ABSTRACT:

The slurry produced as a by-product of construction works has a high water content and contains a large amount of fine clay particles, thus necessitating its flocculation and dehydration for the sake of volume and water content reduction. The purpose of this study is to investigate the consolidation properties of floes of different sizes, made by the application of flocculant to sludge, under lower consolidation pressures. Three types of experimental studies were carried out using clay floes of different sizes. Based on the results of dewatering and consolidation tests, it can be concluded that the floes" compressibility decreases with the increase in their size under consolidation pressures below 10 kPa, and that the hydraulic consolidation test could reliably predict initial deformation under lower consolidation pressures.

INTRODUCTION

In construction works such as shield tunnels or diaphragm walls, a great deal of slurry, called "construction waste sludge", is produced. It has a high water content and contains a large amount of fine clay particles, thus necessitating its flocculation and dehydration for the sake of volume and water content reduction. For the dehydration of construction waste sludge, dehydrators such as filter-presses or belt-presses are commonly used. At the intermediate treatment plant selected for this study (Ichikawa- city, Chiba), a special dehydrator called a "Dehydrum"(Figure 1) is used. The Dehydrum is a large size cylindrical rotor (<1>=3,340 mm and L=10,230 mm), which rotates in a single direction at a slow speed. The consolidation pressure of the Dehydrum is assumed· to be Figure 1: Dehydrum installed at plant. much lower than that of other dehydrators, which are estimated to be approximately 500 kPa to 700kPa. It has been observed at the present plant that the consolidation properties of floes, made by the application of flocculant to sludge, change.according to their sizes.

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