Soil improvement: Kataraja toll road

The city of Jakarta has outgrown its current boundaries. To cope with this rapid growth, it is expanding northward into the Sea of Java. Witteveen+Bos put together a development plan for the 12,000 hectares earmarked for the required land reclamation. A 1,000-hectare section within this larger area, named ‘Pantai Indah Kapuk 2’ (‘PIK2’), will be home to the first waterfront city in Banten Province.

The Kataraja toll road is being constructed in the southern part of PIK2. Given our experts’ familiarity with the area, we were asked to provide technical assistance for soil improvement in connection with the road’s construction. The criteria included a 10-cm residual settlement over 10 years.

Vacuum consolidation system

Phase 1 of the project focused on approximately 5 km of road, for which a platform needed to be constructed to raise the embankment. The subsoil, however, consisted of very soft sediment. To avoid problems such as excessive sediment or instability, the soil needed to be strengthened using a vacuum consolidation pump system. This system extracts water from soil, making it more compact. Using a membrane was not an option due to a lack of filling material.

Effectiveness and performance

To ensure the design was consistent with real-time data, we carried out several back-fitting analyses of monitoring data obtained from a piezometer, vacuum pressure meter, and settlement beacon (including both the extensometer and inclinometer). These analyses took several potential risks into account so as to prepare for possible mitigation measures during the final fill works and paving.

Risks associated with vacuum consolidation efficiency include a torn membrane, water loading, the loading history related to the platform fill, and the presence of sand lenses (which cause the vacuum pressure to drop).

The analyses ultimately proved the system’s effectiveness. Our technical assistance on this project has now been extended to phases 2 and 3, involving another 3 km in the direction of the PIK2 Extension across the Tahang River.

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