EFFECTS OF WATER ABSORPTION AND NEUTRALIZATION PROPERTIES OF CRUSHED SHELL ON STABILIZATION OF ACID SULFATE SOILS

本研究由两种室内试验和野外调查组成，主要内容如下：第一，室内试验的目的是阐明与酸性硫酸盐土壤(包括牡蛎壳中的黄铁矿和碳酸钙)接触引起的pH升高引起的孔隙水波动的机理。实验室试验的第二个目的是弄清酸性硫酸盐土、碎牡蛎壳和稳定剂的混合物的承载能力和强度特性。从化学试验、力学试验和现场测量记录中得到的主要结果如下：(1)将碳酸钙和熟石灰混合到酸性硫酸盐土中，由于形成氢氧化铁的吸水反应、形成氧化铁的脱水反应和溶解碳酸钙的二氧化碳挥发，导致孔隙水量的变化。(2)酸性硫酸盐土的无侧限抗压强度和CBR值，碾碎的牡蛎壳和稳定剂变得比没有贝壳碎片的混合物大。因此，在酸性硫酸盐土中掺入碎牡蛎壳有助于降低稳定剂的添加剂含量。(3)根据用酸性硫酸盐土、碎牡蛎壳和稳定剂的混合物制成的截面的冲击加速度值，它们的承载能力随着时间的推移而逐渐增加，反分析得到的弹性模量值比用不加贝壳的混合物制成的截面要大。

This study consists of two kinds of laboratory tests and a field inventory shown in the following :The first purpose of laboratory tests is to elucidate the fluctuation mechanism of pore water caused by rise of pH which the contact with acid sulfate soil including pyrite and calcium carbonate deriving from the oyster shell induces. The second purpose of laboratory tests is to clarify the bearing capacity and strength characteristics of the mixture of acid sulfate soil, crushed oyster shell and stabilizer. On the one hand, the products expected in a field inventory are the ascertaining of a solidification of the above mixture under exposure condition and the finding of its elastic modulus.The principal results obtained from chemical tests, mechanical experiments and measurement records at in situ are summarized as follows :(1)Mixing a calcium carbonate and slaked lime into acid sulfate soil, the amount of pore water varies due to the water absorption reaction with formation of an iron hydroxide, the dehydration reaction with formation of an iron oxide and the volatilization of carbon dioxide with dissolution of a calcium carbonate.(2)The unconfined compressive strength and CBR value of the mixture of acid sulfate soil, crushed oyster shell and stabilizer have become larger than those of the mixture without shell pieces. Therefore, the mixing of a crushed oyster shell into acid sulfate soil contributes to a reduction in additive content of stabilizer.(3)According to the impact acceleration values measured on sections which have been made by using the mixture of acid sulfate soil, crushed oyster shell and stabilizer, those bearing capacities increase gradually with a passage of time, and those elastic moduli calculated by inverse analysis are greater as compared to sections which have been made by using the mixture without shell pieces.