PEC EPE Geological cheat sheet

Rock mass rating inputs: uniaxial compressive strength, RQD, joint spacing, joint condition, groundwater condition, and joint orientation adjustment; each parameter is scored then summed.

RQD = (sum of core lengths ≥100 mm / total run length) × 100%; use double-tube coring and count only intact, natural breaks - drilling-induced fractures are excluded.

Mohr–Coulomb failure envelope: τ = c + σn·tanφ. Effective stress parameters c′ and φ′ apply to drained/slow loading; total stress parameters apply to undrained/rapid loading in low-permeability rock or soil.

Hoek–Brown criterion for jointed rock: σ1′ = σ3′ + σci·(mb·σ3′/σci + s)^a, where mb, s and a derive from GSI, disturbance factor D, and intact rock constant mi.

Geological strength index (GSI) is estimated from rock mass structure (blockiness, interlocking) and joint surface condition (roughness, alteration); GSI is not a direct measurement.

Discontinuity orientation controls failure mode: planar sliding requires a joint dipping out of the slope at an angle less than the slope face angle but greater than the friction angle; wedge failure requires two intersecting sets.

Stereographic projection: plot poles to discontinuities; a great circle through poles indicates a joint set. Use lower-hemisphere equal-area (Schmidt) nets for density analysis, equal-angle for angular relations.

Site investigation hierarchy: desk study and remote sensing → mapping and geophysics → boreholes with in-situ testing → laboratory testing; ground model is updated iteratively as data accumulate.

Darcy's law: Q = k·i·A; hydraulic gradient i = Δh/L. Lugeon test (packer test) expresses rock mass permeability in Lugeon units; 1 Lu ≈ 1 L/min per metre at 1 MPa.

Effective stress principle: σ′ = σ − u. Reducing pore pressure by dewatering increases effective stress and shear strength, but may cause settlement or induce subsidence in compressible strata.

Factor of safety for a planar slope failure: FS = [c·A + (W·cosψ − u·A)·tanφ] / (W·sinψ), where ψ is the dip of the failure plane and A the plane area.

Infinite slope with seepage parallel to ground surface: FS = [c′ + (γ − m·γw)·z·cos²β·tanφ′] / (γ·z·sinβ·cosβ), where m is the saturated fraction of the slope-normal depth.

Ground improvement selection: grouting for void filling and permeability reduction in rock; jet grouting and deep soil mixing for cohesive soils; vibro-compaction for loose granular soils; stone columns for soft clays and silts.

Rock mass classification for tunnel support: RMR and Q-system (Q = (RQD/Jn)·(Jr/Ja)·(Jw/SRF)) are used to select support; Q is more sensitive to joint roughness and stress conditions.

Landslide hazard assessment requires identification of the slip surface geometry (circular, planar, wedge, toppling) and the controlling groundwater regime, not just the slope angle.

Atterberg limits define soil consistency: liquid limit (LL), plastic limit (PL), plasticity index PI = LL − PL; a high PI indicates high compressibility and volume change potential.

Soil classification: USCS uses grain size (gravel >4.75 mm, sand 0.075–4.75 mm, fines <0.075 mm) and plasticity; AASHTO classification is based on grain size, LL, and PI for subgrade evaluation.

Consolidation: coefficient of consolidation cv from the time-settlement curve (log-time or square-root-time method); primary consolidation settlement Sc = Cc·H·log10((σ0′+Δσ)/σ0′)/(1+e0).

Shear strength of saturated clays: undrained shear strength su from UU triaxial or vane tests; effective stress parameters from CU tests with pore pressure measurement or CD tests.

Rock durability: slake durability index (two-cycle) and Los Angeles abrasion value assess aggregate quality; soundness test (sodium/magnesium sulfate) indicates resistance to freeze-thaw and wetting-drying.

Weathering grade classification (I–VI, fresh to residual soil) governs the engineering behavior of rock masses; grade V and VI materials behave as soils and are tested accordingly.

Construction materials assessment includes source rock petrography, potential alkali-silica reactivity (ASR) testing, sulfate content, and chloride content for concrete aggregate suitability.

Fault classification by slip: normal (extension, σ1 vertical), reverse/thrust (compression, σ3 vertical), strike-slip (σ2 vertical); Anderson's theory relates fault type to principal stress orientation.

Fault activity assessment for engineering: consider recency of movement, recurrence interval, slip rate, and proximity to the site; active faults require setback distances and site-specific seismic hazard analysis.

Earthquake magnitude: moment magnitude Mw = (2/3)·log10(M0) − 6.07, where M0 is seismic moment in N·m; Mw is preferred for engineering because it does not saturate at large rupture sizes.

Ground motion attenuation: peak ground acceleration (PGA) decreases with distance from the source and is amplified by soft soils; site class (A–E) modifies design spectra in codes.

Liquefaction susceptibility: saturated loose sands and silts below the water table, with low plasticity and shallow depth; evaluate using SPT (N1)60, CPT, and shear wave velocity, compared against cyclic stress ratio.

Fold geometry: anticline (older rocks in core), syncline (younger rocks in core); fold hinge and limb orientation affect bedding plane stability in slopes and tunnels.

In-situ stress measurement: overcoring, hydraulic fracturing, and borehole breakouts determine the stress tensor; the ratio of horizontal to vertical stress (K) influences tunnel and shaft stability.

Landslide classification by movement type: fall, topple, slide (rotational/translational), spread, and flow; each has distinct velocity and warning characteristics relevant to mitigation design.

Rockfall hazard: assess block size, slope height, and talus angle; mitigation options include rock bolts, mesh, catch fences, and barriers, selected by trajectory analysis.

Karst terrain: dissolution features (sinkholes, caves, dolines) create high permeability and collapse risk; investigation includes geophysics (electrical resistivity, GPR) and drilling.

Subsidence mechanisms: groundwater withdrawal, mining, and dissolution; monitoring via InSAR, extensometers, and leveling; prediction requires compressibility and extraction data.

Geological mapping deliverables: geological map with cross-sections, engineering geological map showing units by engineering behavior, and a ground model report with parameters and uncertainties.

Geophysical methods: seismic refraction for depth to bedrock and rippability; electrical resistivity for groundwater and contamination; GPR for shallow utilities and voids; each has depth and resolution limits.

Uncertainty communication: report ranges and confidence levels for geotechnical parameters; a single 'design value' without stated basis is not acceptable practice in geological engineering reporting.

SPT N-value correction: (N1)60 = N·CN·CE·CB·CR·CS, where CN corrects for overburden; SPT is not suitable for gravels or rock, and results are equipment-dependent.

CPT interpretation: cone resistance qc, sleeve friction fs, and pore pressure u2 give soil behavior type (SBT) via normalized charts; CPT is continuous and repeatable but cannot sample.

Plate load test: determines in-situ bearing capacity and settlement modulus; the test plate size affects results - scale effects mean results are conservative for full-size footings.

Pressuremeter and dilatometer tests provide in-situ modulus and lateral stress; they are useful in soft soils and for settlement prediction where sampling disturbs the material.

Rock core logging: record recovery, RQD, fracture index, weathering, and joint condition; core orientation is needed to measure true dip and dip direction of discontinuities.

Permeability testing: constant-head and falling-head tests in boreholes; packer tests in rock; pumping tests for aquifer parameters (transmissivity, storativity).

Quality control for earthworks: compaction to specified dry density and moisture content relative to maximum dry density (Standard or Modified Proctor), verified by field density tests.

Bearing capacity: Terzaghi/Meyerhof equations give ultimate bearing capacity qu = c·Nc + q·Nq + 0.5·γ·B·Nγ; apply a factor of safety (typically 2.5–3) to obtain allowable bearing pressure.

Settlement components: immediate (elastic), primary consolidation, and secondary (creep); total settlement must be checked against serviceability limits, not just bearing capacity.

Deep foundations: pile capacity from static formulas (α, β methods) or dynamic testing (PDA, CAPWAP); rock sockets rely on side shear and end bearing in the rock mass.

Excavation support: braced cuts, sheet piles, secant piles, and soil nails; design considers earth pressure, groundwater, and adjacent structures; monitoring of wall deflection is essential.

Slope stabilization methods: regrading, drainage, retaining structures, soil nails, rock bolts, and vegetation; drainage is usually the most cost-effective measure.

Tunneling in rock: stand-up time depends on rock mass quality; sequential excavation and support (NATM) uses monitoring to adapt support to observed behavior.

Groundwater control during excavation: sumps and ditches for shallow, low-permeability conditions; deep wells for high-permeability granular soils; cut-off walls for contaminated or high-inflow sites.

Geotechnical report structure: scope, site description, geology, investigation methods, ground model, design parameters with justification, conclusions, and limitations.

Parameter selection: report characteristic values (e.g., 5th percentile for strength) and state the basis; distinguish between measured, correlated, and assumed values.

Codes and standards: reference the applicable local code (e.g., Eurocode 7, AASHTO LRFD, or national building code) for partial factors and design approaches; do not mix code philosophies.

Risk assessment: identify geohazards (slope instability, liquefaction, karst, subsidence) and rate likelihood and consequence; mitigation design follows the risk ranking.

Monitoring plans: specify instrumentation (inclinometers, piezometers, settlement plates, crack gauges), trigger levels, and response actions before construction begins.

Peer review and verification: independent check of ground model and design parameters reduces the risk of systematic error; document assumptions and their sensitivity.

Data management: maintain a borehole database with coordinates, elevations, and test results; spatial interpolation (e.g., kriging) supports the ground model but must not replace engineering judgment.

Uniaxial compressive strength (UCS) test on intact rock core: ISRM standard uses length-to-diameter ratio of 2–3; correct for size and shape effects when comparing results.

Point load index (Is50) correlates with UCS: UCS ≈ 22–24 × Is50 for many rocks; the correlation is rock-type dependent and should be verified with direct tests.

Brazillian (indirect tensile) test gives tensile strength; direct shear test on joints gives joint cohesion and friction angle for discontinuities.

Rock mass classification: RMR (Bieniawski) ranges 0–100; Q-system gives Q values; both are empirical and should be used with local experience and calibration.

GSI-based Hoek–Brown parameters: for GSI > 25, a = 0.5; for GSI < 25, a depends on GSI; mb = mi·exp((GSI−100)/(28−14D)).

Rock bolt design: length should extend beyond the failure zone; spacing and pattern depend on joint orientation and block size; fully grouted bolts transfer load along the bond length.

Slake durability and swelling tests identify rocks prone to deterioration on exposure; these affect excavation support and slope design in mudstones and shales.

Aquifer parameters: transmissivity T = k·b (b = saturated thickness); storativity S from pumping test analysis (Theis, Cooper-Jacob); these govern yield and drawdown predictions.

Theis equation: s = (Q/(4πT))·W(u), where u = r²S/(4Tt); Cooper-Jacob approximation applies for small u (large time or small radius).

Contaminant transport: advection, dispersion, diffusion, sorption (retardation factor R), and decay; the advection-dispersion equation is the basis for plume prediction.

Retardation factor R = 1 + (ρb/θ)·Kd, where Kd is the distribution coefficient; higher R means slower contaminant migration relative to groundwater.

Groundwater monitoring: install wells with proper screen intervals and seals; sample after purging; analyze for parameters consistent with the contaminant of concern.

Saltwater intrusion: Ghyben-Herzberg relation gives freshwater-saltwater interface depth; over-abstraction in coastal aquifers causes intrusion and requires management.

Dewatering design: estimate inflow using analytical methods (e.g., Dupuit) and verify with pumping tests; consider impacts on adjacent wells, wetlands, and subsidence.

If a slope failure occurs along a pre-existing joint, the joint shear strength (c, φ) controls the analysis, not the intact rock strength; back-analysis of the failure gives the operative strength parameters.

If groundwater is encountered above the expected level, re-evaluate effective stress, slope stability, and excavation support; do not simply increase the factor of safety without understanding the cause.

If SPT N-values are low in gravelly soils, the values may reflect gravel interference, not loose soil; use CPT or large-diameter samplers for verification.

If rock core recovery is low but RQD is high, check for drilling-induced breakage or core loss in weak zones; recovery and RQD together indicate rock mass quality.

If a site is underlain by karst, do not rely on a single borehole to rule out voids; use geophysics and multiple boreholes, and design foundations to span or bridge potential voids.

If a retaining wall shows increasing lateral deflection, check for water pressure buildup behind the wall; drainage is often the missing element in the design.

If liquefaction is suspected, check the groundwater level, soil gradation, and plasticity; mitigation options include densification, drainage, and ground improvement, not just increased foundation depth.

Stress units: 1 MPa = 10 bar = 1000 kPa; 1 kPa = 1 kN/m²; unit weight of water γw ≈ 9.81 kN/m³; unit weight of rock typically 24–27 kN/m³.

Permeability units: 1 m/s = 1000 mm/s; hydraulic conductivity in soils ranges from ~10⁻¹ m/s (gravel) to <10⁻⁹ m/s (clay); 1 Darcy ≈ 9.87×10⁻¹³ m² for intrinsic permeability.

Angle conventions: dip is measured from horizontal (0–90°); dip direction is azimuth clockwise from north; a plane dipping 30° toward 120° is written 120/30.

Stress sign convention: compression positive in rock mechanics; tension positive in some soil mechanics texts - state the convention explicitly in calculations.

Strain units: strain is dimensionless; express as percentage or microstrain (10⁻⁶); modulus E = Δσ/Δε in MPa or GPa.

Seismic units: PGA in g or m/s²; 1 g ≈ 9.81 m/s²; magnitude is dimensionless; intensity scales (MMI) are descriptive, not physical measurements.

Time units: consolidation time in seconds or years; 1 year ≈ 3.15×10⁷ s; convert consistently when using cv in m²/year versus m²/s.

Borehole layout: space boreholes to characterize the site and target critical structures; deepen boreholes below the zone of influence (typically 1.5–2 times the foundation width below the base).

Sampling disturbance: use thin-walled Shelby tubes for soft clays; split-spoon samples are disturbed and suitable for classification, not strength testing; preserve samples and test promptly.

Drilling methods: auger for shallow soils; rotary wash boring for deeper soils and rock; core drilling with appropriate bit and drilling fluid for rock; record drilling fluid loss as an indicator of permeability.

Geophysical logging: caliper, gamma, resistivity, and borehole camera logs complement core; they identify fractures, voids, and lithology changes between samples.

Field vane shear test: suitable for soft to medium clays; correct for plasticity and time effects; not suitable for sandy or gravelly soils.

In-situ stress and permeability testing require careful sealing and stabilization; packer tests should be run at multiple pressures to assess flow regime (laminar vs turbulent).

Sample labeling and chain of custody: record depth, recovery, moisture, and testing schedule; sample quality affects the reliability of design parameters.

Kinematic analysis: use stereonets to check for planar, wedge, and toppling failure; a joint set with poles plotting near the slope face great circle indicates potential planar sliding.

Plane failure condition: joint dip direction within ±20° of slope dip direction, joint dip less than slope dip, and joint dip greater than friction angle.

Wedge failure: intersection line of two joint sets must daylight in the slope face and plunge greater than the friction angle; stability depends on the wedge volume and water pressure.

Toppling: requires steeply dipping joints (dip > ~70°) dipping into the slope, with joint spacing less than the block height; flexural toppling is common in foliated rock.

Tunnel support in squeezing ground: use yielding support and sequential excavation; in rockburst-prone ground, use rock bolts, mesh, and energy-absorbing support.

Rock mass quality for TBM: RMR and Q predict penetration rate and support; abrasive minerals (quartz content) affect cutter wear.

Slope monitoring: prisms, inclinometers, and crack gauges detect movement; set alert and alarm thresholds based on velocity and acceleration trends.

Soil description order: consistency/density, moisture, color, grain size, plasticity, structure, and origin; use standard terms and include depth intervals.

Rock description: strength (field estimate), weathering grade, discontinuity spacing, aperture, infilling, and roughness; record both core and exposure observations.

Weathering grades: I fresh, II slightly weathered, III moderately weathered, IV highly weathered, V completely weathered, VI residual soil; grade affects strength and compressibility.

Discontinuity roughness: use JRC (joint roughness coefficient) or descriptive terms (smooth, rough, slickensided); roughness affects shear strength and dilation.

Fracture index: number of natural fractures per metre of core; high values indicate closely jointed rock and lower rock mass strength.

Groundwater observations: record seepage, inflow rate, and water level during drilling; these inform permeability and pore pressure assumptions.

Logging quality control: cross-check field logs with laboratory test results and geophysical logs; inconsistencies indicate sampling or logging errors.

Limit state design: distinguish ultimate limit state (collapse, excessive deformation) from serviceability limit state (settlement, cracking); apply partial factors to loads and resistances.

Eurocode 7 design approaches: DA1 (factors on actions and resistances), DA2 (factors on actions and resistances, different combination), DA3 (factors on actions and material properties); the choice affects foundation sizing.

Load and resistance factor design (LRFD): apply load factors >1 to loads and resistance factors <1 to capacity; calibration is code-specific.

Factor of safety vs partial factors: FS = resistance/load is a global measure; partial factors separate uncertainty in loads and resistances; do not mix without justification.

Serviceability criteria: allowable settlement varies with structure type (e.g., 25 mm for isolated footings, 50 mm for rafts is a common guide, but project-specific limits govern).

Seismic design: use design response spectra and site amplification factors; liquefaction and slope stability are checked under design earthquake motions.

Verification and documentation: state the design approach, factors, and assumptions; peer review is required for complex or high-risk projects.

Landslide mitigation hierarchy: avoid the hazard, reduce exposure, engineer the slope (drainage, reinforcement, retaining), and monitor; monitoring alone does not reduce risk.

Drainage measures: surface drains, horizontal drains, and trench drains lower pore pressure; the effectiveness depends on permeability and continuity of the drainage path.

Retaining structures: gravity walls, cantilever walls, anchored walls, and soil nail walls; design considers active and passive earth pressures, water pressure, and surcharge.

Rockfall barriers: catch fences and rockfall sheds; design based on block energy (mass × velocity²/2) and trajectory; maintenance is essential.

Debris flow: check for channel confinement, sediment supply, and rainfall thresholds; mitigation includes check dams, channel linings, and avoidance.

Monitoring frequency: increase during construction and periods of heavy rainfall; use automated systems for critical sites with real-time alerts.

Emergency response: predefine trigger levels and response actions; communicate with stakeholders and authorities before an event, not during it.

Model selection: limit equilibrium for slope stability; finite element or finite difference for deformation and complex geometry; distinct element for jointed rock; select based on problem physics.

Constitutive models: Mohr–Coulomb for general soil/rock; Hoek–Brown for jointed rock; modified Cam-Clay for soft clays; the choice must match the material behavior and loading path.

Boundary conditions: model domain must be large enough that boundaries do not affect results; fix or roller boundaries at depth and sides; apply groundwater conditions explicitly.

Parameter sensitivity: run sensitivity analyses on key parameters (strength, permeability, stiffness); report the range of outcomes, not a single deterministic result.

Calibration and validation: compare model predictions with monitoring data (settlement, pore pressure, displacement); adjust parameters within measured ranges.

Mesh and time step: refine mesh near structures and failure zones; time steps must be small enough for consolidation and dynamic analyses.

Limitations: numerical models are tools, not substitutes for geological understanding; state assumptions and limitations in the report.

Observational method: predict behavior, design monitoring, compare observed with predicted, and adjust design/construction; requires predefined contingency plans.

Earthworks: control compaction moisture and layer thickness; test density and moisture at regular intervals; reject material that does not meet specification.

Pile installation: monitor driving resistance or drilling parameters; dynamic testing verifies capacity; integrity testing detects defects.

Ground improvement verification: test treated ground (e.g., CPT, plate load, or sampling) to confirm design assumptions; do not assume improvement without verification.

Excavation safety: slope and shoring design, groundwater control, and monitoring of adjacent structures; daily inspection during active excavation.

As-built records: document actual ground conditions, deviations from design, and testing results; these inform future maintenance and liability.

Handover: provide as-built drawings, monitoring data, and maintenance manuals; include residual risk and inspection schedule.

Acid rock drainage: sulfide minerals (pyrite) oxidize to produce acidic, metal-rich water; test with acid-base accounting and kinetic tests; mitigation includes encapsulation and neutralization.

Contaminant sorption: Kd depends on soil type, pH, and contaminant; batch tests estimate Kd; use conservative values for risk assessment.

Landfill design: liner systems (clay and/or geomembrane), leachate collection, and cover; site selection considers geology, groundwater, and seismic hazards.

Brownfield redevelopment: characterize contamination, assess risk, and plan remediation; geotechnical design must account for contaminated soils and groundwater.

Mine waste: tailings dams require stability analysis, seepage control, and monitoring; failure consequences are high, so design factors are conservative.

Natural attenuation: monitored natural attenuation can be a remediation option if degradation rates and plume stability are demonstrated.

Regulatory framework: environmental permits and standards vary by jurisdiction; identify applicable regulations early in the project.

Spatial variability: soil and rock properties vary; use statistical methods (mean, standard deviation, coefficient of variation) and geostatistics to characterize uncertainty.

Characteristic value: a cautious estimate of the value governing the limit state; Eurocode 7 defines it statistically; state the basis (e.g., mean minus one standard deviation).

Correlation vs causation: correlations between test results (e.g., SPT and strength) are empirical; verify with direct tests for critical designs.

Outlier detection: check data for transcription errors, sampling disturbance, and equipment malfunction before using in design.

Ground model: a 3D interpretation of geology and parameters; update as new data arrive; document the model and its uncertainties.

Risk-based decision making: combine probability and consequence; use quantitative risk assessment for high-consequence hazards.

Communication: present uncertainty clearly to stakeholders; avoid false precision; state assumptions and limitations.

Effective stress: σ′ = σ − u; use effective stress for drained conditions and total stress for undrained conditions in low-permeability materials.

Shear strength: τ = c′ + σ′·tanφ′ (effective); τ = su (undrained); the choice depends on drainage and loading rate.

Consolidation settlement: Sc = Cc·H·log10((σ0′+Δσ)/σ0′)/(1+e0); use Cr for recompression below preconsolidation pressure.

Bearing capacity: qu = c·Nc + q·Nq + 0.5·γ·B·Nγ; factors depend on friction angle and foundation shape/depth.

Slope stability: FS = resisting forces/moments ÷ driving forces/moments; use limit equilibrium methods (Bishop, Spencer) for circular slip surfaces.

Permeability: Darcy's law Q = k·i·A; pumping test analysis gives T and S; packer tests give Lugeon values for rock.

Rock mass strength: Hoek–Brown criterion with GSI, mi, and D; RMR and Q for classification and support design.

RQD is not the same as core recovery; RQD counts only intact pieces ≥100 mm along the core axis, excluding drilling breaks.

GSI is not measured directly; it is estimated from structure and surface condition; do not treat it as a laboratory result.

The friction angle of a joint is not the same as the friction angle of the intact rock; joint roughness and infilling reduce strength.

Liquefaction is not limited to clean sands; silts and gravelly soils can liquefy under certain conditions; plasticity and gradation matter.

A high factor of safety does not guarantee no failure; it depends on the reliability of parameters and the failure mechanism considered.

Dewatering increases effective stress and may cause settlement; it is not always beneficial for adjacent structures.

Seismic magnitude is not the same as intensity; magnitude measures energy released, intensity measures effects at a site.

Geological mapping: record lithology, structure, weathering, and geomorphology; use a consistent scale and legend; map contacts and faults accurately.

Trenching and test pits: expose shallow geology and allow bulk sampling; log walls and base; backfill and compact appropriately.

Geophysics: seismic refraction for bedrock depth and rippability; electrical resistivity for groundwater and contamination; GPR for shallow voids and utilities; each method has resolution and depth limits.

Borehole camera and televiewer: image fractures and bedding; oriented logs give true dip and dip direction; useful in rock mass characterization.

Piezometers and standpipes: measure groundwater levels and pore pressure; install with proper seals; monitor over time to capture seasonal variations.

In-situ testing: SPT, CPT, vane, pressuremeter, dilatometer, and plate load; select based on soil type and design parameter needed.

Sampling: disturbed samples for classification; undisturbed samples for strength and consolidation; preserve and transport carefully.

Rock mass strength is controlled by discontinuities; intact rock strength is an upper bound; scale effects reduce strength with increasing volume.

RMR parameters: UCS, RQD, spacing, condition, groundwater, and orientation; each has a rating; sum gives RMR; adjust for orientation.

Q-system: Q = (RQD/Jn)·(Jr/Ja)·(Jw/SRF); use for tunnel support selection; Q and RMR correlate but are not identical.

Support selection: rock bolts, mesh, shotcrete, steel sets; the choice depends on rock mass quality, stress, and excavation size.

Squeezing ground: weak, high-stress rock; use yielding support and sequential excavation; monitor convergence.

Rockburst: high-stress, brittle rock; use destress blasting, rock bolts, and energy-absorbing support; monitoring of seismicity.

Ground support verification: pull-out tests for bolts, thickness and strength tests for shotcrete; inspect regularly.

Consistency of clays: undrained shear strength su correlates with liquidity index and effective overburden; use vane, UU triaxial, or CPT correlations.

Compressibility: compression index Cc and recompression index Cr from oedometer tests; preconsolidation pressure from Casagrande construction.

Shear strength: drained parameters from CD or CU tests with pore pressure measurement; undrained parameters from UU or vane; select based on drainage conditions.

Permeability: laboratory tests (constant/falling head) on small samples may not represent field-scale permeability; use field tests for design.

Compaction: Standard Proctor (lower energy) vs Modified Proctor (higher energy); maximum dry density and optimum moisture content depend on energy and soil type.

Collapsible soils: metastable structure collapses on wetting; identify with oedometer tests at natural and soaked moisture; mitigate by pre-wetting or compaction.

Expansive soils: high PI and clay minerals (montmorillonite); volume change on wetting/drying; mitigate with moisture control, lime stabilization, or removal.

Feasibility stage: desk study, preliminary ground model, identification of geohazards and constraints; limited investigation.

Design stage: detailed investigation, parameter selection, analysis, and design; peer review for complex projects.

Construction stage: verification testing, monitoring, and as-built records; observational method for uncertain conditions.

Operation and maintenance: monitoring, inspection, and maintenance of geotechnical assets; update risk assessments.

Decommissioning: assess stability, contamination, and long-term monitoring requirements; plan for closure.

Documentation: maintain a project file with investigation data, design calculations, and monitoring records; ensure traceability.

Communication: coordinate with structural, hydrological, and environmental engineers; geotechnical assumptions affect other disciplines.

Competence: work within your expertise; seek specialist advice for complex geology, seismicity, or contamination.

Honesty: report actual conditions and test results; do not suppress unfavorable data.

Objectivity: base conclusions on evidence; disclose assumptions and uncertainties.

Confidentiality: protect client data; share only with authorization.

Public safety: prioritize safety over cost or schedule; report unsafe conditions to appropriate authorities.

Conflict of interest: disclose financial or personal interests that could affect judgment.

Continuing education: maintain knowledge of current standards and methods.

RQD: rock quality designation; percentage of intact core pieces ≥100 mm in a run; indicates degree of jointing.

GSI: geological strength index; a qualitative scale (0–100) describing rock mass structure and surface condition.

Lugeon: unit of rock mass permeability; 1 Lu ≈ 1 L/min per metre at 1 MPa; used in packer tests.

SPT: standard penetration test; blow count for a split-spoon sampler; corrected to (N1)60 for overburden and energy.

CPT: cone penetration test; continuous measurement of cone resistance and sleeve friction; used for soil profiling.

PI: plasticity index; LL − PL; indicates plasticity and volume change potential.

FS: factor of safety; ratio of resisting to driving forces or moments.

PGA: peak ground acceleration; maximum acceleration during an earthquake; used in seismic design.

Borehole depth: extend below the zone of influence; for foundations, 1.5–2 times the footing width below the base; for slopes, below the potential slip surface.

Slope angle vs friction angle: for a dry, cohesionless slope, the stable angle is approximately the friction angle; add cohesion or drainage for steeper slopes.

Settlement limits: common guides are 25 mm for isolated footings and 50 mm for rafts, but project-specific criteria govern; differential settlement is often more critical.

Permeability ranges: gravel >10⁻² m/s; sand 10⁻²–10⁻⁵ m/s; silt 10⁻⁵–10⁻⁷ m/s; clay <10⁻⁸ m/s; use for preliminary dewatering and drainage design.

RQD interpretation: >90% excellent, 75–90% good, 50–75% fair, 25–50% poor, <25% very poor; use with joint condition, not alone.

Rock mass strength: jointed rock strength is typically 10–30% of intact rock strength; use GSI and Hoek–Brown for design.

Monitoring frequency: daily during active construction or rainfall; weekly to monthly during operation; adjust based on trends.

Geological engineering integrates geology, soil and rock mechanics, hydrogeology, and engineering design to solve ground-related problems.

Ground model: a 3D interpretation of geology, properties, and groundwater; it is the basis for all analysis and design.

Uncertainty: inherent in geological materials; manage with investigation, testing, statistical analysis, and the observational method.

Failure mechanisms: identify the controlling mechanism (shear, sliding, toppling, liquefaction, settlement) before selecting analysis methods.

Design: use limit state design with partial factors or global factors; verify serviceability and ultimate limit states.

Monitoring: essential for verification and early warning; define trigger levels and response actions.

Communication: report clearly, state assumptions and limitations, and coordinate with other disciplines.

Have you identified the geological setting and potential geohazards?

Have you characterized the rock mass and soil profile with appropriate tests?

Have you determined groundwater conditions and permeability?

Have you selected design parameters with justification and stated uncertainty?

Have you checked both ultimate and serviceability limit states?

Have you designed a monitoring plan with trigger levels and response actions?

Have you documented assumptions, limitations, and peer review?

Unit weight: γ = ρ·g; ρ in kg/m³, g ≈ 9.81 m/s²; γ in kN/m³ when ρ in kg/m³ and g in m/s² divided by 1000.

Void ratio and porosity: e = Vv/Vs; n = Vv/Vt; e = n/(1−n); n = e/(1+e).

Degree of saturation: S = Vw/Vv; S = w·Gs/e; w = water content, Gs = specific gravity.

Consolidation coefficient: cv = T·H²/t; T is a time factor (e.g., 0.197 for 50% consolidation in the log-time method).

Seismic site amplification: amplify PGA by site factors; soft soils amplify long-period motion; rock sites have lower amplification.

Liquefaction safety factor: FS = CRR/CSR; CRR from (N1)60 or CPT; CSR from PGA and overburden; FS < 1 indicates potential liquefaction.

Rock bolt capacity: pull-out capacity depends on bond strength and embedment length; verify with pull-out tests.

Distinguish between total and effective stress; use effective stress for drained conditions and long-term stability.

Distinguish between intact rock and rock mass; rock mass strength is lower due to discontinuities.

Distinguish between undrained and drained shear strength; select based on loading rate and permeability.

Distinguish between ultimate and serviceability limit states; both must be satisfied.

Distinguish between magnitude and intensity; magnitude is energy, intensity is effect at a site.

Distinguish between RQD and core recovery; RQD excludes drilling breaks.

Distinguish between GSI and RMR; both are classifications but use different inputs and purposes.

ISRM suggested methods for rock characterization, testing, and monitoring; use for rock testing standards.

ASTM standards for soil testing (e.g., D1586 SPT, D4318 Atterberg limits, D2435 consolidation); follow current editions.

Eurocode 7 (EN 1997) for geotechnical design; national annexes may modify partial factors.

Local building codes and seismic design provisions; identify the governing code for the project location.

Environmental regulations for contamination and waste; identify applicable permits and standards.

Industry guidance for slope stability, tunneling, and ground improvement; use recognized references and peer review.

Quality management standards for testing laboratories; ensure accreditation and calibration.

Risk = likelihood × consequence; rank risks and allocate mitigation resources accordingly.

Residual risk: after mitigation, some risk remains; communicate and manage it.

Trigger levels: define measurable thresholds (e.g., displacement rate, pore pressure) and response actions.

Communication: use plain language for non-specialists; provide maps and clear recommendations.

Stakeholder engagement: involve regulators, owners, and affected parties early.

Documentation: keep records of decisions, assumptions, and monitoring data.

Review: update risk assessments as new data and conditions emerge.

Geological engineering requires integrating geology, mechanics, and hydrogeology with engineering design.

Investigation must be planned, staged, and adapted to the geology encountered.

Design parameters must be justified and uncertainty stated.

Failure mechanisms must be identified before analysis.

Monitoring and the observational method manage uncertainty during construction.

Reporting must be clear, honest, and complete.

Professional ethics and public safety guide all decisions.