bASIC SETTING OUT EqUIPMENT Table 3-1: Basic setting out equipment

The basic set of equipment normally used for setting out comprises of: • Ranging rods

• Boning rods (ranging rods with adjustable profiles)

• Travelers (1m long fixed profile on base plate)

• Fish line • Line level

• Tape measures, 5m and 30m

• Sliding hammer (for driving down ranging rods)

• Pegs, wooden and steel • String line

• Hammer (1 kg for driving down pegs)

The above instruments can be used to set out all works including centerline, cross-sections, gradient of the ground, drainage, horizontal, and vertical alignments, and minor earthwork quantities.

Some of the above most commonly used setting out instruments in LIC works are described below:

3.1.1 Reference Pegs

Reference pegs are used to mark the centre lines and transfer levels in road works. They are usually made of wooden stakes although steel rods (400mm long and 12mm diameter) can also be used where readily available. Pegs must be protected with stones and painted for visibility. Reference details should be recorded on a steel plate attached to the pegs or on the wet cast concrete.

Typically there are two types of reference pegs, namely centre line and transfer pegs. Centre line pegs are removed during excavations whilst Transfer pegs are offset at a reasonable distance from the centreline depending on the width of the road. To avoid loss or damage to transfer pegs they are usually embedded in concrete.

10 _{In extremely flat terrain it can often be difficult to determine the natural gradient of the ground. In such cases use of a level instrument may be}

3.1.2 Tape measures

Tape measures are normally made of steel and PVC. Lengths of 10, 20, 30, 50 or 100 metres can be employed efficiently. Steel tapes are expensive, liable to damage and illegibility after a long period of use but are however the most accurate compared to other cheaper materials which tend to stretch and lose their accuracy. Smaller tapes, 2m, 3m or 5m in length, are useful for small construction elements, such as culverts etc.

3.1.3 Ranging rods, profile boards and boning rods

3.1.3.1 Ranging rods

The ranging rods are made of hollow metal tubes, often 25mm diameter galvanized water pipe, with a pointed end of sharpened reinforcement steel. They are normally 2 metres long, and are painted red and white to make them easy to see during setting out. Ranging rods can also be made of wooden or hardened plastic poles. They can be used for setting out vertical and horizontal alignments.

3.1.3.2 Profile boards

A long lasting profile board is made from thin steel plate which is welded to a short length of metal tubing that can slide up and down and be clamped to a metal ranging rod. A useful size for the metal profile boards has been found to be 40 cm by 10 cm, painted red to make it visible against the background of most environments. Profile boards can also be made from timber. Profile boards are used for setting out levels for vertical alignment. See Figure 3-1 below.

3.1.3.3 Boning rods

These are generally manufactured on site from wooden laths to a “T” profile and of uniform height. A simple stand can also be manufactured if preferred as shown in Figure 3-2.

Boning rods are used in sets of 3 and the crosspiece is normally painted, ideally each with a different colour. They are used to establish additional levels between fixed levels (interpolation) or beyond (extrapolation). They are particularly useful to check gradients of culvert trenches and finished final levels (longitudinal and transverse.

The profile boards, ranging and boning rods (travellers) are inexpensive and can easily be made by a local metal work business.

Before starting setting out works, make sure that there are sufficient supply of ranging rods and profile boards. In very compact or rocky ground, it is useful to first make a hole for the ranging rod. This can be done by hammering down a metal spike produced from high tensile reinforcement steel to produce the hole. Crow bars can also be used for this purpose.

A very useful additional tool is a sliding hammer with a weighted head that fits over the ranging rod and can be used to drive the ranging rod into the ground.

130cm 130cm 40cm 40cm 1.5cm 1.5cm 10 cm 10 cm Figure 3-1: Ranging Rod and Profile Boards

3.1.4 Line level

The level of each of the profile boards can be controlled by using a line level. The line level is a short spirit level (about 100 mm long) with a hook at each end to hang it from a nylon string (fish line). It should be hung at approximately the midpoint between the two ranging rods. This instrument needs at least two persons to operate - one at the end of the line, and the second to watch the spirit level. The line operator moves the string up or down until the bubble is centred in the middle. The string line will then

indicate the horizontal line. The line level can be used to:

• Transfer the exact level of one profile board to another profile, thereby ensuring that both are at the same level,

• Measure up or down from a known horizontal level, and set a new level, and • Find the slope between two fixed profile boards.

The line level has an accuracy range of up to about 50 metres beyond which its accuracy might be reduced. It is easy to carry around and with care can be used for setting out levels and slopes not flatter than 1 in 300.

Points to remember when using a line level:

• The string used should be a thin nylon fishing line, enabling the line level to easily slide along the string. • The line level must be placed half-way between the two ranging rods. Use a measuring tape to find the exact

middle point.

• Keep the string tight - do not let it sag.

• The line level is a delicate instrument, look after it - do not throw it around and treat it roughly. • Check the accuracy of the line level regularly in the field.

The following procedure should be followed to check accuracy of line level: • Place two ranging rods 10 metres apart.

• Fix a fish line at 1 metre mark on one of the rods and transfer the level to the other rod using the line level and mark this level.

• Keeping the fish line in place turn the line level around and adjust the fish line again until the bubble centres. • Mark the new level and measure the distance between the two levels.

• If the difference is less than 10 centimetres the correct level shall be in the middle of the two marks. If the difference is more than 10 centimetres then the line level is faulty and should be replaced.