Date of Award
Master of Science (MS)
Civil and Environmental Engineering
Shobha K. Bhatia
Geotextile tubes are used in dewatering applications over many decades for a variety of slurries, sediments, and wastes. With the increased use of geotextile tubes dewatering in recent years, the desire to maximize both the dewatering rate and retention lead to the use of chemical accelerant, which has become a standard practice in geotextile dewatering projects. A variety of small-scale, medium-scale, and pilot-scale test methods are used to assess geotextile tube dewatering performance, including Falling Head Test (FHT), Pressure Filtration Test (PFT), hanging bag test (HBT), Geotextile-tube Demonstration Test (GDT), and Pressure Gravity Dewatering Test (PGDT). However, a very few studies compare different types of dewatering tests and no proper correlations have been developed between test methods.
The scope of this study is to (1) analyze dewatering process on radial and axial directions using a two-dimensional dewatering apparatus, which is basically a cylindrical geotextile tube, where the axial and radial flows are measured separately (2) analytical modelling of 1-D, 2-D, and 3-D dewatering process, and to (3) compare the results of analytical model and the experimental results of 1-D, 2-D, and 3-D dewatering test methods. In the process of comparing different test methods, the effect of multiple filling, final solids concentration, and turbidity of the effluent were considered. Three different tests (PFT, P2DT, and GDT), two different sediments under different solids concentrations and five different geotextiles, including woven, non-woven and geo-composites were used in this study. Relationship between radial filter cake height and flow ratio was (ratio between radial and axial flows of P2DT) observed. The dewatering parameters obtained using analytical modelling were compared between test methods.
The analytical model proposed in this study can be used to predict the dewatering behavior under alternative conditions, including the changes in pumping rates, solids concentration of the slurry being pumped, geotextile tube sizes, number of dewatering cycles, dewatering duration, filling heights, final solids concentration of filter cake, and in cumulative volume of slurry. Analyzing the alternative dewatering scenarios using an analytical model prior to full-scale implementation, without conducting further dewatering performance tests, is a great benefit in terms of material time and money. This study lays out the framework to predict the dewatering behavior of full-scale tests using an analytical model generated from a lab tests, such as Pressurized 2-Dimensional Dewatering Test (P2DT).
The limitations of this analytical model are that the analytical model does not account for the changes in the slurry properties other than the solids concentration and the changes in the overall pressure inside the geotextile tube. Alternative dewatering scenarios including changes in slurry and in pressure requires a performance test to be conducted to determine the dewatering parameters.
Chelvarajah Ratnasamy, Ratnayesuraj, "ANALYTICAL MODELING, TESTING, AND COMPARISON OF 1-D, 2-D, AND 3-D DEWATERING PROCESS" (2017). Theses - ALL. 175.