Maduka Nweke
Every house has a foundation, and every foundation must be constructed efficiently, safely and correctly so it will last.
The materials that make up the building block and the process of building it are equally important; however, one thing that’s often overlooked is the soil supporting them because even foundations need a solid foundation.
Each type of soil has different properties that affect foundations. Generally, soil will be more stable the more rocky and compacted sand/gravel it contains.
Fortunately for homebuilders, the loads involved in most residential construction are relatively light. Following time-proven procedures and steering clear of some common misconceptions will keep you out of trouble in most cases.
For your expenses to be once and streamlined, you must endeavour to make findings and investigate what is commonly in use in the location you are building on.
This will help you to be on the guard not to make a grave mistake that can cost you fortunes to correct. For starters, you can learn a lot about soil conditions on your site by
taking advantage of public-sector resources.
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This style was tested in the United States of America and the outcome gave the impression that checking soil texture before making your house foundation saves a lot of dangers that are not noticeable initially.
The United States Department of Agriculture prepared soil maps for most of the country. Available at no cost at any local USDA branch office, these maps superimpose soil-type delineations over aerial photographs.
By studying these maps and the soil descriptions that accompany them, you can find out information such as whether your site might have a high groundwater table or whether problematic soils such as shrink/swell-susceptible clays might lurk beneath the surface.
For Nigeria to progress in that angle, these steps must be taken and a particular authority or ministry be established to see to it. It will in a very large extent, minimize building collapse.
Having been taken 30 years ago or more, aerial photos often reveal evidence of unsuspected development or manipulation of the site.
An even better source for this type of information is a topographic map from the United States Geological Survey. The map may reveal abandoned cemeteries, farm ponds, wells or the long-forgotten town
dump.
A topographic map may be purchased for a few dollars at outdoor-sporting-goods stores or downloaded at no cost.
Serving as snapshots in time, soil maps and topographic maps can provide valuable insight into human activity that has taken place on land when may be the user was not born.
Don’t forget to check with the local building and engineering departments, as well because they often have a wealth of local information and experience, which they are usually happy to share.
Developers who have built close by or homeowners on adjoining lots are other good sources of information. If your research unearths potential problems, that is, the time to bite the bullet and consult an expert.
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If you uncover no history of activity that may have left problems behind, that’s probably good news, but there may still be things that need attention. “Virgin soil” isn’t inherently problem-free. Muck (decomposed organic material), for instance, may have been undisturbed since mother nature deposited it, but building on it is always a bad idea.
Clay soil can also be troublesome. The strength of clay soils varies inversely with changes in moisture content.
The greater the moisture, the weaker the soil. If clay materials underlie your site, the site plan must provide for positive drainage that will direct surface water away from the structure and paved areas, otherwise, water may penetrate and weaken the foundation.
This is, in fact, a common cause of post-construction settlement problems. If site constraints make it impossible to direct runoff away from the driveway, you should plan to provide lateral drains alongside the driveway to prevent water from accumulating beneath the pavement.
Foundation drains must also be carefully designed to carry groundwater well away from the structure. These measures aren’t cheap, but they cost less than repairs, ill will and neighborhood gossip.
In same way building your foundation on a surface prone to gully erosion could be as dangerous as facing your roofs to hurricane direction because it is bound to be naturally attacked when the
seasons come.
Coarse-particle soils are the best for foundation purposes. The presence of binders in them determines their suitability for a particular purpose.
Among the coarse-grained soils (more than 50 per cent of the total material retains on 75 micron) are of two types. For instance, gravelly soils where more than half of the coarse grains are larger than 4.75 mm.
Also sandy soils where more than half of the coarse grains are smaller than 4.75 mm. There is
also the peaty soil that is usually dark brown or black and is easily compressible because of how much water it can hold. However, during the summer it becomes extremely dry and can even be a fire hazard.
It is very poor subsoil and not ideal for support, as foundations are most stable on soil that does
not shift or change structure.
Clay is made up of tiny particles so it stores water well, but because of its tight grasp on water it expands greatly when moist and shrinks significantly when dry. When clay is moist, it is very pliable, and can easily be moved and manipulated.
These extreme changes put a great deal of pressure on foundations, causing them to move up and down, and eventually crack, making clay a poor soil for support. Silty soil can be smooth to the touch and retains water longer because of its smaller particles.
However, because of its tendency to retain moisture it is cold and drains poorly. This causes the silty soil to expand, pushing against a foundation and weakening it, making it not ideal for support.
Sand/gravel has the largest particles of the different soil types. It is dry and gritty to the touch and does not hold moisture because of the large openings, but drains 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.
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However, when moist, the particles will lose their friction and can be washed away, which can leave gaps beneath the foundation. Loamy soil is the ideal soil type for building foundation.
Typically it is a combination of sand, silt and clay. It is dark in color and soft, dry and crumbly to the touch. Loam is great 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, as long as no miscellaneous soils find their way onto the surface. Types such as bedrock, limestone, sandstone, shale and hard chalk have high bearing capacities.
These are very strong and good for supporting foundations because of their stability and depth. As long as the rock is level the foundation will be well supported.