Consolidating Waste Slurry by Vacuum Preloading with Flocculation
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EXPERIMENTAL INVESTIGATIONS CONSOLIDATING WASTE SLURRY BY VACUUM PRELOADING WITH FLOCCULATION
UDC 624.138.232 Yitian Lu,1 Yajun Wu,1* Gangqiang Kong,2 Kun Niu,1 Jinchun Chai3 1
Department of Civil Engineering, Shanghai University, Shanghai, China; 2College of Civil and Transportation Engineering, Hohai University, Nanjing, China; 3Department of Civil Engineering and Architecture, Saga University, Saga, Japan, *Corresponding author Email: [email protected].
Anionic polyacrylamide (APAM) and quicklime are used to improve vacuum preloading of waste slurry in Shanghai, China. To investigate the influence of these reagents on waste slurry sediment consolidation, tests on laboratory-scale models with and without the reagents were conducted and the results analyzed. Sediment settling was recorded and used to calculate the water content changes during vacuum consolidation. After vacuum consolidation, the water content of sediment samples collected at different distances from the drain at the center of the model were measured and pore properties were determined by mercury intrusion porosimetry. The tests with and without reagents indicated that anionic polyacrylamide (APAM) and quicklime can decrease the water content of waste slurry and change the slurry's properties. In addition, the results of the settlement analysis were used to investigate the characteristics of vacuum consolidation.
1. Introduction Waste slurry from shaft drilling and shield method has increased as construction has increased around the world. To dispose of this slurry, in some cases it is transported to outlying areas and dumped in fields or discharged into rivers or the ocean. This is a serious source of pollution, and more environmentally responsible disposal options are a necessity. Methods such as vacuum drum and disc filtration are used for waste slurry treatment, but the efficiency of consolidating slurry using these methods is limited [1-3]. Vacuum preloading is a method widely used for soil consolidation [4-6] and it can be used to treat waste slurry in the field. Waste slurry consists of small particles and has a low permeability. To increase its permeability, reagents that cause flocculation are used [7]. A new method that combines reagents and vacuum preloading to consolidate waste slurry has been proposed [8]. Previous studies have used organic polymer reagents like anionic polyacrylamide (APAM) and quicklime (essentially CaO) because they are readily available [9]. For this reason, APAM and quicklime were used for the experiments considered by this study. Tests on a model were conducted in a laboratory to investigate the efficiency of vacuum consolidation preloading with and without reagents. The results revealed that the consolidation rate with reagents was higher than the rate without reagents. There is, however, only a limited theoretical explanation for how the vacuum preloading of slurry with reagents increases consolidation efficiency. Therefore, for this paper, the test results from flocculation
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