setting out works

8/6/2019 Setting Out Works

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SETTING OUT WORKS

TOPIC 5


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INTRODUCTION

The process of laying out engineering projects

by placing pegs or marks at the site of works.

The main idea is to define the lines ofexcavation and levels of the works for the

guidance of workers so that construction may

proceed with reference to the already

prepared drawing.

Setting out is the reverse process.


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EQUIPMENT USED

SIGHT RAILS

Consists of a horizontal cross-piece nailed to

a single upright or pair of uprights driven intothe ground.

The upper edge of the cross-piece is set to a

convenient height above the required plane

of the structure.


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Various forms of sight rails


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EQUIPMENT USED

TRAVELLER

Same size and same value with sight rail.

Used to monitor excavation process for cutand fill.


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EQUIPMENT USED

SLOPE RAILS

Used for controlling the side slopes in

embankments and in cutting.


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CONTROLS FOR SETTING OUT

The setting out of work requires the following

two controls:

a) Horizontal control

b) Vertical control


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HORIZONTAL CONTROL

Station must be established within or near the

construction area.

The horizontal control consists of referencemarks of known plan position.


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HORIZONTAL CONTROL

REFERENCE GRIDS

Reference grid are used for accurate setting

out of works of large magnitude. The following types of reference grid are used

i. Survey grid

ii. Site grid


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SURVEY GRID

The one which drawn on the survey plan, fromthe original traverse.

SITE GRID

Used by the designer

As far as possible, the site grid should be

actually the survey grid.


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VERTICAL CONTROL

Establishment of reference marks of knownheight relative to some specified datum.

To establish a number of temporary bench

mark.

The position of TBM should be fixed duringinitial site reconnaissance.

All TBM should be checked, properlyprotected and should be re-checked at regularintervals.


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EXAMPLE CALCULATION

QUESTION 1

A 80m long pipeline will be built and the gradient fromA to B is 1 in 110 and falls from A to B. Reduced level ofpoint A are 20.102m and point B are 20.195m. The

invert level at point A is 18.123m.Calculate:

i. The invert level of point B (17.396m)

ii. Height of sight rails at A and B above ground level if a

3m traveler is to be used.(1.021m & 0.201m)

iii. The depth of excavation at point A and B.(1.979m &2.799m)


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EXAMPLE CALCULATION

QUESTION 2

A straight length of sewer is to be laid

between three manholes P,Qand R. Thefollowing information is available.

SECTION PQ QR

Horizontal Length 60m 30m

Gradient -1:100 -1:50

MANHOLE P Q R

Ground Level 80.760m 80.200m 80.140m

Invert Level 78.430m - -


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continue

Calculate:

i. The invert levels ofQand R. (77.830m &77.230m)

ii. Reduced level of the sight rails at P,Qand R if a3m traveler is to be used to locate the sewerinvert. (81.430m, 80.830m & .m)

iii. The height of sight rails above ground level at

P,Q

and R. (0.670m, 0.630m & m)iv. The depth of excavation at P,Qand R. (2.330m,2.370m & ..m)


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EXAMPLE CALCULATION

QUESTION 3

A culvert with 250m length will be built from section

S1 to section S2 and the gradient from S1 to S2 is 1 in

50 and falls from S1 to S2. Reduced level and invertlevel for section S1 are 23.5m and 21.3m. If reduced

level for section S2 is 18.6m and 2.5m rod traveler is

to be used, calculate:

i. Reduced level on top of peg at S1 and S2(23.8m & 18.8m)

ii. Invert level at S2 (16.3m)


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EXAMPLE CALCULATION

QUESTION 4

Given the data below get from the construction for drainage.

Reduced level at point A=23.470m

Reduced level at point B=22.855m

Distance from A to B = 40m

Depth of excavation at A = 1m

Gradient falls from A to B = 1:100

Traveler length = 2.5mCalculate:

i. Invert level at A and B (22.470m & 22.070m)

ii. Depth of excavation at B (0.785m)

iii. Reduced level of the sight rails at A and B (1.500m & 1.715m)

setting out works

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