Construction of Petronas Twin Tower Piles

The Twin Towers were planned to be built on the site of the former Selangor Turf Club which was flat, green land. But soil studies showed that the site where the buildings were originally planned for, proved unsuitable for the foundation due to the irregularities of the limestone bedrock below that's known as Kenny Hill soil.

Each tower was calculated to weigh 300,000 metric tonnes which would be spread over a large concrete slab called a mat. But that weight exerted 1,140 kilopascals (one kilopascal pressure is equivalent to 1kg exerting pressure on 1sq mm), exceeding the weight-bearing capacity of the soil and enough to cause the foundation to fail.

Moreover, soil tests showed that the bedrock under both towers started shallow, 15m down, but sloped sharply to more than 180m.

To support the immense weight, a depth of 21m (as high as a five-storey!) would have to be excavated for the basement. This also meant penetrating the bedrock at one end but not the other.
Installing concrete-filled piers at the deep end would be difficult, slow and expensive, exceeding normal construction practices. The piers' shortening over time would also produce unacceptable tower tilting. (See diagram a)

KLCCB (Kuala Lumpur City Centre Bhd), the developer of KLCC, finally decided to move the location 60m southeast of the initial site to achieve better support. Here, the bedrock was deeper, thus allowing the buildings to be firmly anchored in at least 55m of soil for each tower basement.
And instead of piers, it was decided an entirely different foundation system was needed. Friction piles (structures narrower than piers), reinforced by grout (a sand and cement mixture), were used.

Excavation began in March 1993.
The contract for the foundation works was awarded to a consortium of French and local companies, Dragages-Bachy-First Nationwide Sdn Bhd.

Every step of preparing the foundation was a technological breakthrough, says Arlida Ariff, then the planning manager of the overall KLCC project.

To dig the foundation, we didn't use hammering in the conventional sense. Instead we excavated the ground using a combined technique of piling and raft foundation (like a big concrete slab); it was the first time the latter technique was being used in the country.

With this technique, when you bore the piles in, instead of circular piles, rectangular or barrette ones were used. Barrette piles are bigger than circular piles, so we could put in fewer number of piles. This also increases the safety margin and poses fewer problems.

That's because the bigger the pile is, the smaller the number we have to put in and the better its ability to withstand tension.

Water was then used to clean and keep the bored hole intact until we poured the concrete in. Until a certain depth, drilling mud or bentonite (a kind of "clayish" liquid)
was used instead of water as it was a stronger substance which could do the job more effectively in deeper parts," explains Arlida who's now the general manager of KLCCB and project management consultant for Putrajaya Holdings Sdn Bhd.

It was also the first time that the Malaysian construction industry would witness the largest amount of concrete poured in its history - 13,200cu m (enough to build 130 double-storey link houses!).
The concrete was continuously poured into the hole for more than 52 hours in order to eliminate construction joints in the pile mat and achieve a smooth finish.

According to KLCCB general manager Hashimah Hashim, then the project manager of Tower One, the construction industry normally uses grade 30 or 40 concrete. For the towers, high-strength grade 80 concrete was used.

The use of such high grade concrete was a transfer of technology from the USA which uses up to grade 110 in the construction industry," he says.
The building of the foundation, from the excavation to its completion, took 12 months to finish.

Barrette Piles Data

 

Construction of Petronas Baratte Piles

Barrette Piles The diaphragm wall panels can work individually, as piles, but with rectangular sections, with high resistance to vertical loads. In this case, they are called barrette piles.

Metodologia Executiva

Excavation:

It starts with the execution of the short wall (wall) tab, along the axis of the wall and buried in the ground, with the usual depth of 1.00 m. The function of this wall is to maintain stable the top of the panels, as well as serve as an initial guide for the digging tool. It also serves as a support and reinforcement tube hopper.
In some cases, very special may be employed guard rails guiding metal or precast concrete, however, are not very advisable, because some characteristics, such as bob and alignment can be compromised. Then, the positioning diafragmadora and starts the excavation with “clam shell” simultaneously with the filling of the hole with mud stabilizer to the projected depth in design. The tool “Clam Shell” penetrates the soil and, when full, the rod is raised and the tool is automatically emptied by opening.
As the excavation proceeds, care should be taken bob excavation tool, as well as the level of the slurry stabilizer, always within the limits of the guardrail guide. The slurry stabilizer has the function of ensuring the stability of the hole (avoiding the use of the coating in soil) and maintaining the suspension resulting from the disintegration of waste terrain.
The procedure is to clean the bottom of the slide with his own digging tool, removing the viscous and dense. In the case of using bentonite slurry, it should fit within the parameters of the mud required to replace it or desarenando pumps it through submersion.

Placement of Armour:

With an assist crane, the armature is hoisted and placed on the panel so as to allow passage of the tube when the hopper for the concrete. The armature is supported on the short wall guide in order to avoid commuting at the time of concreting. Should be established to ensure the roller spacers required overlay.
Along with the armor are placed tubes or plates-knuckle, smeared with mold release and raising up of alignment. When there is need to use the mirror plates, they should also be placed in this point, too greased with release agent.

Concreting:

After placing the reinforcement in the panel, the concrete begins immediately. The system used is the same concrete implementation of bored pile, the submerged, namely that runs upwards in a continuous and uniform manner. To do so, are mounted concreting pipes, hopper. In order to prevent the sludge being mixed with the concrete cast, a ball is placed inside the tube at the beginning of the concrete, which is expelled by the weight of the concrete column.
During the concrete placement, the pipe sections will be executed whenever required, ensuring that the tip of the tube hopper is immersed at least 1,50 meters in the concrete.
Retires, at the beginning of the castable, tubes or plates, gasket and plate mirror. Thoroughly clean the joints of adjacent panels eventually concreted already, by mechanical action of the wiper.

The concrete shall conform to the following specification:

• Cement consumption ≥ 400Kg per m³ to factor a/c ≥ 0,6;
• Aggregate: Stone No. 1, rounded avoids lamellar form, being forbidden the use of powder-stone, sand 35% to 45% by weight of aggregates;
• Rebate = 20 ± 2 cm.

Pre Molded Diaphragm Wall

To reduce the weight of precast wall can be concreted record “in situ”. In this case, it is suggested the use of cast slabs, where the concrete of the plug is held inside the plate.
To ensure the tightness of the joints, the panel with the excavated slurry stabilizer is set to “coulis” (mixture of cement and bentonite + water) before placing the preformed plate.
After placing the preformed plate of concrete, “coulis” fills the space between the seals, preventing the passage of water.

Plastic Diaphragm Wall

The plastic diaphragm wall element forms a “impervious” “coulis” (mixture of cement and bentonite), in proportions that vary depending on the desired permeability, preventing the flow of water or fluid undesirable.

Parede Diafragma Pré-Moldada

Barrette Piles in Foundation System of Petronas Twin Tower : Part 2

Now we will learn about barrette piles. This pile is adopted in structures where high moments and horizontal forces in addition of usual vertical loads have to transferred to ground safely. These are rectangular piles that have a similar construction method of diaphragm wall construction.

As these section to be drilled is large, there boring with auger is avoided, rather an economical procedure is followed by excavating and protecting the sides. In regards to protecting sides, water based slurry like bentonite is used to stabilize and support trench walls while excavation is carried out.

After completion of excavation for barrette, steel cage as reinforcement is lowered and placed in central portion of excavation to be poured with concrete providing sufficient concrete cover around reinforcement. Concreting is done in continuous operation using tremie pipe extending to the bottom of the excavation trench. The procedures maintained are as used in regular pile concreting. We have published many posts regarding pile concreting. You can read those for better understanding.

The slurry provided to stabilize excavation is come out as concrete displaces it filling the volume in trench. The desanding process is used to treat this slurry and to be reused for surrounding barrette excavations. The usual size and depth used are of (0.8-1.2) m wide and 2.8 m length. But a depth of 150m can be achieved with these piles.

The largest foundation application example is Petronas twin towers. We have discussed earlier about foundation system of this mega structures. In Petronas tower, barrettes of 125 m were used that are subsequently embedded by huge raft slab. The massive foundation work was conducted by Bachy Soletanche and takes 12 month to complete.

Barrette Piles in Foundation System of Petronas Twin Tower : Part 1

Petronas Twin Tower is a 452 m high skyscraper located in Kuala Lumpur Malaysia. These great structures (twin towers) were tallest building of world until Taipei 101 was built. 

As foundation system is concerned, we will first discuss about the foundation system and then we will go to the piling types. Geotechnical investigation explored that the actual construction of these mega structures was on soft rock and decayed limestone. Both occupied almost equal portions of construction site. Then engineers were decided to relocate the structure to be sat it on entirely soft rock and moved it to around 61 meter to achieve this. 104 nos piles of an average 125 m piles were used to reach deep bed rock which made it having deepest foundation system of the world.

The single stage largest and longest concrete pouring of the history of Malaysia was conducted to embed this huge number of piles to form a raft from which a retaining wall of 21 meter was raised along a perimeter of more than 1000 meter. The raft had a giant thickness of 4.6 meters having weight of 32500 tonnes. This record was hold unbroken till 2007 in respect of largest pour. The raft comprised 13200 cum of concrete which required 54 hours to pour for each tower.

PETRONAS Twin Towers At A Glance

Number of storeys	88
Height	452 meters above street level
Total built-up area	341,760 sq.meters ( 3.7 million sq. feet)
Design/Architecture	Cesar Pelli & Associates [U.S.] in association with KLCC architects.
Location of skybridge	Levels 41 and 42
Length of skybridge	58.4 meters
Height of skybridge	170 metres above street level
Vertical transportation	29 double-deck high speed passenger lifts in each tower
Number of escalators	10 in each tower
Stainless steel cladding	65,000 sq. metres
Vision glass	77,000 sq. metres
Concrete [various strengths up to grade 80]	160,000 cubic metres in the superstructures [see also foundation description below]
Steel	36,910 tonnes of beams, trusses and reinforcement
Foundation	4.5 metre [15 feet] thick raft containing 13,200 cubic meters of grade 60 reinforced concrete, weighing approximately 32,550 tonnes under each Tower, supproted by 104 piles varying from 60 to 115 metres in length.