Engineering Surveying -1 CE212Measurements

Lecture 2016, September 20

Muhammad Noman

Methods of Direct Measurement

For Direct measurements, several methods and instruments are available1. Pacing2. Passometer3. Pedometer4. Odometer5. Speedometer6. Perambulator7. Judging Distance8. Time measurement9. Chaining

Assignment # 01 (a): To be submitted on or before September 27, 2016

Instruments for Measuring Distance

Chain:

The chain is composed of 100 or 150 pieces of galvanized mild steel wire, 4mm in diameter called links. The ends of each link are bent into a loop and connected together by means of three oval rings. The ends of the chain are provided with handles for dragging the chain on the ground, each wire with a joint so that the chain can be turned without twisting. The length of the chain is measured from the outside of one handle to the outside of another handle.

Types of Chains

1. Metric Chain

Metric chains are made in lengths 20m and 30m. Tallies are fixed at every five-meter length and brass rings are provided at every meter length except where tallies are attached.

To enable the reading of factious of a chain, tallies (tags) are fixed at every five meter length and small brass rings are provided at every meter length.

Types of Chains

2. Gunter’s Chain

It is 66 ft long and is divided into 100 links. Each link is 0.66 ft long. It is very convenient for measuring distance in miles and furlongs. Also for measuring area and when the units of area is an acre.

3. Revenue Chain

It is commonly used for measuring fields in cadastral survey. It is 33 ftlong and divided into 16 links. Each link is 2.0625 ft long.

4. Engineer’s Chain

It is 100 ft long and it is divided into 100 links. Each link is 1 ft in a length. Used in all Engineering surveys.

Types of Tapes

a. Cloth or Linen Tape:

Used for taking subsidiary measurements, such as offset. It is very light and handy. It is easily affected by damp. If wet it shrinks. It stretches easily and likely to twist.

b. Metric Woven Metallic Tape:

They are available in 2, 10, 30, and 50 meters. The tape is made of yarn and metal wire. A metal ring is attached to the outer end of tapes. The length of the tape includes the metal ring.

Types of Tapes

c. Metric Steel Tape:

Tape is available in 1, 2, 10, 30, and 50 meters. The tape is of steel or stainless steel. The outer end is provided with a ring. The length of the tape includes the metal ring.

d. Invar Tape:

For highest precision work the invar tape in used. It is made of an alloy of steel and nickel (36%). Length is 30m-100m.

Instruments for Marking Stations

1. Wooden Pegs:

These are used to mark the positions. They are made of hard timber and tapered at one end. They are usually, 2.5 cm square and 15 cm long.

2. Ranging rods:

Used for making the positions of stations and for ranging. They are circular or octagonal in cross section. They are made in two sizes as 2 meters and 3 meters and are divided in to equal parts each 0.2 m long. They are painted alternatively black and white or red and white

Instruments for Marking Stations

3. Ranging Poles:

Similar to the ranging rods but are heavier, they vary in length from 4 m to 6 m or more. Used in the case of very long lines.

4. Plumb Bob:

The plumb bob is required when measuring the distance along slopes in order to transfer points to the ground. It is also used for testing the verticality of ranging poles.

Instruments for Marking Stations5. Laths:

Useful for ranging long lines, also used over uneven ground where the ranging rod is not visible due to obstructions, they are light, cheap, being white; they are easily visible at a great distance. Unusually 1.0m long

6. Whites:

When the ranging rod is not available or insufficient, whites are used. These are thin strip of bamboo and 40 cm to 1 m in length. One end is sharp and the other end is split for inserting pieces of white papers. They are also useful for temporary marking of counter points.

Errors in Length (Chaining)

Error in length:

The length of line = (L’ / L) x Measured length of line

Error in Area:

True Area = (L’ / L)2 x Measured Area

Error in Volume:

True Volume = (L’ / L)3 x Measure Volume

Note:L’ = Incorrect length of chainL = True length of Chain

Example # 01

• The Length of line measured with a 20m chain was found to be 634.4m. It was afterward found that the chain was 0.05m too long. Find the true length of the line.

Ans: 635.99

Example # 02

The length of line measure by means of a 20m chain was found to be 610.2m known to be 612.0m. What was the actual length of the chain?

Ans: 20.066

Example # 03

• A certain field was measured with a 30m chain and found to contain 43 sq. km. It was afterwards found that the chain was 0.1m too short. What is the true area of the field?

Example # 04, 05

1. The distance between two points measured with a 30m chain was recorded as 216m. It was afterwards found that the chain was 10cm too long. What was the true distance between the points? (Ans: 216.72m)

2. The length of line measured with 20m chain was found to be 372m. The true length of the line was known to be 371m. Find the error in the chain. (Ans: 0.054m)

Assignment # 01 (b) Example 04, 05: To be submitted on or before September 27, 2016

• Thank You