Bored Cast-in-Situ Piles in Difficult Ground A 2 x 660 MW capacity thermal power plant is being developed at Krishnapatnam, Andhra Pradesh. Keller Ground Engineering Pvt. Ltd (Keller) was awarded a contract to execute bored cast-in-situ pile foundations of 760 mm (30 in) diameter length varying from 40 m (131.2 ft) to 60 m (196.8 ft) to support the main plant structures such as boilers, TG, ESP, etc., and balance plant structures such as the cooling tower. All these heavy structures have been proposed to be built on pile foundations. About 2,600 piles were installed using 4 hydraulic rotary rigs during the 12-month project. The top 8 m (26 ft) of subsoil consists of loose to medium dense silty sand having SPT N values ranging from 5 to 10 underlain by soft clay with SPT N values of 2 to 5 to a depth of 29 m (95 ft). This layer is followed by a dense sandy layer up to 40 m (131.2 ft) underlain by hard clay up to 50 m (164 ft) and further followed by dense sand up to borehole termination depth, 60 m (197 ft) below the existing ground level. A dedicated batching plant was erected on site to ensure continuous supply of RMC of over 70,000 cu m (2.5 million cu ft) for a duration of 12 months. Construction of bored cast-in-situ pile foundations Keller has maintained an average production rate of 100 m (328 ft)/rig/day with the highest production rate of 200 m (656) /rig/day during peak production, and installed 12 piles per day utilizing 3 rigs with an additional standby rig. About 2,600 piles have been successfully installed and quality of construction was ensured by conducting more than 30 routine pile load tests at the site. Keller has achieved 500,000 safe man-hours, which shows Keller’s focus on construction safety. The project execution team made continuous efforts to micro plan all activities, cycle time of various stages of execution, regular maintenance of plant and equipment, daily progress meetings, and critical reviews on every activity, which enabled the project’s overall success. Large Scale Piling & Ground Improvement Project challenging driving conditions due to densification of the sandy sub-stratum; and in spite of driving difficulties, 20,673 piles were successfully executed to an average depth of about 17 m (55.8 ft) below the ground. Bored cast-in-situ piles (8640 nos) also formed part of the work (diameters of 500 mm [19.7 ft], 600 mm [23.6 ft], 700 mm [27.6 ft], 900 mm [35.4 ft]) to take up heavy loads. A total of 567 field static load tests formed one of the Stone column construction at Paradip refinery ITD Cementation India Limited was the first company to launch the project for the mega refinery project located at Paradip near the eastern shore of India. More than 29,000 piles of various types and geometric configurations were installed on a fast-track basis in a very short span of 24 months. The majority of the piles were driven cast-in-situ (diameters of 400 mm [15.75 ft], 450 mm [17.7 ft], 500 mm [19.7 ft] and 530 mm [20.9 ft]), which involved driving a closed bottom steel casing. Workers encountered very quality assurance measures for the production piles, which is probably the highest number of load tests performed in a single project in India. Apart from the piling works, ITD Cementation also executed ground improvement works with construction of 9,497 stone columns, each of 900 mm (35.4 ft) diameter and approximately 10 m (32.8 ft) deep by wet vibroflot technology. Major concrete pours were also involved for civil works at this refinery site, of which, two operations involved continuous pours of 3,004 cu m (106,000 cu ft) and 2,785 cu m (98,275 cu ft) of concrete; each of these pours were achieved in 23 and 34 hours respectively. Such continuous concrete pours involved meticulous planning of materials and logistics. 30 • DEEP FOUNDATIONS • JAN/FEB 2013
