| Vacuum consolidation method is suggested to be a dewatering technique of water treatment plant sludge. However, if vacuum pressure is applied directly to the water treatment plant sludge, the only part close to drainage surface is densified, so called partial hardening zone, because of poor gradation/uniformity of particle size of sludge. This partial hardening zone blocks the water flow out of sludge. Therefore, dewatered process appears to stop or dramatically slow down even if the sludge portion further from the vacuum source are not fully dewatered. The water treatment plant sludge classified OH(organic clays) should be improved to MH(inorganic silts) to be dewatered without developing the partial hardening zone. In this study, the wasted coal ash(bottom ash) was totally mixed to improve the characteristics of sludge. The required amount of wasted coal ash was 10% of sludge volume to improve the characteristics of sludge. Laboratory tests was carried out on three different types of soils to find the physical and chemical properties of soils. Vacuum consolidation tests with and without vertical/horizontal drain was performed at the mixed soil to determine if vacuum consolidation method could be used for the dewatering technique and to find the effect of drains. By the results of tests with and without drains, the moisture contents throughout the entire soil samples were much lower than the target moisture content by mechanical methods. The dewatered velocity was dependant on the presence of drain. The time to reach same amount of settlement without drain was approximately 2.0 times longer than with drain. However, There was no difference between with vertical drain and vertical/horizontal drain. |
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