UNIT 5: ENGINEERING GEOLOGY & REMOTE SENSING - EXAM-FOCUSED NOTES

Based on rigorous analysis of RGPV past papers (Jun 2025, Jun 2023, Nov 2023, Jun 2022). Strictly follows the approved blueprint.

I. FUNDAMENTALS OF GEOLOGY & ITS ENGINEERING SIGNIFICANCE

Introduction & Scope

• Engineering Geology: Application of geological knowledge to engineering practice to ensure geological factors are recognized and considered in location, design, construction, operation, and maintenance of engineering works.

• Branches:

  • Main: Physical Geology, Historical Geology, Paleontology.

  • Allied: Mineralogy, Petrology, Structural Geology, Geomorphology, Hydrogeology, Engineering Geology itself.

• Features of Physical Geology: Study of Earth's materials (minerals, rocks), internal & external processes (volcanism, weathering, erosion), and geological structures (folds, faults).

Earth's Structure

• Layers (from surface inward):

  1. Crust: Continental (granitic, ~35-40 km) & Oceanic (basaltic, ~5-10 km).

  2. Mantle: Upper (rigid lithosphere) & Lower (plastic asthenosphere, ~2900 km depth).

  3. Core: Outer (liquid, ~2250 km) & Inner (solid, ~1220 km).

• Diagram:

  DiagramSEARCH: "earth internal structure diagram labeled crust mantle core"

• Rock Cycle: Continuous transformation of rocks among three types due to heat, pressure, and weathering.

  • Process: Igneous → (Weathering/Erosion) → Sedimentary → (Heat/Pressure) → Metamorphic → (Melting) → Igneous.

  • Diagram:

    DiagramSEARCH: "rock cycle diagram simple geological processes"

Application Focus: Importance in Civil Engineering

[!TIP] EXAM TIP: Always link geology to a specific engineering problem (foundation failure, seepage, slope instability).

II. MINERALS: PROPERTIES AND IDENTIFICATION

Definition & Essentials

• Mineral: A naturally occurring, inorganic, solid substance with a definite chemical composition and ordered atomic arrangement (crystal structure).

• Essential Characteristics: Natural origin, inorganic, solid, definite chemical composition, crystalline structure.

Physical Properties for Identification (Key for Exams)

Use a combination, not single property.

Common Rock-Forming Minerals (Megascopic ID)

Chemical Properties & Formation

• General Composition: Elements: O, Si, Al, Fe, Ca, Na, K, Mg (98% of crust).

• Classification: Silicates (most abundant), Oxides, Sulfides, Sulfates, Carbonates, Native Elements.

• Mode of Formation:

  • Igneous: Crystallization from magma/lava (e.g., Olivine, Pyroxene).

  • Sedimentary: Precipitation from solution, accumulation (e.g., Calcite, Halite, Clay minerals).

  • Metamorphic: Recrystallization under P-T (e.g., Garnet, Staurolite).

III. PETROLOGY: STUDY OF ROCKS

Definition & Subdivisions

• Petrology: Scientific study of origin, occurrence, structure, and classification of rocks.

• Subdivisions:

  1. Igneous Petrology: Origin from molten magma/lava.

  2. Sedimentary Petrology: Origin from weathered products.

  3. Metamorphic Petrology: Origin from pre-existing rocks under P-T.

• Importance: Determines engineering properties (strength, durability, permeability) based on mineral composition, texture, and structure.

Igneous Rocks

• Formation: Solidification of magma (intrusive/plutonic) or lava (extrusive/volcanic).

• Texture: Size/arrangement of crystals.

  • Phaneritic (coarse, visible crystals) → Intrusive (e.g., Granite).

  • Aphanitic (fine, invisible) → Extrusive (e.g., Basalt).

  • Porphyritic (large crystals in fine matrix) → 2-stage cooling.

• Structure: Flow bands, vesicles, pillow structures (submarine).

• Key Examples:

  • Granite (Intrusive): Light-colored (felsic), coarse-grained (Quartz, Feldspar, Mica). Excellent foundation rock (high strength, low permeability). Field Desc: Massive, jointed, feldspar often pink.

  • Basalt (Extrusive): Dark-colored (mafic), fine-grained, often vesicular. Good aggregate, but columnar joints can cause seepage. Field Desc: Dark, dense, may have gas cavities.

Sedimentary Rocks

• Formation Process:

  DiagramCANVAS: "1. Weathering & Erosion → 2. Transportation (size sorting) → 3. Deposition (layering) → 4. Lithification (compaction + cementation)"

• Texture: Clastic (fragments), Non-clastic (crystalline, organic).

• Structure: Bedding/Stratification (most important), ripple marks, mud cracks.

• Key Examples:

  • Limestone (Calcite/dolomite): Often fossiliferous, reacts with HCl. Good when pure/strong, but soluble → karst, leakage. Field Desc: Grey/white, may be crystalline or fossil-rich.

  • Sandstone (Quartz grains): Medium-grained, cemented. Strength depends on cement (silica > calcite > clay). Field Desc: Sandy feel, often cross-bedded.

  • Shale (Clay minerals): Finest-grained, fissile (splits along bedding). Poor foundation (low strength, swell with water). Field Desc: Thin layers, dull, feels soapy.

Metamorphic Rocks

• Metamorphic Agents: Heat (recrystallization), Pressure (directed stress → foliation), Chemically Active Fluids (ion exchange).

• Texture: Foliated (planar alignment: Slate, Schist, Gneiss) vs. Non-foliated (massive: Quartzite, Marble).

• Structure: Slaty cleavage, schistosity, gneissic banding.

• Key Examples (Engineering Properties):

  • Slate: Very fine-grained, excellent slaty cleavage, hard, durable. Used for roofing, flooring.

  • Schist: Medium-grained, pronounced schistosity (mica-rich). Weak along planes → slope failure. Field Desc: Shiny mica flakes, wavy layers.

  • Gneiss: Coarse-grained, gneissic banding (light/dark minerals). Generally strong if banding not weak. Field Desc: Banded, segregated minerals.

  • Quartzite (from Sandstone): Non-foliated, very hard, resistant. Excellent foundation/aggregate. Field Desc: Very hard, interlocking quartz grains, breaks through grains.

  • Marble (from Limestone): Non-foliated, crystalline, reactive with acids. Used decoratively, but dissolves. Field Desc: Crystalline, reacts with HCl, may be veined.

Megascopic Study (Field ID)

Look for: Color, Grain Size, Texture, Structure, Hardness, Reaction (HCl).

• Granite: Light, coarse, interlocking grains, 2-3 minerals visible.

• Basalt: Dark, fine, dense, may have vesicles.

• Limestone: Grey/white, may have fossils, effervesces with HCl.

• Sandstone: Sandy feel, grains visible, cemented.

• Gneiss: Banded (alternating light/dark layers).

• Slate: Slaty cleavage (breaks into thin, flat slabs), fine-grained.

IV. STRUCTURAL GEOLOGY & ROCK MASS CHARACTERIZATION

Orientation Data

• Outcrop: Visible exposure of rock at surface.

• Strike (☢): Direction of line formed by intersection of planar feature (bed, fault) with horizontal plane. Measured as azimuth (e.g., N30°E).

• Dip (⤢): Angle of inclination of planar feature measured perpendicular to strike from horizontal (0°-90°). Also give dip direction (e.g., SE).

• Diagram:

  DiagramSEARCH: "strike and dip diagram geology labeled"

Folds

• Parts: Limb (side), Hinge (max curvature), Axial Plane (plane dividing fold symmetrically), Axis (line of max curvature along hinge).

• Classification (Mode of Occurrence):

  • Anticline: Axial plane divides older rocks in core. Upfold (∩). Can be asymmetric or recumbent (nearly horizontal axial plane).

  • Syncline: Axial plane divides younger rocks in core. Downfold (∪). Often associated with anticlines.

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

  • Dome: Upwarped in all directions (older core). Basin: Downwarped in all directions (younger core).

• Diagram:

  DiagramSEARCH: "types of folds anticline syncline monocline dome basin diagrams"

Faults

• Parts: Fault Plane, Fault Scarp (surface expression), Throw (vertical displacement), Heave (horizontal component), Slip (total displacement).

• Classification:

  • Normal Fault: Hanging wall moves down relative to footwall. Extensional regime. Dip ~60°.

  • Reverse/Thrust Fault: Hanging wall moves up relative to footwall. Compressional regime. Low-angle reverse = Thrust.

  • Strike-Slip Fault: Movement parallel to strike. Shear regime. Left-lateral (sinistral) vs. Right-lateral (dextral).

• Diagram:

  DiagramSEARCH: "fault types normal reverse thrust strike-slip diagram"

Joints

• Definition: Fracture with no measurable displacement.

• Significance: Control weathering, groundwater flow, slope stability, quarrying.

• Types:

  • Systematic: Regular orientation, pattern (e.g., columnar joints in basalt).

  • Non-systematic: Random.

  • Mural Joints: Vertical joints dividing rock into columns/pillars. Crucial for slope stability in quarries/cuts.

• Diagram:

  DiagramSEARCH: "columnar joints basalt mural joints diagram"

Unconformities

• Definition: Surface of non-deposition or erosion separating younger from older rocks.

• Significance: Represents gap in geological record, often weak zones, controls groundwater, important for resource exploration.

• Types:

  • Angular Unconformity: Older rocks tilted/eroded, overlain by flat-lying younger rocks. Most obvious.

  • Disconformity: Parallel layers, but with erosion surface (hard to detect).

  • Nonconformity: Igneous/metamorphic basement overlain by sedimentary.

  • Paraconformity: Parallel layers, no obvious erosion, but time gap (fossil evidence).

• Diagram:

  DiagramSEARCH: "types of unconformities angular disconformity nonconformity diagram"

Other Structures: Dome & Basin

• Dome: Circular/elliptical upwarp; oldest rocks at center. Drilling reveals younger outward.

• Basin: Circular/elliptical downwarp; youngest rocks at center. Drilling reveals older outward.

• Diagram:

  DiagramSEARCH: "dome and basin structure geological map cross section"

V. GEOLOGICAL PROCESSES & HAZARDS

Weathering

• Definition: In-situ disintegration/decomposition of rocks due to atmospheric agents.

• Types:

  • Mechanical/Physical: Breakage without chemical change (freeze-thaw, thermal expansion, exfoliation, salt crystal growth).

  • Chemical: Alteration of mineral composition (solution, hydrolysis, oxidation, hydration, carbonation).

  • Biological: Plant roots, burrowing, organic acids.

• Factors Controlling: Climate (most important), Rock Composition/Structure, Topography, Time.

• Process:

  DiagramCANVAS: "1. Joints provide access → 2. Water/air/roots enter → 3. Physical/chemical breakdown → 4. Formation of regolith/soil"

• Effect on Engineering Properties: Decreases strength & durability, increases permeability (in fractured rock), causes volume change (clay swelling), leads to slope instability.

Fluvial Processes (River)

• River as Agent: Erosion (hydraulic action, abrasion, solution), Transportation (solution, suspension, saltation, traction), Deposition (when competence/velocity drops).

• Depositional Landforms:

  • Point Bar: Inside of meander bend (sandy/gravelly).

  • Floodplain: Broad, flat area flanking river (silty/clayey).

  • Natural Levee: Raised banks along river from deposition during floods.

  • Delta: At river mouth (triangular, distributaries).

  • Alluvial Fan: At mountain front (fan-shaped).

• Engineering Significance: Floodplains/deltas have poor bearing capacity, high compressibility, liquefaction risk. Point bars may shift. Levees can fail.

Groundwater

• Definition: Water below water table in zone of saturation.

• Formation: Infiltration of precipitation, stored in pores/fractures of rocks.

• Properties Controlling Water-Bearing Capacity:

  • Porosity (n): $$\displaystyle n = \frac{V_v}{V_t} \times 100\% $$ (Volume of voids / Total volume). Storage capacity.

  • Permeability (k): Ability to transmit water (Darcy's Law: $$\displaystyle Q = k i A $$). Flow capacity.

  • Specific Yield (Sy): Drainable water by gravity (for unconfined aquifers). Useful water.

  • Specific Retention (Sr): Held by capillary forces. $$\displaystyle n = S_y + S_r $$.

• Water-Bearing Capacity of Rocks:

  • Igneous: Low (except highly fractured/jointed basalt/granite). Primary porosity low.

  • Sedimentary: High (well-sorted sandstone, gravel, limestone with solution channels). Primary porosity high.

  • Metamorphic: Variable (low in massive quartzite/marble; high in foliated schist/gneiss with foliation planes acting as conduits).

• Importance: Foundation seepage/piping, slope stability (pore pressure), construction dewatering, water resource.

Seismology

• Earthquake: Sudden release of energy causing ground shaking.

• Focus/Hypocenter: Point within Earth where rupture starts.

• Epicenter: Point on surface directly above focus.

• Magnitude (Richter Scale): Energy released at source. Single value, logarithmic (each unit = 10x amplitude, ~32x energy). Objective.

• Intensity (Mercalli Scale): Effects on surface (damage, human perception). Varies by location, subjective (I-XII).

• Major Causes: Tectonic (fault movement, 90%+), volcanic, landslides, reservoir-induced, nuclear explosions.

Other Exogenic/Endogenic Processes (Brief)

• Volcanoes: Types (shield, composite, cinder cone). Hazards: lava flows, ash, pyroclastics, lahars, gases.

• Sea & Oceans: Coastal erosion (wave action, longshore drift), deposition (beaches, spits, bars). Hazards: erosion of coastal structures, tsunami.

VI. ENGINEERING APPLICATIONS & SITE INVESTIGATIONS

Dams

• Purposes: Water storage (irrigation, domestic, hydroelectric), flood control, recreation.

• Comprehensive Geological Investigations:

  1. Foundation: Rock type (igneous/metamorphic best), structure (avoid faults/joints), strength, permeability (groutability), seismicity.

  2. Reservoir: Leakage potential (through soluble rocks, faults, unconformities), siltation rate (erosion in catchment).

  3. Alignment: Stable slopes, avoid landslides.

  4. Materials: Availability of construction materials (aggregate, clay for core).

  5. Seismicity: Active fault zones = no-go.

• Site Selection Factors:

  DiagramCANVAS: "Checklist: 1. Suitable Foundation Rock 2. Impermeable Reservoir Bed 3. Narrow Canyon 4. Good Construction Materials 5. Low Seismicity 6. Accessible"

• Case Studies of Failures (Geology-Related):

  • St. Francis Dam, USA (1928): Failure due to weak, foliated schist foundation with faults; poor geological investigation.

  • Malpasset Dam, France (1959): Fault zone in gneiss foundation not properly grouted; seepage led to piping and collapse.

Tunnels

• Geological Factors:

  • Rock Type & Mass: Intact strength, RQD (Rock Quality Designation), joint condition (spacing, persistence, filling).

  • Structural Geology: Faults, folds, joints → weak zones, water inflow, squeezing ground.

  • Groundwater: High pressure → inflow, reduced friction, consolidation.

  • In-situ Stresses: Can cause rock burst (hard rock) or squeezing (weak rock).

  • Geothermal Gradient: Heat in deep tunnels.

Canals

• Considerations:

  • Alignment: Avoid unstable slopes, landslide zones, fault crossings.

  • Subsoil: Low permeability (clay/silt) to minimize seepage. Avoid highly permeable gravel/sand.

  • Foundation: Adequate bearing capacity, low shrink-swell potential.

  • Drainage: Cross-drainage structures (aqueducts, syphons) where crossing streams/depressions.

  • Siltation: Source area erosion control.

Impact on Structures (Weathering Effect)

• Foundations: Weathered rock has lower bearing capacity, higher compressibility → uneven settlement.

• Slopes: Weakening along discontinuities → landslides.

• Construction Materials: Weathered rock produces poor quality aggregate (flaky, weak).

• Underground Structures: Weathered zone → increased seepage, roof fall in tunnels.

• Corrosion: Chemical weathering products (acids, salts) can corrode concrete/steel.

VII. REMOTE SENSING (RS) & GEOGRAPHIC INFORMATION SYSTEM (GIS)

Remote Sensing Fundamentals

• Definition: Science/art of obtaining information about objects/areas without physical contact, by analyzing data acquired by sensor (not human eye).

• Types:

  • Based on source: Passive (sunlight/emitted radiation - e.g., optical), Active (sensor emits - e.g., Radar, LiDAR).

  • Based on platform: Ground-based, Airborne (aircraft), Spaceborne (satellites).

• Components: Energy Source (Sun/sensor), Interaction with atmosphere/target, Sensor (detects/records), Processing, Interpretation/Application.

• Elements (Resolution):

  • Spatial: Ground coverage per pixel (e.g., 30m for Landsat). Detail.

  • Spectral: Number/wavelengths of bands (e.g., multispectral: 3-15 bands; hyperspectral: hundreds). Material ID.

  • Radiometric: Sensitivity to brightness/radiance levels (bits: 8-bit=256 levels). Discrimination.

  • Temporal: Revisit time (days). Change detection.

Applications in Engineering Geology

Key Exam Topics: Always mention specific use-case.

1. Site Suitability Mapping: For dams, towns, highways (slope, geology, land use).

2. Landslide Hazard Zonation: Identify previous landslides (scars, deposits), slope, lithology, drainage.

3. Groundwater Prospecting: Lineaments (fractures), drainage patterns, soil moisture indices.

4. Post-Disaster Assessment: Earthquakes, floods, landslides (damage mapping).

5. Quarry/Mine Mapping: Inventory, environmental impact.

6. Coastal/Shoreline Change: Erosion/accretion monitoring.

7. Geological Mapping: Lithology, structural mapping (folds, faults) in inaccessible areas.

8. Volcano Monitoring: Thermal anomalies, gas emissions, deformation.

Visual Interpretation Techniques

• Using image elements to identify objects:

  • Tone/Color: Relative brightness/color (e.g., water = dark; sand = light).

  • Texture: Roughness/smoothness (e.g., forest = coarse; water = smooth).

  • Pattern: Spatial arrangement (e.g., orchards = regular; alluvial fans = fan-shaped).

  • Shape/Size: Geometric form (e.g., reservoir = curved; building = rectangular).

  • Shadow: Reveals relief/height.

  • Association: Objects occurring together (e.g., villages near roads/rivers).

Geographic Information System (GIS)

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

• Basic Components: Hardware, Software, Data, People, Methods.

• Use in Resource Mapping:

  • Mineral: Overlay geology, structure, geochemistry, geophysics to predict occurrences.

  • Water: Watershed delineation, aquifer mapping, groundwater potential zones (overlay slope, geology, drainage, land use).

  • Land Use/Land Cover: Classification from RS imagery, change detection.

• Use in Site Selection (Multi-Criteria Decision Making):

  • Steps:

    1. Define criteria (e.g., for dam: slope < 15°, granite/gneiss, < 5km from fault, < 50mm/year rain).

    2. Create thematic layers (geology, slope, fault buffer, rainfall) in GIS.

    3. Assign weights to criteria.

    4. Overlay analysis (e.g., Weighted Overlay) to produce suitability map.

  • Advantages: Handles large spatial data, objective, reproducible, integrates RS.

• Applications in Civil Engineering:

  • Route alignment (highways, railways, pipelines).

  • Urban planning, infrastructure management.

  • Environmental impact assessment.

  • Disaster management (flood inundation modeling).

VIII. SYNTHESIS & INTERCONNECTED TOPICS

• Correlation:

  • Rock Type + Structure → Groundwater: Fractured igneous/metamorphic (joints/faults) store water. Porous sedimentary (sandstone) store water. Impervious rocks (clay, unfractured granite) are aquitards/aquicludes. Folds create structural traps (anticlines).

  • Weathering + Rock Strength → Foundation Design: Weathered zone → shallow foundations may be inadequate; need piles to reach sound rock. Shale/Schist require special design due to planes of weakness.

  • Geological Maps/Cross-Sections: Essential tools showing distribution of rocks, structures (strike/dip of beds, faults), and topography. Used to predict subsurface conditions (e.g., "V" of outcrop pattern indicates dip direction of fold).

• Integrated View for Projects: A safe dam site requires massive, unfaulted, low-permeability granite/gneiss foundation (rock type + structure), low seismicity (hazard), no soluble rocks in reservoir (weathering/karst), and adequate construction materials (resource). GIS integrates all these spatial data layers for optimal selection. RS provides initial reconnaissance data (geology, lineaments, land use).