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 column, i.e. 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.
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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.
Finally, we propose that the spun pile will be chosen to use in this piling system because it is more practical and more economical if compare to others, such as bore pile and cylinder piles.