Two IAA-winning projects demonstrate the benefits
of geotextile tubes for marine engineering.
Award of Excellence
TenCate Geosynthetics, Pendergrass, Ga., USA
The Embraport Container and Bulk Liquid Terminal was permitted for construction on the north shore of the port of Santos, Brazil, estuary in a tidal zone that would require importing approximately 1.5 million cubic meters of select fill material to reach a platform elevation of +3.5m, taking into consideration settlement of the existing subgrade during and after construction.
Through the sediment sampling process, it was determined that the required access channel and turning basin were overlaid with 600,000 cubic meters of contaminated sediments that had to be removed and deposited in a secure upland disposal facility. This finding and subsequent required action increased the cost and construction timeline of the project. The cost of these requirements threatened the economic viability of the project.
An economic alternative
The dewatering cell subcontractor had to provide and install geotextile tube units capable of filling to a height of 2.2 meters, with a capacity of 35.2 cubic meters per meter of a slurry with a specific gravity=1.43, and provide an overall minimum factor of safety of 4.3 or greater against circumferential, axial, and fill port rupture.
The engineered textile captured 99.9 percent of all suspended solids while having an effluent quality discharge capable of being discharged back into the native estuary and generating internal dry solids equal to or greater than 55 percent.
The geotextile tube units containing the residual dewatered contaminated sediments were required to have sufficient tensile reinforcement to provide a factor of safety equal to or greater than 2.25 when a 0.80-meter pavement section has been installed and subjected to a load of 187tonf/m2 (ton force per square meter). The geotextile tube structure had to have a 50+-year service life when subjected to hydrocarbon concentrations of 50 percent at ambient temperatures of 30Â° C.
This beneficial use concept would eliminate the requirement for an upland disposal facility (requiring the purchase of additional land for this facility or using part of the Embraport site as the facility), and eliminating the 600,000 cubic meters of expensive imported select fill.
The geotextile tube containment and dewatering beneficial-use concept had to demonstrate through performance testing that it could meet stringent environmental guidelines for performance during construction. This included testing containment removal efficiencies and consolidation, providing high factors of safety against rupture during construction, proving survivability when subjected to severe overburden loading conditions or up to seven stacked layers of 20-foot and 40-foot maximum loaded ocean containers, and ensuring longevity demonstrated through accelerated testing.
The containment and dewatering design concept proved that it met all environmental and geotechnical requirements by being subjected to severe preconstruction performance testing and during the installation and construction phase of the Embraport project. The dewatering cell and polymer dosing system had to perform, without interruption of the dredging operation, by receiving the dredged contaminated sediments at a rate of 1,400 cubic meters per hour. This performance requirement was met, and this phase of the project was completed within the 18-month allowable time frame.
Because the owner selected and implemented the geotextile tube containment and dewatering solution for on-site beneficial use of dredged contaminated sediments, he realized a savings of more than $50 million USD.
The carbon footprint was reduced by 7,903 metric tons of CO2 equivalent by adapting the geotextile tube containment and dewatering technology to securely contain and consolidate the dredged contaminated sediments on-site.
This concept allowed completion of the construction within the allowable time frame, and met all of the Brazilian environmental regulations with regard to removal and containment of the contaminated sediments, quality of effluent return to the native environment, and service life of the project.
Outstanding Achievement Award
ACE Geosynthetics, Taichung, Taiwan, Republic of China
For a geotextile tube application on a containment breakwater at Ras al-Khaimah, United Arab Emirates, the design for the project used several types of geotextile tubes, which were produced with:
- 70-I polypropylene woven geotextile fabric
- 8.6-meter and 12.9-meter circumferences
- lengths from 10 meters to 50 meters
- 13.8-meter width with 20-meter and 50-meter scour apron
The geotextile tubes were built for the main independent body of the breakwater, with cover riprap was installed as armor protection.
The new fish port site is located inshore, beside a groin. The client proposed to build a new L-shaped optimization breakwater accommodating the existing groin with a total enclosure length of 700 meters, forming a fish port.
Authorities assessed a cost-effective, fast construction and safe scenario to build this breakwater, because in the United Arab Emirates (UAE) most breakwaters are rubble mound types. But there was a problem using rubble to construct this breakwater because rubble is a high-cost material. So alternatives were considered.
The geotextile tubes and geotextile apron in the design built the 700-meter breakwater. There are a total of four layers of geotextile tubes stacked to reach a 6.5-meter height, plus two layers of rock at 0.5 meters and 2 meters.
Upon completion in 2013, the structure now reaches the designed height of 9 meters. Sand is contained effectively with the geotextile tubes, and construction was completed smoothly and on schedule.
The use of geotextile tubes with sand replaced the rock rubble style and saved construction costs in this area. This project is a classic case of the successful application of geotextile tubes for marine engineering.