PEC EPE Geological flashcards
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32 cards. Read the term and the definition here. The deck at the top of this page is optional.
- RQD
- Rock quality designation: the percentage of intact core pieces longer than 100 mm along the core axis in a run, excluding drilling-induced breaks; indicates the degree of jointing in a rock mass.
- GSI
- Geological strength index: a qualitative 0–100 scale estimated from rock mass structure (blockiness, interlocking) and discontinuity surface condition (roughness, alteration); used to derive Hoek–Brown parameters.
- Hoek–Brown criterion
- An empirical failure criterion for jointed rock: σ1′ = σ3′ + σci·(mb·σ3′/σci + s)^a, where mb, s, and a depend on GSI, the intact rock constant mi, and the disturbance factor D.
- Mohr–Coulomb criterion
- A linear shear strength envelope: τ = c + σn·tanφ; effective stress parameters c′ and φ′ apply to drained conditions, while total stress parameters apply to undrained conditions in low-permeability materials.
- Effective stress
- The stress transmitted through the soil or rock skeleton: σ′ = σ − u, where σ is total stress and u is pore pressure; it controls strength, compressibility, and deformation in drained conditions.
- Darcy's law
- Groundwater flow rate through a porous medium: Q = k·i·A, where k is hydraulic conductivity, i is hydraulic gradient (Δh/L), and A is cross-sectional area; valid for laminar flow.
- Lugeon test
- A packer test in rock that measures permeability in Lugeon units; 1 Lu corresponds to about 1 litre per minute per metre of test section at 1 MPa injection pressure.
- Factor of safety
- The ratio of resisting forces or moments to driving forces or moments for a potential failure mechanism; a value greater than 1 indicates stability, with required values set by design codes.
- Standard penetration test
- A field test driving a split-spoon sampler into soil and counting blows per 300 mm; the N-value is corrected to (N1)60 for overburden stress and energy, and is used for soil profiling and liquefaction assessment.
- Cone penetration test
- A continuous in-situ test pushing a cone into the ground while measuring cone resistance, sleeve friction, and pore pressure; used for soil behavior type classification and stratigraphy, but it does not recover samples.
- Liquefaction
- Loss of shear strength in saturated loose sands and silts under cyclic loading, such as earthquakes, when pore pressure rises to equal confining stress; assessed using SPT, CPT, and shear wave velocity data.
- Moment magnitude
- A magnitude scale based on seismic moment: Mw = (2/3)·log10(M0) − 6.07, where M0 is in N·m; it does not saturate for large earthquakes and is preferred for engineering hazard assessment.
- Peak ground acceleration
- The maximum acceleration experienced at a site during an earthquake, expressed in g or m/s²; it depends on magnitude, distance, and local site conditions, with soft soils amplifying motion.
- Atterberg limits
- Water content boundaries defining soil consistency: liquid limit (LL), plastic limit (PL), and shrinkage limit; the plasticity index PI = LL − PL indicates plasticity and volume change potential.
- Consolidation settlement
- Time-dependent compression of saturated soil under load due to pore water expulsion; primary settlement Sc = Cc·H·log10((σ0′+Δσ)/σ0′)/(1+e0) for normally consolidated soil.
- Preconsolidation pressure
- The maximum effective stress a soil has historically experienced; determined from an oedometer curve using Casagrande construction; it distinguishes normally consolidated from overconsolidated behavior.
- Undrained shear strength
- The shear strength of a saturated soil under undrained conditions, denoted su; measured by UU triaxial tests, field vane, or CPT correlations; used for short-term stability in clays.
- Bearing capacity
- The maximum pressure a foundation soil can support without shear failure; ultimate bearing capacity from Terzaghi or Meyerhof equations, divided by a factor of safety to give allowable pressure.
- RMR
- Rock mass rating (Bieniawski): a 0–100 classification summing ratings for uniaxial compressive strength, RQD, joint spacing, joint condition, groundwater, and joint orientation adjustment; used for support design.
- Q-system
- A tunnel rock mass classification: Q = (RQD/Jn)·(Jr/Ja)·(Jw/SRF), where the terms describe block size, joint shear strength, water, and stress; used to select tunnel support.
- Planar sliding
- A rock slope failure along a single discontinuity; requires the joint to dip out of the slope at an angle less than the slope face but greater than the joint friction angle.
- Wedge failure
- A rock slope failure involving two intersecting discontinuity sets; the intersection line must daylight in the slope face and plunge more steeply than the friction angle for instability.
- Toppling failure
- A rock slope failure where steeply dipping joints (usually over 70°) dip into the slope and blocks rotate forward; common in foliated or columnar rock masses.
- Acid rock drainage
- Acidic, metal-rich water formed when sulfide minerals such as pyrite oxidize on exposure to air and water; assessed by acid-base accounting and mitigated by encapsulation or neutralization.
- Retardation factor
- A parameter describing contaminant transport delay relative to groundwater flow: R = 1 + (ρb/θ)·Kd, where Kd is the distribution coefficient; higher R means slower migration.
- Transmissivity
- The rate at which water flows through a unit width of aquifer under a unit hydraulic gradient: T = k·b, where k is hydraulic conductivity and b is saturated thickness; determined from pumping tests.
- Observational method
- A construction approach: predict behavior, design monitoring, compare observations with predictions, and adjust design or construction as needed; requires predefined contingency plans and trigger levels.
- Limit state design
- A design philosophy distinguishing ultimate limit states (collapse, excessive deformation) from serviceability limit states (settlement, cracking); partial factors are applied to loads and resistances.
- Characteristic value
- A cautious estimate of a geotechnical parameter governing a limit state; defined statistically in Eurocode 7 and stated with its basis, such as mean minus one standard deviation.
- Slake durability index
- A measure of rock resistance to weakening and disintegration during wetting and drying cycles; determined by a two-cycle test and used to assess durability of mudstones and shales.
- Los Angeles abrasion
- A test measuring aggregate resistance to fragmentation and wear in a rotating drum with steel balls; lower values indicate stronger aggregate suitable for concrete and road construction.
- Weathering grade
- A classification from I (fresh) to VI (residual soil) describing rock alteration; grades V and VI behave as soils and require soil mechanics testing and design approaches.