Engineering geology lecture 3 Flashcards
What is the definition of disconformity?
Unconformity between parallel layers of sedimentary rocks which represent a period of erosion or non-deposition
(nonconformity is the same but with igneous or metamorphic rocks)
What do geological maps tell and not tell us?
- determining geological features
- interpret the cross-sectional profile of the site
- geological maps typically dont present specific to an exact location, we need to investigate by digging out the ground or by boroing a hole
- collect the spill of the drill in a bag if digging
What are the equations for apparent and true dip?
tan(da) = tan(dt)sin(Sxs-Sb)
or
tan(da)= tan(dt)cos(Sxs - Tdt)
da is the apparent dip dt is the true dip Sb is the strike Tdt is the true dip direction Sxs is the bearing of the cross-section
What is angular uncomformity?
Horizontal parallel strata of sedimentary rock that are deposited on tilted and eroded layers
What is the point of ground investigation?
Assesses ground conditions prior to starting a construction project
Checks for
- suitability of the site for the proposed project
- site conditions and ground properties
- potential geotechnical/ geological
What are the three phases of ground investigation?
Initial stage
Main stage
Monitoring
What does the intial stage of ground investigation involve?
- Desk study of available data
- walkover survey and visual assessment
- preliminary report and scope of works
What does the main stage of ground investigation involve?
- Field work (geological mapping, geophysics, test pits, boreholes/oring)
- Laboratory testing (soils and rocks)
- Final report
What is the point of a borehole?
to extract a length of soil and/ or rock from the earth
- the overall soil/rok can be broken during the process or kept intact
- samples taken at the site are examined either on site or back in the laboratory
What are the three different characteristics that are used in the description of rocks?
Material
Discontinuity
Mass
What are some examples of a material characteristics?
Strenght, bedding/layering, colour & name
What are some examples of discontinuity characteristics?
Bedding, jointing and shear orientation, spacing, roughness, shear etc.
What are some examples of mass characteristics?
Rock material + discontiuties - rock mass
Overall structure particularly discontinuous
Fracture stat (TCR, SCR, RQD, FI)
What is important to record when core logging?
- Inclination
- Rougness
- aperture
- infill
- surface condition/ colour
roughness -> infill may be hard to assess
What causes weathering in rocks?
Water, ice, acids, plants, animals, changes in temperature and wind
What does RQD stand for
Rock quality designation
What is RQD used for?
The quality of rocks such as adegree and depths of weathering, zones of weakness and fracturing
What are different kinds of joint roughness found in boreholes?
- Stepped slickensided
- stepped rough
- undulating rough
- undulating slickensided
- planar slickensided
- planar rough
What are different kinds of joint fill?
- gouge thickness > Amplitude
- Softening - Fine
- non-softening - fine
- softening - medium
- no fill
What does joint aperture mean?
The gap between splits
What are the mechanisms of failure in rocks?
- Shear failure
- compaction
- cavity
- landslides
What causes shear failure?
Weak rocks
What causes compaction?
Clay, peat, fill
What causes cavity failure?
caves, mines
