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Figure 4.13. Rock aperture sizes

Figure 4.13. Rock aperture sizes

The above provides greater sub-division of aperture sizes compared to BS 5930. The changes are:

• three sub-divisions for >10mm, compared with only one in BS 5930;

• one more sub-division in the range up to 10mm;

• in providing additional sub-divisions, some of the descriptive terms now have different definitions: for example, 'tight' now refers to 0.1-0.25 mm not 0.1-0.5 mm and 'open' refers to 0.5-2.5 mm not 2.5-10 mm, which becomes 'moderately wide'.

4.4.4 Weathering

When describing the rock material a four basic terms are to be used: fresh, discoloured, disintegrated, and decomposed. These basic terms may be amplified by use of qualifying terms, e.g. 'wholly' or 'partially' discoloured.

For a rock mass, a six stage weathering scale (0 to 5) is provided: fresh, slightly weathered, moderately weathered, highly weathered, completely weathered, and residual soil. More appropriate weathering classification systems have been developed for specific rock types and EN ISO 14689 allows these to be used provided they comply with the general guidance given in the standard.

The weathering terms adopted by EN ISO 14689 are a significant departure from BS 5930: 1999, reverting to the outdated terms given in BS 5930:1981.

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