Believe it or not but the soil is one of the most important and also most forgotten thought when buying a plot of land. … Soil tests reveal what the eye sometimes cannot. It helps to determine varying physical and chemical characteristics of the soil which can change considerably within a small area.
Every home’s foundation sits on a massive soil deposit which is most of the time a very, very unique mix of different particles.
The foundation of a home is the main support system and must be constructed efficiently and safely so it will last. The most important factor when designing your foundation is the soil type that lies underneath it and most people don’t recognise that the soil type in regions around Trinidad are almost always different! The type of soil can greatly affect building costs of the foundation and must be an important factor to consider when buying land!
This blog aims to explain the different types of soils you may come across when investing in real estate and which soil types are most suitable for home construction.
Before you start building a house, you should carefully examine the quality of the soil on site using a qualified engineering firm to carry out a soil survey. Different soils can greatly impact the design costs for foundations and should be understood at a scientific level before purchasing.
Peaty soil is usually dark brown and can be compressed quite easily because of how much water it can hold. However, during the summer it becomes extremely dry. Peaty soil is a very poor subsoil and not ideal for support, as foundations are most stable on soil that does not shift or change structure. Building on peaty soil is very expensive and may sometimes even require expensive foundation piles in areas that have ground water.
Silty soil retains water longer because of its tiny particles. However, because of its tendency to retain moisture it drains very poorly. This causes soil expansion when moist, which pushes against the foundation and weakens it, making it horrible support.
Clay soils stores water well, but because of its tight hold on water it expands greatly when wet and shrinks when dry. When clay is moist, it is very pliable, and can easily be moved and manipulated. These changes put a lot of pressure on foundations, causing them to move up and down, and eventually crack, making clay a poor soil for support. What makes this matter worse is that clay soil deposits are usually found near the mouths over rivers and along the perimeters of bays (wet areas). Most engineers recommend foundations with much more depth to help resist the additional forces that clay soil cause on a home’s foundation.
Sand/gravel has the largest particles of the different soil types. It is dry and does not hold moisture because of the large openings, and therefore drains very easily. When compacted and moist it holds together fairly well, and if compacted these make for good soils to support a foundation because of their non-water-retaining properties. However, when moist, the particles will lose their friction and can be washed away, which can leave gaps beneath the foundation. As well as the fact that loose saturated sand deposits that are located in seismically active regions are prone to liquefaction during earthquake periods and can lose all structural ability and bearing capacity. This soil type requires deep pile foundations in most instances and this is a very expensive construction method.
Loam is the ideal soil type because it has a combination of sand, silt and clay. Loam is perfect for supporting foundations because of its evenly balanced properties, especially how it maintains water at a balanced rate. Loam is a good soil for supporting a foundation and building on this type of soil is usually much more cost effective.
Bedrock, limestone, sandstone, shale and hard chalk have extremely high bearing capacities. This makes these rocks ideal for the construction of foundations because of their stability and depth. Once the rock is level over the construction area then the foundation will be very well supported requiring a much less expensive foundation design.
If you already purchased land without understanding the soil type beforehand, don’t worry!
With the development of modern technology, there are many ways of giving any soil a proper consistency. Soil improvement can be used to enhance the structural properties of weak or compressible soils.
Soil Improvement Techniques:
1.) Removal and replacement : This is a cost effective method which can be used when the poor soil deposit is relatively small, and where groundwater levels are very deep.
2.) Vibro-compaction : For poor, loose sandy soils, vibration and compaction can be used to increase the soil’s structural ability.
3.) Chemical Stabilization: For weak clay soil deposits, pulverized fly ash can be mixed into the existing soil to reduce its compressibility and increase its strength.
Soil types vary greatly across Trinidad and Tobago. The following UWI Link shows a Table of Soils types present across both Islands: Soil Types Across Trinidad and Tobago
When purchasing land in Trinidad and Tobago, it is very important to know what soils may be present in each location. Soil type can greatly increase the building cost of the foundation for different types of structures. Knowing the type of soil present can help you plan for unforeseen construction costs and can also be a great negotiation topic to include in conversations with the land owner to bring down the price of the land. Always remember to carry out soil surveys and contract a Civil and Geotechnical Engineer before doing any foundation construction.
Disclaimer: All information presented above is very informal and we always advise that you seek professional advice from a local geotechnical or civil engineer before conducting any construction project in Trinidad and Tobago. Do not use the information above as a guide book for any construction project, or home renovation. All soils behave very differently under seismic motion and depending on its moisture content and therefore you should always seek professional advice from local Civil Engineers.