In-depth notes explaining how geological structures affect engineering practice, types of foundations, tunnels, shrinking and swelling of clay, radon gas, brownfield sites and remediation
Engineering Geology
How Geological Structures Affect Engineering Practice
Direction of Planar Features Water Table Must be Kept Low in a Quarry
• Increased risk of landslide if bedding planes • High water table means high pore pressure
are angled towards a quarry face • Higher pore pressure decreases
• Steeper angle of dip increases the risk of cohesion/friction so the slope can slip
movement
Grade of Weathering Joint Density – number of joints in an area
• Weathered rocks are weaker • More joints increases permeability
• Weight on top of the weak rocks will cause • Water in rocks increases the weathering
it to squash/collapse that occurs, so the rock is weaker
• The slope will collapse due to the inability
of the weaker rocks to hold it back
Joint or Fracture Continuity
• Rocks with joints and fractures have high secondary porosity, leading to high permeability
• Water can move more fluidly/easily through rock, weathering it and making it easier
Rock Head – the boundary between solid rock and overlying unconsolidated sediment
Types of Foundation
CN Tower Toronto
• Built on weak (incompetent) rock – shale
• Slab/raft foundations spreads the 110,000 tonnes of mass across the weak rock
Leaning Tower of Pisa
• Built on very weak, unconsolidated sediment
• To stabilise it engineers:
- 1934 – grout extraction into ground
- 1970 – ground water extraction
- 1993 – 600 tonnes of lead added to north side
- 1995 – increased lead to 900 tonnes
- Cables hold it in place
- Extraction of soil under tower which moved it back to the north slightly
Building/Catastrophic Collapses from Around the World
Istanbul, Turkey
• Steel supports fell due to the weight of the rock pushing against concrete retaining wall
• Rock bolts broke so concrete moved away from the rock behind it
• Rock was fractured/without bedding planes so easily fell
• Ground was saturated with groundwater or from a burst pipe
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