EFFECTS OF CARBONATE ON SEABED FORMATION

土壤中胶结作用的机理还没有很好的理解。对胶结作用的认识不足，阻碍了岩土工程的进一步发展，也影响了地质学和沉积学对成岩作用过程的认识。在这项研究中，碳酸盐对海底的形成，与强度发展的影响，主要是研究。为了寻找海底碳酸盐胶结发育情况，通过对海底碳酸盐含量、抗剪强度以及含水量、比重、含水量、孔隙比、粒度分布等物性参数的测定，在东京湾、相模湾、骏河湾、大坂湾、鹿儿岛湾和濑户内海等不同地点采集的样品中进行了测定。这些因素之间的相关性表明，海底的胶结作用主要是由于碳酸盐的包裹作用。结果表明，强度随深度的变化主要取决于碳酸钙含量的变化。此外，研究还发现碳酸钙通过聚集作用促进海床固结，从地球化学和地质学角度，可以通过碳酸钙含量预测土颗粒的沉降速率。这种预测方法需要假设碳酸钙以恒定速率沉积在海底。在本研究中，所获得的碳酸钙的沉淀速率为0.95 g/cm^2/1000 y。在各种方法的比较中，碳酸盐法与碳<14>法、关键层法的预测结果一致，而与<210>铅法的预测结果不一致。

The mechanism of cementation in soils has not been well understood. The lack of information on the cementation prevents from the further progress of geotechnical engineering and better understandings of diagenesis process in geology and sedimentology. In this study, effects of carbonate on the formation of seabed, in relation to strength development, is mainly investigated. In order to find carbonate-cementation development of seabed, carbonate content, shear strength and physical properties such as water content, specific gravity, water content, void ratio, grain size distribution, etc., were measured on the samples obtained from various sites, such as Tokyo bay, Sagami bay, Suruga bay, Osaka bay, Kagoshima bay and seto inland sea. The correlations between these factors show that the cementation of seabed is mainly due to the contained carbonate. It is found that the deviation of strength with depth is mainly dependent on the variation of calcium carbonate content. Furthermore, it is found that the calcium carbonate can promote consolidation of seabed by the aggregation effects.From the geochemical and geological points of view, the sedimentation rate of soil particles can be predicted from the calcium carbonate content. This prediction method needs an assumption that calcium carbonate precipitates on the sea bottom with a constant rate. In this study, the precipitation rate of calcium carbonate obtained is 0.95 g/cm^2/1000y. In the comparison using various methods, the prediction of sedimentation rate obtained from the carbonate method accords with those obtained from ^<14>C and key bed methods, but not from ^<210>Pb method.