solidification of cooled magma. Intrusive (plutonic), below surface; Extrusive (volcanic), on surface.
Granite (igneous intrusive rock), basalt (grey to black extrusive volcanic rock), quartz (lattice of silica (SiO2) tetrahedra)
consolidation of sediments
75-80% of the Earth's land area. As sediment deposition builds up, the overburden pressure squeezes the sediment into layered solids in a process known as lithification (rock formation). Sedimentary rocks are laid down in layers called beds or strata.
Conglomerate (large grains in clay matrix), sandstone (Medium round grains in calcite matrix -composed of quartz and/or feldspar), shale (harder laminated)
Also, chalk & limestone
Important geological factors in rock masses:
Intact rock: Intact rock is defined as rock containing no significant fractures.
Discontinuities: is a general term denoting any separation in a rock mass with low tensile strength.
In-situ stress: is pre-existing state of tress in the rock.
Pore water: Pore fluids existing in rock masses.
Time influence : Time component affects engineering performance of rock structure.
The most useful description of the mechanical behaviour of intact rock is...
the stress-strain curve.
Rock discontinuities/Rock structure
•Faults – discontinuities on which shear displacement has taken place
•Beddings – divide sedimentary rocks into beds of strata
•Joints – breaks of geological origin along which there has been no displacement
Fossil shell beds
Uniaxial Compressive Strength:
measures the stress at which a sample will break in unconfined compression
A stress-strain plot will have a characteristic shape. Initially it will be linear as the sample shortens and swells and then curved as permanent distortion occurs.
•Young’s modulus (E)
•Poisson’s ratio (n)
•Unconfined compressive strength (UCS or sigmac)
Description of Discontinuities
•Orientation – is described by the dip and dip direction of the line of steepest declination in the plane of discontinuity (stereographic projection)
•Spacing – refers to the average spacing between adjacent discontinuities
•Persistence – The discontinuity trace length
•Roughness – The inherent surface roughness relative to plane of discontinuity
•Aperture – The perpendicular distance between adjacent rock walls
•Filling – The material that separates the adjacent rock walls
(p43, p60 week 2 lecture notes)
Strength of jointed rock masses (Hoek’s 1983 Rankine Lecture)