SUSTAINABLE AND INNOVATIVE APPROACHES FOR GEOTEXTILE TUBE DEWATERING TECHNOLOGY

Date of Award

December 2016

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Civil and Environmental Engineering

Advisor(s)

Shobha Bhatia

Keywords

Centrifuge Test, Dewatering, Fibers, Geotextile Tubes, Pressure Filtration Test, Residual Flocculant Detection

Subject Categories

Engineering

Abstract

Geotextile tube dewatering technology has been widely used over the past two decades for dewatering high water content slurries. The dewatering process in geotextile tubes mainly aims to decrease the volume of the dewatered slurry. Geotextile tubes provide an innovative containment solution that offer the following advantages: convenient placement and quick setup; high efficiency; low cost; labor conservation; and low environmental impact (Fowler et al. 1996, Lawson, 2008).

Several industries such as dredging (Satyamurthy and Bhatia 2008, Yee et al. 2012), mining (Watts and Trainer, 2009), and food processing (Lawson, 2008), in addition to coal combustion by-product treatment (Muthukumaran and Ilamparuthi 2006) and municipal wastewater treatment (Fowler et al. 2005), have successfully implemented geotextile tubes for dewatering high water content waste products. Dredging industry, however, comprises the major area of application of geotextile tubes due to the large volume of the slurry material dredged annually. It is estimated that, in the US alone, 194 million cubic yards of sediments are dredged annually to maintain harbors, commercial waterways, and other water bodies (USACE 2015).

In spite of the successful utilization of geotextile tubes for dewatering wide variety of high water content slurries, there still exist several indispensable issues that must be addressed.

Geotextile tube technology lacks standardization and is still highly dependent on the experience of the dewatering contractors and practitioners. In the same way, dewatering project success and the governing parameters are still vaguely defined. Furthermore, due to the very limited reporting of case studies about geotextile tubes failure (physical failure or due to environmental restrictions), introduction of innovative materials or testing methods for geotextile tube project performance is advancing at very slow pace. A major concern on this aspect is the excessive use

of chemical accelerants/flocculants without assessing the safety of its usage and its effect on water organisms. An equally important issue is the lack of natural sustainable alternatives to the synthetic flocculants. Furthermore, there is a missed link between small scale tests and field scale tests. Moreover, while some geotextile tube studies (for example: Plaut and Stephens 2012, Zhu et al. 2014) have evaluated the stress distribution in geotextile tube material during filling stages and under the effect of geotextile tube stacking, no work has been done to evaluate the strength of the of the retained sediments.

In this study, four key issues that are central to the geotextile tube applications are identified and investigated: (1) introducing new natural flocculants as an alternative to the widely used synthetic flocculants; (2) developing new practical test method that helps evaluating the retained sediments final solids content and final volume in a geotextile tube; (3) providing methodology for measuring the shear strength of the retained sediments; and (4) introducing new test methods for assessing the residual flocculant concentration in the effluent that seeps through the geotextile tube.

Five cationic starch-based polymers were introduced as a sustainable alternative to the widely used synthetic flocculants. The efficacy of the natural flocculants was assessed using jar test and pressure filtration test. Additionally, a new small scale, easy to use, relatively quick centrifuge test was used to determine the maximum possible solids content and the final volume of the contained retained sediments in a geotextile tube. Moreover, synthetic fibers were evaluated for their possible effect on improving the shear strength of the retained sediments. The shear strength was evaluated using lab vane test, fall cone test, unconsolidated undrained (UU) triaxial test. A specially designed pressure filtration test was designed at Syracuse University to allow transferring a relatively undisturbed sample to the UU test apparatus. Finally, two test

methods, streaming current method and China clay settling rate method were used to determine the concentration of the residual flocculants in geotextile tube effluent. The tests were performed on four different soil types with different properties that are typically encountered in dredging projects, Tully sand, Tully fines, Elliott silt loam, and kaolin. In addition, five synthetic and five natural (starch-based) flocculants were used. Three fibers types with different properties were also used. Based on the results of this study, it was found that the natural starches are very comparable to the synthetic ones in terms of their effect on increasing dewatering rate and solids retention. Additionally, the data obtained from centrifuge tests were compared with case studies obtained from geotextile tube literature. Centrifuge test allowed for reasonably accurate prediction of the retained sediments solids content and final retained sediments volume for all the studied cases. Additionally, it was found the use of fibers not only improves the undrained strength of the retained sediments by 100%, they also allow for increasing the dewatering rate and decreasing the optimum dosage needed for flocculation. Finally, streaming current method and China clay settling rate method were successfully used for assessing the residual flocculants concentrations in the effluent of geotextile tubes. A detection concentration as low as 0.5 parts per million (ppm) was possible through the use of streaming current method.

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