Deformation characteristics of clays at deep position of ground and its time dependency

本研究以大阪湾仙州海域更新世沉积物为研究对象，研究了原状粘土的力学特性与时间的相关性。并提出了预测地表变形的方法。主要结论如下：1.研制了一种半高压恒速应变固结仪。对大阪湾仙州外海更新世原状粘土的固结特性进行了研究。首先，研究了应变速率、背压等试验条件对固结特性的影响。在等应变固结试验中，发现应变速率对固结屈服应力有显著影响。更新世原状粘土具有比冲积粘土更高的屈服应力，可以采用半高压恒速应变固结装置。通过小型三轴试验研究了更新世沉积物中原状粘土的不排水剪切特性。进行了重塑粘土的不排水剪切试验，研究了老化对重塑粘土剪切特性的影响。原状粘土和重塑粘土的对数最大偏应力与孔隙比之间均呈线性关系。结果表明，初始孔隙率对抗剪强度的影响可以用孔洞指数或e_L.3来排除。提出了一种利用小型三轴试验和固结试验确定更新世原状粘土弹粘塑性参数的方法。通过三轴试验变形行为的数值模拟分析和人工岛的施工，考察了所确定参数的可靠性。

In this study, the effect of time dependency on the mechanical characteristics of undisturbed clays is investigated, which is in the Pleistocene deposits at the off-Senshu area in Osaka Bay. Also, the method for predicting deformation of the ground is proposed. The main conclusions are summarized as follows:1. A constant rate of strain consolidation apparatus for semi-high pressure was developed. The consolidation characteristics of undisturbed clays taken from the Pleistocene deposits at the off-Senshu area in Osaka Bay was investigated. Firstly, the effect of such test conditions as strain rate and back pressure on the consolidation characteristics was investigated. It is found that the strain rate significantly affects consolidation yield stresses in the constant rate of strain consolidation tests. Next, a constant rate of strain consolidation apparatus for semi-high pressure could be applicable to the undisturbed clays in the Pleistocene deposits, which have higher yield stresses than the alluvial clays.2. The undrained shear characteristics of the undisturbed clays in the Pleistocene deposits was investigated through mini-triaxial tests. The undrained shear tests of the reconstituted clays were carried out to investigate the "aging" effect on shear characteristics. The linear relationship between logarithmic maximum deviator stresses and void ratios was observed on both the undisturbed and reconstituted clays. It was shown that the effect of initial void ratio on shear strengths can be excluded through using the void index or the e_L.3. A method for determining elasto-viscoplastic parameters for the undisturbed clays in the Pleistocene deposits using mini-triaxial tests and consolidation tests was proposed. The reliability of the determined parameters was investigated through the numerical simulation analysis of deformation behavior in triaxial tests and construction of a man-made island.