Case story

Mirafi® PP - Construction of Breakwater

Indonesia, Sumatra

Project Data

Project	Breakwater Reinforcement & Filtration
Location	Bengkulu Port, Sumatra, Indonesia
Owner	N/A
Products used	Mirafi® PP200-40

Overview

Complete in March 1985, the new Port of Bengkulu, located at Pulau Baai along the West Coast of Sumatra, Indonesia is an important gateway for the economic development of the Bengkulu region.

Key to the design of the port were two rubble breakwaters with approximate crest length of 390 m and 420 m, and containing some 500,000 m² of rock in sizes up to 7 tons. The head of the southwest breakwater was constructed with blocks weighing up to 10 tons.

Design Solutions

The engineering challenges on this project were numerous. The seabed comprised soft marine clay, complicating the dumping of rock. Scour of the tie of the breakwater caused by wave pressure differentials was also a concern. Whilst these problems can be solved using stone and rock and conventional engineering techniques, it was decided to solve the problems by installing a high tenacity reinforcement geotextile under the entire structure. The geotextile was also required to act as a filter, and prevent the effects of scour of in the fine marine silt along the toe of the berm.

To perform these functions the geotextiles used had to withstand the drop energy of bedding stones and armor rocks without puncturing, as well as be capable of filtering the fine silt particles.

Mirafi® PP200-40 geotextile, with special loops woven into the edges of the fabrics to facilitate laying using bamboo was specified for the project.

Construction

To facilitate the installation process the Mirafi® PP woven geotextle was sewn into large wide panels. The geotextile was fastened to a bamboo lattice using the loops woven into the fabric at regular intervals to form a geotextile fascine mattress that was then floated out into position using barges.

The geotextle fascine was lowered by ballasting with bedding stones. The advantage of this method of laying is that the fascine remains stable whilst ballasting and requires only a relatively thin layer of bedding stones to be able to sink the mattress. The grid structure of the bamboo resists sliding of the bedding stones as the mattress slowly sinks into position.

This project was the first such application of geotextiles using this technique to be undertaken in Indonesia. Placement of the first rocks began in September 1983 and both breakwaters were completed by December 1984. A total of 110,000 m² of Mirafi® PP200-40 were installed.

Today the breakwater remains, as constructed, and integral part of the Bengkulu Port, and proving the durability of Mirafi® geotextiles in marine engineering works.