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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!!
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