So you are planning to build your new house, Congrats! You must be breaking your back getting a fabulous design; an appealing façade, various flooring options, sanitary fittings, wood work, electrical system, glass, aluminum and what not. All these must be consuming you, just natural! Your imagination is captive to all these because they have strong aesthetic appeal and ‘they’ are advertising on TV and social media. But did you think about the foundation of your building? Probably not! Because it is invisible and no one is advertising it.
Well fact of the matter is that the foundation is the most important part of your building but unfortunately least attended too. Under normal conditions, the conventional methods of foundation construction will work perfectly fine but what if the your plot happens to be on filled up area, has high ground water or just naturally the soil down there is not strong enough to bear the load of your building. To understand why foundation is so critical, you must know the functions of the foundation which include:
- Distribution of loads from the structure to soil evenly and safely so that there is no differential settlement of building resulting in cracks and ultimate collapse.
- Anchoring the building into the ground so that under lateral loads building will not move and prevent uplift of building in case of swelling of ground.
- Preventing the building from overturning due to lateral forces generated by earthquakes or strong wind storms etc.
- Giving level surface for the construction of super structure.
For foundation to perform these functions effectively, it must be built in a way that it interacts with soil adequately in accordance with the bearing capacity of the soil. Therefore, knowing the soil conditions is equally critical for which soil investigation must be carried out by experts. Most of the people would try to avoid the investigation expense thinking that my neighbor built without investigation and his building is fine up to now. Well! you might not be as lucky as your neighbor is. Therefore, spend this money which is sure to save you a lot of cost on later retrofitting.
Only a good investigation can really determine the foundation type which your building would require. However, we may make some generalization. In plain areas of Punjab and Sindh i.e. from Jhelum unto Sukkur along the G.T. Road, the strata is mostly formed of lose to medium dense clay with a varying thickness sand layer at 12-15 meters deep. You would hardly find rock at the surface or beneath. However, presence of ground water with sulfates and chlorides cannot be ignored. Ordinarily, shallow foundations like isolated or continuous footings of RCC with special chemical additives should suffice.
However, if you are a plot owner which is created from reclaimed land from filled up ditches, rivers and/or sea you must be extra, extra cautious. This practice is common in DHA Karachi, Behria town Islamabad and many other new housing projects in the vicinity of Islamabad. That is the most troublesome area because probably reclamation is not carried out in line with recommended engineering practices which are not good for laying foundations even for a double storey ordinary house.
Ordinary foundation construction is not working in these areas. There have been frequent reports of structure failures, leaving the builder bewildered. Even deep foundations built on piles have failed because of poor investigation, bad designing, bad workmanship and above all builder’s insistence to avoid costs (which he/she ultimately has to pay). The most suitable foundation in these conditions is still piled foundations but the piles which are deep enough to cross through the fill and penetrate deep into undisturbed naturally competent bearing strata. Similarly, the piles have to be large enough (in terms of dia) to resist buckling under load when constructed in very long lengths.
Precast Micro Piles of special steel or iron which can be installed with drilling or driving method with dynamic grouting offer an excellent alternative to Concrete Piles. These micro piles may sound a little expensive compared to concrete piles but they work.
If you are building on really deep fill, you would need to take extra precautions. The load of the building will be borne by the piles but where will the load of the floor go. The beneath the floor will continue to settle over the period which cause the floor also to settle. Therefore, it is better to cap the piles with a continuous raft. The same raft will act as your floor too.
Keeping all the above narrations of problems associated with building on the fill and limitations of the ordinary foundations, it is strongly recommended to have a thorough investigation and letting an expert to design your building’s foundation. Happy Building…….
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