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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.

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_<10> of original sand to percentage of particles finer than D_<10> 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.

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_<10> of original sand to percentage of particles finer than D_<10> 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.