MODEL: MC 8 D, MC 22
Comacchio is expanding its presence throughout the West Coast of the United States.
An increasing number of drill rigs is being successfully used in small and large scale projects from San Diego to Seattle.
Three Comacchio drill rigs are currently working in San Francisco, on a jobsite located in 444 Townsend Street, not far from the Giants baseball stadium. The project involves an upgrade of an existing two-storey building, aimed to extend it to five stories and improve the building's seismic performance.
To achieve this, approximately 350 micropiles are being installed both in the narrow alleyways around the building and in the 2.4 m (8 ft) high basement.
The soil in the project area consists of a very soft layer of Bay Mud that rests on a hard bedrock located at a variable depth (between 18 and 34 m (60 to 110 ft). To improve seismic resistance, the micropiles installed outside of the building have to be permanently cased using 12 inch casings up to 7.6 m (25 ft) deep, whereas the micropiles inside the building are cased up to 4.6 m (15 ft). Inside these casings the client elected to drill with 73 mm SAS hollow bars with an 8.5 drill bit.
“This choice was made because we are drilling in alleyways outside, on paved walkways and it would be hard to control fluids and remove spoils, if we used rod and casing to drill. The SAS bars are also much quicker to drill. The one concern on this selection was if we could penetrate the rock effectively, as its very hard. The original plan was to drill with a thin grout to the pile tip and then flush that out with a thick grout. This idea was soon replaced by using a thick grout right from the start, due to the spoils removal and disposal difficulties and costs”, explains Daraius Tata, Sales Manager at Hammer & Steel, the local Comacchio dealer, who not only supplied the equipment, but also provided for the training of the operators on site.
The MC 22 is being used for the micropiles outside the building. Due to its 10 m (33 ft) long stroke, it allows to screw in a 25 ft long casing in one pass. Subsequently, 3 m (10 ft) long SAS hollow bars are used to drill inside the casings. The kinematics of the MC 22 allows for easy operation in the narrow spaces around the building. Depending on rock depth and hardness, productivity can reach four piles a day.
The most challenging part of the project is the installation of micropiles inside the building, which is performed by means of two Comacchio MC 8 D drill rigs.
The standard features of the MC 8 D include a telescopic mast providing 950 to 2100 mm (3 to 7 ft) feed stroke, effectively adapting to various headroom conditions without requiring the use of mast extensions. To maximize the stroke of the rig in the 2.4 m (8 ft) headroom, the concrete pile footing cutout in the basement was enlarged to accommodate the mast and clamps of the MC 8 D, in order to increase headroom to 3 m (10 ft), allowing for the use of 1 m (3 ft) long hollow bars and casings. By means of the high torque Comacchio rotary head equipping the machine, providing 2400 daNm (17,700 lbf ft) torque, casings are introduced for the first 4.6 m (15 ft), followed by the 73 mm hollow bars up to 34 m (110 ft) deep.
“The side shifting of the winch proved to be very useful in the handling of the drilling equipment” – explains Daraius Tata, “and so did the extremely compact design of the Comacchio rotary head R 2400F, that allows to work in close proximity to the wall”. The MC 8 D also features a unique roll-off system that allows for easily removing of the power pack from the rig. Thanks to this system, the power pack can be placed at 20 m distance from the rig, thus reducing noise, emissions and physical footprint and providing for a better work environment for the operators on site.