bridges and large buildings

• All heavy structures need solid foundations  - firm bedrock. 
• Piles:

  • Concrete columns containing steel rods 
  • Placed in holes drilled through unstable or unlithified rocks into bedrock
  • Support weight of structure 
• Sediments on surface - remove them and build on bedrock 
• Buried valley (soft sediment) - drive piles through soft sediment into bedrock 
• Old mine shafts - fill shaft and cover with reinforced concrete 
• Limestone caves - fill with concrete 
• Leaning tower of Pisa:

  • Built on shallow foundations of sand and clay 
  • Sinking started when 3rd floor was built 
  • Bells removed to reduce weight 
  • 600 tonnes of led at base to help stability 
  • Removed sand below one side to control subsidence