Environmental Engineering Reference
In-Depth Information
Figure 14.3.
Layout of rockfill roller trial (Bertram, 1972).
14.5.2
Field rolling trials
Field rolling trials are often carried out for larger dams:
(a) before construction, to ascertain the degree of breakdown of rock under rollers, the result-
ing density and particle size distribution, permeability and modulus of compressibility;
(b) during construction, to confirm the number of passes of the roller required to achieve
the required density of compaction.
Figure 14.3 from Bertram (1972) details a layout for roller trials on rockfill.
Bertram makes the following points:
1. An area sufficient to give 25-30 measuring points is necessary to overcome non uni-
formity in the rockfill;
2. The grids can be set out as shown (1.5 m) or 1.2 m
1.3 m or 1.5 m
2.1 m;
3. Measurements should not be taken less than 3 m from the edge;
4. Several layers (4 to 5 minimum) are required.
For construction, the specification usually requires that trials be carried out on the
embankment, requiring an area of about 200 m
2
for each of the test areas.
In the trials, the settlement of the surface of the rockfill is measured after each pass of
the roller and the results plotted as average settlement (or % settlement) vs number of
passes.
Figures 14.4
and
14.5
show the results of roller trials at Murchison Dam, and at
Boondooma Dam.
The Boondooma Dam trials show the effect of watering the rockfill.
It can be seen that the additional compaction achieved after, say, 4 or 6 passes is rela-
tively small. Since this additional compaction is often being achieved largely by break-
down of the upper part of the layer, it is common to limit the number of passes to 4 or 6,
seldom more than 8.
A key factor is any trial rolling is for equipment representative of what will be used on
the dam to be used in the trial. Too often, for example, the equipment is too small or not
enough water can be got to the trial rolling site, so the benefits of the trial are lost.
