**4.3**.

**Fieldwork procedure**

If it is necessary to measure a distance accurately then use the following procedure.

(a) Check the tape against a standard tape.

(b) Using a theodolite for ranging, set out pegs on line, no more than 20 m apart to reduce the effect of sag. Ensure that these pegs are firm in the ground. Line

a nail in on the top of each peg.

(c) Each leg is now treated separately. Note the air temperature. Hold 0.100 m on one end of the tape and read it at the other, applying standard tension. The

distance should be measured three times and the mean value noted. Note in the Remarks column whether sag correction needs to be applied.

(d) Determine the slope of each leg or the differences in height for slope corrections.

(e) Remove all the intermediate pegs and then line them in again in a different position for the second measure of the distance.

(f) Booking: All fieldwork and subsequent calculations are recorded in the fieldbook in a tabular form as in figure 4.8.

**4.4.Calculations**

The results of the calculations are tabulated in the field book as shown in Figure 4.8. Again each leg is treated separately.

Date: levels taken for

From to

Figure – Booking of linear measurements.

a) Calculate the measured distance; Reading – set on (0.100 m). This measured distance is used for all corrections except slope.

b) Calculate standard, tension, temperature, and sag corrections using the measured distance.

c) Apply all the corrections to the measured length to give a corrected slope length.

d) Apply the slope correction to the slope length {(c) above} to give the horizontal distance for the leg.

e) Add all the individual horizontal distances together to give a total horizontal distance.

**4.5.Setting out distances**

Setting out a horizontal distance necessitates applying corrections for temperature, sag, standard, tension and slope to that horizontal distance to arrive at a

distance to arrive at a distance to be measured in the field. Whilst this is possible for most systematic errors, applying a slope correction in advance is quite

difficult. Step chaining can, of course, be used but only where a high degree of accuracy is not required.

A simple approach to setting out a distance accurately over sloping ground is to locate a peg, on the correct line and at approximately the correct distance.

Measure the distance to this peg, applying whichever corrections are deemed necessary. If the trial peg position is within 1-2 m of its required position, then the

difference can be measured with a pocket tape ensuring that it is held horizontal. This approach is similar to that described in paragraph 5 – Electromagnetic

distance measurement

**4.6.**

**Maintenance of equipment**

(a) Steel tapes are very brittle and need to be used carefully to avoid breaking them.

(b) Do not allow vehicles to drive over such a tape as this could break the tape or cause it to be badly kinked.

(c) When work with a tape is complete, wind it back into its box using a cloth to remove surplus mud, etc.

(d) Lightly oil the tape each week to prevent rusting.

(e) Do not leave tapes lying on the ground, always wind them back into their boxes.

(f) Do not drag tapes along the ground. Lift them clear of the ground when moving.

(g) Fibreglass tapes can be washed in soapy water when dirty. Wipe the surplus water off and allow to dry naturally outside the box.