LIQUEFACTION STRENGTH CHARACTERISTICS OF GARAVEL-CONTAINING SANDY SOILS UNDER LOWER NUMBERS OF CYCLES AND ELEVATED CONFINING PRESSURE

由于1995年的兵库县南部地震（阪神-淡路地震灾害），神户港岛含砾石的Masado土被极度液化，被认为比干净的沙子更不容易液化。本文介绍了马萨多土液化特性试验研究的结果。首先，对神户港岛复原土样和原状土样进行不排水单调压缩和拉伸试验。再造土样品采用两种不同级配的Masado土，本研究采用两种不同的土样制备方法***。在重构土样品的一系列试验中，发现了以下实验结果：在不同的制样方法和围压下，土样的孔隙比相同，应力状态相同。压缩载荷和拉伸载荷的稳态包壳倾角不同，因此，压缩载荷和拉伸载荷的稳态偏离应力不同。在相变状态下，水沉淀法制备的土样平均有效应力低于湿夯法制备的土样。在完整土样的一系列试验中，发现完整土样主要表现为膨胀特性。完整土样的孔隙比与平均有效应力之间的关系表现出很大的离散性，这可能是由于土样的级配变化所致。然后，安装了大型三轴试验装置，该装置具有液压致动器，可以将恒定振幅运动和随机地震运动应用于土样，并进行了一系列实验。首先，对Toyoura致密砂进行了不排水循环试验，并将试验结果与现有公布的试验结果进行了验证。然后，对1995年兵库县南部地震时记录的地震运动进行了不排水试验，并对密集的Toyoura沙进行了强运动特征（即脉冲型或振动型）的影响进行了检验。最后，对Masado土进行了等幅和地震运动不排水试验，发现Masado土在较低循环次数下的液化强度低于密集的Toyoura砂，地震运动特性对Masado土的液化影响较小。少

Due to 1995 Hyogo-ken Nambu Earthquake (Hanshin-Awaji Earthquake Disaster), gravel-containing Masado soils at Kobe Port Island were extremely liquefied, which were considered to be less liquefiable than clean sand. This study shows the outcome of experimental investigations on liquefaction characteristics of Masado soils.First, undrained monotonic compression as well as extension tests were carried out on reconstituted soil samples and intact soil samples recovered from Kobe Port Island. For reconstituted soil samples two different Masado soils having different gradations were used, and two different preparation methods of soil samples ***e adopted in this study. In the test series on reconstituted soil samples, the following experimental findings were found. Stress states at steady states of information are the same independent of sample preparation methods and confining pressures, in the void ratios of the soil samples are the same. The inclinations of the steady state envelopes for … More compressive and extensional loadings differ, accordingly, the deviator stresses at steady states for compressive and extensional loading are different. At states of phase transformation, mean effective stress achieved by the soil samples prepared by water sedimentation are lower those prepared by wet tamping. In the test series on intact soil samples, it was found that the intact soil samples shows mainly dilative behavior. The relationship between void ratios and mean effective stresses for the intact soil samples shows much scatter, probably due to a variation in gradations of the soil samples.Then, large-scale triaxial test apparatus with a hydraulic actuator, which enables constant amplitude motions as well as random earthquake motions to be applied to soil samples, were installed, and a series of experiments were carried out. First, undrained cyclic tests were performed on dense Toyoura sand, and the test results were verified against the existing published test results. Then, undrained tests subject to the earthquake motions, which were recorded at the time of 1995 Hyogo-ken Nambu Earthquake, were performed on dense Toyoura sand, and the influence of the characteristics of strong motions, I e. impulse-type or vibration-type, was examined. Finally, undrained tests under constant-amplitude and earthquake motions were performed on Masado soils, and it was found that liquefaction strengths of Masado soils are lower than those of dense Toyoura sand at lower number of cycles, and the characteristics of earthquake motions have less influence on the liquefaction of Masado soils. Less