Site investigation - Practical Engineering Geology - page 145

Figure 4.15
Approach to
characterise rock
mass. First stage is
to split into units by
eye. Units/zones
will be used in later
analysis and design.

5 5

4 4

3 3

2

2

1 1

? ?

How to start to describe? How to start to describe?

Stand back, split into zones or units by eye, then
characterise each one separately.
During characterisation, on close examination
you might well need to refine or change your
original differentiation Might split on:

Stand back, split into zones or units by eye, then
characterise each one separately.
During characterisation, on close examination
you might well need to refine or change your
original differentiation. Might split on:
- geology (dykes/sills separately)
- colour
- degree of weathering
- percentage of included boulders
-jointing style
-perceived hazards

Figure 4.16 Once
the broad units/
layers have been
identi

1. FIRST SPLIT
EXPOSURE INTO UNITS

3. DESCRIBE EACH MATERIAL
IN EACH UNIT (as appropriate)

￿ Geology

Colour codes as
appropriate

￿ Percentage corestones/
boulders
￿ Jointing style and intensity;
structure including faults,
folds

ed, each
needs to be
characterised.

Colour

Textures/fabric
Particle size distribution

Grain size

￿ Weathering grades
￿ Other characteristics such as
seepage, vegetation, hazards

Field tests (hammer,knife)
Schmidt hammer
Penetrometer; vane

Strength

Slake test

Cohesion

2. WITHIN EACH
MAPPABLE UNIT

Infiltration test

Permeability

￿ Geological origin

￿ Where heterogeneous, the
proportion of fine fraction to
coarse fraction

Mechanical
Decomposition

Degree of
microfracturing

￿ Shape, size and distribution of
coarse fraction
￿ Jointing pattern, structures
(characterise these)

Chemical
Decomposition

Scratcheability
Decomposition grade