Cause Investigation of Abnormal Settlement Phenomenon in Pleistocene Clay Layers by Experimental Examination of Clay Structural and Mineralogical Composition Changes

本研究利用应变路径控制三轴仪，探讨更新世黏土之K_0固结特性。与传统的测试相比，这种测试的优点进行了描述。采用弯曲单元法测量剪切模量，间接观察颗粒结构的变化。此外，使用扫描电子显微镜直接观察颗粒结构。从这项工作中可以得出以下结论。应变路径控制试验的优点在于：试件的应变和超静孔压可以自由控制，即使在大应变范围内也能保持均匀;可以精确控制粘土的排水模式和K_0固结模式，缩短试验时间.应变路径控制的K_0固结试验结果表明，更新世粘土具有非常典型的固结特性，孔隙比减小 关于我们 艾德在预固结应力后迅速膨胀。这种行为在重构高岭土样品中不明显。K_0值在固结前应力值附近减小，固结后迅速增大，并趋于稳定。这似乎是由于在预固结应力之后粘土中发生的结构性变化。在K_0固结试验过程中，剪切模量G逐渐增大到100（MPa），之后基本保持不变。在G中，这个变化点的孔隙比恰好与在预固结应力之后快速变化的孔隙比一致。这种变化的主要原因可以被认为是更新世粘土的结构性变化显着的预固结应力后.利用扫描电子显微镜（SEM）观察了更新世粘土的微观结构。尽管在测试前的样品中观察到完整的硅藻，但在测试后采集的样品中观察到大量被破坏的硅藻。可以认为，硅藻骨架的破坏是前期固结应力作用后孔隙比迅速减小的原因之一。在本研究中，没有观察到粘土颗粒的连接结构的变化，这被认为是在前期固结应力附近的孔隙比迅速降低的另一个原因。少

In this research, the K_0-consolidation characteristics of Pleistocene clay were examined using the strain-path controlled triaxial apparatus. The advantages of this test are described when compared with the conventional tests. Shear modulus was measured using bender element system to observe the change of particle structures indirectly. In addition, the particle structures were observed directly using the scanning electron microscope. The following concluding remarks can be obtained from this work.1. The advantages of the strain-path controlled test were shown in the following : Strain and excess pore pressure in a specimen can control freely and can keep homogenous even in the large strain domain ; the drained mode and the K_0-consolidation mode of clays can be controlled exactly and their testing times can be shortened.2. The result of this strain-path controlled K_0-consolidation test showed the very characteristic consolidation behavior of Pleistocene clay ; the void ratio decreas … More ed rapidly just after the pre-consolidation stress. This behavior is not apparent in a reconstituted kaolin clay sample. The K_0 value decreased to the pre-consolidation stress, then increased rapidly after that, and became a steady value. It seems that such results were due to structural change occurring in the clay just after the pre-consolidation stress.3. The shear modulus G during the K_0-consolidation test gradually increased to 100 (MPa), then it almost kept constant after that. The void ratio of this changing point in G precisely agrees with the one changed rapidly just after the pre-consolidation stress. The main cause of this change G can be recognized to be structural changes of Pleistocene clay significantly just after the pre-consolidation stress.4. The microscopic structure of Pleistocene clay was observed using the scanning electron microscope (SEM). A large number of diatoms destroyed were observed in the sample taken after a test although intact diatoms were observed in the one before a test. It can be considered that one of the causes for the rapid reduction of the void ratio just after the pre-consolidation stress is the frame of diatoms destroyed. In this research, the change of link structures of clay particles was not observed, which was considered as another cause of the rapid reduction of void ratio near the pre-consolidation stress. Less