Setia City Res@Setia Alam
(The Challenges and Solutions on Full Bored Pile Foundation)
(by Ms. Supia Kilat, Design Engineer and Mr. Lai Chee Yong, DGM-Operations) (2016 Oct-Dec)
This development project is located at Setia Alam which comprises of 3 blocks high rise condominium with 35 storey including 5 storeys of podium car park with a few unit of retail shops. The foundation is under Contractor Alternative Design which consist of 496 number of bored pile with sizes ranging from 600mm to 2200mm diameter. The total construction duration in contract is 9months which including piling and pilecap works.
Alternative Design Proposal
We proposed a full bored pile foundation system to replace the original combination of bored piles and spun pile system. We introduced 2 types of concrete grade, i.e. G35 and G40 for various sizes of bored pile in order to optimise the pile working load and hence optimise the pile length. Based on the soil investigation data during the tender stage, the piling layout was divided into 4 Zones and all the piles were designed basing on soil friction and end bearing.
There is a 12m depth of alluvial deposit in the top soil layer which consists of very loose to loose Silty CLAY with dark grey colour. The contribution of geotechnical capacity of the pile length is almost negligible in this soft soil layer. But the most critical issue that make us worry is the soil stability during deep pilecap excavation work and the difficulties are shared in the next construction challenge page. After this 12m deep of soil, a typical sedimentary rock formation of highly weathered sandstone is encountered. All the rock sample cores are less than 100% recovery and mostly 0% in RQD. Therefore, we decided not to consider as rock socketed pile to avoid argument in rock definition during construction stage.
From the instrumented test pile result, we are able to achieve average ultimate soil skin friction of 3XSPT-N (kpa), average ultimate friction of highly decomposed sandstone of more than 500kPa and ultimate end bearing capacity more than 3800kPa.
The most challenging of this project during design stage is the pile designation with considering pile to pile spacing 2.5d in tower area due to very close 2 adjacent columns position. It was actually can be designed for single pile at a column. But due to the pile spacing requirement, these ‘Single-Piles’ were spaced out by 2.5d and combined with a pilecap. Therefore we decided to combine the 2 or 4 columns into a pilecap. All of the pilecaps were designed by using SAFE software and Prokon programme in order to get a more accurate pilecap reinforcement and forces.
Upon completion of the project, there are 1nos of instrumented MLT on BP1200, 1nos of subsequent MLT on BP1800 and 25 nos of PDA testing have been carried out to verify the performance of working piles at various zone. All the test results were shown in compliance to minimum factor of safety of more than 2.0 in geotechnical capacity.
Construction Challenge (By Mr. Lai Chee Yong)
The bored pile construction for this project is quite direct due to the ample space and flat ground. The challenge would be maintaining the flat ground and accessibility of routes for the continuation of subsequent works. As with many projects, time is of essence to the timeline of the project. At peak, 5 boring rigs were deployed to site together with 4 cranes and 6 units of excavators. The entire site looks like a chess board where our Assistant Project Manager, Encik Asrul Abidin must plan each and every move in order not to let any of these machines has time to rest. It was like a war zone with no enemy but the project completion time.
Fortunately, with the support from the project team, the bored pile progressed smoothly. The project was fast ahead of schedule until the sub-structure works starts. Now, the chess game has begun to become more challenging as the arsenals must make way for excavation for the RC sub-structure works.
3xx number of piles, 1xx number of pile caps and 3 number of gigantic liftcore pile cap in 9 months. The team knew that the RC excavation work must be hastened and there was no time for error. However, not every plan A will turned out to be exactly a plan A, the team were forced to have a plan B when they encountered some ground movement while excavating the final liftcore pile cap. Some adjacent bored piles were deviated during the liftcore excavation.
In line with the commitment to deliver a quality work, the management has given full support to abandon the deviated piles and immediately re-mobilised a piling rig to re-construct the affected piles. The project team worked diligently around the clock and received much harassment from the local authority as they fight to complete the work in overdrive. Bravo to the project team as their struggle and perseverance did pay off. They manage to handover the project on the dot.