Saturday, October 15, 2011: 05:35:47 PM


Drilling with a Difference

Sanjoy Chakrabarty explains the rationale behind using CFA technology

Sanjoy Chakrabarty,  MD of Soilmec, India

India is among the fastest-growing destinations for infrastructure development. Today, many private infrastructure projects are coming up in the country, giving rise to a strong demand for good quality equipment. Private infrastructure project developers and contractors who execute projects are generating a sizable demand for foundation equipment that is safe to operate. With this in mind, Soilmec recently introduced its internationally-acclaimed Continuous Flight Auger (CFA) technology in India for the very first time.

CFA technology has been used in Europe since a long time, and is patronised by a large number of European nations. This technology is trusted for its stability, minimalistic operating costs and its unique ability to operate with great ease in almost any type of ground. CFA, which is globally referred to as ‘dry pile’, helps to increase functional productivity at sites, while also offering a bevy of environmental benefits such as an exponential reduction in sound emissions and other pollutants.

The technology can perform in every kind of soil, irrespective of individual peculiarities, without the use of bentonite. This helps in minimising the use of allied machinery, such as those that pertain to tanks, management costs and subsequently, overall piling costs. CFA technology can perform with much less manpower, generating cost productivity for the contractor. Environmentally, the technology is also quite safe, since the extracted soil is not contaminated with bentonite.

The drilling method allows excavation in a wide variety of soils—dry or water-logged, loose or cohesive-and also the ability to penetrate through low capacity, soft rock formations such as loamy clays, limestone and sandstone, etc. No shocks or vibrations are induced when the system is in action. Also, the equipment is sound-proof, as per law requirements, making it the most convenient piling method for construction in town centres.

Besides, since no bentonite mud is needed for the excavation, the need for special provision and space for the side plant is reduced and there is no danger of bentonite contamination. As a result, the various problems attributed to the disposal of the excavated materials are simplified. The reduced volume of soil brought up to surface by the flight auger translates into less amount of excavated material that has to be transported to the disposal point.

Piling it Right
A wide range of diameters (from 40–140 cm) and depths of up to 33 m, allows CFA equipment to easily overcoming problems pertaining to the execution of the pilings. The mother company’s experience of approximately 30 years in the execution of CFA pile enables it to operate the system even in difficult grounds, with the use of different teeth and augers.

CFA equipment generally consists of a flanged or tubular-type leader (depending on the pile depth), and a crawler unit on which the leader is mounted. The actual drilling is performed by a helicoidal steel plate welded to a central hollow stem, which has teeth at its lower part to help it penetrate through the ground. A disposable cap, fitted as plug at the end of the stem, prevents the entry of soil when the auger string is driven down into the earth. During the operation of this technology, the ground is partially pressed sideways by the auger penetration, which results in compaction of the soil all around the shaft.

The hydraulic drilling rigs—SR-40 and SR-60 are mounted on a Caterpillar turret, while the SR-50, SR-70 and SR-100 are mounted on a Soilmec carrier. All of them can be used for cased bore piles with casing driven directly through rotary head, or optionally by casing oscillator powered by the base carrier itself, deep bored piles stabilised by drilling fluid or dry hole, CFA piles by means of auger string, displacement piles, and soil-mixing. The SR-50, SR-60, SR-70 and SR-100 are equipped with the Drilling Mates System (DMS) on a 12-inch touch screen for to monitor and control the operating parameters. The SR-70 and SR-100 can be converted with a hydraulic grab for diaphragm walls. SR-80 and SR-90 can be converted into Diaphragm Wall base machine to work with a hydraulic grab.

Practical Matters
Soilmec became the first company in India to carry out CFA at a depth of up to 18 m, with a diameter of 600 mm where cage was driven to an 18 m depth. The technology was used at a Rajpura site, and the seamless execution has paved the way for an all-new piling scope in India. CFA was further used in key projects across Bangladesh. The company recently completed the Saibad water treatment plant project, and is currently undertaking the active management of two flyover projects in Dhaka. In addition, it has extended its bouquet of CFA services to its customers in Bangladesh, and is also selling this revolutionary technology in the country, converting the sale of seven other machines in Bangladesh. Soilmec firmly believes that that CFA is the future of foundation engineering technology.

The dynamic and physical load tests of the experimental piles done in Rajpura strength to the belief that CFA can go on to become one of the most acceptable and economical piling methods in India. Soilmec provides CM-50, CM-120, CM-700, CM-1200, CM-7000, RSeries and the SR-Series of the CFA rigs, depending on the scope, depth to be drilled and usage of the rigs. The company has displayed the CFA conversion kit for fitting on a standard SR-40 (the next development for CFA) at the recently-concluded BC India summit. This demonstration attracted a lot of attention due to the eco-friendliness and efficiency of the technology.

Given that there have been no disadvantages reported as of yet, it is safe to say that CFA is the future of foundation engineering technology. However, there is a lot of training and expertise that is required to use it most efficiently. Thus, one must look for a vendor who will offer necessary training and a ready supply of spares.

The author is the MD of Soilmec, India

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