Building on a firm foundation
What does the cervical, thoracic and lumbar vertebrae all found in human anatomy have in common with strip, raft and pad foundations found in building construction? The cervical, thoracic and lumbar vertebrae all form part of vertebral column or the back bone of a human and they are responsible for most if not all of our movements. They are also responsible for the stable functioning of other body functions by providing a stable foundation on which our limbs can find support. My limited physiological knowledge also tells me that damage to the back bone is one of the most detrimental injuries to a human. So how does these information tie in with the foundation of a house? The foundation or the sub structure holds everything together in a house. From the doors to the windows, from the sockets to the taps, from the paint to the tiles; no single component of a house is as important as a good foundation. Just like the spine in human anatomy, the foundation is what holds everything else together. It is therefore imperative that adequate time and resources are allocated in the construction of a house to ensure that it has a solid foundation.
A good foundation is one that is able to safely transfer all the dead and imposed loads from a structure to the ground beneath it. The dead loads refer to the foundation’s own weight, the weight of walls, doors, windows, tiles and roof. Dead loads are the vertical forces that are perpetually imposed on the ground below and hardly ever change. Imposed loads on the other hand are loads that change with time, this can be forces imposed on the roof due to rain and wind, forces on the floor slab imposed by occupants and furniture arrangements and the like. The foundation therefore is supposed to transfer all such loadings from the building to firm strata below.
And where do we start in ensuring a good foundation for a building? Most seemingly complex endeavours normally have very simple and straight forward answers and building a strong foundation is no exception.
As I have mentioned above “a good foundation is one that is able to safely transfer all the dead and imposed loads from a structure to the ground beneath it.” Therefore since ALL the loads of the structure will eventually be transmitted to ground below the structure it is important to conduct a proper ground investigation. For large complex structures like shopping malls, large school and hospital blocks, communication towers and the like; this will involve engaging a geologist who will prepare a geotechnical report based on actual site investigations. This is because such structures transmit complex loadings and forces on their foundations and exact site conditions must be verified to ensure safety. However, for your humble 3 bedroom house, ground investigation might just involve rolling up your sleeves, taking a pick axe and a spade and digging trial pits at the site of the proposed house. Your main aim will be to examine the kind of soil or rock formation that exists on your site. Before embarking on digging the trial pits it will also be prudent to find out if there are any service lines like electrical ducts, sewer lines, water lines or fibre optic cable lines that pass through the site and mitigate against damage to them. This might involve requesting the service providers to relocate them before starting construction. The trial pits investigation should yield three very important results namely; depth to firm strata, presence of ground water and type of firm strata. All of these have a direct bearing on the cost and type of foundation as well as the type of foul water disposal system that will be suitable for the house. It will be possible at this stage to tell for example whether to use a pad or a strip foundation on the house or whether to have a septic tank or a conservancy tank for the toilet water.
After determining the type of firm strata, the depth to firm strata, presence or absence of ground water and the type of soil on site; a building professional will be able to advise on the kind of foundation that should be used for the structure. Basically it will be the most economical and safe foundation option amongst the various types of substructure options that will suit the site conditions as well as the building design.
Most site soil conditions including the dreaded black cotton soil can be made to transmit the weight of a building. Bridges like the Mtwapa Bridge and the New Nyali Bridge at the coast have been made to pass over the ocean and still carry their own weight and the weight of vehicular traffic. I therefore find it’s nonsensical and comical for someone to suggest that house or a boundary wall has cracks due to the fact that it is built in an area that has black cotton soil. To paraphrase from Hosea of old who wrote centuries ago; your wall is cracking because of lack of knowledge. Don’t blame the ground or the weather.
Most of the enduring buildings and structures in Kenya have one thing in common; a firm foundation and knowledgeable construction techniques. When Giovanni Battista Cairati was commissioned to build Forte Jesus de Mombaça or Fort Jesus in Mombasa in 1593, he must have used his engineering knowledge and conducted a proper ground investigation before laying his foundation. He would have done the same if he had been commissioned to build the fort in Ruai or Kamulu and it is safe to assume that the fort would still be standing centuries later. Why pray tell does a simple two meter high masonry boundary wall built in Nairobi develop cracks a couple of months after it has been built? The answer to this boils down to the quality of the foundation, and the knowledge or lack thereof, of the builders.
Till next time, keep well and keep safe.
Fundi Mjanja.
What does the cervical, thoracic and lumbar vertebrae all found in human anatomy have in common with strip, raft and pad foundations found in building construction? The cervical, thoracic and lumbar vertebrae all form part of vertebral column or the back bone of a human and they are responsible for most if not all of our movements. They are also responsible for the stable functioning of other body functions by providing a stable foundation on which our limbs can find support. My limited physiological knowledge also tells me that damage to the back bone is one of the most detrimental injuries to a human. So how does these information tie in with the foundation of a house? The foundation or the sub structure holds everything together in a house. From the doors to the windows, from the sockets to the taps, from the paint to the tiles; no single component of a house is as important as a good foundation. Just like the spine in human anatomy, the foundation is what holds everything else together. It is therefore imperative that adequate time and resources are allocated in the construction of a house to ensure that it has a solid foundation.
A good foundation is one that is able to safely transfer all the dead and imposed loads from a structure to the ground beneath it. The dead loads refer to the foundation’s own weight, the weight of walls, doors, windows, tiles and roof. Dead loads are the vertical forces that are perpetually imposed on the ground below and hardly ever change. Imposed loads on the other hand are loads that change with time, this can be forces imposed on the roof due to rain and wind, forces on the floor slab imposed by occupants and furniture arrangements and the like. The foundation therefore is supposed to transfer all such loadings from the building to firm strata below.
And where do we start in ensuring a good foundation for a building? Most seemingly complex endeavours normally have very simple and straight forward answers and building a strong foundation is no exception.
As I have mentioned above “a good foundation is one that is able to safely transfer all the dead and imposed loads from a structure to the ground beneath it.” Therefore since ALL the loads of the structure will eventually be transmitted to ground below the structure it is important to conduct a proper ground investigation. For large complex structures like shopping malls, large school and hospital blocks, communication towers and the like; this will involve engaging a geologist who will prepare a geotechnical report based on actual site investigations. This is because such structures transmit complex loadings and forces on their foundations and exact site conditions must be verified to ensure safety. However, for your humble 3 bedroom house, ground investigation might just involve rolling up your sleeves, taking a pick axe and a spade and digging trial pits at the site of the proposed house. Your main aim will be to examine the kind of soil or rock formation that exists on your site. Before embarking on digging the trial pits it will also be prudent to find out if there are any service lines like electrical ducts, sewer lines, water lines or fibre optic cable lines that pass through the site and mitigate against damage to them. This might involve requesting the service providers to relocate them before starting construction. The trial pits investigation should yield three very important results namely; depth to firm strata, presence of ground water and type of firm strata. All of these have a direct bearing on the cost and type of foundation as well as the type of foul water disposal system that will be suitable for the house. It will be possible at this stage to tell for example whether to use a pad or a strip foundation on the house or whether to have a septic tank or a conservancy tank for the toilet water.
After determining the type of firm strata, the depth to firm strata, presence or absence of ground water and the type of soil on site; a building professional will be able to advise on the kind of foundation that should be used for the structure. Basically it will be the most economical and safe foundation option amongst the various types of substructure options that will suit the site conditions as well as the building design.
Most site soil conditions including the dreaded black cotton soil can be made to transmit the weight of a building. Bridges like the Mtwapa Bridge and the New Nyali Bridge at the coast have been made to pass over the ocean and still carry their own weight and the weight of vehicular traffic. I therefore find it’s nonsensical and comical for someone to suggest that house or a boundary wall has cracks due to the fact that it is built in an area that has black cotton soil. To paraphrase from Hosea of old who wrote centuries ago; your wall is cracking because of lack of knowledge. Don’t blame the ground or the weather.
Most of the enduring buildings and structures in Kenya have one thing in common; a firm foundation and knowledgeable construction techniques. When Giovanni Battista Cairati was commissioned to build Forte Jesus de Mombaça or Fort Jesus in Mombasa in 1593, he must have used his engineering knowledge and conducted a proper ground investigation before laying his foundation. He would have done the same if he had been commissioned to build the fort in Ruai or Kamulu and it is safe to assume that the fort would still be standing centuries later. Why pray tell does a simple two meter high masonry boundary wall built in Nairobi develop cracks a couple of months after it has been built? The answer to this boils down to the quality of the foundation, and the knowledge or lack thereof, of the builders.
Till next time, keep well and keep safe.
Fundi Mjanja.
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