BUILDINGS

1
BUILDINGS
2
Shallow Foundations

• rafts
• pads
• strips

Raft
Pads
3
Deep Foundations

• piles

What type of foundations to build depends on

• depth to rockhead

• depth to water table

• geological structures

• rock properties

4
Buildings
So the factors geologists assess before
constructing a large structure should include

• Jointing

• Dip of bedding

• Faults

• Cleavage

• Depth to water table

• Depth to rockhead

• Weathering

• Rock properties

• Radon gas concentrations

5
Leaning Tower of Pisa
Depth to water table affects the stability of the
foundation material by affecting the pore water
pressure
Very weak sediment. Buildings need high
foundation strength
Saturated sediments compress subside under load
Water table
Foundations
A
10m
Variable, soft, silty deposits - unconsolidated
Clay deposits are prone to settlement under load
Very soft clays - consolidated
B
40m
Load causes water to be squeezed out
Dense, consolidated sandstones
C
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Seismic Survey
- Depth to rockhead
Unconsolidated, porous compressible
soil
?
Seismic waves speed slow
rockhead
Consolidated, rigid less compressible
bedrock
Seismic waves speed fast
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Seismic Survey
- Depth to rockhead
Seismic recording stations
Seismic source
drift
?
rockhead
bedrock
8
Seismic Survey
- Depth to rockhead
direct seismic wave
drift
?
rockhead
bedrock
refracted seismic wave
9
Seismic Survey
- Depth to rockhead
drift
rockhead
bedrock
Arrival time of direct waves
time
Arrival time of refracted waves
distance form seismic source
10
Seismic Survey
- Depth to rockhead
Point of transformation
drift
V1 3km/s
rockhead
V2 5km/s
bedrock
Arrival time of direct waves
Point of transformation
time
5km
Arrival time of refracted waves
distance form seismic source
11
Electrical Resistivity Survey
- Depth to water table
Transmitting electrodes
Receiving electrodes
Wenner array of 4 electrodes

• Speed of electrical transmission increases with
  increasing water content.

• Higher water table means reduced electrical
  resistivity.

12
Radon Gas

• Colourless
• Odourless
• Tasteless
• Radioactive gas

If concentrations build up it can cause lung
cancer
10 15,000 deaths in USA Canada every year
Produced by radioactive decay of 238 Uranium in
granite
13
Radon Gas pathways
HOUSE
Concentrations build up in unventilated rooms
spaces
Pipes other services
BASEMENT
Pore spaces in rocks soils
Joints cracks in rocks
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Radon Gas
RADON GAS