Leveling

Leveling : is the procedure used to determine difference in elevation between points that are some distance from each other

General Terms Elevation: is a vertical distance above or below reference datum Level line: is a line in level surface, a level surface is a curved surface. Mean sea level: reference datum that is universally employed in surveying studies

Leveling Concepts

Types of Surveying Levels Automatic Digital Tilting Dumpy Rotary Laser

Engineers’ Automatic Level

Definitions for differential levelling Bench Mark (BM): is a permanent point of known elevation ( published) Temporary Bench Mark: (TBM): is semi permanent point on known elevation. (nails in the rod of trees, not publish) Turning Point (TP): is a point temporarily used to transfer an elevation. Back sight: is a rod reading taken on a point of known elevation. Height of Instrument (HI): is the line of sight through the level. HI= Elev. BM + BS

Foresight (FS):is a rod reading taken on TP, BM , TBM to determine its elevation. HI-FS= Elev. of TP(or BM or TBM) Intermediate Sight (IS): is a rod reading taken in any other point where the elevation is required. HI-IS=Elev.

Leveling Procedure – One Setup

Leveling Procedure – One Setup

Leveling Procedure – One Setup

Leveling Procedure – Multiple Setups

Ex 1: complete accompanying set of differential leveling and perform the arithmetic check. Station BS (m) HI (m) FS (m) Elevation (m) BM3 1.613 133.005 TP1 1.425 1.927 TP2 1.307 1.710 TP3 1.340 1.273 0.780

Ex 2: complete accompanying set of differential leveling and perform the arithmetic check. Station BS FS Elevation BM7 4.368   82.206 TP1 6.907 4.538 TP2 4.680 8.800 TP3 3.730 5.978 TP4 8.464 5.245 3.598

Peg Test: The purpose of this test is to check the line of sight through the level is horizontal.

Peg test - Place two stakes at distance of (60-90 m) apart. - The level is setup midway(paced) between the two stakes - Road readings are taken at both locations. - If the line of sight through the level is not horizontal, the errors in road readings (Δl1) at both points A &B are the same. - The level is moved to the one of the points (A). - Road then held at A and then at B and normal sighting is taken (a2 &b2).

Peg test Example : refer to peg test figure First setup: Rod reading at A, a1= 1.075 m Rod reading at B, b1= 1.247 m The difference in elevation =0.172 m Second setup: Rod reading at A, a2= 1.783 m Rod reading at B, b2= 1.946 m The difference in elevation =0.163 m

Peg test From second setup there is an error. The second reading b2 would have been 1.783+0.172= 1.955 m While the reading is 1.946 m. So the error (Δl2) = 0.172-0.163= 0.009 m along 60m distance The error is 0.009/60= 0.00015 m/m . Therefore, the collimation factor C is equal to 0.00015 m/m

Ex 3: Four stations C, A, B, and D were set out in a straight line such that CA = AB = BD = 30 m. A level was set up at C and readings of 2.135 and 1.823 were observed on vertically held staff at A and B, respectively, when bubble was at the Centre of its run. The level was then set up at D and readings of 2.026 and 1.768 were again observed at A and B, respectively. Determine the collimation error of the level and correct difference in level of A and B.

Ex 4: Fig. 1 shows a rectangle ABCD, in which A, B, and C are the stations where staff readings were obtained with a level set up at E and D. The observed readings are given in Table below. If A is a bench mark having elevation of 150 m, calculate the correct elevations of B and C.

1) What is the elevation of point B? 2) What is the leveling error? Ex 5: You must establish the elevation of point B from point A (elevation 216.612 m) A & B are on opposite sides of highway. Leveling is used with the following results: Setup at A side of the highway RR on A= 0.673 m RR on B= 2.416 m and 2.418 m Setup at B side of the highway RR on B= 2.992 m RR on A= 1.254 m and 1.250 m 1) What is the elevation of point B? 2) What is the leveling error?

Level Loop Adjustment E= 186.273-186.258= 0.015 Correction= cumulative dist./total distance BM Loop distances (km) Field elevation correction Adjusted Elevation 20 186.273 201 0.8 184.242 0.003 202 2.4 182.297 0.008 203 3 184.227 0.010 4.7 186.258 0.015

Mistakes in levelling 1- Misreading the meter rod value. 2- Not holding the rod in the correct location. 3- Resting the hand on the tripod while reading the rod 4- Entering the rod reading incorrectly (switching BS and FS). 5- Making mistakes in the note reduction arithmetic, 6- Mistakes in rod reading that do not form part of arithmetic check. Such as intermediate sights.

Suggestions for leveling work 1- Tripod legs should be tightened. 2- The surveyor should read the rod at either the top or the bottom of the cross hair. 3- Never move the level before a FS is taken. 4- Check to ensure that the level bubble remains centered. 5- Arithmetic can be eliminate by having the other crew members checking the notes. 6- All crew members should try to develop strict routines for doing their works.