Site investigation techniques - Geotechnical Engineering of Dams - page 205

Figure 5.22. Systematic boxing of drill core. (a) Empty core box labelled ready for use (b) Partly filled

box during drilling.

- For inspection by those reviewing dam safety during the operating life of the dam. To

allow this, core should be stored indefinitely.

The characteristics of most significance to the project will usually be:

- the substance strength;
- the lengths of the individual pieces of core;
- the lengths and positions of core losses;
- he length, position and engineering character of important defects such as sheared or
crushed zones

- the engineering character of joint surfaces;

- the depths at which significant changes in rock substance type or strength occur.

The systematic method of boxing core is illustrated by Figure 5.22 and Table 5.4 . This
method “reconstructs” the core in the core box, to scale, packed with all joint or broken
faces fitting, without any spacers apart from sections of core loss. The box is constructed
in compartments of convenient lengths - usually either 1 m or 1.5 m - which become the
“scale” for use by the driller and others who examine the core.
Changes in moisture content can produce significant changes in substance strength.
Representative samples should be sealed, as wrapping in the thin plastic film used for food
is only effective in the short term.
Core can deteriorate rapidly on exposure and should be stored inside in covered boxes.
This is a particular problem for some shales and siltstones which can slake to soil within
several days of sampling.