Geoscience Reference
In-Depth Information
6.7 Relative change in strength between rock
weathering grades
•
The rock strengths change due to weathering and vary significantly depending on
the type of rock.
•
Rock weathering by itself, is not sufficient to define a bearing capacity. Phyllites
do not show significant change in intact rock strength but often have a significant
change in defects between weathering grades.
Table 6.7
Relative change in rock strengths between rock weathering grades (Look
and Griffiths, 2004).
Rock
Relative change
in intact strength
Type
Weathering
Argillite/greywacke
DW
1.0
SW
2.0
FR
6.0
Sandstone/siltstone
DW
1.0
SW
2.0
FR
4.0
Phyllites
DW
1.0
SW
1.5
FR
2.0
Conglomerate/agglomerate
DW
1.0
SW
2.0
FR
4.0
Tuff
DW
1.0
SW
4.0
FR
8.0
•
The table shows a definite difference between intact rock strength for SW and FR
rock despite that weathering description by definition, suggests that there is little
difference in strength in the field (refer Table 3.4).
6.8 Parameters from rock weathering
•
A geotechnical engineer is often called in the field to evaluate the likely bearing
capacity of a foundation when excavated. Weathering grade is simple to identify,
and can be used in conjunction with having assessed the site by other means (intact
strength and structural defects).
•
The field evaluation of rock weathering in the table presents generalised strengths.
•
Different rock types have different strengths e.g. MW sandstone may have similar
strength to HW granite. The table is therefore relative for a similar rock type.
•
Including rock type can make a more accurate assessment.
Search WWH ::
Custom Search