Park Residence @Medini
Additional SI Borehole for optimisation of pile length design
(by Ms. Yap Fui It, Design Engineer) (2015 Oct-Dec)
This is one of the prime residential development project in Medini Johor which comprises of 3 blocks high rise condominium with 40 storey, 44 storey and 46 storey respectively, including 10 storeys of podium car park with a few unit of retails. The foundation is under Contractor Alternative Design using 243 number of bored pile with sizes ranging from 600mm to 2000mm diameter and 67 number of caisson pile with sizes ranging from 2200mm to 2600mm diameter. The total construction duration is 7 months which including piling and pile cap works. The most challenging of this project is the determination of pile length where the actual ground condition is partly in Sedimentary formation of Sandstone and partly in poor residual Granite formation. The later was encountered during the additional soil investigation and actual bored pile construction.
Alternative Design Proposal
We proposed a combination of bored pile and caisson pile with mostly single pile system to replace the original full bored pile in multiple piles group arrangement. Based on the available soil investigation data during the tender stage, the piling layout was divided into 8 zones for pile length design.
Based on our earlier experience in Encorp Marina project in the same area, we have confidently designed the optimum pile length in the Sedimentary formation area in order to keep our pricing competitive.
As per the provision of Bill of Quantity, 10 nos. of additional soil investigation borehole, ABHwere being carried out. We started to find out the unpredictable ground condition at ABH2 in Zone 2.Decision was made to add ABH11 near to the earlier BH1 for verification andABH12 to find out the transition zone in between Zone 1 &2. Unfortunately, ABH12 was the worst result and the required pile length more than 60m! In order to have more confident in determining the pile length within the transition zones, we then immediately decided to do ABH13 & 14 in that problematic area.
On the other hand, ABH11 was shown very good result as compared the earlier BH1 and ABH1. Finally, with the additional total 14 nos. of ABH, we then confidently designed the pile length in respectively zones.
However, we encountered some of the pile length in 2 adjacent zones were different too much after our preliminary design stage. As such, we decided to further divide into sub-zones for the pile lengthin transition area.
There were twocontour mappings were prepared which indicated the designed pile length for bored pile type BP1800 and BP1200, according tothe ABH results. Then, we only demarcated all the zones’ boundary lines according to these mapping.
Nevertheless, our design process and review were not stopped here! We encountered Granite bedrock in Zone 1B, 1D & 4 with depth ranging from 43m to 55m during the actual bored pile construction. It was a big surprise to us as none of the BH and ABHencountered Granite bedrock or boulder even to the depth of 60m.As such, we reviewed the pile length design in consideration of soil friction and rock socket. In addition, the rock samples were sent for rock point load test to verify the adopted design parameters for rock socket length calculation.
Upon completion of the project, total 3 nos. of subsequent MLT and 37 nos. of PDA testing have been carried out to verify the performance of working piles at various Zones. All of the test results were shown in compliance to minimum factor of safety of more than 2.0 in geotechnical capacity.
We wish to take this opportunity to thank the Consultant Engineer who has spent a lot time with us in the pile design issues and they are very helpful and responsive.