How it began
Sedyatmo, an engineer and official of the state electricity company PLN, had to erect seven high-voltage towers across the swamps of Ancol in Jakarta in 1961. The line was to carry power from the Tanjung Priok station to the Senayan sports complex for the 1962 Asian Games. Two towers had been built on conventional foundations with great difficulty and five remained. He proposed a concrete slab with concrete pipes fixed monolithically beneath it, and the five towers were finished on time.
Before it existed
On swampy ground builders relied on piled foundations that reach down to a hard layer. At Ancol this conventional approach was slow and hard to carry out, and only two of the seven towers had been completed with it when the deadline approached. The builders also found piling slower and more expensive than the new system.
How it works
A reinforced concrete slab 10 to 15 inches thick rests on the soil. Reinforced concrete pipes 1.2 or 1.5 meters in diameter and 1.5 to 3.5 meters long are cast under it at intervals of 2 to 2.5 meters. The pipes do not carry the slab like columns. They are held upright by the passive pressure of the surrounding soil and so keep the thin slab stiff, which lets the whole structure float on soft ground without reaching a hard layer.
How it spread
The system was used for hundreds of high-voltage towers, aircraft hangars in Jakarta and Surabaya, and the runways, taxiways and apron of Soekarno-Hatta International Airport, as well as the toll road to the airport built across swamp. A 1981 account by the former head of the firm that built it lists patents in Indonesia, Belgium, Canada, France, Germany, Great Britain, Italy and the United States.
Where it stands today
The north runway of Soekarno-Hatta airport, built in 1977 and 1978 on the system, remains in service and has been the subject of engineering studies. The airport toll road is named after Sedyatmo. A lighter variant with steel tubes, called Cakar Ayam Modifikasi, was applied on a toll road near Makassar completed in 2008.
