Construction of the artificial beach

Project description

The work involves constructing the “El Salitre” artificial beach situated at Tocopilla, 1,532 km from Santiago (the capital of Chile). The El Salitre beach is close to a port region which is served by a local thermoelectric power station. Due to the loading and unloading of mineral coal, the beach area was dark in colour and suffered from various contamination making it unsuitable to be used by the population. The objective of the initiative to revitalise the El Salitre beach was to improve the quality of life of the local population of 27,000 inhabitants by investing 7.5 million US dollars in order to recover an available coastal area by creating an artificial beach with an area of 24,000 m² opposite the town centre. The construction of two breakwaters and submerged breakwater was evaluated as the best solution to protect the new beach against the action of the waves and currents of the Pacific Ocean. By dredging and encapsulation of 29,000m³ contaminated sand replaced with 26,000m³ of clean white sand imported to the area, 250 linear metres of beach were created. The encapsulation of contaminated sand was enabled by using geotextile SoilTain CP tubes as cores of the costal structures

Solution

The solution consisted of constructing two breakwaters, the northern breakwater 120m long and the southern breakwater, 199m long. These structures were built with SoilTain PP 200/200 CP Tubes filled hydraulically with contaminated sand covered with rocks. In order to avoid the erosion of the subsoil next to geotextile tubes. Scour aprons with anchor tubes were installed prior to placing the geotextile tubes. With a width of 6metres the scour aprons are placed beneath the tubes in such a manner that they provide a strip of 2.5metres of erosion protection along the tubes. In a preliminary stage, filling trials and tests were executed in order to develop an installation strategy for the present challenging site conditions. Wave heights up to 4 metres had to be taken into account for installation because the project is located exposed to the forces of the Pacific Ocean. As result an installation frame was designed, keeping the unfilled geoextile elements (tubes and scour aprons) in place till they are filled and therefore ballasted. After the necessary preparation works had been carried out, the construction of the northern and southern breakwater was started. The southern breakwater core accommodates 40 geotextile tubes and 6 scour aprons, whereas the northern breakwater core consists of 12 tubes and 9 scour aprons. Different tube lengths have been applied in order to create overlapping tube stacks up to three layers high, which were required to achieve the structure design height. For positioning and placing the tubes also in deeper water a crane in combination with the frame was used. The wave load resistance of the frame as well as the positioning accuracy was increased by using concrete blocks as ballast for achieving a total frame weight of 13 tons. Furthermore the construction sequence was adapted to the site conditions. In order to protect the tube installation from wave influences, the stones for the final armour layers were placed around the ongoing installation spots acting as a wave shelter. After completion of tube filling, a 500 g/m² non-woven was placed across the tubes, which functions as a mechanical protection layer for the tubes against the rock. Subsequently the rock cushion layer was carefully installed on top of the non-woven. The final outer armour rock layer is composed of stones with a unit weight ranging from 2 to 10 tons.

Benefits

With the use of SoilTain PP 200/200 CP the contaminated material could be used as filling material for the geotextile tubes. Also, due to the shortage of rocks at the location, the core of the breakwaters made out of SoilTain Tubes provided material and resource savings.
The tubes were produced of SoilTain PP 200/200 CP, a woven geotextile developed for hydraulic applications and made out of UV stabilized yarns with a minimum tensile strength of 200kN/m. The project was completed successfully, improving the quality of life for the local population.