Module 5, rock shit Flashcards
what section includes the upper most part of mantle and the crust
lithosphere
The movement between adjacent plates falls into three broad categories
convergent
divergent
transform
Mafic meaning?
used for silicate minerals, magmas, and rocks which are relatively high in the heavier elements. The term is derived from using the MA from magnesium and the FIC from the Latin word for iron, dark and dense (basalt and gabro)
Felsic meaning?
used for silicate minerals, magmas, and rocks which have a lower percentage of the heavier elements, and are correspondingly enriched in the lighter elements, such as silicon and oxygen, aluminum, and potassium, light, quartz
when to use thin arch dam
narrow valley, strong abudments, aghgreagate, cement
when to use gravity dam
narrowish valley, strong footprint, aggregate, cement
embankmnet dam
any valley, stable abutments
physical weathering processes
unloading thermal expansion frost shattering salt crystallisation root growth wetting and drying
chemical weathering
hydrolysis
oxidation
dissolution
leaching
what is hydrolysis
breakdown of silicate minerals in water to form clays
what is oxidation
rusting of ferrous rocks
what is dissolution
ions dissolving into the water
what affects soil behaviour
particale size shape size distribution stress history contact geometry pore space bonding deformation
where get soil for dam?
reservoir footprint
What are the ground conditions required for an earthquake to trigger liquefaction?
Loose, non-cemented, water-saturated granular soil (mainly sand)
What are the common effects of liquefaction on foundations?
Loss of bearing capacity, loss of frictional strength, and differential settlement
What soils exhibit expansive behaviour?
Mixed-layer clays
Name three common causes of ground subsidence.
Natural cavern collapse (in areas of karst or other soluble rock types) Mining-induced or tunnelling-induced settlement Tectonic movement (coastal subsidence following subduction zone earthquakes) Dewatering (void space collapse due to over-pumping groundwater or hydrocarbons)
What physical characteristics control the overall mechanical behaviour of rock?
Discontinuities -fractures, joints, faults
What type of plate margin is New Zealand located on?
Convergent (subduction)in the north and south, with a translational component (the Alpine fault zone) in the middle
What geological time period is of most importance for engineering?
The most recent, Quaternary era.
What are the prominent Quaternary soil types found in New Zealand?
Loess (wind-blown silt), alluvial (river sands and gravels), and volcanic ash. Glacial soils are more common in the Southern Alps.
What rock type makes up the majority of the bedrock in the South Island?
The basement rock for much of the South Island is Torlesse Greywacke, a sedimentary rock (mostly sandstone)
How does unloading affect a rock mass?
Physical relaxation results in the development of ground-parallel fractures/joints; these decrease in frequency with depth. Delamination along near-surface joints leads to rock slides on slopes above the friction angle of the material.
