Part III. Architecture of civil buildings

“High buildings have a low foundation”

Thomas Fuller (writer)

Unit 8

raft foundation	b) strip foundation	c) pad foundation

F igure 8.1 Types of Foundation

1. Match the columns:

raft foundation	a) is basically a strip, or ribbon, of insitu concrete running under all the loadbearing walls
strip foundation	b) is used to support individual point load such as that due to a structural column
pad foundation	c) is used to spread the load from a structure over a large area, normally the entire area of structure

2 A) What is the purpose of foundations? Express your opinion in 3-5 sentences.

Read the following passages and compare your ideas:

1. The main purpose of the foundation is to distribute the structural load over a large bearing area without causing bearing capacity failure and excessive settlement to obtain a level and hard strata or bed for building operations to increase the stability of the structure as a whole.

2. A good strong foundation ensures good strong stable ground for a good strong and lasting structure. If you build a house on sand and the sand around one of the corners of the house washes away due to rain water falling off your building the building will begin to sink in that corner and the result will eventually begin cascading further along the buildings edges and sides until the entire building is consumed by leaning caused by unstable ground.

3. При наших совсем не «плюсовых» зимах слой грунта сверху промерзает. Вода, содержащаяся в нем, замерзает и  расширяется. И грунт вспучивается, в зависимости от количества воды в его замерзшем слое. Коэффициент расширения у сильнопучинистых грунтов иногда достигает 12%, а обычно – около 10. Это означает, что при глубине промерзания 1,7 м грунт может приподняться на 10-15 см.  Чтобы эти зимние вспучивания не разрушили или не перекосили дом, и нужен фундамент.

3 Discuss the following:

• Write a paraphrase. • Say whether you agree or not, and why.

4 A) Transcribe the following words:

drought, load-bearing, strength, weight, artificial, endanger, plumbing, superimposed, depth, specific.

b) In what context do you think the following words and phrases will appear in the text?

•ground level •stability •protection•natural foundation •artificial foundation •loads and pressure •concrete•specific conditions of the building •types

c) Read the text quickly and check your answers:

Foundations

The foundation is the part of the construction where the base of the building meets the ground.

Foundations are usually placed below ground level because the surrounding ground provides:stability, protection against impact, protection from the extremes of weather such as excessive rain or drought.

Although the depth will vary according to the conditions on site, the best load-bearing ground is normally 900 mm below the surface.

The choice of foundation depends on:

1. the strength of the natural foundation;

2. the weight of the building and its loads.

Foundations are divided into two types:

1. The natural foundation. This is the ground underneath the base of the building after the excavations are completed;

2. The artificial foundation. This is the structure that lies between the building and the natural foundation.

An artificial foundation transfers the loads from the building to the ground. This prevents settlement or building movement, which might cause instability and endanger the occupants.

The following building loads place the most pressure at the bottom of the building, where the artificial foundation is located (Figure 8.2.):

1. Dead loads. These are the weights of all the fixed parts of the building such as the walls, floors, roofs, ceilings and services such as sanitary fittings and plumbing;

2. Superimposed or live loads. These are the weights of the people, furniture and machines that will occupy the building after the completion;

3. Wind loads. These are the pressures on the walls and roof from the wind. The pressure from wind loads on foundations is more important in tall buildings.

The artificial foundation lies between the natural foundation and the building. Its purpose is to: transfer the building loads to the soil and spread the load evenly across soil that can support the load.

When choosing the correct type of artificial foundation the following conditions should be considered:

1. the load-bearing capability of the ground;

2. the depth where the suitable load-bearing soil can be founded;

3. the distance from trees which can affect the stability of the soil;

4. the level of the water table;

5. the normal variation in the water table;

6. the total weight of the building. If the building is heavier than the soil that was removed, then there will be some settlement as the soil adjusts to the new load.

Although concrete is the preferred material for the construction of the artificial foundations, the form will depend on the specific conditions of the building and environment.

Figure 8.2 Loads on natural and artificial foundations

Types of Foundation

Many small buildings are constructed with load-bearing walls on strip foundations. But you may find out that the soil requires alternative types of foundation which are:

• concrete strip foundation;

• deep strip foundation;

• raft foundation;

• piled foundation;

• pad foundation;

• stepped strip foundation.

5 Read the text again and answer the questions that follow (1-5):

1. Give the definition of the term “foundation”.

2. What building loads does artificial foundation carry?

3. What is the purpose of artificial foundation?

4. What are the principle conditions when choosing the correct type of a foundation?

5. What types of foundations have you read about?

Follow-up

6 a) Find the synonyms for the following words:

foundation, to be placed, protection, excessive, to be completed, natural, artificial, settlement, to occupy, to cause, purpose, to support, to transfer, to be considered, environment, to be constructed, to require.

b) Explain the words in bold from the text and make up sentences of your own. Use English-English dictionary to help you.

7 Give the English equivalents to the following and use 5 of them in small situations:

Часть конструкции, естественное основание, искусственное основание, вызывать неустойчивость и подвергать опасности жителей, собственный вес конструкции, рабочая/подвижная нагрузка, ветровая нагрузка, учитывать следующие условия, устойчивость грунта, уровень грунтовых вод, несущие стены, типы фундамента.

8 Which questions could you ask to get these answers?

1. Geotechnical engineering, being important in many branches such as military, mining, petroleum and in our case civil engineering, concerned with the engineering behavior of earth materials.

2. The capacity of soil to support the loads applied to the ground is called bearing capacity.

3. A shallow foundation is a type of foundation which transfers building loads to the earth very near the surface, rather than to a subsurface layer or a range of depths as does a deep foundation.

4. Piles should be placed on the center line of the walls that need support.

5. Pile foundations are used in the areas where the other kinds of foundations cannot be constructed.

9 Fill in the gaps with derivatives of the words in capitals:

TYPES OF FOUNDATION Part I The concrete strip foundations in Figure 8.3. are used most frequently. They consist of 1) _____ mass concrete strips poured in the bottom of trenches. These foundations will support load-bearing walls which are centered on the concrete strips to spread the 2) _____ from the walls, roofs and other floor loads evenly. The concrete strip is usually a uniform width and depth. Figure 8.3Concrete Strip Foundation The foundation must be wide and deep enough to avoid soil movement that could cause 3) _____. Depending on soil conditions, the maximum depth may be 900 mm. building regulations may suggest the 4) ____ minimum width for strip foundations. The concrete must be at least as thick as its projection from the base of the wall. This ensures that the pressures of the building loads are distributed in the concrete at an angle of 45°. The deep strip foundation in Figure 8.4. is a 5) _____ of strip foundations. Deep strip foundations are usually dug out with a mechanical 6) _____, which cuts a narrow trench that is backfilled with concrete up to ground level. These foundations use more concrete, but reduce the cost of masonry walls and may remove the need for timber support for the trenches. Figure 8.4 Deep Strip Foundation Raft foundations are a good 7) _____ if the soil has a poor bearing capacity or if the building loads are quite small, because the cost of8) _____ separate foundations is eliminated. The oversite concrete slab that forms the ground floor of the building becomes the raft foundation (Figure 8.5.). Figure 8.5 Raft Foundation The slab can be thickened at the edges with an edge beam and thickened underneath internal load bearing walls. Mesh 9) _____ increases the strength of the raft foundation and distributes the pressures of the building loads 10) _____.

CONTINUE PRESS STABLE SUIT VARY EXCAVATE SOLVE DIG REINFORCE EVEN