It is an easily agreeable fact that the foundation is one of the most important aspects of a house. A foundation can be thought of as a simple structure, which only requires steel bars (reinforcements) and concrete. But in order to decide what type of foundation that should be put, how it should be laid, from what elevation, etc, it is generally compulsory to conduct a Soil Investigation first. No matter how strongly we build a chair, if we place it on the mud it will be drowned. Similarly, no matter how strongly you build a foundation, using huge amounts of concrete and steel bars, the strength of it also depends on the “Allowable Bearing Capacity” of the soil it is laid on. Sometimes, even though the top most layers appear to be strong, when it is tested 50-60 feet below, the strength appears to be an illusion.
This sort of issue is mainly found in buildings based on marshy lands or paddy fields. Most people prefer to build homes besides a water stream or paddy field, but there is a high chance that such lands have very low bearing capacity on the soil. Especially since the soil water levels are quite high in such areas, a huge effort and expense will be needed to be spent on lying the foundation to ensure the strength.
Most of the time, a skilled and experienced engineer can do a relatively accurate assumption based on simple tests such as drilling a few holes in random areas on the land and testing the soil in these areas. While complex tests are not necessary in most cases, sometimes it requires more effort than others.
In such cases, the soil tests need to be conducted as deep as the earth’s basement rocks. While this sounds like an expensive test, in comparison to the cost of building your new home, it will cost you even less than 1% of that value.
There are several types of Foundations that can be laid for building a home. Isolated bases/ Pad footings is considered one of the most commonly used type. In areas with lower bearing capacities, Strip Foundations or Raft Foundations may be laid.
When a good soil cannot be found at a considerable depth, digging deep until a good soil is found and laying basement rocks on that soil before laying the foundation is the most common method. But this requires the advice and supervision of experts since it has the possibility of damaging neighbouring lands and also needs to be properly laid to ensure the safety of the new building too.
Another special instance that needs to be considered is if the foundation is being laid on a very steep slope. In such a case, unless the foundation is laid with professional support, there is a tendency of the building getting pushed down the slope. Most probably such buildings will require the permission and authorization of the National Building Research Organization too.
When a strong soil cannot be found at a considerable depth, Pile Foundations may have to be laid. This used to be considered quite high in expenses, but with the advance in technology in Sri Lanka now, this method is commonly found. In such instances, the drilling is compulsory up to the basement rock, to test the soil.
Soil testing before building a home has been conducted even in our ancestors’ times. Before we have moved into the Western technologies we discussed so far, our ancestors also have discovered and used multiple ways of soil testing in ancient times. These indigenous technologies used by our ancestors are discussed in detail in the book “වාස්තු විද්යාව හෙවත් ගෘහ නිර්මාණ ශිල්පය” by Mr. Hermanis Appuhami.
In ancient times, with the low population, finding a suitable land to build a home was not that difficult. But today, with the ever-increasing population, the situation has reversed as such, that we must somehow build a foundation based on the type of land we can acquire.
Honestly, with the increasing industrialization, the lands on less-industrialized areas are under very high demand. Based on this demand, the remaining lands may not always have good bearing capacity or be the best for building a land. Therefore, it is compulsory that when building a home, it is done responsibly with the proper guidance and observation of the relevant experts, to ensure the safety of you and everyone around you.
Article by: Eng. Mangala Silva
Translated By: Udari Mohotti
Professional in charge – Civil Engineering
BSc.Eng(Hons), MEng (St. Eng.Designs), C.Eng.,FIE(SL),MSSE(SL),IntPE(Sri Lanka), GREENSL® AP
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