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The general principles of foundation design are as below;
- To safely transfer the building load directly from the point of application to the ground where the building sited and to make sure that the loads are suitably distributed through the ground (underneath soil strata).
- Ability and safely to provide resistance of uplift forces exerted by the building itself, possible overturning moments produced by wind load
- Capability to resist the the settlement force, subsidence, differential movement and any others possible ground or underground movement due to earthquakes.
In general technological practice the column design load can safely transfer to the ground and appropriate distribute through the ground by using Pad foundation approach. But, for this 10 storey building, the calculation that the most heavily Clumn C1 load is quite substantial and this definitely will require a huge size of pad footing and practically may cause massive of overlapping. In addition, the provision of reinforcement, formwork, construction effort and etc relatively will increase drastically. Hence, due to this unpractical process (construction of huge pad footing), in our experience and in terms of economic view point, we will not adopt pad footing in this 10 storey height building.
However, we propose to adopt deep foundation via a piling system as a viable solution to distribute the loads to a greater depth soil where normally will located the greatest ultimate bearing capacity. Through the borehole logs report, we analysed that the 29.0m depth from ground level is sandstone and bed rock strata. While soil strata between depth of 2.3m to 7.2m from ground level is consists of firm to stiff silty gravelly clay with occasional boulder. Subsequently 7.2m to 29.0m is stiff sandy clay.
This deep foundation via piling system has the economic advantages compare to the overall foundation system. For instances, if compare with raft foundation system where in principle the load will transfer to the whole piece of raft foundation slab averagely and this is not cost effective. However, through this piling system the load especially large load can effectively distribute to the hard soil strata via lesser numbers of column. Therefore the piling system is more economic and practical in terms of construction method.
For deep foundation, a lot of construction issues possible to due with during the piling process. There are complicated excavation where involving of earthwork support, existence of ground water cause need dewatering process and others hazards of due to unexpected ground contaminate substances. However with this 'spun pile' is able to solve the above construction issues as its design characteristic and advantages as mention below
- High Bending Moment And Crack Resistance
- Inherent strong jointing and reliable welding
- Driving Efficiency
- Large Bearing Capacity
This spun pile able to apply in various types of soil condition because it is highly effective in resisting bending moment and axial tensile stress.
The welded joint has a strength at least equal to that of the concrete portion of pile.
The driving efficiency of this spun pile is due to it hollowed, round geometry, shape. Therefore, only need a smaller hammer and subsequently will reduce the working noise and able to achieve a faster construction process or better speed construction.
The spun pile concrete compressive strength is exceeding 60N/mm2 and this is able to achieve a results of large bearing capacity in it pile section. The Table A below shown the design characteristic of spun pile .
The below shown the ICP Precast Pretensioned Spun Concrete Piles, Design To Malaysian Standard (MS) ISO 9002 : 1991 and also generally comply with JIS A 5335: 1987, Pretensioned Spun Concrete Piles and modified to Suit B.S. 8004: 1986-Foundation and B.S. 8110:1985 (Pleased refer Appendix I - ICP P. Piles Catalogue for further details)
Finally, we propose that this spun pile will be chosen to use in this piling system because of it characteristic design advantages and also more practical at construction point of view for this 10 storey office building. It is also more sensible for pre allocating of additional design load for possibly increased of building height in the future. Besides it is also more economical if compare to others piling approaches, such as bore pile and cylinder piles.
- Construction Technology 5, Heriot-Watt University
- SCIB Concrete Manufacturing Sdn. Bhd.)
- ICP, Industrial Concrete Product Sdn Bhd)