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By- Kokebe Yifru -Adama University Department of Civil Engineering & Arc- 20010/2011

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3. TIMBERING & EXCAVATIONS

3.1 IntroductionExcavation & Earth work IncludesSite clearance

Removal of trees, bushes and Vegetations

Removal of termite hills

Removal of structures

Excavation

Topsoil Excavation

Excavation to reduce levelsExcavation for foundation

Backfilling

Disposal of excavated material

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3. TIMBERING & EXCAVATIONS

3.1 Introduction cont The earth work of foundation of a building involves the

following operations:-

1.

Preparing Foundation plan

2.

Setting out of foundation trenches

3.

Excavation of foundation

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3.2 Setting out

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3. TIMBERING & EXCAVATIONS

3.2 Setting out foundation trenches

Setting out or ground tracing is the process of laying down

the excavation lines and center lines etc. on the ground,

before excavation is started.` 'Setting out', as practiced on civil engineering and

building sites, is the locating of the works to beconstructed, ensuring that they are dimensionally within

permissible tolerances and correctly constructed.

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3. TIMBERING & EXCAVATIONS

3.2 Setting out.` Setting out is essentially an aid to the labour force

and must necessarily be provided in a form that is

easy for them to use and understand; the information

must be reliable and must be available as and when

required.

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3. TIMBERING & EXCAVATIONS

3.2 Setting out.

` Errors in setting out will in most cases result inremedial works which will be expensive. Whatever lines

or levels are provided should be checked to be sure of

their accuracy, and they should be provided to the

foreman efficiently so that he can have the necessary

confidence in them.

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3. TIMBERING & EXCAVATIONS

3.2 Setting out foundation

trenches cont..Steps in marking points-

1.

Establish reference points

2.

Fix wooden pegs and batten boards (poling boards) around

the site to excavated. Each peg may be projected about 25-50mm above ground

level and may be driven at a distance of

about 2m from the edges

of excavation;

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3. TIMBERING & EXCAVATIONS

Steps in marking points-

3.

Mark the center line of the walls;

4. Mark the plinth lines:-these are

lines making the inside and the outside of walls;

5. Check the right angles ( by stretching strings and formingtriangles with sides 3, 4 and 5 units, and for big projects

using surveying equipments)

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3. TIMBERING & EXCAVATIONS cont.

3.2 Setting out foundation trenches c0nt..

Steps in marking points-

6. If all dimensions are correct and all corners are at their

angles, mark the cutting lines on the ground (using lime)

NB-

It is essential to have permanent reference marks, which should

not get disturbed as the excavation proceeds.

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3.3 Excavation of foundation

trenches

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3. TIMBERING & EXCAVATIONS cont.

3.3 Excavation of foundation trenches

Excavation of foundation trenches can be done either

manually with the help of conventional implements (spade,

pick axe, etc) or with the help of special mechanical

equipments. (Read)

Working safely in excavations

The most important rule is to make sure that the sides ofthe excavation are always supported or safe from collapsing.

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3.4 Timbering of foundation

trench

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3. TIMBERING & EXCAVATIONS cont.

3.4 Timbering of foundation trench

The process of supporting the sides of foundation trenches

by means of wooden members is called timbering of

foundation trench.

When the depth of foundation trench is large, or when the

sub soil is loose, the side of foundation trench may

irregularly form a cave like hollow (concave). The problem

can be solved by timbering.

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3. TIMBERING & EXCAVATIONS cont.

3.5 Methods of Timbering of foundation trench

1.Stay bracing

Used in fairly firm soil.

When the depth of

excavation is

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3. TIMBERING & EXCAVATIONS cont.

3.5 Methods of Timbering

2. Box Sheeting

Is adopted in loose soil.

When the depth of

excavation is

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3. TIMBERING & EXCAVATIONS cont.

3.5 Methods of Timbering

3. Vertical Sheeting

Is adopted for soft ground. When the depth of

excavation is

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3. TIMBERING & EXCAVATIONS cont.

3.5 Methods of Timbering

4. Runner system

Used in extremely loose and soft ground, which needs

immediate support as excavation progresses.

Similar to vertical sheeting or box sheeting, except that in the

place of vertical sheeting, runners, made of long thick wooden

sheets or planks are provided.

The runners are driven about 30cm in advance of the progress

of the work, by hammering.

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3. TIMBERING & EXCAVATIONS cont.

3.5 Methods of Timbering

5. Sheet piling

This method is adopted when-1.

The soil is soft or loose

2.

The depth of excavation is large

3.

The width of the trench is large

4.

There is sub-soil water

Sheet piles are designed to resist lateral earth pressure. Are driven in the ground by mechanical means (pile driving

equipment).

They can be used for excavating to a very large depth.By - Kokebe Yifru -Adama University Department of Civil Engineering & Arc- 2009/2010

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3. TIMBERING & EXCAVATIONS

Assignment

1.

Discuss the methods of improving safe bearing

capacity of soils.

2.

Explain the problems of foundations on black cotton

soil briefly.(max

10 pages)

Summary

By Group 4

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Thank You!!