Hello Friends, Today In this article we will discuss about the Very Basic and Important Topic of Civil Engineering that is Types of building foundations in Different Soils. As we know that Civil Engineering is a core Branch of Foundation That Deals with Different Different Types of foundation in Different Types of soils, Cause all the soils has Different Properties having Different Soil Strength. We Decide only By Knowing the Properties of soil that which types of Foundation we have to build in which area.
So, Today Let’s know about Types of building foundations in Different Soils.
- 1 Know about Types of soil For Types of building foundations
- 2 Which Type of Foundation You should Choose?
Know about Types of soil For Types of building foundations
A good starting point is to call your local authority Building Control department. They should be willing, informally, to give you an idea of the typical soil type in the area you are building, and the sort of foundation that is appropriate.
Soil can be categorized into, sand, clay, silt, peat, chalk, and loam – it is based on the dominating size of the particles within a soil.
Initially, the best way to tell which soil type you have is by feeling it. In short, clay soil feels sticky when wet and smears if you rub it between your fingers, while a sandy soil feels gritty and won’t stay together. It’s wise to test the soil from different locations in your garden, as it can vary enormously.
Building foundation on Rock Soil
Rocks such as limestone, granite, sandstone, shale and hard solid chalk have a high bearing capacity. The rock may simply need to be stripped back and leveled off to build from.
Rock can be impervious, so topsoil is likely to require drainage as it is not possible to build soakaways to dispose of rainwater or surface water. Off-mains drainage options will also be very limited.
Building foundation on Chalk Soil
This type of soil can be either light or heavy but always highly alkaline due to the calcium carbonate within its structure.Strip foundations are commonly used in chalk. Providing the chalk is not too soft, widths of 450mm for low-rise buildings are acceptable. The depth of the foundation must be below any frost action (700mm). If the chalk is soft, it will need to be excavated until firm chalk is reached.
Chalk soils can be prone to erosion so be wary of hollows or caves.
Building foundation Gravel and sandy Soil
Dry compact gravel, or gravel and sand subsoils are usually adequate for strip foundations. Generally a depth of 700mm is acceptable, as long as the ground has adequate bearing capacity.
This type of soil is light, warm, dry and often acidic with a low amount of nutrients. It is often known as a light soil due to its high proportion of sand, and little clay – clay weighs more than sand. Beneficially, it has quick water drainage which makes it easy to work with.
Sand holds together reasonably well when damp, compacted and uniform, but trenches may collapse and so sheet piling is often used to retain the ground in trenches until the concrete is poured.
Building foundation on Clay Soil
This type of soil is made of over 25% clay – and, because of the spaces found between clay particles, clay soils hold a high amount of water. Unsurprisingly, this soil will drain slowly and will take longer to warm up in the Summer, combined with drying out and cracking in Summer months.
The first 900-1,200mm layer of clay is subject to movement due to expansion and shrinkage depending on moisture content, so it is generally necessary to excavate foundations to a depth where the moisture content of the clay remains stable. British Standard 8004 recommends a minimum depth of 1m for foundations But if there are, or were, trees nearby, depths of up to 3m may be necessary.
In clay, prior to concreting the foundations, the trench is often protected from heave by lining it with a compressible layer (e.g. Clayboard).
Building foundation Firm clay over soft clay Soil
A traditional strip foundation is sometimes acceptable but it is important not to overdig as this may increase the stress on the softer clay beneath. A common solution is to dig wide strip foundations with steel reinforcement — however an engineered foundation may be necessary.
Building foundation on Peat
Peat and loose waterlogged sand are very poor subsoils. If the peat can be stripped back to find suitable load-bearing ground of at least 1.5m depth, strip foundations may be suitable for Building foundation. A reinforced raft foundation will likely be required.
Building foundation on Filled ground
Where ground has previously been excavated and filled, it is generally necessary to dig down to a level beneath the area of the fill.
Sloping sites require stepped foundations. Guidelines are given in the Building Regulations.
Which Type of Foundation You should Choose?
In a Strong Building Foundation, A continuous strip of concrete supporting load-bearing walls. For a single story building strip foundations will typically be 450mm wide and at least 200mm deep and for two stories 600mm wide and 200mm deep.
Deep Strip Foundations: Deep strip foundations: Where strip foundations need to be at a lower level to reach soil with suitable bearing capacity, a wider, deeper trench can be dug to work in, and the strip foundations dug and poured at a lower level. Walls are then built up to ground level in masonry.
Wide Strip Foundations: Wide strip foundations: Where the soil is soft or of low load-bearing capacity, deep strip foundations can be used to spread the load over a larger area, reinforced with steel so that the loading per m² is diminished.
Trench Fill Foundation
Trench Fill Types of Building Foundation does not apply everywhere; Due to the high cost of labor, deep strip foundations have largely been replaced by trench fill. Trenches are dug to a depth where the subsoil provides sufficient load-bearing capacity, and the whole trench is filled with concrete. Steel reinforcement may be added in areas close to trees.
Compared to deep strip foundations, trench fill minimizes the width of the dig and the labor and materials required for building masonry below ground level, offsetting the cost of the additional concrete.
A reinforced concrete raft or mat is used on very weak or expansive soils such as clays or peat. They allow the building Foundation to ‘float’ on or in the soil. A raft is used where the soil requires such a large bearing area that wide strip foundations are spread too far, making it more economical to pour one large reinforced concrete slab. A raft is an alternative to piles as it can be less expensive.
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