The entire contract was awarded to to M/s Larsen & Toubro Limited. The project included a three-level basement (about 14 m or 46 ft excavation) in loose to medium dense silty sands. The site in general consists of 3 m (10 ft) of non-plastic to low plastic silty clay followed by poorly graded fine sand with silt up to 27 m (89 ft). The groundwater table was found at about 10 m (33 ft) below the existing ground level. The retention system designed for the proposed excavation was a 20 m (66 ft) deep peripheral D-wall supported by three levels of inclined temporary ground anchors. Keller installed inclined soil anchors of capacities ranging from 50 to 70 tonnes (55 to 77 tons). The length of anchors varied from 16 m to 22 m (52 ft to 72 ft) for different levels and capacities. A hydraulically operated Casagrande C6 rotary drill rig was used for boring. The grout mix included special additives. Workers injected the primary grout, allowing for about 2 hours of initial setting time. Then, secondary grout was carried out under high pressure for all anchors. The high-pressure secondary grout fractured the primary grout and forms effective bond with the surrounding soil. Engineers tested all anchors after the curing period according to the pre-determined design locking loads. Shiplift facility for ABG Shipyard Diaphragm walls were used for quay walls and the slip dock area. A majority of the diaphragm wall comprised T-panels (also called buttressed panels) each 5 m wide, 1,000 mm thick (16.4 ft wide, 40 in thick) with a length of 38 m (125 ft). Trenching of T- panels was done using hydraulic rigs with Kelly mounted grabs. The reinforcement cages weighed up to 32 tonnes (35.3 tons) and in many cases involved three service cranes for lifting operation, with final lowering undertaken by a 136 tonne (150 ton) capacity crane. Productivity rate for the T-panel was, on an average, 5 days with bulk of the time consumed in trenching operations (3 days). Lowering of the cages and the stop ends were done in single piece involving precision monitoring and skilled supervision. This was a fast track project, and the contractor transformed the marine piling into a typical land piling scheme by constructing a temporary rockfill cofferdam that surrounded the working pile area. The area inside the cofferdam was filled up to +12 m (+39.4 ft) level with locally available soil. Subsequently after construction of the shiplift platform, fill was removed to form the facility. The cofferdam solution reduced the project time by more than 50%. Large Diameter Bored Piles, Chennai Metro Rail Station Diaphragm Wall Construction for ABG Shipyard at Dahej Diaphragm walls are increasingly used in India’s infrastructure projects such as metro stations, riverfronts, forebays of intake wells and in harbour facilities. ITD Cementation had been involved in a prestigious project at Dahej, an emerging industrial port town of Gujarat state in Western India. This shiplift system, now completed, is the largest in the world (232.6 x 47.3 m or 763 x 155 ft) having a lifting capacity of 180,000 DWT (198,400 tons). ITD Cementation installed large-diameter bored cast-in-situ piles (464 40 and 24 in thick exceeding 204,500 ft ) and civil works for various harbour components. diaphragm wall (1,000 and 600 mm thick exceeding 19,000 m or 2 38 • DEEP FOUNDATIONS • JULY/AUG 2013 nos. of 1,500 and 1,200 mm diameters or 59 and 47 in), a 2 The maximum diameter of bored piles in India is generally 1,200 to 1,500 mm (47 to 69 in) diameter. Recently, L&T GeoStructure proposed a 2,500 mm (98.4 in) diameter bored cast-in-situ pile to replace barrette piles for the Chennai Metro Rail Project at Mannadi station, Chennai, India. AFCONS Infra- structure Ltd is the main contractor who proposed 2,500 mm x 2,500 mm (98.4 in x 98.4 in) size barrette piles. The subsoils comprise sands, sandy clay up to 29 m (95 ft) below ground followed by Charnockite, a metamorphic rock with unconfined compressive strength around 150 MPa (21,800 psi). The piles are to be socketed around 4 to 5 m (13 to 16 ft) in this rock. The main contractor deployed a hydraulic Kelly grab and hydraulic rotary piling equipment to excavate the barrettes. To meet the stringent schedule requirements, the main contractor had to change some procedures. They mobilized a Bauer BG36 Hydraulic piling rig along with 1,000 mm (39.4 in) diameter roller bit core barrel, 2,500 mm (98.4 in) diameter soil bucket, soil auger and 2,500 mm (98.4 in) diameter cross cutter with round shank chisel. In rock, the initial perforation drilling was done with 1,000 mm (39.4 in) diameter core barrel with 4 or 5 perforations made followed by drilling with 2,500 mm (98.4 in) diameter cross cutter. Boring in soil could be completed in around 11 hours while the drilling in rock took around 2 to 3 days to achieve the 4 to 5m (13 to 16 ft) socket lengths. In contrast, barrette excavation took between 2 to 4 weeks. The time saved in drilling 2,500 mm (98.4 in) diameter was significant. The industry can profit from better tools and drilling procedures, provided they can be commercially supported by reasonable rates for drilling.
