Engineering Surveying 2: Prof. Madya Sr Hj. Mohammed Yaziz Hj. Ahmad [ C405 ] [ 013-3380758 ]

ENGINEERING SURVEYING 2 PREPARED BY

PROF. MADYA Sr HJ. MOHAMMED YAZIZ HJ. AHMAD [ C405 ] [ 013-3380758 ] PUSAT PENGAJIAN SAINS UKUR & GEOMATIK FAKULTI SENIBINA, PERANCANGAN & UKUR UNIVERSITI TEKNOLOGI MARA SHAH ALAM

2009

PRECISE LEVELLING LECTURE 2 (3 HOURS)

INSTRUCTIONS FOR PRECISE LEVELLING

Assoc.Prof. Sr Dr. Hj. Abd. Manan Hj. Samad

LECTURE CONTENT • • • • • • • • • • •

Method of reading Tolerance Setting-up Bubble Adjustment Line of Sight Verticality of Staffs Observation Periods Setting of Turning Points Directions Criterion for Rejection Differences in Level

Assoc.Prof. Sr Dr. Hj. Abd. Manan Hj. Samad

METHOD OF READING • •

Readings are to be made with the telescope in the normal position only (the bubble on the left of the instrument) Readings are to be made in the following sequence/order; • 1. Backsight: • A. Lower stadia • B. Upper stadia • C. middle stadia (level)

• 2. Foresight: • D. Middle stadia (level) • E. lower stadia • F. upper stadia

• 3. Foresight • G. middle stadia (level)

• 4. Backsight • H. middle stadia (level)

Assoc.Prof. Sr Dr. Hj. Abd. Manan Hj. Samad

BOOKINGS Obsn.No:

Date:

Time

Temp.

Staff Reading Backsight

Foresight

Note: Back staff at BM A

Stadia

Level

Level

Stadia

B

C

D

F

A

H

G

E

Diff. In height

J=(B+A)

K=(C+H)

L=(D+G)

M=(F+E)

Bring forward

N=(B-A)

P=(C-H)

Q=(D-G)

R=(F-E)

Total

Distance: Nx100=T

Distance: Rx100=U

Reduced Level is 10.000m

Observer

(K/2-L/2)=S 10.0000 S+10.0000

Dr ASM

Assoc.Prof. Sr Dr. Hj. Abd. Manan Hj. Samad

OBSERVATIONS REQUIREMENTS 1.

The time taken between reading C&D and G&H should be reduced to a minimum

2.

Between reading F – G, the telescope is to be dislevelled by turning the gradienter screw and carefully relevelled by the use of the same screw only

3.

Readings are to be made to the nearest 0.00001 m

Assoc.Prof. Sr Dr. Hj. Abd. Manan Hj. Samad

TOLERANCE Readings must be cancelled and reread if; –

The sum of the stadia readings does not agree with the sum of the two level readings on the same staff and to within 0.0050 meter

–

The difference between the two level readings on the same staff is more than 0.0006 meter

Assoc.Prof. Sr Dr. Hj. Abd. Manan Hj. Samad

BUBBLE ADJUSTMENT •

Footscrews must not be altered during a sight.

•

Bubble adjustments being made by the use of the gradienter screw

Assoc.Prof. Sr Dr. Hj. Abd. Manan Hj. Samad

LINE OF SIGHT •

Line of sight should not pass close to the ground. Readings must not be made to the lowest 0.3 m of the staff

•

The optimum length of sight is about 40m (Max 50m)

•

The back and forward staffs should be equidistant from the precise level instrument, to within 1m

Assoc.Prof. Sr Dr. Hj. Abd. Manan Hj. Samad

VERTICALITY OF STAFFS Staffs must be tested weekly • •

Using plumbob – for verticality Face-to-face comparison

Assoc.Prof. Sr Dr. Hj. Abd. Manan Hj. Samad

OBSERVATION PERIOD •

Observations should be made in the early morning and late afternoon.

•

Observation must be discontinued when the atmospheric conditions make observations difficult

Assoc.Prof. Sr Dr. Hj. Abd. Manan Hj. Samad

SETTING TURNING POINTS

•

Turning points should be in position at least half an hour before use

•

The day’s work must always be closed on BM or culvert.

Assoc.Prof. Sr Dr. Hj. Abd. Manan Hj. Samad

CRITERION FOR REJECTION

•

Sections must be relevelled if the discrepancy between forward and backward levelling (double runs) exceeds (0.003 √ K) meter where K is the distance in kilometers.

Assoc.Prof. Sr Dr. Hj. Abd. Manan Hj. Samad

DIFFERENCE IN LEVEL

•

The difference in level will be obtained from the mean difference of the two level line readings.

•

Stadia line readings are to serve as a check on gross error only and are not to be included in the computations

Assoc.Prof. Sr Dr. Hj. Abd. Manan Hj. Samad

CALCULATION PROCESS Obsn.No:

Date:

Time

Temp.

Staff Reading Backsight

Foresight

Note: Back staff at BM A

Stadia

Level

Level

Stadia

B

C

D

F

A

H

G

E

Diff. In height

J=(B+A)

K=(C+H)

L=(D+G)

M=(F+E)

Bring forward

N=(B-A)

P=(C-H)

Q=(D-G)

R=(F-E)

Total

Distance: Nx100=T

Distance: Rx100=U

Reduced Level is 10.000m

Observer

(K/2-L/2)=S 10.0000 S+10.0000

Dr ASM

Assoc.Prof. Sr Dr. Hj. Abd. Manan Hj. Samad

Example of Calculation Obsn.No: 1

Date: 29.2.2004

Time: 9.00am

Temp: 25

Staff Reading Backsight

Foresight

Note: Back staff at BM A

Stadia(cm)

Level(cm)

Level(cm)

Stadia(cm)

300.292

279.469

76.52

97.251

258.65

279.471

76.523

55.769

Diff. In height

2.02949

558.942

558.94

153.043

153.02

Bring forward

12.34500

41.642

-0.002

-0.003

41.482

Total

14.37449

Distance(m)

41.642

Distance(m)

41.482

Reduced Level is 12.345m

Obsever

Dr ASM

Recorder

Dr ASM

Assoc.Prof. Sr Dr. Hj. Abd. Manan Hj. Samad

Terima Kasih

Assoc.Prof. Sr Dr. Hj. Abd. Manan Hj. Samad