WJEC – Geology of the Human Environment (GL3) – Jan 2004
2.
Figure 2a shows the influence of slope height on maximum stable slope
angles for clay and fractured limestone under dry and saturated conditions.
Figure 2a
Refer to Figure 2a.
(a)
(i)
State the maximum stable slope angle of a 60 metres high cliff
composed of saturated fractured limestone.
[1]
………………………………… degrees
(ii)
Explain how groundwater can affect the stability of rock.
[2]
…………………………………………………………………………………………..
…………………………………………………………………………………………..
…………………………………………………………………………………………..
(iii)
Give two reasons why curve X is most likely to represent
the relationship for saturated clay.
[2]
1………………………………………………………………………………………...
………………………………………………………………………………………….
2………………………………………………………………………………………...
………………………………………………………………………………………….
(b)
With the aid of an annotated diagram(s), explain how problems of
ground instability may be associated with the dip of strata in rock
cuttings.
[3]
(c)
Figure 2b shows four methods of stabilising a hill slope (P,Q.R,S).
Figure 2b
(i)
With reference to Figure 2a, explain why cutting steps into the
face (method P) is used to stabilise the hill slope in Figure 2b.
[2]
…………………………………………………………………………………………..
…………………………………………………………………………………………..
…………………………………………………………………………………………..
(ii)
Choose one other method used to stabilise the slope in
Figure 2b (Q,R,S) and explain its use in this situation.
[2]
…………………………………………………………………………………………..
…………………………………………………………………………………………..
…………………………………………………………………………………………..
Total 12 marks
Notes for answers
These represent suggested answers and do not necessarily represent all the possible
acceptable alternatives of a mark scheme.
Question 2
(a)
(i)
40 degrees (38-42)
[1]
Reduces the friction/cohesion – or equivalent
(credit water can aid cohesion)
Pore pressure
Lubrication
Weight/heavier
Effect of weathering/erosion
(max 2)
[2]
Graph/clay with the lowest stable slope angles or visa versa
Clay is the least stable/strong when wet or visa versa
Clay incompetent/plastic/flows/expands
[max 2]
[2]
(ii)
(iii)
(b)
(c)
Diagram(s) (2 max)
Annotation (2 max)
(i)
(ii)
- Total 3 (DIP of planes only)
[3]
Reduces slope height (accept pressure/weight)
Allows for a steeper slope angle
Catch falling blocks
Reverse slope reduces water flow on lower free face
(2 max)
[2]
Q.
Gabion –
flexible/strong/permeable
retaining wall/toe protection/sed. trap
on low gradient slope
R.
Mesh nets –
controls rock fall
of weathered material from rock face
supports soil formation/vegetation
on steeper slope
S.
Rock bolts /anchors – tie loose fractured strata
to more stable strata
on steeper slopes
(2 max each)
[2]
Total 12 marks
ESTA would like to thank the WJEC for allowing this question to be published on GEOTREX. Any
comments should be directed to the Subject Officer for Geology at the WJEC. 15/04/2007