Engineering geology lecture 2 Flashcards
What is a metamorphic rock?
The solid-state transformation of pre-existing rock into texturally or mineraloically distinct new rock as a result of hight temperature, pressure or both
What are the three types of metamorphic rocks?
- thermal or contact metamorphism (temperature)
- Dynamic or dislocation metamorphsim (stress)
- Regional (temperature + stress)
Where is the pressure and temperature path?
Down tectonic plates
What is re-crystalisation?
When the cement void spaces crystalise into interlocking crysals, containing the original crystals
What are foliations in sedimentary rocks called?
Cleavage
above a certain size they become schistosity, and then gneiss banding
What kind of metamorphism is required to form marble?
contact
What are some tests that are done on rocks?
- Brazilian tensile test
- point load test Is(50)
- unconcfined compression test
What is the equation for the point load test?
IS_50 = P/De^2
Is_50 is the uncorrected point load strength index
P is the failure load
De is the equivalent core diammeter
What factors determine rock strength?
- Laminations
- Seams
- Weathered zones
- inclusions
How is UCS (uniaxal compression strength) determined
From tests on individual samples
What do UCS’ provide us with
A measure of the rock strength at a location and depth
How do you identify the potential slide of an unfavourable orientation?
If the cleavage is slanted inwards
What affects the engineering behaviour of soils?
Its geological history
Transported soils - variability = function of the energy of deposition
In- situ soils- variability = function of weathering
Man-made soils - variability = function of the person who made it
Also stress history and the degree of consolidation can affect properties
What are two tests that can be done on soils to assess their strength?
Oedometer
Standard triaxial test
What is the weakness of the standard triaxial test?
It is slow and really expensive
