CIVE1105 Geological Setting

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CIVE1105 Geological Setting
2013-06-25 12:29:06
Geological Plates Tectonic

Description Week 2 & 3 lecture notes summary. Exam
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  1. The main mechanical components in rock mass
    Intact rock; defined as rock containing no significant fractures

    Rock Mass; consists of intact rock and discontinuities
  2. Elementary Rock Types
    • Metamorphic
    • Igneous
    • Sedimentary
  3. Metamorphic
    • products of the metamorphism which transforms naturally occurred rocks by temperature, pressure and chemical process.
    • Marble (fine-coarse grained), Slate, micro-fine grained, laminated), Schist (coarse grained), Gneiss (altered granite)
  4. Igneous
    • 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)
  5. Sedimentary
    • 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
  6. 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.
  7. The most useful description of the mechanical behaviour of intact rock is...
    • the stress-strain curve.
  8. 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
  9. Geological fault
    • Normal (extension)
    • Reverse (compression)
    • Thrust
  10. Geological bedding
    • Planar
    • Current
    • Ripple-marked beds
    • Fossil shell beds
    • Graded
    • Cut-and-fill
  11. UCS
    • Uniaxial Compressive Strength:
    • measures the stress at which a sample will break in unconfined compression
  12. Elastic Parameters
    • 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)
  13. 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)
  14. Strength of jointed rock masses (Hoek’s 1983 Rankine Lecture)
    • Intact
    • Single joint
    • Sparsely jointed
    • Densely jointed
    • Compacted rockfill
    • Spoil

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