BY: RIJANTO P HADMODJO, former CEO OF CAKAR BUMI corp.
During the last decades many, new foundation system have been developed with various and sophisticated equipment: All of them have the same goal, i.e. more bearing capacity, quicker and easier to execute, more economical, as regard to the costs and less problems with the neighboring buildings. But very few, if any, deal with foundation system, which can solve the problems on soft soil without looking for hard layers .
The following system which I would like to bring forward is one that specially has been invented to meet the “soft soil problems”. It is a simple method with a good bearing capacity, named by the inventor as. CAKAR AYAM (literally mean Chicken Claw) foundation.
This Cakar Ayam .foundation was invented by Prof .Dr. Ir Sedijatmo in 1961, when was constructing electric high-tension tower in the area of Ancol. At that time we (Indonesians) were preparing feverously the facilities for the Asian Games 1962.
The high-tension towers were be finished within a very short time, and would connect the electric-power station, in Tanjung Priok with the sport-venues, in Senayan.
Seven towers should be built in the Ancol area and only 2 were just finished, where the other 5 were to be completed within couple months
As all of us know the Ancol area at that time was a swampy area and it was very hard to make the foundation in the conventional way so he had to find out a new method quickly to overcome this problem.
On a bright morning he got an intelligent idea to build .the tower on a foundation consists of a concrete slab to which concrete pipes were fixed underneath monolitically, clawing in the earth. This idea comes soon to be realized and the Cakar Ayam Foundation was born.
The, calculation was made very roughly and we ( Cakar Bumi corp.) got a dimension of a slab and pipes two and half times heavier than we use to apply at the moment(now), but anyway this system is much cheaper and quicker to execute than the piling foundation used for the previous 2 towers.
With firm confidence that this system was the solution, the 5 towers were finished in due time and now we can still see ( them)
Since that time Prof. Sedijatmo is looking for a more exact and more economical computation-method and after passing various processes we now came to the dimension which more or less becomes a standard.
For those who is not familiar yet with this foundation system, the Following explanations. may be useful.
BASICALLY IS A FLOATING CONCRETE SLAB ACTS AS FOUNDATION
This Cakar Ayam foundation consists of a reinforced concrete slab of 10 to 15 inches thick depending on the construction that should be borne and the condition of the soil underneath.
Underneath the slab reinforced concrete pipes are monolithically fitted
With a distance between the axes of each pipe of 2 or 2,50 m, while the length of the pipe-varies between 1,50 to 3,50 m. The length of the pipe also depends on the load and the soil condition. The pipe diameter is 1,2Q m or 1,50 m and the thickness of the pipe is 8 cm.
The reinforcement (steel bars) for the pipe is single, while for the slab is double. Figure no. 1 (not yet available) gives a typical illustration. In principle, the Cakar Ayam foundation is applicable on the softest soil to the hardest soil, but according to our experience it is most economical if applied on soils with a bearing capacity of 1,5 to 3,5 ton/m2 although many times we also use for harder soils as it is still money saving. The basic idea of the Cakar Ayam foundation is utilizing the soil characteristic that is not or/not properly utilized by other types of foundation, namely the passive-soil pressure.
The (relatively) thin concrete slab is floating on the -soil and its stiffness is obtained through the pipes underneath and-the pipes stay vertical because of the passive-soil pressure (that prevail)in the soil. This combination makes the Slab and the pipes in the soil together a stiff construction that is not easy to bend.
If put above the soil it will be a very weak construction so if we compare this system with a slab with stiffening beams the latter has an internal stiffness above the soil which the Cakar Ayam foundation-has not, because as mentioned previously the Cakar Ayam foundation obtain her stiffness through the passive-soil pressure. It is clear that this will mean a reduction on volume of the reinforced concrete and is consequently more economical for the same bearing capacity.
We would like to ask your attention that the function of the pipes underneath the slab is not to support the slab as it is the case with a conventional “slab and beam construction ”, but is to stiffened the slab entirely instead.
The Cakar Ayam system foundation structure is patented in: Indonesia, Belgium, Canada, France, Germany, Great Britain, Italy, and The USA.
Jakarta Indonesia, March 4, 1981
The Cakar Ayam have been applied in many and various building throughout Indonesia as well as the world.
The most noticeable are two runways ( each 3660mx60m )and Aprons at The Soekarno-Hatta International Airport. And also the 14 km beautiful access toll road to the Airport which built almost entirely on swamp and soft soil and virtually float above them. And the road is named after the CAKAR AYAM inventor Prof Dr. Sedijatmo in honour of him.
After more than 2 decades of operation, the road is still the same as it was when first used despite yearly undue inundating cause of massive improper swamp landfill and reclamation venture just north a third length of the road.
The picture above is a toll road project in Makasssar. Note that the 50 cm diameter steel pipe is take place the concrete pipe as it is apparently even more easier and cheaper to built.