SETTING OUT

 Setting out is the process of transferring the dimensions from the working
drawings to the site on the ground.
 Steel tapes should be used up to 30m.
 Linen or plastic coated tapes should be avoided in measuring long distances
as they are liable to stretch.

 Tools and materials

i. Panga
ii. Club hammer
iii. Pegs
iv. String
v. Nails
vi. Spike (sharp stick)
vii. Building Square
viii. Profile boards
ix. Pencil
x. Hand saw
xi. Spirit level
xii. Plumb bob
xiii. Tape measure
xiv. Claw hammer
xv. A sledge hammer of weight 2kg.
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 Procedure of Setting out Circular Buildings
i. Centre peg c is driven in position (R + M) metres long from the reference
point S.
 A nail is fixed at the top of the peg

ii. A string is measured equal to the length of the radius required and then
one end of it is tied to the centre peg while the other is fixed to a spike.

iii. The string is stretched and the wall boundary marked.

A uniform tension should be applied to the string while marking to maintain
the radius required.

iv. The pole positions are the marked around the circumference.
 If the wall is to be constructed of bricks, blocks or stones, then the trench
width would have to be marked.
Later the wall thickness is marked on the foundation strip.
 The marks for the trench and the wall width is done by repeating step (iii)
using the appropriate radii.
 A trammel could be used to mark the width of the trench and the wall
thickness.

Advantages of Using a Trammel

i. A trammel could be used to mark the width of trench and wall thickness.
ii. There is no problem encountered because of tension.
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Methods of setting out rectangular buildings

 There are three methods of setting out namely:
i. The 3:4:5 methods
ii. The builder’s square method
iii. The use of leveling instruments
  The 3:4:5 methods
i. The reference points S1 and S2 are located on the site boundary.
ii. The positions of peg A and B are located by measuring the distances S 1A
and S2B and pegs driven in position.

iii. A string is stretched between A and B.

 This is the baseline (face line) of the building.

iv. Along line AB the position of the corner ‘C’ is located

v. The right-angled corner of the building at ‘C’ is set out.
 The setting out of a right angled corner may be done using different
methods.
a) Peg ‘C’ marking the corner of a building is driven in position.
b) A distance of 3 units from peg ‘C’ is measured along the baseline AB and
‘C1’ fixed in position.
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c) Peg ‘C2’ is located by measuring 5 units from ‘C1’and 4 units from ‘C’
respectively, thus forming a right angle at ‘C’.
vi. A string is stretched from ‘C’ to ‘E’ through ‘D’.
 The position of peg ‘D’ is located by measuring to width.
vii. Peg ‘G’ is located along baseline AB by measuring to length of the building.
viii. By establishing right angles at ‘D’ and ‘G’ the corner ‘K’ can be located.
ix. Check the diagonals and erect profile boards.
x. Mark the position of the wall on the profiles with either nails or saw cuts.
  Advantages of 3:4:5 methods
a) Simple to use
b) Does not require any calculations.
c) Can be applied to large buildings.
d) Accuracy of setting out is self evident.
e) In the event of error is simple and quick to rectify.

 Disadvantages3:4:5 methods
i. Two tape measures are required which may be difficult to obtain in rural
areas.
ii. Effects of wind on tapes and line may lead to inaccurate work especially on
long buildings.

The Builder’s Square Method

i. Set out the front or building line in the usual manner with pegs or marks at
the required distances.

ii. Place the builder’s square so that the front line touches one side of the
square right through its length.
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 iii. Stretch lines from the centre peg so that it is parallel to the second side of
the square and establish the third peg.

iv. With the aid of a tape measure mark out the breadth and length of the
proposed building.

v. Transferring the builder’s square to the remaining corners and repeating

the above operations; a simple rectangular building can be set out.

vi. After establishing the four corner pegs profiles may be erected the same
way as described above.

Advantages of Builder’s Square Method

i. Simple to use.
ii. Does not require any calculations.
iii. Can be very accurate when used for small rectangular buildings.
iv. Quick in application.

Disadvantages of Builder’s Square Method

i. Unseasoned timber can twist and warp leading to errors when used.
ii. Unsuitable for long buildings.

The site square method

Advantages site square method
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i. Can be used for large buildings with some accuracy.

ii. Transfer of lines to profile boards is done easily.

 Disadvantages site square method

i. The range of accuracy is limited to 33m.
ii. Distances cannot be read off the instrument directly but need to be
measured with a tape measure.
 Profile Boards
 A profile board is a framework made of stout pegs driven into the ground
and a horizontal cross board nailed onto them.
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  Profiles are used as guides to establish the position of walls and foundation
trenches.
When erecting profiles, it is required that each of them should be level and
clear off the walls to be constructed.
 A spirit level is used when leveling the cross-boards.
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To avoid splitting the cross board during erection, pegs are hammered
alternately while maintaining an appropriate level profile.
 The trench width and the wall thickness are marked on the profile boards
using either nails or saw cuts.
Strings are stretched between the marks of opposite profiles to establish
the trench width and wall thickness.
 The trench lines are transferred to the ground using plumb bob or spirit
level and marked using a panga or a jembe.
  This method of transfer could also be used when transferring wall line to
the foundation strip.

EXCAVATION OF SHALLOW FOUNDATIONS

 Excavation is the process of removing the soil until a firm solid ground is
reached.

 It is the requirement of the Kenya building code that foundation be taken

down to a firm base.

The depth to which the foundation is laid depends on the nature of the
building.

 Excavation to the required depth is carried out by hand (manual)on small

jobs and by machines for bigger jobs.

Factors Influencing the Methods of Excavations

 Methods of excavation to be used are governed by:

i. The size of the area

ii. Volume of soil to be excavated

iii. Type of soil on site

iv. Time factor

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v. Availability of equipment

vi. Depth of excavation

Manual Excavation
 It is the removal of soil from excavation using hand tools such as:
 i. Jembe

ii. Pick axe

iii. Mattock

iv. Panga

v. Spade/shovel

vi. Wheelbarrow

vii. Claw hammer

viii. Sledgehammer

ix. Iron pans/metal karais

x. Crow bar

xi. Hand auger

Mechanical Excavation
 It is the removal of soil from trenches using machines.

 These machines includes:

i. Drag line

ii. Power shovel

iii. Back hoe/back –actor

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iv. Clam shell

v. Front bucket

Timbering
  Timbering is a term used to refer to the temporary supports used to
support the sides of excavations from collapsing which may result in
accidents.

 It is sometimes called planking and strutting.

 The sides of excavations will need support to:

i. Protect the operatives (workers) while working in excavations.

ii. Keep the excavations open by acting as retaining walls of the sides of the
trench.

 Over a short period of time many soils may not require timbering.

Factors to Consider when Timbering

i. Depth of excavation

ii. Type of soil to be excavated

iii. Weather condition

iv. Duration the trench will remain open

v. The safety of the surrounding property and roads. Any collapse or ground
movement may affect the foundations of surrounding property, causing
settlement.
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vi. The nature of the ground can also be determined whether supports are
required during excavation or whether the supports can be provided after
completion of the excavation.

vii. The method of excavation

 A machine bucket will not be affected by a trench collapse whereas a man

might be killed.
 viii. The ease of removal of the support during the backfilling operation.

ix. The safety of the workmen working in the trench. The workmen are at risk
from:

a) The sides of the trench collapsing

b) Soil falling from the sides of the excavation.

c) Materials falling into the trench from above.

d) Other men falling into the trench.

e) The operating machinery in operation.

f) Vehicles being driven into the excavation.

Safety and Good Working Attitudes

i. Traffic

 Movement of trucks, wagons and other mechanical equipment should not

be allowed to be close to the trench.

ii. Ladders

 Ladders should be provided with suitable steps along the trench so that
laborers may escape to safety in case of accidents.

iii. Safety helmets

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 It is very likely that some timber may fall when timbering and may injure a
laborer.

iv. Supervisor

 There must be a supervisor to look after the welfare of the workers working
in the trench. A lone worker should not be allowed to enter the excavation.
  After the end of the day’s work it should be assured that all the workers
have come out of trench.

v. Fencing and lighting

 Site of excavation trenches should be fenced with barbed wire and

permanent guards should be appointed to prevent any animal or person
falling into the trench.

 If possible red lights should provide light in the night in thre night to
prevent accidents

vi. Safety of adjacent structures

 If foundations of adjacent structures is unsafe because of this excavation , it

should be given proper temporary supports with the help of shores.

vii. First aid box

 First aid boxes should be provided to treat injuries at site itself.

Methods of preventing trench collapse

a) By timbering.
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b) By building retaining walls.

c) By battering the sides of trenches.

d) By use of shores (shoring).

 Simple Side Supports
i. Timbering in hard soils
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ii. Timbering in firm soils

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iii. Timbering in loose dry soils

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iv. Timbering in loose wet soils

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