン関数の表面波成分の抽出を試み, 既往の深部地盤モデルの検証のための基礎的検討を行った。同地域の16地点における１年間以上の微動連続観測データを用いた地震波干渉法に基づく処理を行い, 周期２～６秒の帯域での相互相関関数を求めた。地震記録と比較することによって, 絶対振幅を議論しなければ, 得られた相互相関関数は地震記録の表面波と波形の山谷がよく一致しており, 地震波干渉法によって微動データからグリーン関数の表面波成分を抽出できることを実証的に確認した。得られた相互相関関数のマルチプルフィルター解析によって, 表面波の群速度の推定を得た。既存の深部地盤のS波速度構造モデルに対する理論値と観測値の比較を行った結果, 関東平野内部や相模湾の多くの地点では, 群速度の理論値と観測値がよく一致していた。しかし, 既存のモデルで地震基盤が露頭していると仮定されている伊豆半島や関東山地では, 観測された群速度は理論値よりも小さく, この地域のモデル修正の必要があることがわかった。これらの結果から深部地盤モデルの検証に地震波干渉法が有効に活用できることがわかった。<br>

H/V spectral ratio of microtremor is used to estimate dynamic properties of the soil by applying a theory based on a horizontal layer assumption. It is often the case, however, that there exists an irregularity such as a slope in reality. Characteristics of H/V ratio of such an irregular ground are not well understood. In this study, H/V ratio of an irregular ground with a slope has been examined through microtremor measurements and 2-D finite element analysis. Comparison between those results shows that the characteristics of H/V ratio change drastically due to the influence of landform and soil structure irregularity.

斜面が洪積台地の地震動増幅特性に与える影響を把握するために、斜面近傍地盤の地盤調査、地震観測、2次元有限要素法解析を行った。地盤調査結果に忠実な斜面沿いに軟弱な層が分布する地盤モデルと、軟弱な層が分布しない地盤モデルにより、有限要素法解析を行った結果、軟弱な層が分布することによる地盤増幅効果は非常に大きいが影響範囲は狭く、斜面の形状に起因する地盤増幅効果はそれほど大きくないものの遠方に及ぶことが判明した。さらに、斜面による地震動増幅の要因である反射波の分布を把握し、斜面の影響が遠方に及ぶ原因は斜面での表面波の生成にあるが、表面波が優勢になると地盤増幅も小さくなることを確認した。

In this paper, the results of PS-logging conducted in Chiba city and the northwest area of Chiba prefecture are used to estimate S-wave velocity of the surface ground. This area consists of diluvial formation, alluvium and filling soil. Based on the regression analysis, expressions that give S-wave velocities of sandy soils and cohesive soils from SPT <i>N</i>-values and depth are proposed, as well as standard values of S-wave velocities for humic soil(peat) and Kanto loam.

Effects of nonlinear properties of surface soil on the variation in strong ground motion and damage to wooden houses within Ojiya city during the 2004 Mid Niigata Prefecture earthquake, are examined, based on field investigation including boring and microtremor measurements, as well as strong motion observation. It is revealed that the maximum response of wooden houses, i.e., damage level, could mainly be controlled by strong ground motion with a period of about 1-2 s. Such a period range was significantly amplified in the damaged sites due to strong soil nonlinearity while it was not in the slightly damaged sites due to week soil nonlinearity.

The December 26, 2004 Sumatra-Andaman earthquake that registered a moment magnitude (M-w) of 9.1 was one of the largest earthquakes in the world since 1900. The devastating tsunami that resulted from this earthquake caused more casualties than any previously reported tsunami. The number of fatalities and missing persons in the most seriously affected countries were Indonesia 167,736, Sri Lanka - 35,322, India - 18,045 and Thailand - 8,212. This paper describes two field visits to assess tsunami effects in Sri Lanka by a combined team of Japanese and Sri Lankan researchers. The first field visit from December 30, 2004 - January 04, 2005 covered the western and southern coasts of Sri Lanka including the cities of Moratuwa, Beruwala, Bentota, Pereliya, Hikkaduwa, Galle, Talpe, Matara, Tangalla and Hambantota. The objectives of the first field visit were to investigate the damage caused by the tsunami and to obtain eyewitness information about wave arrival times. The second field visit from March 10-18, 2005 covered the eastern and southern coasts of Sri Lanka and included Trincomalee, Batticaloa, Arugam Bay, Yala National Park and Kirinda. The objectives of the second visit were mainly to obtain eyewitness information about wave arrival times and inundation data, and to take relevant measurements using GPS instruments.

The peak ground acceleration (PGA) of 13.08 m/s(2) recorded at K-NET station in Ojiya city during the 2004 Mid Niigata Prefecture earthquake was 1.5-2 times greater than either of the other nearby stations on a similar soft soil (JMA) and on the outcrop rock (SSI). Those at K-NET during earthquakes with less intensity, however, tended to be smaller than those at JMA. The variation in relative magnitude of PGA with earthquake intensity is probably due to the difference in site conditions between K-NET and JMA. Field investigation including boring, PS logging, and spectral analysis of surface wave methods as well as laboratory tests on undisturbed samples obtained from the sites from this and previous studies reveal near-surface soil profiles and their nonlinear dynamic soil properties at both stations. Equivalent linear dynamic analysis is then performed using the detected soil profiles and properties for the two sites with the motions recorded at SSI as input outcrop motions. It is shown that, despite its very low shear wave velocity of about 50 m/s, the near-surface peat at K-NET exhibits weaker nonlinearity with larger damping at small strains but with smaller damping at large strains than does the near-surface silt at JMA. This might have had strong effects on the extremely large peak acceleration at K-NET during the main shock as well as on the variation in relative magnitude of PGA between K-NET and JMA during earthquakes of different intensity.

Strain-dependent shear moduli and damping factors of surface soils at K-NET and JMA stations in Ojiya are estimated not only from cyclic torsional shear tests on undisturbed samples obtained at the sites but also from back-calculation of transfer function of the strong motion records between either of the two sites and a nearby rock outcrop site. Both laboratory test and back-calculation of strong motion records indicate that the near-surface peat at K-NET shows weaker nonlinearity than the near-surface silt at JMA, which might have had strong effects on the observed ground motions including those in the Mid Niigata Prefecture Earthquake in 2004 at the two sites.

The peak ground acceleration at K-NET in Ojiya during the Mid Niigata Prefecture Earthquake in 2004 is significantly larger than that at JMA in Ojiya, while the trend reverses in other earthquakes with less intensity. Strain-dependent shear moduli of surface soils at both stations are estimated based on the accelerograms obtained only at the ground surface together with in-situ tests including boring and PS logging. Despite its low shear wave velocity, the near-surface peat at K-NET show weaker nonlinearity than the near-surface silt at JMA, which might have had strong effects on the observed ground motions at the two sites during different earthquakes.

The December 26, 2004 Sumatra-Andaman earthquake that had a magnitude of 9.0 was one of the largest earthquakes in the world since 1900. The devastating tsunami that resulted from this earthquake caused more casualties than any previously reported tsunami. The number of fatalities and missing persons in the most seriously affected countries were Indonesia - 167,736, Sri Lanka - 35,322, India - 18,045 and Thailand - 8,212. This paper describes two field visits to assess tsunami effects in Sri Lanka by a combined team of Japanese and Sri Lankan researchers. The first field visit from Dec. 30, 2004 - Jan. 04, 2005 covered the west, SW and south Sri Lanka and included the cities of Moratuwa, Beruwala, Bentota, Pereliya, Hikkaduwa, Galle, Talpe, Matara, Tangalla and Hambantota. The second field visit from March 10-18, 2005 covered the NE, east, SE and south Sri Lanka and included Trincomalee, Batticaloa, Arugam Bay, Yala National Park and Kirinda. The main objectives of the field surveys were to investigate the damage caused by the tsunami and to gather eyewitness information of wave arrival times.

2004年12月26日インドネシアスマトラ島沖でM9の地震が発生し, それによって引き起こされた津波がインド洋周辺諸国に多大なる被害を及ぼした. 我々は, 地震発生から4日後にスリランカに入国し, スリランカ南西部で現地調査を実施し, 現地の目撃証言から得られた記録を元に津波到達時刻を推定した. その結果, スリランカ南西部では, 最大波高を示す津波の前に, 一波, ないし二波の津波があり, 最大波高を示す波は9時～11時にかけて南東から南西に沿って伝播していた.

In order to examine the local site effects on the strong motion records of the 1999 Chi-Chi earthquake in Taiwan, microtremor measurements are conducted using arrays of sensors at 11 strong motion stations. Shallow shear wave velocity profiles of these stations are estimated based on an inverse analysis of both microtremor dispersion characteristics and H/V spectra. Equivalent linear analysis is conducted using the estimated Vs profiles. It is shown that local soil conditions including nonlinear soil behavior might have had significant effects on the ground motion and performance of buildings during the earthquake.