ENGINEERING GEOLOGY & REMOTE SENSING (CE-405) - Unit 3 Short Notes

UNIT 3: ENGINEERING GEOLOGY & REMOTE SENSING

A. FUNDAMENTALS OF MINERALS & ROCKS

1. Minerals: Definition & Classification

• Definition: Naturally occurring, inorganic, solid substance with ordered atomic arrangement and definite chemical composition (or variable within limits).

• Classification:

  • Rock-forming vs. Accessory: Rock-forming constitute >90% of crust (e.g., quartz, feldspar); accessory are minor (e.g., zircon, magnetite).

  • Essential vs. Non-essential (in a specific rock): Essential minerals define rock name (e.g., quartz in sandstone); non-essential are incidental.

• Mode of Formation:

  • Igneous: Crystallization from magma/lava (e.g., feldspar, mica).

  • Sedimentary: Precipitation from solution, accumulation (e.g., calcite, halite).

  • Metamorphic: Recrystallization under P-T conditions (e.g., garnet, staurolite).

[!TIP] Exam often asks for "essential minerals" – specify in context of a given rock type.

2. Physical & Chemical Properties of Minerals

Physical Properties (for field identification):

Chemical Properties:

• Composition: Determines class (silicates, carbonates, oxides, etc.).

• Solubility: Carbonates dissolve in HCl; halites in water.

• Acid Reaction: Carbonates (calcite, dolomite) effervesce with cold/warm HCl.

• Oxidation: Iron-bearing minerals (pyrite, biotite) rust/stain.

[!TIP] Always link property to identification method: streak plate for streak, HCl for carbonates, hardness kit for scratch.

3. Petrology: Definition & Subdivisions

• Definition: Study of rocks—origin, composition, occurrence, classification, and interrelationships.

• Subdivisions:

  • Igneous Petrology: Magma crystallization, rock types (granite, basalt).

  • Sedimentary Petrology: Processes of weathering, erosion, deposition, lithification.

  • Metamorphic Petrology: Solid-state recrystallization under P-T-fluid conditions.

• Importance in Engineering Geology: Predicts rock behavior (strength, durability, weathering) based on origin and mineralogy.

4. Igneous Rocks

• Definition: Formed by solidification of molten magma (intrusive) or lava (extrusive).

• Texture: Grain size (phaneritic = coarse, aphanitic = fine, glassy), arrangement (porphyritic = large crystals in fine matrix).

• Structure: Flow bands, vesicles (gas cavities), columnar joints.

• Megascopic Study & Engineering Properties:

  | Rock | Composition | Texture | Engineering Properties | |------|-------------|---------|------------------------| | Granite | Felsic (quartz, feldspar) | Coarse-grained | High strength, low porosity, good foundation; may have sheet joints; durable but can fracture. | | Basalt | Mafic (pyroxene, plagioclase) | Fine-grained, often vesicular | High density, good aggregate; columnar joints may cause seepage; weathering to clay. |

5. Sedimentary Rocks

• Definition: Formed by accumulation and lithification of sediments/precipitates.

• Texture:

  • Clastic: Based on grain size (gravel, sand, silt, clay), sorting, rounding.

  • Non-clastic: Crystalline (evaporites), biogenic (fossiliferous), chemical (precipitates).

• Structure: Bedding (layers), lamination (thin beds), cross-bedding, ripple marks.

• Formation Steps: Weathering → Erosion → Transportation → Deposition → Burial → Lithification (compaction + cementation).

• Key Rocks:

  | Rock | Composition | Texture | Engineering Properties | |------|-------------|---------|------------------------| | Limestone | Calcite (CaCO₃) | Clastic or crystalline | Variable strength; soluble (karst → sinkholes, seepage); may be fossiliferous. | | Sandstone | Quartz-dominated | Clastic (sand-sized) | Porosity/permeability control groundwater; cement type (silica > strong, calcite > weak) affects durability. | | Shale | Clay minerals | Clastic (clay-sized), fissile | Low permeability, high plasticity when wet → swelling, low shear strength; poor foundation. |

6. Metamorphic Rocks

• Definition: Pre-existing rocks transformed by heat, pressure, and/or fluids (solid-state).

• Agents: Directed pressure (differential stress), temperature, hydrothermal fluids.

• Texture:

  • Foliated: Planar alignment of minerals (slate, schist, gneiss).

  • Non-foliated: Granoblastic (quartzite, marble).

• Common Engineering Rocks:

  | Rock | Parent Rock | Metamorphic Grade | Engineering Properties | |------|-------------|-------------------|------------------------| | Slate | Shale | Low | Slaty cleavage → splits thin; brittle; used for roofing, flooring. | | Schist | Mudstone/shale | Medium | Pronounced foliation → weak planes; anisotropic strength; slope instability. | | Gneiss | Granite/shale | High | Banded (light/dark minerals); strong but foliation may cause weakness. | | Quartzite | Sandstone | Any | Very hard, resistant; interlocking quartz grains; excellent aggregate. | | Marble | Limestone | Any | Recrystallized calcite; used in construction; soluble (caverns). |

[!TIP] Link metamorphic rock to parent: slate from shale, marble from limestone, quartzite from sandstone.

7. The Rock Cycle

• Diagram: Circular flow showing:

  • Igneous → (weathering/erosion) → Sediments → (lithification) → Sedimentary → (burial/heat) → Metamorphic → (melting) → Magma → (cooling) → Igneous.

  • Metamorphic can also melt to igneous or uplift/weather to sedimentary.

• Significance: Explains interconversion; engineering properties depend on history (e.g., fractured granite vs. unfractured).

B. STRUCTURAL GEOLOGY & GEOMORPHOLOGY

1. Geological Structures: Primary & Secondary

• Primary: Formed during rock formation (e.g., bedding in sedimentary, flow bands in igneous).

• Secondary: Formed after rock formation (folds, faults, joints).

• Strike: Direction of line formed by intersection of a planar feature (bed, fault) with a horizontal plane. Measured with compass.

• Dip: Angle of inclination from horizontal (0°–90°), plus direction of dip (azimuth).

• Notation: Dip direction and angle (e.g., 30° NE). Strike is perpendicular to dip direction.

• Outcrop: Exposed portion of rock body. Pattern controlled by structure (e.g., V-shaped in valleys for dipping beds).

• Field Measurement: Use Brunton compass; record strike/dip of beds, joints, faults.

[!TIP] Common pitfall: Confusing strike (horizontal line) with dip (inclination). Always sketch: strike line, dip arrow, angle.

2. Folds

• Definition: Bend in layered rocks due to compressional stress.

• Parts:

  • Limb: Two sides of fold.

  • Hinge: Line of maximum curvature.

  • Axial Plane: Plane dividing fold symmetrically.

  • Axis (Crest line): Line along hinge.

• Classification:

  • By Mode of Occurrence:

    • Anticline: Upward arch; oldest rocks in core.

    • Syncline: Downward trough; youngest rocks in core.

    • Monocline: Step-like fold (one limb nearly horizontal).

    • Dome: Circular anticline; plunges in all directions.

    • Basin: Circular syncline.

  • By Shape:

    • Open: Gentle, limbs dip < 70°.

    • Isoclinal: Tight, limbs parallel.

    • Overturned: One limb tilted beyond vertical.

    • Recumbent: Axial plane nearly horizontal.

• Engineering Significance:

  • Groundwater: Anticlines often trap water (permeability along hinge).

  • Tunneling: Avoid axial zones (fractured); follow limbs.

  • Slope stability: Folded strata may have weak orientations.

3. Joints

• Definition: Fractures without displacement (opening only).

• Origin: Tension (exfoliation), cooling (mural joints), unloading, tectonic.

• Types:

  • Mural Joints: Vertical joints in igneous intrusions (e.g., basalt columns) from cooling contraction.

  • Systematic Joints: Regular pattern (e.g., orthogonal sets).

  • Random Joints: Irregular, no pattern.

• Engineering Significance:

  • Increase permeability → seepage in dams.

  • Reduce rock mass strength → slope failure, tunnel spalling.

  • Control weathering depth.

[!TIP] Distinguish joints (no movement) from faults (with displacement).

4. Faults

• Definition: Fracture with measurable displacement.

• Components:

  • Fault Plane: Surface of rupture.

  • Fault Scarp: Steep slope from displacement.

  • Throw: Vertical component of displacement.

  • Heave: Horizontal component perpendicular to strike.

  • Slip: Net displacement vector.

• Classification:

  • Strike-Slip (Transform): Horizontal movement; e.g., San Andreas.

  • Dip-Slip:

    • Normal Fault: Hanging wall moves down (extensional).

    • Reverse/Thrust Fault: Hanging wall moves up (compressional; thrust low-angle).

  • Oblique-Slip: Combination of strike and dip slip.

• Engineering Significance:

  • Seismic hazard (ground rupture, shaking).

  • Dam/tunnel foundations unstable.

  • Groundwater conduit → leakage.

  • Avoid active faults in critical structures.

5. Unconformities

• Definition: Surface representing missing geological time due to non-deposition or erosion.

• Types:

  • Angular Unconformity: Tilted/eroded rocks overlain by flat-lying strata.

  • Disconformity: Parallel layers with erosion surface (hard to recognize).

  • Nonconformity: Sedimentary overlying igneous/metamorphic.

  • Paraconformity: Parallel layers with time gap but no obvious erosion.

• Engineering Importance:

  • Weak zones (weathered, fractured) → foundation failure.

  • Potential aquiclude/aquifer boundaries.

  • Slope instability along unconformity.

6. Geological Work of Rivers

• Processes:

  • Erosion: Hydraulic action, abrasion (corrasion), solution (corrosion).

  • Transportation: Traction (rolling), saltation (bouncing), suspension, solution.

  • Deposition: When velocity decreases (overload, gradient drop).

• Depositional Landforms:

  • Plains: Floodplains (periodic flooding deposits silt).

  • Deltas: At river mouth (distributaries, interdistributary bays).

  • Alluvial Fans: Cone-shaped at mountain front (coarse to fine).

  • Natural Levees: Raised banks from overbank deposition.

  • Point Bars: Inside meander bends (lateral accretion).

• Engineering Importance:

  • Foundation Conditions: Alluvial deposits may be loose, compressible.

  • Flood Risk: Deltas, floodplains prone to inundation.

  • Erosion: Bank erosion threatens structures; scour at bridges.

  • Water Resource: Deltas, alluvial fans often have high groundwater.

7. Other Geomorphological Agents (Brief)

• Glaciers:

  • Erosional: Cirques, arêtes, horns, fjords.

  • Depositional: Moraines (lateral, terminal, ground), drumlins, eskers.

  • Engineering: Glacial till variable (boulders in matrix); ice-contact deposits loose; post-glacial rebound.

• Sea & Oceans:

  • Erosional: Cliffs, wave-cut platforms, sea arches, stacks.

  • Depositional: Beaches, spits, bars, tombolos.

  • Engineering: Coastal erosion, sedimentation at harbors, salt weathering.

• Volcanoes:

  • Types: Shield (fluid lava, gentle slopes), Composite/Stratovolcano (explosive, steep), Cinder cone (small, pyroclastic).

  • Hazards: Lava flows, ashfall, pyroclastic flows, lahars, volcanic gases.

  • Engineering: Avoid active zones; use volcanic materials (ash, pumice) cautiously.

C. ENGINEERING GEOLOGY APPLICATIONS

1. Importance of Geology in Civil Engineering

• General Principles: Earth materials are construction foundation; geological processes govern stability, durability, cost.

• Examples:

  • Foundations: Bedrock vs. soil; weak zones (faults, weathered rock) cause differential settlement.

  • Dams: Foundation impermeability, reservoir leakage, abutment stability.

  • Tunnels: Rock mass quality, groundwater, fault crossings.

  • Road Cuts: Slope stability (dip slope failure, joint-controlled).

  • Quarrying: Rock quality for aggregate (hardness, fracture, weathering).

2. Dam Engineering

• Definition: Barrier across river/stream for storage/control.

• Purposes: Water supply, irrigation, hydroelectric, flood control, recreation.

• Comprehensive Geological Investigations for Site Selection:

  1. Foundation Geology: Competent, unweathered rock; low permeability; no active faults/joints; favorable orientation (dip into upstream).

  2. Reservoir Geology: Impermeable basin (no leakage through faults, karst); stable slopes (no landslides).

  3. Abutment Slopes: Stable rock/soil; no potential for slides.

  4. Seismicity: Low earthquake risk (avoid plate boundaries, active faults).

  5. Construction Materials: Nearby sources of aggregate, clay for core, rock for cofferdam.

• Past Dam Failures & Geological Causes:

  • Vajont Dam (Italy, 1963): Landslide into reservoir (geological: weak, foliated rock slope) → overtopping.

  • Teton Dam (USA, 1976): Foundation on faulted, weathered rhyolite → piping through joints.

  • Malpasset Dam (France, 1959): Fault zone in gneiss → foundation slip.

[!TIP] Dam site selection = "FOUNDATION + RESERVOIR + ABUTMENTS + SEISMICITY + MATERIALS".

3. Tunnel Engineering

• Geological Factors:

  • Rock Mass Quality: Use RMR or Q-system; avoid weak, fractured zones.

  • Structural Weaknesses: Faults (zones of crushed rock), joints (spacing, condition), folds (axial zones fractured).

  • Groundwater: High pressure → support problems, inflow; map aquifers.

  • Geothermal Gradient: Heat increases with depth (ventilation, equipment).

  • Ground Support: Determined by rock mass class (shotcrete, bolts, steel sets).

4. Canal Engineering

• Considerations:

  • Alignment through stable formations (avoid faults, landslides).

  • Minimize seepage: use clayey soils, line canal; avoid permeable sands/gravels.

  • Erosion-resistant banks: rock or vegetation.

  • Slope stability: cut slopes in sound rock; benching in soil.

  • Cross-drainage: geological control for syphons, aqueducts.

5. Groundwater

• Definition: Water below water table in saturated zone.

• Formation: Infiltration → percolation → accumulation in aquifers.

• Key Terms:

  • Water Table: Upper surface of saturated zone.

  • Aquifer: Permeable rock/soil yielding usable water.

  • Aquiclude: Impermeable layer (e.g., clay, unfractured rock).

  • Aquitard: Low-permeability layer (slows flow).

• Properties Controlling Water-Bearing Capacity:

  | Rock Type | Primary Porosity | Secondary Porosity | Permeability Controls | |-----------|------------------|--------------------|----------------------| | Igneous | Very low (intercrystalline) | Fractures, vesicles (basalt), weathering | Fracture density, connectivity; basalt may be good aquifer if vesicular/fractured. | | Sedimentary | Intergranular (sand, gravel) | Dissolution channels (carbonates) | Sorting (well-sorted high), cementation (calcite reduces), grain size. | | Metamorphic | Low | Folds (axial zones), foliation planes, fractures | Foliation may create anisotropy; schist/gneiss may have high fracture permeability. |

6. Weathering

• Definition: In-situ breakdown of rocks by physical, chemical, biological processes.

• Types:

  • Physical (Mechanical): Freeze-thaw, thermal expansion, exfoliation, salt crystal growth.

  • Chemical: Hydrolysis (feldspar → clay), oxidation (iron minerals → rust), carbonation (calcite dissolution), hydration (mineral swelling).

• Factors Controlling Weathering:

  • Climate: Wet/tropical → chemical; arid → physical.

  • Rock Composition: Minerals susceptible (feldspar, calcite) vs. resistant (quartz).

  • Rock Structure: Joints increase surface area → deeper weathering.

  • Topography: Steep slopes → less weathered (erosion removes); gentle → thick regolith.

  • Time: Longer exposure → deeper weathering.

• Effect on Rock Strength:

  • Reduces cohesion, increases porosity.

  • Creates weak zones (saprolite).

  • Depth profile: fresh rock → partially weathered → completely weathered → residual soil.

• Impact on Structures:

  • Foundations: Settlement on compressible weathered rock.

  • Slopes: Weathered zones failure (planar, circular).

  • Durability: Aggregates may degrade (e.g., alkali-silica reaction).

7. Earthquakes

• Definitions:

  • Magnitude: Energy released (Richter scale - logarithmic; Moment magnitude - more accurate, based on fault area, slip, rigidity).

  • Intensity: Effects on surface (Mercalli scale - I to XII, based on damage).

  • Focus (Hypocenter): Point of origin within Earth.

  • Epicenter: Point on surface directly above focus.

• Causes:

  • Tectonic: Plate boundaries (divergent, convergent, transform) - most common.

  • Volcanic: Magma movement.

  • Reservoir-Induced: Large dams (pore pressure, loading).

  • Human-Induced: Mining, fracking, reservoir impoundment.

• Seismic Hazards & Geological Considerations:

  • Ground shaking (site effects: soft soils amplify).

  • Liquefaction (saturated sands).

  • Surface rupture (avoid active faults).

  • Landslides (seismic shaking on slopes).

  • Tsunamis (submarine earthquakes).

  • Design: Avoid active faults; liquefaction assessment; soil improvement.

D. REMOTE SENSING & GIS IN ENGINEERING GEOLOGY

1. Remote Sensing: Fundamentals

• Definition: Science of acquiring information about objects without physical contact, using sensors mounted on platforms.

• Objective: To study Earth's surface and atmosphere systematically.

• Components:

  1. Energy Source (Sun or active like radar/laser).

  2. Atmosphere (scattering, absorption - affects signal).

  3. Target (Earth surface - reflectance/emission).

  4. Sensor (records energy - multispectral, hyperspectral, thermal, microwave).

  5. Platform (satellite, aircraft, drone).

  6. Processing (raw data to georeferenced image).

  7. Interpretation/Analysis (visual or digital).

• Types:

  • Optical: Multispectral (few broad bands, e.g., Landsat), Hyperspectral (many narrow bands, e.g., AVIRIS).

  • Thermal: Measures emitted heat (e.g., Landsat TIRS).

  • Microwave (RADAR): Active, penetrates clouds, sensitive to surface roughness/moisture (e.g., Sentinel-1).

  • LiDAR: Laser pulses for high-resolution DEM/topography.

• Elements (Interaction Sequence):

  Energy Source → Atmosphere Interaction → Target Interaction → Sensor → Transmission → Processing → Interpretation.

2. Practical Applications in Engineering Geology

• Geological Mapping: Lithology, structural mapping (faults, folds, lineaments), alteration zones.

• Landslide Hazard Zonation: Slope, drainage, vegetation, land use from imagery.

• Groundwater Potential Mapping: Lineaments (fractures), drainage density, lithology.

• Environmental Geology: Pollution (oil spills, effluent), land degradation, mining impacts.

• Site Selection: Dams, tunnels, roads, urban expansion (terrain, geology, access).

• Monitoring: Active faults (InSAR), deformation, post-disaster assessment (earthquake, flood).

• Quarry/Mine Planning: Volume estimation, waste dump stability.

3. Visual Interpretation Techniques

• Use image elements:

  • Tone: Relative brightness/darkness (lithology, moisture).

  • Texture: Smooth (water, urban) vs. rough (forest, rocky).

  • Pattern: Arrangement (drainage pattern - dendritic, trellis).

  • Shape: Geometric (fields, buildings) vs. natural (rivers).

  • Size: Relative scale (river vs. canal).

  • Shadow: Reveals relief (use low-sun angle images).

  • Association: Context (alluvial fan at mountain front).

• Stereoscopic Interpretation: Using overlapping stereo pairs (e.g., aerial photos, satellite stereo) for 3D view → better terrain/structural analysis.

4. Geographic Information System (GIS)

• Definition: Computer system for capturing, storing, analyzing, managing, and presenting spatial (geographic) data.

• Core Components:

  • Hardware: Computer, storage, GPS.

  • Software: ArcGIS, QGIS.

  • Data: Spatial (maps, imagery, DEM) + Attribute (tables).

  • People: Users, managers.

  • Methods: Procedures, models.

• Use in Resource Mapping:

  • Integration: Overlay multiple layers (geology, soil, hydrology, land use, climate).

  • Spatial Analysis: Buffer zones, overlay (intersect, union), network analysis.

  • Example: Mineral potential - combine lithology, structure, geochemistry, geophysics.

  • Groundwater: Combine lineaments, drainage, slope, lithology.

• Application in Site Selection:

  • Multi-Criteria Decision Analysis (MCDA):

    1. Identify criteria (geology, slope, access, distance to road, seismicity).

    2. Assign weights (importance).

    3. Standardize layers (e.g., slope: <10° = suitable, 10-30° = moderate, >30° = unsuitable).

    4. Overlay with weighted sum → suitability map.

  • Example: Dam site - combine bedrock outcrop (geology), low seismicity, gentle slopes, reservoir basin, distance to materials.

5. Integration of RS & GIS

• RS provides spatial data layers (e.g., satellite imagery for lithology, DEM from LiDAR for slope, SAR for deformation).

• GIS integrates these with other vector data (faults, roads, wells) and performs spatial analysis for engineering geology decisions.

• Workflow: RS data acquisition → preprocessing → classification/feature extraction → import into GIS → overlay with other spatial data → analysis → decision support.

[!TIP] RS = "data acquisition"; GIS = "data integration & analysis". Use RS for mapping, GIS for multi-layer evaluation.

\boxed{\text{End of Unit 3 Notes}}
Focus on definitions, diagrams (strike/dip, folds, faults, rock cycle), engineering properties of key rocks (granite, shale, marble, slate), dam/tunnel site criteria, RS-GIS integration.