setting out lecture

7/21/2019 Setting OUt Lecture

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Topic 7: Setting out


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Aims

-Understand the roles of the various different types of personnel who are involvedin the setting out process

-Understand the aims of setting out

-Refer to the different types of plans that may be used in the setting out process

-Appreciate the good working practices that should be undertaken in order thatthe aims of setting out can be achieved

-Understand the procedures required to ensure that the horizontal and verticalcontrol requirements of setting out operations can be met

-Set out design points on site by a number of methods

-Apply horizontal and vertical control techniques to second-stage setting outoperations

-Appreciate the application of laser instruments in surveying and setting out


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What is setting out?

A definition of setting out, often used, is that it is the reverse of surveying.

Whereas surveying is a process for forming maps and plans of a particular site orarea, setting out begins with plans and ends with the various elements of aparticular plan correctly positioned on site.

However most techniques and equipment used in surveying are also used in

setting out i.e. while surveying may be the opposite of setting out, the processesand instruments are almost identical.

The International Organisation for Standardisation (ISO) define setting out as:

Setting out is the establishment of the marks and lines to define the position andlevel of the elements for the construction work so that works may proceed with

reference to them. This process may be contrasted with the purpose ofsurveying which is to determine by measurement the position of existing features.


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-Setting out is one application of surveying

-Most of the techniques and equipment used in surveying are also used in settingout

-Mistakes in setting out can be costly

-For setting out to be undertaken successfully good work practices should be

employed

-There are three parties involved in the construction procedures: the employer,the engineer and the contractor

-Although the engineer checks the work, the setting out is the responsibility of the

contractor

-The cost of correcting any errors in the setting out has to be paid for by theContractor, provided the engineer has supplies reliable information in writing


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Principles of setting out

The main aim of setting out is to ensure that the various elements of the schemeare positioned correctly in all three dimensions.

Horizontal control techniques

In order that the design of the scheme can be correctly fixed in position, it isnecessary to establish points on the site which the E, Ncoordinates are known.

These are horizontal control points and, once they have been located they canbe used with a positioning technique to set out E, N coordinates of the design

points.

Two factors need to be taken into account when establishing horizontal controlpoints.

1. The control points should be located throughout the site in order that all the

design points can be fixed from at least two or three of them so that the work canbe independently checked.

2. The design points must be set out to the accuracy stated in the specifications


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The accuracy must be obtained throughout the whole network and this can beachieved by establishing different levels of control based on one of the

fundamental tenets of surveying: working from the whole to the part.

In practice, this normally involves starting with a small number of very accuratelymeasured control points (known as first level or primary control) which enclosethe area in question and then using these to establish second level or secondary

control points near the site.When establishing the control network care needs to be taken that the tolerancesspecified are met.

An example if working from the whole to the part using two different levels of

control are shown in the next diagram. In this, the first level of control is providedby a traverse which is run through the site in question to provide a number of well

positioned primary control points.

These in turn are used to establish a second level of control, in this case

secondary site points at each of a series of baselines which define importantelements of the scheme.


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On some schemes the same control points that were used in the production of

the site plan prior to design work are used for setting out. These muse be re-measured before setting out as positions may have changed for a number ofreasons.

Horizontal control points should be located as near as possible to the site in openpositions for ease of working, but well away from the construction area and trafficroutes to avoid them being disturbed.


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The construction and protection of control points is very important. Wooden pegsare often used for non-permanent stations.

For permanent control points it is recommended that they be constructed with

concrete as shown below.


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Baselines

A baseline is a line running between two points of a known position. Anybaselines required to set out a project should be specified on the setting out plan

by the designer and included in the contract.

Baselines can take many forms: they can be simply two specified points joined,

they can run between two buildings, they can mark the boundary with an existing

building/development or they can mark the centre line for a new road.

Baselines can be used in a number of different ways:

- Where a baseline is specified to run between two points then once the points

have been established on site, the design points can be set out from the baseline

by offsetting using tapes (as seen below).


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A design point D is to be set out at right angles to a baseline AB from point Cwhich lies at a distance y from point A. The required offset distance from C to D

is x. Distances xand y will be given by the designer and will usually behorizontal distances.

- Primary site control points, such as traverse stations E & F in the figure below

can be use to establish a baseline AB by angle and distance lvalues.


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Subsidiary offset lines can then be set off at right angles from each end of thebaseline to fix two corners R and S of building Z. Once R and S have been

pegged out, the horizontal length of RS is measured and checked against itsdesigned value. If it is within the required tolerance, points R and S can be usedas a baseline to set out the corners T and U.

- Design points can be set out by taping known as distances from each end of abaseline as shown below.


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At point A on building X is set out by taping dimensions 1 and 2 from the baselineand point B by taping dimensions 3 and 4. As before, the set out lengths of AB is

then checked against its designed value and within tolerance, it can be used as abaseline to set out corners C and D.

-In some cases, the designer may specify a baseline that runs between points on

two existing buildings. Design points are then set out from this line either byoffsetting at right angles or by measuring distances from points on the line. Theaccuracy of this method depends upon how well the baseline can be established

and how the dimensions required to set out the design points are known.

The accuracy of the baselines method increases if two baselines at right anglesto each other are used.

Design points can be established either by measuring and offsetting from both

lines, or a grid system can be set up to provide additional control points in thearea enclosed by the baselines.


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Reference grids

A control grid enables points to be set over a large area. Several different gridscan be used in setting out

-Survey grid: is drawn on the survey plan from the original traverse or network.The grid points have known eastings and northings related either to some

arbitrary origin or to the national grid.

-Site grid: is used by the designer. It is usually related in some way to the

survey grid and should, if possible, actually be the survey grid, the advantage ofthis being that if the original control stations have been permanently marked thenthe design points will be on the same coordinate system and setting out is greatly

simplified.


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- The structural grid is established around a particular building or structure whichcontains much detail such as columns, which cannot be set out with sufficient

accuracy from the grid site.

-The secondary grid is established inside the structure from the structural gridwhen it is no longer possible to use the structural grid to establish internalfeatures of the building as the vision becomes obscured.

Offset pegs

Whether used in the form of a baseline or a grid, the horizontal control points are

used to establish design points on the proposed structure.

Once excavations for foundations begin, the corner pegs will be lost. To avoid

this extra pegs called offset pegs are used


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Vertical control techniques

In order that design points on the works can be positioned at their correct levels,vertical control points of known elevation relative to some specified vertical datum

are established. To ordnance datum is commonly used and levels on the site arereduced to a nearby OS benchmark.

Transferred or temporary benchmarks

The positions of TBMs should be fixed during the initial reconnaissance so that

their construction can be completed in good time and they can be allowed tosettle before levelling them in. In practice, 20mm diameter steel bolts and 100mmlong, driven into existing steps, ledges, footpaths etc are ideal.


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If TBM are constructed at ground level on site, a design to that shown belowshould be used.

There should never be more that 80m between TBMs on site and the accuracy oflevelling should be within the following limits:

Site TBM relative to the MBM 0.005m

Spot levels on soft surfaces relative to a TMB 0.010m

Spot levels on hard surfaces relative to a TBM 0.005m


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Sight Rails

These consist of a horizontal timber cross piece nailed to a single upright or apair of uprights driven into the ground (see below)

The upper edge of the cross piece is set to a convenient height above therequired plane of the structure, usually to the nearest 100mm, and should be a

height above ground to ensure convenient alignment by eye with the upper edge.


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Sight rails are usually offset 2 or 3 metres at right angles to construction lines toavoid them being damaged as excavations proceed.

Travellers and boning rods

A traveller is similar in appearance to a sight rail on a single support and isportable. The length of the upper edge to its base should be a convenient

dimension to the nearest half metre.

Travellers are used in conjunction with sight rails. The sight rails are set someconvenient value above the required plane and the travellers are constructed so

that their length is equal to this value.


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As excavation works proceeds, the traveller is sighted in between the sight rails

and used to monitor the cutting and filling.

Slope rails or batter boards

For controlling side slopes on embankments and cuttings slope rails are used.For an embankment the slope rails usually define a plane parallel to the slope of

the embankment offset by a convenient distance:


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For a cutting the slope rails can either be used to define the actual plane of the

slope or an offset plane as shown below:


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The advantage of the above method being that additional slope rails may be

added as excavation proceeds.

The advantage of this method being that the slope rail can be lower in heightand may make it easier to sight along than the example above.


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Positioning Slope Rails

In order to position slope rails we must first locate the toe of the embankment.

Consider the embankment below, which runs from A to B with a width of 12m.Point C is on the existing ground level. The sides of the embankment are toslope at 1 in s. the procedure is as follows:


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1.From the Road Design / Plans obtain the reduced level of A.

2. Peg out point C by measuring a distance 6m horizontally from F at rightangles to the centreline.

3.Peg out points at 5m intervals from point C towards and beyond T.

4. Measure the reduced level on the ground surface at the first 5m peg

5.Calculate the proposed reduced level of on the embankment slope above thispoint from:

6. Compare the measure and calculated values at the 5m point, if the groundlevel measured is lower than the calculated slope level, the toe is located a

further 5m away from C.

7. Repeat the procedure for the 10m peg, the calculation becomes:


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Once the Toe has been located the wooden uprights of the slope rails can be

hammered in at some offset from the embankment/cutting. The next stage is

to calculate the required reduced levels at which the tope edges of the sloperails must be fixed to the wooden uprights.


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For an embankment, assuming that a 1.5m traveller is to be used as shown, the

reduced levels of P and Q should be obtained using (it is assumed that the

RL at the toe is known):

For a cutting the reduced levels of R and S should be obtained using (it isassumed that the RL at edge of the embankment is known):


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Profile boards

These are similar to sight rails but are used to determine the corners and sides

of buildings. Offset pegs are normally used to enable building corners to berelocated after foundation excavation. Profile boards are normally erected near

each offset peg and used in the same way as a sight rail.


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A variation on corner profiles is to use a continuous profile all around the

building ser to a particular level above the required structural plane.

The advantage of a continuous profile is that the lines of the internal walls canbe marked on the profile and strung across to guide construction.


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Coordinate positioning techniques

For setting out by coordinates to be possible, a control network consisting of

coordinated points (with heights) must be established on site. These areobtained by using theodolites, tapes, GPS and total station.

Setting out using a theodolite and tape

To set out using coordinates by theodolite and tape, one of the following

procedures is used:

1. Angle and distance from two control points e.g. from point A below, can be

set out from a control point S using one of two methods:

Using the inverse calculation, determine the horizontal length l(SA) and the

whole circle bearings of ST and SA.


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The following steps are used when setting up a free station point:-The theodolite is set up at some suitable place in the vicinity of the points

which are to be set out hence the title free station as the choice of theinstrument position is arbitrary.

-Any angular resection is carried out to fix the position of the free station point.-The coordinates of the free station are calculated

Following this, setting out continues as before and the required design pointsare ser out using the theodolite at the free station point.


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Although setting out can be conducted using theodolites, tapes (and levels) in

what might be sometimes called traditional methods, a lot of work on site is

done using total stations and GPS equipment.

When setting out by so-called traditional methods, direct methods of angle and

distance are taken to position structures and other works from nearby control

points or from baselines.

Following this, offsets and profiles are put in place to define the main lines of abuilding and provide vertical control for second stage setting out.

Despite their popularity on site, these well-established methods have the

disadvantages that the horizontal and vertical components of setting out have to

be done separately (levelling must be used for any heighting), they can be time

consuming if a lot of points have to be set out, and they require at least twopeople to do the setting out.


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Setting out by total station

To use a total station for setting out, it must be levelled and then centred over a

control point in the same way as for a theodolite. As before this must be donecorrectly otherwise the subsequent readings taken with the instrument will not

give the correct results.

Having set up the total station, it has to be orientated horizontally to the sitecoordinate system and it may also have to be orientated vertically. Forhorizontal orientation, the coordinates of the control point at which theinstrument is set up are entered into the total station.

An adjacent control point is then chosen as a reference point (reference object)and the coordinates for this site are also keyed in. To orientate the total station,the RO is sighted and the horizontal circle orientation programme automaticallycomputes the bearing from the total station to the RO.

For vertical orientation, the height of collimation of the total station has to bedetermined. If the height of the control point at which the total station is known,

this is entered into the instrument or is already stored in the control point data.


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Once the total station has been orientated it can be used for setting out

horizontal positions either using the coordinates of the points to be set out

directly or using bearing and distance values calculated from these coordinates.Two approaches can be used.

-When the coordinates of the point to be set out are used, these are usually

contained in the file together with the coordinates of the control points for theproject, and this is downloaded to the total station before work commences.

-If the bearing and distance to be set out are known, these can also be used for

setting out. They are entered into the total station and, as soon as theappropriate key(s) are pressed to activate this is setting out mode, theinstrument once again displays the difference between the entered and

measured bearing values.


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Setting out by GPS

For setting out by GPS, an RTK system is required consisting of two geodeticreceivers working in precise relative mode.

One of these will be permanently located at a base station and the other (the

rover) will move around the site and take the measurements needed for

positioning design points.

In common with all other setting out methods, GPS is based on a controlnetwork, which must be in place before any work can start.

Control points with positions defined on the site grid are needed for basestations, for determining transformation parameters when deriving site

coordinates from GPS coordinates.

Depending on the site, control can be local and based on an arbitrary

coordinate system or it can be connected to a national system.


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For small local sites a control network consisting of at least three but preferably

five points with known site coordinates and heights is required for determining

transformation parameters.

This can be surveyed using a total station and traverse methods.

On large sites, whether they cover an extensive area or are long linear sitessuch as those occurring on road and railway projects, site control is often basedon national control.


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Applying the principles of setting out

Stages in setting out

As the works proceed, the setting out falls into two broad stages.

First stage setting out

In practice, first stage setting out involves the use of many of the horizontal andvertical control methods and positioning techniques . The purpose of this stageis to locate the boundaries of the works in their correct position on the groundsurface and to define the major elements. In order to do this, horizontal andvertical control points must be established on or near the site.

Second stage setting out

Second stage setting out continues on from the first stage, beginning at the

ground floor slab, road sub-base level etc. Up to this point, all the control will beoutside the main construction, for example, the pegs defining building corners,

centre lines and so on will have been knocked out during the earthmoving workand only the original control will be undisturbed.


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Examples of setting out

Setting out a pipeline

This operation falls into the first category of setting out.

General considerations: sewers normally follow the natural fall in the land and

are laid at gradients which induce self-cleansing velocity. The figure belowshows a sight rail offset at right angles to a pipe line laid in a granular bedding

trench.

f


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Horizontal control: the working drawings will show the directions of the sewer

pipes and the positions of the manholes. The line of the sewer is normally

pegged at 20 to 30m intervals using coordinate methods of positioning fromreference points or in relation to existing detail. The direction of the line can besighted using a theodolite and pegs.

Vertical control: involves the erection of sight rails some convenient heightabove the invert level of the pipe.

Erection and use of sight rails: the sight rail uprights are hammered firmly into

the ground, usually offset from the line rather than straddling it. Using a nearbyTBM and levelling equipment, the reduced levels of the tops of the uprights.

Where the natural slope of the ground is not approximately parallel to the

proposed pipe gradient, double sight rails can be used as shown in the next fig.Often it is required to lay storm water and foul water sewers in adjacenttrenches. Since the storm water pipe is usually at a higher level than the foul

water pipe, it is common to dig one trench to two different levels as shown infig 2 on the next slide.


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B th i th t ll d i diff t i ht il il d t th


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Both pipe runs are then controlled using different sight rails nailed to the same

uprights.

Pipe laying: on completion of the excavation, the sight rail control is transferredto pegs in the bottom of the trench as shown below

Setting out a building to ground floor level


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Setting out a building to ground-floor level

This process falls into the first category of setting out. It must be remembered

when setting out that, since dimensions, whether scaled or designed, arealmost always horizontal, slope must be allowed for in surface taping on sloping

ground. The steps involved in setting out a building are as follows:

-Two corners of the building are ser out from a baseline, site grid or control

points-From these two corners, the two other corners are ser out using a theodolite toturn off the right angels as shown below

-Diagonals are checked

-Profile boards are placed at each corner


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If a structural grid in used (as in a), the distances from the secondary site

control points to abutment design points A, B, C and D must first be calculated.

They are then set out either using a theodolite to establish the directions and

steel tapes to measure the distances or by using a total station.

-If coordinates are used as shown (b) the bearings and distances from the


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If coordinates are used as shown (b), the bearings and distances from the

secondary site control points to A, B, C and D are calculated from theirrespective coordinates such that each design point can be established from atleast two control points.

-Once points A, B, C and D have been set out, their positions should be

checked by measuring between them and also measuring to them from control

points not used to establish them initially.

-Offset pegs are established for each of A, B, C and D to allow excavation andfoundation work to proceed and to enable the points to be relocated as and

when required.

-Once the foundations are established, the formwork, steel or precast units can

be positioned with reference to the offset pegs.

Controlling vertically


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Controlling vertically

One of the most important second stage setting out operations is to ensure thatthose elements of the scheme which are designed to be vertical are actuallyconstructed be so, and there are a number of techniques available by which thiscan be achieved.

Particular emphasis is placed on the control verticality in multi-storey structures.In order to avoid repeating information earlier in this chapter, the followingassumptions have been made.

- Offset pegs have been established to enable the sides of the building to be

located as necessary.-The structure being controlled has already had its ground floor slab constructed

and the horizontal control lines have already been transferred.

Plumb-bob methods

The traditional method of controlling verticality is to use plumb-bobs, suspendedon piano wire or nylon. A range of weights is available (from 3 kg to 20 kg) andtwo plumb-bobs are needed in order to provide a reference line from which the

upper floors may be controlled.

In an ideal situation, the bob is suspended from an upper floor and moved until


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In an ideal situation, the bob is suspended from an upper floor and moved until

it hangs over a datum reference mark on the ground floor slab.

If it is impossible or Inconvenient to hang the plumb-bob down the outside of thestructure, holes and openings must be provided in the floors to allow the plumb-bob to hang through, and some form of centring frame will be necessary to

cover the opening to enable the exact point to be fixed.


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Transferring height from floor to floor


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Reduced levels must be transferred several times during the second stagesetting out operations as the construction proceeds from floor to floor. Onemethod by which this can be done is to use a weighted steel tape to measurefrom a datum in the base of the structure as shown in FIG A.

The base datum levels should be set in the bottom of lift wells, service ductsand so on, such that an unrestricted taping line to roof level is provided. Thelevels should be transferred to each new floor by always measuring from thedatum rather than from the previous floor.

Each floor is then provided with TBMs in key positions from which normallevelling methods can be used to transfer levels on each floor. Alternatively, if

there are cast-in situ stairs present, a level and staff can be used to level up and

down the stairs, as shown in FIG B. Note that both up and down levelling mustbe done as a check.


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Setting Out Example 1 : Setting Out a pipeline using sight rails and a


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Traveller

An existing sewer at P is to be continued to Q and R on a falling gradient of 1 in150 for plan distances of 27.12m and 54.11m consecutively, where the positionof P, Q and R are defined by wooden uprights.

Level reading to staff on TBM (RL 89.52m) = 0.39mLevel reading to staff on top of upright at P = 0.16mLevel reading to staff on top of upright at Q = 0.35mLevel reading to staff on top of upright at R = 1.17m

Level reading to staff on invert of existing sewer at P = 2.84m

All readings are taken at the same instrument position.

Solution


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Height of collimation of instrument = 89.52 + 0.39 = 89.91m

Invert level at P = 89.91-2.84 = 87.07m

This gives:

Sight rail top edge level at P = 87.07 +2.5 = 89.57m

Level of top of upright at P = 89.91 0.16 = 89.75

Hence

Upright level sight rail level = 89.75 89.57 = +0.18m

Therefore the top edge of the sight rail at P must be fixed 0.18m below the topof the upright.

Fall of sewer from P to Q = -27.12 x (1/150) = -0.18m

Invert level at Q = 87.07 0.18 = 86.89m

Sight rail top edge level at Q = 86.89 +2.50 = 89.39m

L l f t f i ht t Q 89 91 0 35 89 56


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Level of top of upright at Q = 89.91-0.35=89.56mUpright level sight rail level = 89.56 89.39 = 0.17m

Therefore the top edge of the sight rail must be fixed 0.17m below the top

upright at Q.

Fall of sewer from P to R =

Invert level at R = 87.07 - 0.54 = 86.53m

Sight rail level at R = 86.53 + 2.50 = 89.03m

Level of top of upright at R = 89.91 -1.17 = 88.74m

Upright sight rail = 88.74 - 89.03 = -0.29m

Therefore the top edge of the sight rail must be fixed 0.29m above to the top of

the upright at R, i.e. the upright must be extended.

m54.0150

11.5412.27=

+

Setting Out Example 2 : Setting Out by intersection


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A rectangular buildings having plan sides of 75.36 and 23.24m was set out withits major axis aligned precisely east-west. The design of the coordinates of theSE corner were (348.92, 591.76) and this corner was fixed by theodoliteintersection from two stations P and Q whose respective coordinate were

(296.51, 540.32) and (371.30, 522.22). The other corners were set out by

similar methods.

When setting out was completed, the sides and the diagonals of the buildingwere measured as a check. To help with this the existing ground levels at the

four corners of the proposed structure were determined by levelling:

SE(152.86m) SW(149.73m) NE(151.45m) NW(146.53m)

Calculate the respective horizontal angles (to the nearest 20) that were set off

P relative to PQ and at Q relative to QP in order to intersect position SE


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P relative to PQ and at Q relative to QP in order to intersect position SE.

Calculate the surface check measurements that should have been obtained forthe four sides and two diagonals (assuming even gradients along the surface).

Calculation of and

Let the corner SE of the building be X:

Easting of X 348.92 Northing of X 591.76

Easting of P 296.51 Northing of P 540.32E

PX

+52.41 NPX

+51.44

Therefore by rectangular to polar conversion:

Bearing PX = 45o3207

Easting of X 348.92 Northing of X 591.76

Easting of Q 371.30 Northing of Q 522.22EQX -22.38 NQX +69.54



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Bearing QX = 342o0937

Easting of Q 371.30 Northing of Q 522.22

Easting of P 296.51 Northing of P 540.32E

QP

+74.79 NQP

-18.10


Bearing PX = 103o3617

This gives:

Angle = bearing PQ bearing PX = 58o0410

Clockwise angle to be set off P relative to PQ = 360o - 58o0410 = 301o5600Angle = bearing QX bearing QP = 58o3320

Clockwise angle to be set off P relative to PQ = 360o - 58o0410 = 301o5600

(angles rounded to nearest 20 as specified)

Calculation of surface checks


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Recall that slope correction = + (h2/2L):

From SE to SW, h = 156.82 149.73 = 7.09 h2 = 50.27

From NE to NW, h = 151.42 146.53 = 4.92 h2 = 24.21

From SE to NE, h = 156.82 151.42 = 5.37 h2 = 28.84

From SW to NW, h = 149.73 146.53 = 3.20 h2 = 10.24

Hence the slope distances for all four sides should have been:

SE to SW =

NE to NW =

SE to NE =

SW to NW =

m59.7533.036.7536.752

27.5036.75 =+=

+

m52.7516.036.7536.752

21.2436.75 =+=

+

m86.2362.024.2324.232

24.2824.23 =+=

+

m46.2322.024.2324.232

24.1024.23 =+=

+

For the diagonals:


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Horizontal diagonals = m

From SE to NW, h = 156.82 146.53 = 10.29 h2 = 105.88

From SW to NE, h = 151.45 149.73 = 1.72 h2 = 2.96

Slope distances:

SE to NW =

SW to NE =

86.78)24.23()36.75( 22

=+

m53.7967.086.7886.782

88.10586.78 =+=

+

m88.7802.086.7886.782

96.286.78 =+=

+

Setting Out Example 3 : Using Site Rails


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The six corners of a proposed L shaped excavation shown below have been setout on site and offset pegs haven been established to help define the sides ofthe excavation.

The proposed formation level of the surface of the excavation at point R is95.72m. The surface is to fall at 1 in 150 from R to W and is to rise at a slope of1 in 100 at right angle to the line RW.

To help with excavation sight rails are to be erected above the offset pegs foruse with a 2m traveller.

Given the reduced levels of the offset pegs calculate the heights of the sight

rails to be used at P1, P2, P3 and P4.


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rails to be used at P1, P2, P3 and P4.

Solution: for line P1RWP2

Formation level at P1 = 95.72 + (3/150) = 95.74m

Formation level at P2

= 95.72 (48/150) = 95.40m

For offset peg P1Required top of sight rail level = 95.74 + 2.00 = 97.74m

Actual to of peg level = 96.95m

Therefore, distance above P1

= 0.79m

For offset peg P2


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Required top of sight rail level = 95.40 + 2.00 = 97.40m

Actual to of peg level = 96.45mTherefore, distance above P1 = 0.95m

Solution: for line P4UTP3

Formation level at Z = 95.72 - (15/150) = 95.62m

Formation level at P3 = 95.62 (28/100) = 95.90m


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3 ( )Formation level at P4 = 95.62 - (3/100) = 95.59m

For offset peg P3

Required top of sight rail level = 95.90 + 2.00 = 97.90m

Actual to of peg level = 97.12m

Therefore, distance above P1 = 0.78m

For offset peg P4

Required top of sight rail level = 95.59 + 2.00 = 97.59mActual to of peg level = 96.75m

Therefore, distance above P1 = 0.84m

Setting Out Example 4: Using Slope Rails


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An embankment was constructed with a formation width of 36m and a formation

level of 103.59m. The traverse slope at right angle to the centre line was 1 in 12and the side slopes 1 in 2. Slope rails were used with a 1.50m traveller heldvertically to monitor the formation of the embankment.

The point R (ground level at CL) had a level of 85.08m. the slope rails on either

side of the embankment were attached to verticals A and B on the left and C


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and D on the right. These were positioned as shown above. The tops of the

vertical stakes A, B, C and D were levelled as 80.54m, 80.81m, 90.59m and89.89m respectively.

Using this information calculate the slope that were set out along the ground

surface from point P at right angle to the centre line to establish the centres of

stakes A, B , C and D.

Calculate the Vertical distances that were set out from the tops of the stakes A,

B, C and D to fix the top edges of the sight rails in their correct positions.

Solution

The parameters of the embankment are : h = (103.59 - 85.08+ = 18.51m; n = 2

S = 12; b = 18m

For a two level cross section :

mnhbs

WL

16.47212

)51.18)2(18(12

)(

)(=

+

+=

+

+=


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Wg = greater side widthWL = lesser side widthh = depth of cut on the centre line from the existing to the proposed levels

1 in n= side slope1 in s = ground on the traverse slope

b = formation width

The slope distances set out were:

For stake A = WG + 1.0 + 1.0 = 68.02mFor stake B = WG + 1.0 = 67.02mFor stake C = WL + 1.0 = 48.16

For Stake D = WL + 1.0 + 1.0 = 49.16m

mns

nhbsW

G 02.66

212

)51.18)2(18(12

)(

)(=

+=

+=

ns 212)( ++

But the transverse slope = 1 in 12 hence:

T l11


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Transverse slope =

Therefore to the centre of stake A =

To the centre of stake B =

To the centre of stake C = 48.33m and centre of stake D = 49.33m

Vertical distances:

For stake B:

RL of the top of the rail = RLP + 1.50 0.50RLP = existing RL on the centreline (WG/12)RL of the top of rail = 85.08 (66.02/12) + 1.50 0.50 = 80.58mRL of the top of the stake was given as 80.81m

''49'4504cos

12

1tan

1 o=

mo

26.68''49'4504cos

02.68=

mo

25.67''49'4504cos

02.67=

vertical distance = (80.58 - 80.81) = -0.23m.

th t d f th l il t b t 0 23 b l th t f th ti l


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the top edge of the slope rail must be set 0.23m below the top of the vertical

stake B.

For Stake A:

The top of the rail is 0.50m below the top of the rail at stake B, hence:

RL of the top of the rail = 80.58 0.50 = 80.08mVertical distance = (80.08 80.54(given)) = -0.46mTherefore the top edge of the slope rail at A must be fixed 0.46m below the top

of the stake.

For stake C:

RL of the top of the rail = RLQ +1.50 0.50RLQ = existing RL at R + (WL/12)85.08 + (47.16/12) + 1.50 0.50 = 90.01m

Vertical distance = (90.01 90.59(given)) = -0.58m

Therefore the edge of the slope rail at C must be fixed 0.58m below the top of

the stake.

For Stake D:

Th t f th il i 0 50 b l th t f th il t t k C h


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The top of the rail is 0.50m below the top of the rail at stake C, hence:

RL of top of the rail = 90.01 0.50 = 89.51m

Vertical distance = (90.01 90.59) = -0.38m

setting out lecture

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