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10. Appendix 1
The measurement of texture depth by the sand patch method
Apparatus and material
This consists of:
1.
A pair of dividers capable of measuring radii up to 20 cm.
2.
A rule marked off in mm.
3.
A cylinder 8 cm high with an internal diameter of 2 cm.*
4.
A flat wooden disc of 6½-cm diameter with a hard rubber disc
of the same diameter stuck to one face; this rubber facing
should be about 1½ mm thick.
It is convenient to attach to the other face a short spigot or
dowel to serve as a handle.
5.
A container for the sand. A 250 cc plastic beaker would be
found convenient for this purpose.
6.
A soft hand brush.
7.
A quantity of sand which will pass a No. 52 B.S. sieve and be
retained on a No. 100 B.S. sieve. Natural sand with a
rounded particle shape should be used.
Preparation of a conversion table
Calculate the exact volume of the cylinder. If the volume of the
cylinder is V, the texture depth, TD, will be given by
being the radius of the sand patch. Prepare a
table showing TD for values of R' in increments of
1 mm from 5 cm to 18 cm.
Test procedure (see Fig. 2)
The surface to be measured must be dry and should first be
swept with a soft brush. Fill the cylinder with sand; when full
gently tap the base of the cylinder three times on the road surface
and then top up the cylinder with sand and level the top with a
straightedge. Pour the sand into a heap on the surface to be
tested. In windy conditions the use of a tyre to surround the sand is
recommended. Spread the sand over the surface, working the disc
with its face kept flat, in a circular motion so that the sand is spread
into a circular patch with the surface depressions filled to the level
of the peaks.
V
TD =
, R
πR
2
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