BUILDINGS Shallow Foundations rafts pads strips Raft Pads
BUILDINGS
Shallow Foundations • rafts • pads • strips Raft Pads
Deep Foundations • piles What type of foundations to build depends on: • depth to rockhead • depth to water table • geological structures • rock properties
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
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 A B C Saturated sediments compress & subside under load Foundations 10 m 40 m Water table Variable, soft, silty deposits - unconsolidated Very soft clays - consolidated Dense, consolidated sandstones Clay deposits are prone to settlement under load Load causes water to be squeezed out
Seismic Survey soil - Depth to rockhead Unconsolidated, porous & compressible ? Seismic waves speed = slow rockhead Consolidated, rigid & less compressible bedrock Seismic waves speed = fast
Seismic Survey - Depth to rockhead Seismic recording stations Seismic source drift ? rockhead bedrock
Seismic Survey - Depth to rockhead direct seismic wave drift ? rockhead bedrock refracted seismic wave
Seismic Survey - Depth to rockhead drift rockhead bedrock Arrival time of direct waves time Arrival time of refracted waves distance form seismic source
Seismic Survey - Depth to rockhead drift Point of transformation V 1 = 3 km/s rockhead V 2 = 5 km/s bedrock Point of transformation time 5 km Arrival time of direct waves Arrival time of refracted waves distance form seismic source
Electrical Resistivity Survey Transmitting electrodes - Depth to water table Receiving electrodes Wenner array of 4 electrodes • Speed of electrical transmission increases with increasing water content. • Higher water table means reduced electrical resistivity.
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 Radon GRANITE Produced by radioactive decay of 238 Uranium in granite
Radon Gas pathways HOUSE Concentrations build up in unventilated rooms & spaces BASEMENT Pore spaces in rocks & soils Pipes & other services Joints & cracks in rocks
Radon Gas RADON GAS
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