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東北地方太平洋沖地震では福島県会津若松市にて大規模な盛土崩壊が発生した。崩壊した盛土では液状化の痕跡が確認され，盛土材は火山性堆積物であることから粒子破砕の影響が懸念された。火砕流堆積物は全国各地に幅広く分布しており，人工盛土への適用事例も多い。本研究では現地採取土を用いて，等方圧密やせん断による盛土材の粒度変化を調査するほか，静的および繰返し載荷試験により強度特性を把握した。三軸圧縮試験より，福島現地採取土は有効応力p’=100 kPaまでの等方圧密で粒子破砕率が急激に増加すること，粒子破砕率の増加に伴い，せん断抵抗角が大きく低下することを明らかにした。また，得られた力学特性を用いて盛土崩壊事例に対し地震時変形解析を実施した。その結果，解析値が実変位量を再現し，液状化強度曲線より算出した残留強度と粒子破砕によるせん断抵抗角の減少を考慮することで妥当な解析結果が得られることを示した。, A large-scale slope failure of embankment, which consists of volcanic sediment, at Aizu-Wakamatsu City in Fukushima Prefecture occurred due to The 2011 off the Pacific coast of Tohoku Earthquake. Some signatures of liquefaction have been observed in the collapsed embankment. When investigating the embankment slope failure mechanism, it is necessary to study the effects of particle breakage. In this study, some static and repeated triaxial tests were conducted for the soil material sampled from the site in order to investigate the change of the particle size distribution with isotropic consolidation stress and shear stress and the effect on the shear strength characteristics due to the particle breakage. From the test results, it was revealed that the sampled soil, subjected to the effective isotropic consolidation stress of 100kPa or less, increases the particle breakage amount rapidly and the shear resistance angle is significantly reduced with the increase of the particle breakage amount. Subsequently, seismic deformation analysis was carried out for the slope failure of the embankment based on the mechanical properties obtained in the test. As a result, a reasonable analysis result was obtained by considering the calculated residual strength based on the liquefaction strength curve and the reduction characteristics of shear resistance angle due to particle breakage.

さんご石灰質砂の圧縮特性と粒子破砕の影響を一次元圧縮試験により明らかにした。主な結果は次のようである。(1) 石灰質砂はシリカ質砂に比べて圧縮性が著しい。(2) 圧縮指数は圧縮応力の増加に伴い0.5まで増加する。(3) 粒子破砕に及ぼす圧縮応力の影響の程度は初期間隙比に関係なく圧縮応力と圧縮降伏応力の比で評価できる。(4)圧縮応力の増加に伴う間隙比の減少は粒子破砕の程度に支配される。(5) 粒子破砕を伴う応力レベルでのクリープ変形は磨耗を伴う粒子間の相対変位によってもたらされることが推察される。(6) 一次元圧縮条件下ではクリープひずみ速度の対数とクリープ経過時間の対数の関係は2つの折点を持つ線形関係で表される。, Coral sands are consist of such bioclastic as coral, shell, foraminifera, etc. in that particles are relatively soft and can easily be broken. In this paper in order to investigate the effects of the particle breakage on the compressibility and creep deformation of coral sand, the one-dimensional compression tests up to a vertical stress of 62.72MPa and the one-dimensional creep tests under a constant vertical stress of 11.76MPa. The materials used are coral sands obtained from eight different locations in coral reefs around Ryukyus Islands, south west part of Japan. The compressibility of sand is controlled by the particle breakage. The degree of particle breakage is uniquely related to the ratio of the compressive yield stress to the maximum applied stress. Creep deformation is significant after an elapsed loading time of 1000 minutes. The time dependence of the compressibility is caused by the abrasion on the particle surface because of the increase in the percent finer than 0.075mm during creep process., 紀要論文

琉球石灰岩中の砂礫のせん断に伴う粒子破砕とひずみの関係を調べるために琉球石灰岩の砕石を用いて圧密排水せん断試験を実施した。主な結果を以下に示す。(1)粒子破砕は,軸ひずみの増加に伴い破砕がほとんど生じない領域から破砕が顕著に生じる領域そして破砕量の増加割合が徐々に減少する領域へと変化する傾向にある。(2)粒子破砕は,側圧の増加に関わらず軸ひずみ3%付近から10%付近の間で顕著に生じる。(3)表面積は軸ひずみの増加に伴い増大するが,その増加割合は軸ひずみの増加とともに徐々に減少する。(4)せん断中に加えられた消散エネルギーは,軸ひずみの増加にともない増大し,その後消散エネルギーの増加割合は徐々に減少する傾向にある。(5)表面積の増加は粒子破砕に消費される消散エネルギーの増加と関係づけられる。, The consolidated drained shear test was carried out on crushed Ryukyu limestone in order to clarify the relationship between particle breakage and shear strain. Shear test carried out at confining pressures of range from 49kPa to 294kPa. The gravel used was reconstructed from 2mm particle size to 9.5mm. In order to examine the effect of shear strain on particle breakage, the grain size distribution of the sample was examined at stage of various axial strain. The amount of particle breakage was evaluated at the percentage passing of 2mm particle size. The particle breakage was remarkably occurred in range of axial strain from 3% to 10%, regardless of the confining pressure. The surface area of specimen increases with the increase in axial strain. The dissipation energy consumed for friction and particle breakage increases with the increase in the axial strain. It is shown taht the increase in the surface area with particle breakage is related to the dissipation energy for crushed Ryukyu limestone., 紀要論文

圧縮応力による粒子破砕の程度と圧縮性に及ぼす粒子破砕の影響を把握するため2種類の石灰質砂について乾燥状態と水侵状態で50MPaまでの一次元圧縮試験を実施した。主な結果は以下のようである。(1) 圧縮性は細粒な砂より粗粒の砂において大きい。また, 圧縮性に及ぼす水侵の影響は小さい。(2) 圧縮試験におけるe-log σ_v関係には降伏点みられ, この降伏圧縮応力を境に圧縮指数C_cは増大する。同様に粒子破砕も顕著となる。(3) 圧縮応力の増加による粒子破砕に伴って粒径0.075mm以下の細粒分が増加するが, ある程度細粒分が増加すると, 圧縮応力の増加に伴う粒子破砕量の増加割合は低減する。(4) 破砕係数BcはMarsalの方法による粒子破砕量B_MおよびLeslieの方法による粒子破砕量ΔFと相関関係にある。(5) 破砕係数B_cの増加に対して圧縮指数C_cが急激に増加することから, わずかの粒子破砕で圧縮性が顕著とならことが認められた。, A series of one-dimensional compressive tests has been performed on skeletal calcareous sands in order to investigate a degree of particle breakage under compressive stress. The tests were carried out on dried and saturated samples in each sand up to vertical stresses of 50MPa. The amount of particle breakage is evaluated with the index Bc defined as the ratio of percentage of particles of sand after test finer than D_ of original sand to percentage of particles finer than D_ of original sand. The compressibility of sand is measured by the compression index C_c calculated as the mean slope of the void ratio -log (vertical stress) curve for each increment of vertical stress. Test results show that there is little effect of saturation on particle crushing and compression of sands. According to the change of gradation curves with applied stress, it is found that the ratio of the increasing in the amount of particle breakage to the increasing in applied stress is decreased with the increasing in fine grain content finer than 0.075mm due to particle crushing. The value of C_c is rapidly increases with the increasing in B_c. It is concluded that the compression is mainly due to the breakage of particle under a wide range of vertical applied stress., 紀要論文