Geomechanics 1: Week 1
Foundations for buildings:
Ø Normally, house loads are small
Ø Can be supported on surface footings
Ø Shallow footings are used widely
How do we design?
Ø Soil properties
Ø Classify ground
Ø Design Footing
Piled Foundations
Ø Rock socketed piles were used for the Rialto
Ø Transfers load from top to harder rock layer
Ø Steel tube and the bucket-type auger are often used in Melbourne
Bridge foundations
Ø Because of soft soils and high concentrated loads
Ø Piles up to 60m long used
Ø Challenging Design- Both wind and waves, traffic(dynamic)
Transmission Tower foundations
Ø Complex loading
Ø Large tension, compression and lateral loads
Ø Most soils weak in tension
Ø Piled foundation, anchors are used
Foundations for offshore structures
Ø Very challenging foundation project
Ø Platform is supported by driven piles
Ø 2m diameter piles driven into the seabed with a 150 tonne hammer
Ø Challenges- Remote/high waves
Earth retaining structures
Ø No room to allow for a wide embankment
Ø Retaining wall is required
Ø Challenge is to design for lateral pressure on the wall
Ø Clay, sand, rock??
Excavations stability
Ø Geotechnical Engineers also need to know if the excavation will be stable
Ø In this case the soil is standing unsupported
Ø Types of soils/rocks dictate the slope design
Ø Top-down excavations in urban areas
Tunnels
, Ø Tunnels are drilled through soils/rocks
Ø Needs to support vertical and horizontal stresses around tunnels
Ø Can be challenging to design support system
Ø TBM design (type of rocks?)
Ø TBM- For rocks or Soils (or combinations of drill & blast + TBM
Road Pavements
Ø Ground supports the freeway
Ø Loads are generally moving
Ø We ensure that the ground does not fail and
Ø Also does not deform under this moving load
Railways
Ø Reactive soil results ‘roller coaster’ ride
Ø Require proper assessment of sub-grade
Ø We also design railways
Runway/taxiway
Ø Pavement design principles are also used for airport runways, where you get very
large impact loads
Ø The 5 km long crawler way to the launch pad for the 16,000 tonne space shuttle
needs a pavement of 2m total thickness
Water retaining Structures (Dam):
Ø Rock fill dam constructed mainly from boulders as small as fist size to 1m
Ø Resist large horizontal load, and
Ø Retain the water
Ø Challenge is to ensure no leakage of water
How do we investigate ground? Site investigation - Drilling, sampling, insitu tests
Laboratory testing of soil/rock samples
Drilling Rig
Ø Rigs like these are purpose-built for soil and rock investigation
Ø It is common to drill, sample and test the foundation materials to depths in excess of
100m- civil eng
Ø Mining/Petroleum eng- few kilometers
Ø Drilling is so vital to get information on the round
Foundations for buildings:
Ø Normally, house loads are small
Ø Can be supported on surface footings
Ø Shallow footings are used widely
How do we design?
Ø Soil properties
Ø Classify ground
Ø Design Footing
Piled Foundations
Ø Rock socketed piles were used for the Rialto
Ø Transfers load from top to harder rock layer
Ø Steel tube and the bucket-type auger are often used in Melbourne
Bridge foundations
Ø Because of soft soils and high concentrated loads
Ø Piles up to 60m long used
Ø Challenging Design- Both wind and waves, traffic(dynamic)
Transmission Tower foundations
Ø Complex loading
Ø Large tension, compression and lateral loads
Ø Most soils weak in tension
Ø Piled foundation, anchors are used
Foundations for offshore structures
Ø Very challenging foundation project
Ø Platform is supported by driven piles
Ø 2m diameter piles driven into the seabed with a 150 tonne hammer
Ø Challenges- Remote/high waves
Earth retaining structures
Ø No room to allow for a wide embankment
Ø Retaining wall is required
Ø Challenge is to design for lateral pressure on the wall
Ø Clay, sand, rock??
Excavations stability
Ø Geotechnical Engineers also need to know if the excavation will be stable
Ø In this case the soil is standing unsupported
Ø Types of soils/rocks dictate the slope design
Ø Top-down excavations in urban areas
Tunnels
, Ø Tunnels are drilled through soils/rocks
Ø Needs to support vertical and horizontal stresses around tunnels
Ø Can be challenging to design support system
Ø TBM design (type of rocks?)
Ø TBM- For rocks or Soils (or combinations of drill & blast + TBM
Road Pavements
Ø Ground supports the freeway
Ø Loads are generally moving
Ø We ensure that the ground does not fail and
Ø Also does not deform under this moving load
Railways
Ø Reactive soil results ‘roller coaster’ ride
Ø Require proper assessment of sub-grade
Ø We also design railways
Runway/taxiway
Ø Pavement design principles are also used for airport runways, where you get very
large impact loads
Ø The 5 km long crawler way to the launch pad for the 16,000 tonne space shuttle
needs a pavement of 2m total thickness
Water retaining Structures (Dam):
Ø Rock fill dam constructed mainly from boulders as small as fist size to 1m
Ø Resist large horizontal load, and
Ø Retain the water
Ø Challenge is to ensure no leakage of water
How do we investigate ground? Site investigation - Drilling, sampling, insitu tests
Laboratory testing of soil/rock samples
Drilling Rig
Ø Rigs like these are purpose-built for soil and rock investigation
Ø It is common to drill, sample and test the foundation materials to depths in excess of
100m- civil eng
Ø Mining/Petroleum eng- few kilometers
Ø Drilling is so vital to get information on the round
