CANISTER-DRILLING FRICTION PILES FOR NAIROBI’S TALLEST TOWERS
Nairobi, Kenya, will be getting a new skyline soon. The Pinnacle Towers will truly tower over all other buildings in the city, and claim the title of Africa’s tallest building. The development is a complex that consists of two high-rise buildings: a 984’ (300 m) tall, 66-story office tower and 659.5’ (201 m) tall, 40-story Hilton hotel with a retail podium over four floors of car parking. When it’s completed, Pinnacle Towers will be nearly twice the height of Nairobi’s second tallest building, the UAP Tower at 531.5’ (162 m).
Frankipile International Projects Ltd, a Keller Company, is one of the many contracting and engineering firms working at the site. Franki works throughout Africa, and is a specialist in highly technical, foundation projects.
Many companies can drive piles, auger holes or use conventional core drilling systems to bore foundation holes, but Franki’s low profile canister drills, or LP Drills, from Center Rock Inc. (CRI) of Berlin, Pennsylvania, USA gives them an advantage.
Works Manager, Ryan Goss said, “This sort of rock needs multi hammers. We wouldn’t have tendered this project if we didn’t have LP Drill technology.”
Early in the project, another contractor used a 31.5” (800 mm) conventional roller-cutter core drill rather than the Center Rock LP Drill to drill the rock portion of the first hole. That first bore hole took 3-1/2 weeks to clean the 69’ (21 m) hole to depth.
The Center Rock 32” (800 mm) LP Drill averaged 10’ (3 m) an hour on this job. Goss said, “We could use roller teeth/bits, but time wasted is a killer. Most jobs, like this one, have a penalty for being late.”
Franki has three canister systems for this project’s 380 piles in varying diameters of 48” (1,219 mm), 42” (1,054 mm) and 32” (800 mm).
Franki matches the right tool to the soil or rock condition. The holes of this job each required its own combination of boring techniques. In addition to the Center Rock canister drills, tooling included augers and drilling buckets.
While the LP Drill is operating, each of its hammers is cutting its assigned portion of the hole, chipping away at its portion of the entire hole face during a full 360-degree rotation. The driller makes full use of the range of travel from the air hoses, rotating the canister drill a full turn in one direction and then a full turn to the other.
Once the top of the calyx basket moves below the surface, any cuttings that the flushing air cannot blow out the top of the hole fall into the basket. When the basket is full, the driller trips out of the hole and swings the drill to the side. Lifting the basket dumps the cuttings, and the drill goes back in the hole. Once drilled, a rebar cage is lowered and concrete fills the hole.
LP Canisters drill a structurally better hole
Advantages that the Center Rock LP Drill systems give Franki are clear in comparison to other boring techniques that could have been used on this job. Large-diameter hammers have pistons so heavy, it takes up to nine, 33 m3/min (1200 cfm) compressors to lift it. This would require a much larger footprint for the job.
Another drawback of a single piston hammer drill is the amount of energy such a large system transfers to the formation beyond the hole face. Rock fractured beyond the intended borehole weakens the formation, undermining the pile’s purpose. Center Rock canister systems use energy much more efficiently, without compromising formation integrity.
Before Jim Rose was a CRI International Sales Representative, he was a service technician for CRI. He explained that Center Rock works with customers at the start of each job, then sending a technician with every LP Drill sold.
“We don’t sell out of a catalog,” Rose said. “Each drill has its purpose. When that drill goes to its intended project, we follow the tool on its setup to make sure the customer knows how to run it. We want every customer to start out knowing everything about their drill.”
Part of a job setup is to know the capabilities of the drill rig. Rose said, “I’ve got to know the rig to show them how their drill will work with an LP Drill. We want our products working at 100 percent efficiency on the job. I won’t let a client fail because of the rock, the drill or the equipment.”
Ryan Goss says Franki doesn’t always need its three Center Rock LP Drills, “But when they are needed, it’s great to have them in the tool box. We couldn’t do this project in the timeline allowed without Center Rock.”
The Pinnacle Tower Complex is expected to be completed in 2019.