The Field Book

  

THE FIELD BOOK

The notebook in which field measurements are noted is known as the ‘field book’. The size of the field book is 20 cm x 12 cm and it opens lengthwise. Field books may be of two types:

1.      Single –line, and

2.      Double-line.

1.      Single-line field book :

In this type of field book, a single red line is drawn through the middle of each page. This line represents the chain line, and the chainages are written on it. The offsets are recorded, with sketches, to the left or right of the chain line. The recording of the field book is started from the last page and continued towards the first page. The main stations are marked by ‘’ and subsidiary stations or tie stations are by ‘’

2.      . Double-line field book:

In this type of field book, two red lines, 1.5 cm apart, are drawn through the middle of each page. This column represents the chain line, and the chainages are written in it. The offsets are recorded, with sketches, to the left or right of this column. The recording is begun from the last page and continued towards the first. The main stations are marked by ‘’ and subsidiary or tie stations by ‘’ this type of field book is commonly used.

A. Problems on Entering Records in Field Book

Problem 1 While measuring a chain line AB, the following offsets are taken. How would you enter the field book?

(a) A telegraph post is 10 m perpendicularly from chainage 2.5 m to the right of the chain line.

(b) A road crosses obliquely from left to right at chainage 10 m and 14 m. Perpendicular offsets are 2m and 3m to the side of the road from chainage 5m and 20 m respectively.

(c) A tube-well is 5m perpendicularly from chainage 30 m to the left of the chain line.

(d) Total chainage of AB is 45 m.

Problem 2 The base-line AC of a chain survey is measured and the following records are noted. Make the necessary entries in a field book.

(a) The corners of a building are 9 and 9,5m from chainage 7.5 and 18 m to the left of the chain line. The building is 7m wide.

(b) A 4 m wide road runs about parallel to the right of the chain line. Offsets are 2, 2.1, 2.2, and 2.15m at chainages 0, 20, 40, and 55.5m respectively.

(c) A check line is taken from the sub-station at chainage 25 m to the left.

(d) The total chainage of the base-line is 55.5m.

(e) The fore bearing and back bearing of the base-line are 30⁰30’ and 210⁰3C’ respectively.

Problem 3 Enter the field book according to the following field notes:

(a) Chainage of line AB is 95.5m

(b) The offsets to the pond at the left of the chain line are as follows:

Chainage – 10, 15,20,25,30 m

Offset – 16, 12,10,14,20 m

(c)    The offsets to the river at the right of the chain line are:

Chainage – 5,25,40,80 m

Offset -13, 17, 19, 19.5m

B. Precautions to be Taken While Entering the Field book

1. All measurements should be noted as soon as they are taken.

2. Each chain line should be recorded on a separate page. Normally it should start from the bottom of one page and end on the top of another. No line should be started from any intermediate position.

3. Overwriting should be avoided.

4. Figures and hand-writing should be neat and legible.

5. Index-sketch, object-sketch and notes should be clear.

6. Reference sketches should be given in the field book, so that the station can be located when required.

7. The field book should be entered in pencil and not in ink.

8. If an entry is incorrect or a page damaged, cancel the page and start the entry from a new one.

9. Erasing a sketch, measurement or note should be avoided.

10. The surveyor should face the direction of chaining so that the left-hand and right-hand objects can be recorded without any confusion.

11. The field-book should be carefully preserved.

12. The field-book should contain the following:

 (i) name,

(ii) Location, and

(iii) Date, of the survey,

(iv) Name of party members, and

(v) Page index or chain line.

3.8. PROCEDURE OF FIELD WORK

Field work of chain survey should be carried out according to the following steps:

1. Reconnaissance

Before starting survey work, the surveyor should walk over the whole area to be surveyed in order to examine the ground and determine the possible arrangement of the framework of the survey. During this investigation, he should examine the indivisibility of the main survey stations. He should ensure that the whole area is enclosed by main survey lines, and also that it is possible to form well-conditioned triangles. He should observe various objects and boundary lines carefully and select the survey lines in such a manner that the objects can be located by short offsets. The base-line should preferably be taken through the centre of the area and on fairly level ground.

2. Index sketch

After a preliminary inspection of the area, the surveyor should prepare a neat hand sketch showing the arrangement of the framework and approximate position of the objects. He should note the names of the stations on the sketch maintaining some order (clockwise or anticlockwise). The fieldwork should be executed according to this index sketch. The names and sequence of chain lines should be followed as directed in the index sketch. The ‘base-line’ should be clearly indicated in the index sketch.

3. Marking the stations on the ground

After reconnaissance, the stations are marked on the ground by wooden pegs. These pegs are generally 2.5 cm square and 15 cm long and have pointed ends. They are driven into the ground firmly, and there should be a height of 2.5 cm above the ground. The station point is marked with a cross so that it can be traced if the wooden peg is removed by somebody.

4. Reference sketches

To take precautions against station pegs being removed or missed, a reference sketch should be made for all main stations. It is nothing but a hand sketch of the station showing at least two measurements from some permanent objects. A third measurement may also be taken.

5. Taking measurements of the survey lines and noting them in the field book

Ranging and chaining is started from the baseline, which should be measured carefully. The magnetic bearings of the base-line are measured by the prismatic compass. These measurements are noted in the field book showing the offsets to the left or right according to their position. Then the other survey lines are ranged and chained maintaining the sequence of the traverse. The offsets and other field records are noted simultaneously. The check lines and tie lines are also measured and noted at the proper place. The station marks are preserved carefully until fieldwork is completed.