Forming piles for the world’s tallest building is a challenge, but proving the capacity of the foundations was no simple task either. GE reports on progress at Saudi Arabia’s Kingdom Tower.
Bauer reported in January that it had completed work to construct the 270 piles to support the new tower. But, before above ground work could get underway, final testing of the foundations was needed. Fugro Loadtest had been working with foundation designer Langan International before the project moved onto site. It then worked with contractor Bauer throughout the foundation installation work to prepare for the testing phase.
“The challenge of building such a tall tower in unknown ground required a detailed investigation into the ground conditions and load carrying capabilities of the soils at varying depths,” says Fugro Loadtest managing director Melvin England.
“Langan was tasked with providing guidance for the foundation design and engaged Fugro Loadtest for a full-scale load testing programme.
“Several questions were asked of the testing programme: which would be the better option for the foundations, conventional piles or a barrette foundationsolution and what would be the optimum depth of foundation?
“Would a bentonite or polymer slurry be preferable over a natural water slurry? As the tower would be situated in an active earthquake zone, would the soil resistance degrade with cyclic loading? In order to answer these questions, the foundation testing programme was designed into two phases.”
In the first phase a test programme of two piles and two barrettes was undertaken by Soletanche Bachy, one pile and barrette to be 45m in length and the other pair to be 75m in length founding in siltstone and degraded sandstone deposits. Each pile and barrette was constructed with a multi-level Osterberg-cell (O-cell) arrangement consisting of two levels of loading. Cyclic loading was planned into the testing schedule to ascertain the soil susceptibility to degradation under cyclic loads.
A second test programme of two piles was undertaken by Huta Foundation Works. The piles were 45m and 75m length and constructed with a multi-level O-cell arrangement. A fully instrumented lateral load test was also performed on one of the test piles with 10 levels of inclinometers to measure the lateral deflection. Lateral loads were applied at the pile head using a calibrated jack and load cell.
“For the O-cell test piles, the excavation was calipered for diameter, shape and verticality profile after final clean-out using the Sonicaliper,” says England. “Once the testing had been completed, an evaluation was undertaken to enable a suitable foundation solution to be found. The results indicated that piles would perform adequately and that there was no indication of any friction degradation of the deformed sandstone strata under cyclic loading. Results of strain gauge analysis allowed the unit friction to be assessed and a preferred foundation solution to be put forward by Langan International based on the findings for a hybrid pile raft of varying pile length.
The foundations installed at the site by Bauer include 72, 110m long and 1.5m diameter piles, 154, 1.5m diameter piles to depths of between 49m and
89m and another 44 piles with a diameter of 1.8m to 50m depths.
As required by the project specification, three test piles were installed to 48m depth and a fourth was constructed to 108m during the main works. The excavation for each O-cell test pile was calipered for diameter, shape, profile and verticality after final clean-out using a Sonicaliper. The four O-cell prooftests were performed successfully at the required test load of 75MN and the O-cells were grouted after testing to restore the structural integrity and for incorporation into the structure.
In addition to the preliminary testing, 16 of the permanent piles were installed with Geokon model 4911-4 sister bar strain gauges as permanent instrumentation in the pile raft. All of the permanent piles were also tested for integrity by using the cross-hole sonic logging tests and Tomography 3D profiling.
Now the foundations are complete, construction of the above ground structure is underway and is being undertaken by the Saudi Binladin Group with project management by Mace and EC Harris.
Reaching for the skies
Work on the Kingdom Tower and other buildings on the 50ha plot is the first of three phases of the Kingdom City development, designed by Hok, that will result in construction over a 5.2km2 area.
The second phase of the work being undertaken by project developers Jeddah Economic Corporation and Kingdom Holdings will focus on infrastructure
development for the new city, which is located 20km to the north of the existing city of Jeddah. Details of the third phase have not yet been released.
The Kingdom Tower, designed by Adrian Smith and Gordon Gill Architecture, will be the centre point of the new development and will include a luxury hotel and serviced apartments, luxury apartments, a 65,000m2 retail mall and office space. Reports on the development also suggest that the tower will include the world’s highest observatory.