軟弱な水成チュウ積地盤土における非排水強さの力学的特性に関する研究

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The present study is designed to investigate the mechanical characteristics of alluvial clays in shore and lake-reclamation areas, and to bring forth a theory for rational and economical stability analysis applicable on the foundation-ground of reclamation dike. Soil layers in the areas on which reclamation-lands have been constructed are divided, on the basis of topographical consideration and investigated data, into estuary delta layer and sea-or lake-bottom clay layer. The latter, containing many problems concerning mechanical stability of soil, is classified into three types ; still water type, compound I type and compound II type. The following is made clear after the investigation carried out on soil explorations and field experiments in the Ariake Sea and the Shiranuhi Sea. That is, (1) in fresh alluvial clay, void ratio or water content generally decreases exponentially with the increase of depth or pressure, seeming to be in the state of equilibrium at water content near the liquid limit. The pore water at the shallow part of marine clay layers of still water type is of high salt density. The clays containing much amount of very fine particls below 2μ in diameter are of high sensitivity, owing to the froculation act at sedimentation and to the chemical bonding force derived from agglutinative action of salts. They are in the state of equilibrium at watar content higher than the liquid limit, some of them having pre-consolidation pressure which is larger than over-burden pressure. It seems that they also are normally consolidated clay, having endowed with structural strength.(2) Unconfined compression strength is generally small, being proportional to over-burden pressure. It is proved, in thick clay layer, that in analysing stability immediately after loading the analysis should be based on undrained shear strength. This is applicable not only to the natural ground, but also to the ground consolidated by added load.(3) The settlement of constructed dike roughly coincides with the value calculated, basing on one-dimentional consolidation theory. Some experiments are performed for the purpose of confirming the relation between undrained strength and void ratio (or water content), or that between undrained strength and soil structure (or stress history). Results of the experiments using natural samples and some samples in which the water content are controlled by triaxial consolidation and by airdrying show that some exponential relation exists between water content and unconfined compression strength, though rather scattered, and varies in accordance with the difference of soil structure (or stress history). On the other hand, unconfined compression strength is proportional to consolidation pressure, being unconcerned with soil structure or stress history. This relation is applicable also to the state under the process of consolidation, by taking account of the effective consolidation pressure at the respective time. The result is proved to be theoretically based on Mohr-Coulomb's criteria, and undrained shear strength is expressed in the form of the function of effective consolidation pressure. The conclusion of the present study is as follows : -The undrained shear strength of the alluvial clays, such as saturated clay forming the foundation ground of reclamation dike in the Ariake Sea, depends on the effective consolidation pressure brought forth by loading. This character is tenable, regardless of the existence of structural strength by agglulinative action. Therefore, the relation between the effective consolidation pressure and the undrained shear strength including the consolidation under way is to be given by the total stress expression of the results of consolidated-undrained triaxial tests. It is proposed that tangent of the angle of shearing resistance φ_<cu> should be used as the coefficient of shear strength increase (ratio of the increment of shear strength to the increment of effective consolidati
鹿児島大学の論文
1973-03-24

軟弱な水成チュウ積地盤土における非排水強さの力学的特性に関する研究

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