Unit 3 Types of Foundations

1. Introduction

1.1 Read the text title and hypothesize what the text is about. Write down your hypothesis.

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1.2 What do you know concerning this issue? List your ideas in the table left column “I know”.

I know	I have learnt

3. If you know answers to these questions write them down in the space given after each question.

1	What is a foundation?
2	How are foundations classified?
3	Where are T-shaped foundations used?
4	What is one of the most common types of foundations?
5	What materials are used to make a foundation wall?
6	Why can cracks appear?
7	Where are spread footers buried?

4. Circle in the list the words and expressions you know. Write down their translation in the table and calculate the percentage of your lexical competence.

1	earthquake		9	a shallow foundation
2	to rest on …		10	to extend across…
3	piles of timber		11	a soil layer
4	a wire mesh		12	a footprint
5	to be suitable		13	an extra support
6	soil compressibility		14	a residential building
7	frost line		15	to distribute loads
8	to prevent		16	drilled shafts

Foundation of a structure is like the roots of a tree without which the tree cannot stand. The construction of any structure, be it a residence or a skyscraper; starts with the laying of foundations. Before designing the foundation, the type of soil is determined. Depending on whether the soil is hard soil or soft soil, a specific type of foundation is adopted.

The foundation of a home or building is essential to the value and safety of the structure.

Foundations are broadly classified into shallow foundations and deep foundations. The depth of the foundation means the difference of level between the ground surface and the base of the foundation. If the depth of the foundation is greater than its width the foundation is classified as a deep foundation.

S hallow foundations are commonly used in smaller structures such as residences and small buildings whose floor height is limited to 10m whereas Deep Foundations are used in Skyscrapers.

There are various types of foundations used in construction and they will vary with the geographic location, climate, soil, and needs of the structure.

Strip Foundation. One of the most common foundations, where trenches are made for all load bearing walls and then deeper trenches are dug to lay the footings. The trench is usually dug until hard soil, rock or clay is reached. The size of the trench, foundation footings and foundation wall will depend on the amount of load the structure will bear. Strip foundation is one of the simplest and universally accepted forms for the foundation of a building.

Raft Foundation. When the surface soil and the subsurface soil is weak and has the tendency to shift, a normal strip foundation is not usable, as the soil will shift under the load and weaken the foundation. This foundation covers the entire area of construction. A wood form is built and concrete is poured to fill it. Iron mesh is also inserted in the concrete to avoid cracking of concrete.

Pile Foundation. They are substitutes to a conventional foundation wherein a much deeper and more costly foundation would be needed. Soil conditions are usually the cause for using a pile foundation. The basic pile foundation consists of a series of concrete columns piled 4 meters below the surface soil on solid sub soil. The concrete piles used in this kind of foundation can either be precast types or piles can be set at the site.

The various types of foundations will focus on residential construction and include: -slab on grade, -T-shaped,-frost protected, -pile,-continuous (spread footings), -foundation walls.

A Slab-on-Grade foundation is one of the most common types of foundations. It is relatively simple, quick, and inexpensive to construct. This foundation is suitable in geographic areas that do not freeze often. There are many variations of concrete slabs depending on the purpose of the slab.

As the name suggests, a slab is a single layer of concrete, several inches thick. The slab is poured thicker at the edges, to form an integral footing; reinforcing rods and strengthening the thickened edge. The slab normally rests on a bed of crushed gravel to improve drainage. Casting a wire mesh in the concrete reduces the chance of cracking. A slab on grade is suitable in areas where the ground doesn't freeze, but it can also be adapted with insulation to prevent it from being affected by the frost heaves

T-shaped. T-shaped foundations are used in areas where the ground freezes. First, the footing is placed below the frost line and then the walls are added on the top. The footing is wider than the wall, providing extra support at the base of the foundation. Second, the wall are constructed; and finally, the slab is poured between the walls.

F rost Protected. This method only works with a heated structure. It relies on the use of two sheets of rigid, polystyrene insulation—one on the outside of the foundation wall and the other laid flat on a bed of gravel at the base of the wall—to prevent freezing, which is a problem with slab-on grade foundations in areas with frost. The insulation holds heat from the structure in the ground under the footings and prevents heat loss from the edge of the slab. This heat keeps the ground temperature around the footings above freezing. A Frost Protected foundation is also suitable for geographic areas that freeze frequently. This type of foundation has the advantage that it is poured at one time versus the three step process of a T-Shaped foundation.

P ile foundations. Foundations relying on driven piles often have groups of piles connected by a pile cap (a large concrete block into which the heads of the piles are embedded) to distribute loads which are larger than one pile can bear. Pile caps are typically connected with grade beams to tie the foundation elements together; lighter structural elements bear on the grade beams while heavier elements bear directly on the pile cap.

The piles (also called piers and beams) are also one of the most common types of foundations. Piles are steel, pressure treated wood, or concrete columns that are either driven into the soil or placed in excavated holes. The piles provide support by transferring weight or load to the underground soil. The piles extend downward until a stable soil layer or rock is reached. The piles will also extend above the soil line and will be arranged in a linear fashion so that a beam may be placed on top of two or more piles. The walls and floors of the structure are thus supported by the beams resting on the top of the piles. This foundation method is suitable in areas where the soil is unstable, coastal areas, and sites with steep slopes.

A spread footing. It is a type of structural component that acts as a base for a building's foundation. These components are constructed from concrete, and are often reinforced with rebar or steel to add additional support. Depending on the size and configuration of the building, spread footers can be buried just below ground level or several feet below the surface. In cold climates, footers are always placed below the frost line.

While traditional spot footings only have a single point of contact with the foundation, spread footers extend continuously across the entire building footprint. Grade beams also extend across the entire footprint, but they tend to distribute loads to specific points, while a spread footing transfers the load to the entire ground, not a single point. This makes grade beams the best choice for very unstable soil, while spread footers require the soil to be fairly stable all around.

F oundation Walls. It is another one of the basic types of foundations. This method is found in structures with basements. It uses the basement walls as the foundation walls for transferring the weight of the building to the ground. Usually the walls are made from poured concrete or hollow concrete blocks filled with concrete. Both methods are reinforced with steel or rebar.

A foundation wall is a wall which rests on the footers of the foundation, and provides support for the weight of a house. Problems with the foundation wall will ultimately lead to problems with the house, up to and including complete structural failure.

A number of materials can be used to make a foundation wall. Poured concrete is a common and popular choice, with some contractors using modular walls. Blocks, bricks, and stone can also be used. In all cases, the materials must be load bearing, and the wall needs to be designed and built so that the weight will be distributed evenly over the footers of the house. One of the most common problems with foundation walls is cracking. Cracks can appear because the wall was built in a hurry, backfilled before the concrete had a chance to cure, or not properly reinforced. Earthquakes and settling of the underlying ground can also result in cracking of the foundation. Damaged foundations can be replaced. The house is usually raised on jacks which support the weight of the house while the foundation work is done.

When building a new house you need to know where to start. The start is the foundation. There are many types of foundations that you can use for a house. Which one you choose all depends on the type of a house you want. Most houses have concrete foundations, but you can also have foundations made of stone, wood, and brick.

• Concrete foundations are used more than the others because they are less expensive and last for a very long time. Concrete foundations can be used in many settings, and climates.

• Brick foundations are more costly, but are worth it. They are very good foundations to use in areas that are commonly affected by tornados, because they tend to withstand the strong wind better that the other types of foundations.

• Stone is a very good to use as a foundation because it lasts for a very long time. Stone foundations will cost you some money, but in the end the stone will give your new home a very natural look.

• Wood foundations are strong. They are not used as often as the others because; there are so many things that can go wrong with them. Weather, and animals such as termites, can ruin the foundation. In the long run this should be your last choice of foundations, they are less expensive to build, but also costly to fix.