"Every building requires foundation to support their weight. The type of foundation will depend on the soil type"
Image Source: https://civiconcepts.com/blog/types-of-foundation
Before purchasing a house or land to redevelop it, it is paramount to understand the different types of foundation for a building. There are two main types of building foundation, deep foundation like piling and shallow foundation like footing and raft. Deep foundation are usually constructed for area with weaker soil which will result in large settlement if shallow foundation is adopted. Shallow foundation is only able to be constructed on moderately strong or strong soil.
The cost of deep foundation depends on the thickness of the weak soil layer as the deep foundation requires to rest on competent soil layer. As the soil has to be relatively strong in order to construct shallow foundation, shallow foundation are usually constructed within 1 to 2m from the proposed ground level. On average, the cost difference between deep foundation and shallow foundation is around 200k SGD. Therefore, it is extremely important to understand the soil properties before purchasing any house or land for redevelopment.
Even though Singapore is a very small country, the soil varies greatly and generally are divided into 4 main types, Bukit Timah Formation, Jurong Formation, Old Alluvium and Kallang Formation.
As the name suggest, Bukit Timah Formation can be found in Bukit Timah area and also the North region of Singapore. Bukit Timah Formation is one of the strongest soil type in Singapore and is generally suitable to construct shallow foundation. However, not all Bukit Timah area has Bukit Timah Formation.
Jurong Formation are mainly found in Western Singapore and are generally relatively strong. However, Jurong Formation does not necessarily guarantee the usage of the shallow foundation. Jurong Formation also has issue of cavity if limestone is present which requires large volume of concrete to fill the void if encountered.
Old Alluvium are mainly found in Eastern Singapore and are generally relatively strong. Old Alluvium are mainly sandy soil which means they are very permeable and excavation cost may be higher as water tight excavation method are required.
Kallang Formation are mainly found in Southern and South Eastern Singapore. It mainly comprises of soft marine clay with very high water content. Deep foundation are required for buildings in Kallang Formation as the soil is very soft and weak which result in extremely large settlement to the building and its vicinity.
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