ENGINEERING GEOLOGY AND GEOHAZARDS

Question 1

Shallow and deep tunnels

Answer 1

Shallow
-dig trench and fill in roof
-e.g London underground

Deep
-dig tench in sea bed, place tube,
infill
-e.g istanbul

Question 2

Tunnels in hard rock

Answer 2

• e.g igneous and metamorphic
• drill and blast
  -slow and expensive
  -overbreak - too much explosive
  -underbreak - not enough explosive

Question 3

Tunnels in soft rock

Answer 3

• e.g sedimentary
• boring machine
  -cheap and easy to dig
  -needs lining to prevent collapse

Question 4

Problems with tunneling

Answer 4

• Soft rock
  -collapse + leakage (e.g clay)
• variation in strength
  -lateral variation, weathering, lithification
• permeable
  -flooding in tunnel
• dip
  -tunnel crosses beds, bedding
  planes may slip
• faults
  -weak, permeable, movement
• planar weaknesses
  -weak, permeable, slippage
• folds
  -change in dip, slippage
• groundwater
  -flows along joints, saturate clays

Question 5

Ground improvement methods

Answer 5

• Grouting
• steel ribs
• rock bolts
• mesh and shotcrete
• rock drain

Diagram 25