Land surveyingAssignment 07

M.Z.M safran To Mr.Mahendra De HND in QS/20/36 . Submission date 20/01/2011

Land surveyingAssignment 08

M.Z.M safran To Mr.Mahendra De HND in QS/20/36 . Submission date 20/01/201

1. Describe,

a) Dumpy Level

The dumpy level is used to measure height differences used in combination with a leveling staff. Levels can be transferred from a bench mark and new levels can be established very accurately over distances up to 100 meters. There are several types of dumpy levels on the market, each with its own system. It is recommended that engineers or surveyors should practice using the instrument by checking its accuracy before taking it into the field.

In dumpy level…………… Three main parts: telescope, leveling tube, leveling head Line of collimation (line of sight) joins center of objective lens to

intersection of cross hairs Optical axis – line through center of objective lens and perpendicular

to vertical lens axis Cross hairs – thin wires attached to cross-hair ring, or lines etched

on glass plate that is enclosed by cross-hair ring.

4 adjustable capstan screws used to adjust cross hairs up and down or left and right by loosening and tightening cross hair capstan screws

Tilting Level

Tilting level consists of a telescope attached with a level tube which can be tilted within few degrees in vertical plane by a tilting screw.

The main peculiarity of this level is that the vertical axis need not be truly vertical, since the line of collimation is not perpendicular to it. The line of collimation, is, however, made horizontal for each pointing of telescope by means of tilting screw. It is mainly designed for precise leveling work.

In tilting level ……………………….

Instrument roughly leveled with circular spirit level

Just before reading rod, telescope precisely leveled by raising/lowering eyepiece end of telescope using tilting screw.

Tubular level used for final leveling operation bubble usually split in two longitudinally and two

half ends are brought into coincidence – here telescope is precisely leveled

Accuracy of center level bubble with tubular scale graduate at 2 mm 1/5 division or 0.4 mm With split bubble: 1/40 division or 0.05mm

Level tube

Filled with alcohol or other liquid with low freezing point

Upper surface ground to form circular arc Sensitivity of bubble directly related to radius of curvature of bubble tube

Larger radius – more sensitive is level tube

02. What is series leveling? How would you reduce your levels adopting the rise and fallmethod?

Series Levelling can be described as the procedure of moving the instrument through a succession of points. At each level position a BS and FS is read and booked. See diagram at the lower right. details. This procedure becomes necessary when heights are needed at a number of points or the BM is some distance from the site of interest.

Series levelling should commence and terminate on points of known RL (BMs).

Referring to the diagram on the lower right the field procedure is a follows:

1. The instrument is set up approximately 50m to 100m away from the BM (point A) and a staff reading to the nearest 0.001m is observed and booked. (picture of the staff)

2. The staff is moved to the FS position (point B) and again the observation is observed to 0.001m and booked. (example of the booking sheet)

Care should be taken that the BS distance is equal or nearly equal to the FS distance.

This point (A) is referred to as a change point and must be a firm physical object.

3. The level is then moved to point 2 approximately 50m to 100m from staff, as shown in the diagram above. A BS reading is then observed to the staff at B to the nearest 0.001m.

4. If any levels are required to objects in the immediate area of the level, then intermediate levels are taken and booked in the intermediate sight column.

5. The staff is then moved to the next change point (C) and a FS reading taken.6. These steps are repeated until the end of the leveling run is reached - the last point

(FS) should always be a point of known RL. When the observations are complete:-The observations are then reduced as shown here. Steps at top right

4.212

4.153 0.556

0.718

2.518 3.729

Station BS FS Rise Fall RL Remarks BM 4.212 23.918 CP1 4.153 0.718 3.494 27.412 CP2 2.518 0.556 3.597 31.009 B 3.729 1.211 29.798 Total = 10.883 5.003 7.091 1.211 29.798 minus 5.003 1.211 23.918

= 5.880 5.880 5.880

At any instrument setting the first sight taken is called a ‘back sight’ (BS). The final taken is called the ‘foresight’ (FS).

In leveling the term ‘reduced level’ is used to denote the height of any point above the datum.

All leveling must be properly recorded in a field book as following table.

= Total rise – total fall = Last RL – first RL

allall

FSBS

I. Check equalities in last row in the table.II. Discrepancy -> arithmetic mistake(s) (unrelated to accuracy of

measurements).

At any instrument setting the first sight taken is called a ‘back sight’ (BS). The final taken is called the ‘foresight’ (FS).according to this in above mentioned table ‘A’ is therefore a back sight and the reading of 3.500is entered in the BS column. The description of the observed points is entered in the ‘remarks’column. in this example the foresight to ‘B’ and the reading 1.000 is entered in the FS column. The rise or fall of the ground is calculated by always subtracting the second reading from the first. If a positive result is obtained there is a rise between the points. Similarly a negative result indicates a fall of the ground.

In this example…….BS ‘A’ = 3.500m FS ‘B’ = 1.000m difference (A-B) =+2.500m(Rise)

In leveling the term ‘reduced level’ is used to denote the height of any point above the datum. Since ‘A’ lies 90.500m above datum, this figure is entered in the reduced column alongside ‘A’.The reduced level of ‘B’ is the algebraic sum of the reduced level A and the rise or fall from A to B.

Reduced level A = 90.500m Rise A to B = 2.500mTherefore Reduced level A = 93.000m

03. Describe how would you carry out a longitudinal section for a proposed road way?

Longitudinal sections

A ground profile along the central longitudinal line of an existing, or proposed, road, pipeline, railway, canal, etc., is termed a longitudinal section. To draw longitudinal sections the elevation of points along the ground line is required, usually at a standard horizontal interval, such as 20 meters etc. as well as at every change of slope along the line or where natural, or artificial features, disturb the ground profile. These points are normally staked out using a total station andleveled using an automatic level. The required levels are then reduced from which the relevant sections can be drawn. When drawing up a longitudinal section the ratio between the horizontal scale and vertical scale is exaggerated, the vertical scale being 1:5 or 1:10 times that of thehorizontal scale.

04. With the help of a clear diagram, indicate how you would draw the profile of a

longitudinal

Longitudinal ProfilesStep 1: On the centre line of the road, fix the first profile board. This profile may be already in position as the last profile from the previous setting out. If not, measure 1m up from the existing ground level, and mark this level on the ranging rod. Fix a profile board to the ranging rod so that the top edge of the profile board is at the mark made on the rod.

Step 2: Go to the centre line ranging rod at the other end of the road section and repeat the procedure, measuring up 1m from the ground level.

Step 3: By sighting in the intermediate profiles from one end, fix profile boards on the intermediateranging rods along the centre line so that they are all at the same level. x 100 %10

level differenceslope =

Step 4: Check the height of each profile board above the ground level. If the height is approximately 1m, there is no need to adjust them and you can use the level of the profile as it is.If the height of the profile boards is greater or less than 1m by 10cm, then inspect the line. There may be humps or depressions along the line. The set out line will in most cases smooth out these variations. However, it may be that the set out line is over a hill or a dip in the terrain. In such cases, it is necessary to adjust the profiles to avoid too much excavation works as shown in the two figures below. Adjust the profile at position D so that it is 1m above the ground and then lift the profiles at B, C and E to sight in line with the profiles at A to D and D to F. This exercise will reduce the amount of excavation works.

Step 5: Transfer the levels to the ranging rods at the outer end of the side drains. Start with the beginning of your road section. Using a string and a line level, transfer the level of the profile board at the centre line to the ditches on the both sides of the road. Once the levels are set out with profile boards, mark the levels on pegs next to each ranging rod. Repeat this procedure for the same two ranging rods at the other end of the road section and for any intermediate profile along the centre line that was lifted or lowered to reduce excavation works. Then, sights in the intermediate side drain levels. You will notice that the height of the drain profile on the low side of the centre line is more than 1m in most cases. This is because we have started from higher grounds, and since the road is level, the lower side drains will be less deep.

Step 6: Mark the levels for the centre line on pegs placed next to the ranging rods along the centre line. Now use the centre line profile boards to set out intermediate pegs placed at every 5 m along the centre line. This is easily carried out with a 1m traveller. Mark these pegs at the point where the bottom of the traveller touches the peg, when lined up with the profiles. On all the centre line pegs, mark the level of the crest of the camber 0.25m above the 1m level on the pegs. You have now set out the profiles for the levelling of this road section.

Step 7: Place the levels of the shoulders along the road. For this, it is useful to havea traveller 1m high. If we line up the traveller along the line between the two side drain profiles, the bottom of the traveller will show the correct level of the shoulder. Place pegs every 5m along the edge of the shoulder, and using the traveller, mark these pegs at the point where the bottom of the traveller ends when it lines up with the profiles.

Step 8:Locate and set out the mitre drains. It is important that the mitre drains are set out before the excavation works for the side drains and camber is commenced.

Step 9:Set out with string line the side drains that needs to be excavated. Remember to leave out the mitre drain block-offs