EFFECTS OF CARBONATE ON SEABED FORMATION

土壤胶结的机理尚未得到很好的了解。关于胶结作用的信息的缺乏阻碍了岩土工程的进一步发展，也阻碍了地质学和沉积学对成岩作用过程的更好理解。本研究主要研究碳酸盐对海底形成与强度发展的影响。为了了解海底碳酸盐胶结发育情况，对东京湾、相模湾、鹤鹤湾、大阪湾、鹿儿岛湾、濑户内海等地的岩样进行了碳酸盐含量、抗剪强度、含水量、比重、含水量、孔隙比、粒度分布等物理性质的测量。这些因素之间的相关性表明，海底胶结作用主要是由含碳酸盐引起的。研究发现，强度随深度的偏差主要取决于碳酸钙含量的变化。此外，还发现碳酸钙通过聚集效应促进海底固结。从地球化学和地质的角度来看，碳酸钙含量可以预测土壤颗粒的沉降速率。这种预测方法需要假设碳酸钙在海底以恒定速率沉淀。本研究获得的碳酸钙沉淀率为0.95 g/cm^2/1000y。不同方法对比发现，碳酸盐岩方法预测的沉积速率与^<14>C和关键层方法预测的沉积速率一致，而与^<210>Pb方法预测的沉积速率不一致。

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.