Buenaventura Bay, Colombia
Source: World Dredging Mining & Construction
One of the first geotextile tube applications in Colombia was for construction of confined disposal area islands that will be used for containment and dewatering of fine-grained maintenance dredged materials.
The project is located on the San Antonio Inlet, Buenaventura, Colombia. The dredged material containment area is the first of two oval shaped islands planned in this riverine and tidal environment. This new and innovative construction methodology involved hydraulically filled geotextile tubes with a sandy fill material.
The geotextile tubes were positioned end to end to provide a perimeter dike for dredged material containment in tidal variations of 4.0 m twice a day.
After the oval shaped islands are completed they will serve as dredged material containment facilities until they are filled and stabilized. After they are stabilized they will be planted in Mangrove trees and other native vegetation and will be used exclusively for environmental purposes.
The dredged material containment project is located about 8.0 km inland from the Pacific Coast adjacent to a 10 m deep navigation channel that serves the south part of the island of Buenaventura. New port developments have caused a need for new work deepening, maintenance dredging, and additional disposal areas. Existing dredged material disposal areas have either been filled to a capacity or have deteriorated because of inadequate maintenance and design.
An attempt to construct a disposal area using cement and rock filled gabions adjacent to the city of Buenaventura on the San Antonio Inlet has been abandoned because of environmental and foundation conditions. Another disposal area located across the river in an area planned for Port of Solo was constructed using small sand bags but it has been completely filled with maintenance dredged materials and is no longer in service.
Permission to construct dredged containment facilities for fine grained dredged materials in Colombia has become very difficult because of environmental constraints by local and state governments. The navigation channels leading into this area are constantly dredged. Disposal alternatives are limited to non-existing upland disposal areas or transport 80 km offshore in the Pacific Ocean.
Transport and disposal in the ocean was not considered to be economically feasible when compared to disposal islands constructed with geotextile tubes.
Several alternatives such as construction of upland disposal sites and dumping in the river adjacent to the navigation channel were met with environmental concerns and were not allowed.
An upland dredged material disposal area was not an option because of potential damage to Mangrove trees, poor foundation conditions and limited space. Construction of dikes on poor foundation materials, in open water with 4.0 m high tides twice a day was not considered to be technically feasible without the use of geotextile tubes.
The 1100 m circumference of the oval shaped island design was oriented to minimize obstruction to river currents. The oval shaped dredged material disposal areas were designed using 20 m circumference, 3.0 m high geotextile tubes fabricated with a GT500 woven polypropylene geotextile fabric.
This fabric has an area opening size of 0.425 mm and a wide width tensile strength in the machine and cross direction of 70.0 and 96.3 KN/M respectively. Seam strengths were about 50 to 60% of these values.
At a height of 3.0 m the geotextile tubes contained about 22 m3 per linear meter of dredged material. The first disposal area was about 200 m wide and 300 m long and the second one will be about 300 m wide and 600 m long and they were estimated to contain about 200,000 and 600,000 m3 of maintenance material respectively.
The construction plan was to fill eleven 100 m long geotextile tubes hydraulically with sandy dredged material from the navigation channel to form the perimeter dike for the ocean shaped disposal areas.
The geotextile tubes positioned along the proposed alignment were temporarily anchored during filling with 4.0 m long metal poles that were attached to nylon straps presewn along each edge of the geotextile tubes.
Initial filling attempts resulted in too many light weight fine materials in the far end of the 100 m long geotextile and tidal fluctuations caused the first geotextile tube to get slightly off the proposed alignment. To minimize this effect the geotextile tubes were filled in increments of 25 m with sand with the unfilled portion resting on a small barge until the next 25 m of geotextile tubes was needed.
Initially the contractor used an Ellicott® Series B890 dredge, the "Don David", but experienced some problems keeping the geotextile tubes in place against a 1.2 m/second tidal flow. This was caused by the geotextile tubes being inflated with 2.200 m3 of water in one hour, before sufficient solids were retained to weigh them down.
This was solved by replacing the Series B890 dredge with a 12 inch (305mm) Ellicott® Series 370 cutterhead dredge, the "Doña Sara" with 100 m of discharge line. With the smaller dredge all the excess water was drained through the fabric and the remaining filling ports maintaining the geotextile tubes deflated until sufficient sand weighed them down.
Construction of the geotextile tube perimeter containment dike for the first oval shaped dredged material containment facility was successfully completed this spring and is currently being used as a dredged material disposal area. Construction of the second oval shaped disposal area will begin soon.
The use of geotextile tubes to form the perimeter dike for the dredged material containment facility has proven to be constructable, and technically and economically feasible. Construction of the disposal area perimeter dike would not have been successful without the use of geotextile tubes.
Excerpted from World Dredging Mining & Construction
By Jack Fowler, Ph.D., PE, Geotec Assocs., Vicksburg, MS
Eduardo Martinez, Pres., Dragados Hidraulicos, Bogota, Colombia
Nicolas Ruiz, Civil Engineer, Bogota, Colombia
Carlos Ortiz, Bogota, Colombia