UNIT 4: ENGINEERING GEOLOGY & REMOTE SENSING (RGPV EXAM-FOCUS)

1. Introduction to Geology & its Branches

Geology: Scientific study of the Earth's physical structure, substance, history, and processes (lithosphere, hydrosphere, atmosphere).

Branches:

Importance in Civil Engineering:

• Foundation design: Rock/soil bearing capacity.

• Quarrying: Source of construction materials (aggregates, limestone).

• Hazard assessment: Landslides, earthquakes, liquefaction.

• Water resources: Groundwater location, dam sites.

• Tunnels & slopes: Stability analysis based on rock structure.

Structure of Earth (with sketch):

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

• Mantle: Upper (rigid, lithosphere) & Lower (plastic, asthenosphere).

• Core: Outer (liquid, Fe-Ni) & Inner (solid, Fe-Ni).

Rock Cycle: Continuous transformation among igneous → sedimentary → metamorphic → igneous via processes like melting, cooling, erosion, burial, and metamorphism.

2. Mineralogy

Mineral: Naturally occurring, inorganic, homogeneous solid with definite chemical composition and ordered atomic arrangement.

Physical Properties for Identification:

1. Color: Often unreliable (variable impurities).

2. Streak: Color of powdered mineral (more reliable). Test: rub on unglazed porcelain.

3. Luster: Way surface reflects light (metallic, vitreous, earthy, etc.).

4. Hardness: Resistance to scratching (Mohs Scale: 1=Talc to 10=Diamond).

5. Cleavage: Tendency to break along smooth planes (related to crystal structure).

6. Fracture: Breakage pattern (conchoidal, hackly, uneven).

7. Crystal Form: External shape (e.g., cubic for halite).

8. Specific Gravity: Density relative to water (dense minerals >3.5).

9. Tenacity: Cohesion (brittle, malleable, flexible).

Chemical Properties: Solubility, reaction to acid (calcite effervesces), magnetism.

Rock-Forming (Essential) Minerals: Quartz, Feldspars, Mica (biotite/muscovite), Amphibole, Pyroxene, Olivine, Calcite, Dolomite, Clay minerals.

Crystallography:

• Elements of Crystal: Faces, edges, corners.

• 7 Crystal Systems: Cubic, Tetragonal, Hexagonal, Trigonal, Orthorhombic, Monoclinic, Triclinic.

Mode of Formation:

• Igneous: Crystallization from melt/magma.

• Sedimentary: Precipitation from solution, accumulation, or alteration.

• Metamorphic: Recrystallization under P-T conditions.

3. Igneous Rocks

Definition & Origin: Formed by solidification of molten magma/lava.

Characteristics:

• Mineral Composition: Felsic (Si-rich, light), Mafic (Mg/Fe-rich, dark), Ultramafic.

• Texture: Grain size (phaneritic = coarse, aphanitic = fine, glassy), arrangement.

• Structure: Flow bands, vesicles, pillows (submarine).

Classification:

Megascopic Study:

• Granite: Light-colored, coarse-grained (visible quartz, feldspar, mica), equigranular.

• Basalt: Dark-colored, fine-grained, often vesicular, may show columnar jointing.

Engineering Properties of Granite:

• High strength ( UCS 100-250 MPa).

• Low porosity & permeability → excellent foundation, aggregate.

• High durability, resistant to weathering.

• Massive, jointed → may require grouting.

Engineering Significance:

• Positive: Load-bearing capacity, dimension stone, aggregate.

• Negative: Jointed masses → slope instability, seepage.

4. Sedimentary Rocks

Formation Process (with sketch):

1. Weathering & Erosion: Breakdown of pre-existing rocks.

2. Transportation: By water, wind, ice, gravity (size sorting).

3. Deposition: Sediment settles (energy decrease).

4. Lithification: Compaction + cementation → solid rock.

Characteristics:

• Layered (stratified) structure.

• Fossils common.

• Porosity & permeability often high (good aquifers).

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

Common Types:

• Limestone: Calcite (CaCO₃), fossiliferous, reacts with HCl.

• Sandstone: Quartz grains cemented (silica/calcite/iron oxide).

• Shale: Clay/silt-sized particles, fissile (splits along layers).

Megascopic Study:

• Limestone: Light-colored (white/gray), may be crystalline/fossiliferous, hard but reacts to acid.

• Sandstone: Medium-grained, feels gritty, colors vary (red, brown, tan).

Engineering Properties of Shale:

• Low to medium strength ( UCS 10-100 MPa).

• High porosity & water absorption → swelling, weakening when wet.

• Fissile → prone to slope failure along bedding.

• Poor foundation material unless buried deep.

Engineering Significance:

• Limestone/Sandstone: Good foundation/aggregate if unweathered.

• Shale: Problematic – swelling, low shear strength, erosion gullies.

5. Metamorphic Rocks

Definition: Pre-existing rocks (protolith) transformed by heat, pressure, and chemically active fluids without melting.

Metamorphic Agents:

• Heat: Recrystallization (contact metamorphism).

• Pressure: Directed stress → foliation (regional metamorphism).

• Fluids: Enhance ion mobility, new mineral growth.

Texture & Structure:

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

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

Classification:

Common Types:

• Slate: Fine-grained, slaty cleavage (splits into thin sheets), from shale.

• Schist: Medium-coarse, schistosity (visible mica flakes).

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

• Quartzite: Very hard, interlocking quartz grains, from sandstone.

• Marble: Crystalline, reacts with acid, from limestone.

Megascopic Study:

• Gneiss: Distinctive banding, coarse-grained.

• Slate: Dull, smooth, breaks into thin, flat slabs.

Engineering Properties:

Engineering Significance:

• Quartzite: Excellent aggregate, road metal, dimension stone.

• Slate: Roofing, flooring (but check cleavage orientation).

• Schist: Problematic – major discontinuity, slope failures.

6. Structural Geology

Orientation of Rock Bodies:

• Outcrop: Visible exposure of rock at surface.

• Strike (⦁): Direction of line formed by intersection of plane with horizontal surface.

• Dip (↘): Angle of inclination measured perpendicular to strike, from horizontal (0-90°). Dip direction is downslope.

Folds:

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

• Classification by Mode of Occurrence:

  • Anticline: Arch, older rocks in core.

  • Syncline: Trough, younger rocks in core.

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

• Classification by Shape:

  • Symmetrical, Asymmetrical, Overturned, Recumbent (limbs nearly horizontal).

Engineering Significance of Folds:

• Anticlines: Often good for oil/gas traps; may cause tensile stress → fractures → seepage.

• Synclines: May accumulate sediments; water-bearing.

• Tight/Overturned folds: Complex stress, weak zones along axial planes.

Joints:

• Definition: Fracture without displacement.

• Types:

  • Mural Joints: Vertical, wall-like (columnar joints).

  • Columnar Joints: Hexagonal columns (basalt cooling).

  • Sheet Joints: Sub-horizontal, exfoliation (granite).

• Case Studies: Joints control groundwater flow, slope failures, blasting patterns in quarries.

Faults:

• Definition: Fracture with displacement.

• Components: Fault Plane, Hanging Wall, Footwall, Fault Scarp, Throw (vertical), Heave (horizontal).

• Classification:

  • Normal Fault: Hanging wall down (extensional).

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

  • Strike-Slip Fault: Horizontal displacement (San Andreas type).

Case Studies of Fault Hazards:

• Surface rupture: Destroys structures directly (e.g., 1999 İzmit earthquake).

• Seismic hazard: Ground shaking, liquefaction.

• Seepage: Faults act as conduits/barriers for groundwater.

Unconformities:

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

• Types:

  • Angular Unconformity: Tilted older rocks overlain by flat-lying younger.

  • Disconformity: Parallel layers with erosion gap.

  • Nonconformity: Sedimentary over igneous/metamorphic.

  • Paraconformity: No obvious erosion, time gap.

• Importance: Indicates missing geological time, potential weak planes, groundwater barriers.

Dome & Basin:

• Dome: Upwarped, strata dip away in all directions (older core).

• Basin: Downwarped, strata dip toward center (younger core).

• Significance: Structural traps for hydrocarbons; dome = good for foundations (radial drainage).

7. Geomorphology & Surface Processes

Rivers:

• Geological Work:

  • Erosion: Hydraulic action, abrasion, solution.

  • Transportation: Traction, saltation, suspension, solution.

  • Deposition: When energy decreases.

• Depositional Landforms:

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

  • Delta: At river mouth (distributaries).

  • Floodplain & Levees: Natural embankments from overbank deposition.

  • Point Bar: Inner bend of meander (sand/gravel).

Weathering:

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

• Types:

  • Mechanical: Freeze-thaw, thermal expansion, exfoliation, salt crystallization.

  • Chemical: Hydrolysis, oxidation, carbonation, hydration.

• Factors: Climate (temp/rainfall), Rock composition/structure, Topography, Time, Organisms.

• Effect on Engineering Properties:

  • Strength ↓: Disintegration → reduced bearing capacity.

  • Volume change: Clay minerals swell → foundation heave.

  • Slope stability: Weathered zones → failure surfaces.

  • Durability: Aggregates degrade in concrete.

Groundwater:

• Formation: Infiltration → percolation → saturation zone.

• Key Terms:

  • Water Table: Upper surface of saturation zone.

  • Aquifer: Porous/permeable layer storing/yielding water.

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

• Properties Controlling Water-Bearing Capacity:

  • Porosity (n): $$\displaystyle n = \frac{V_v}{V_t} \times 100\% $$ (V_v = void volume, V_t = total volume).

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

  • Fracture Density: Critical in igneous/metamorphic rocks.

• Variation by Rock Type:

  | Rock Type | Porosity | Permeability | Typical Aquifer? | |-----------------|-------------------|------------------------|----------------------| | Igneous (massive) | Very Low (0-1%) | Very Low (fracture-controlled) | Only if fractured | | Sedimentary | Moderate-High (5-30%) | Moderate-High (sand/gravel) | Excellent (sandstone, limestone) | | Metamorphic | Low (0-5%) | Low (foliation/fracture-controlled) | Only if fractured |

• Importance: Foundation seepage, slope stability, water supply, construction dewatering.

Earthquakes:

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

• Epicenter: Point on surface directly above focus.

• Magnitude: Energy released (Richter scale, moment magnitude). Logarithmic.

• Intensity: Effects at location (Mercalli scale, I-XII). Varies with distance, geology.

• Causes: Tectonic (plate boundaries), volcanic, reservoir-induced, mining.

Volcanoes:

• Types & Hazards:

  • Shield: Fluid basalt, gentle slopes, less explosive.

  • Composite/Stratovolcano: Explosive (andesite/rhyolite), pyroclastic flows, lahars.

  • Cinder Cone: Small, short-lived.

• Hazards: Lava flows, ash fall (roof collapse), pyroclastic flows (extremely hot), lahars (mudflows), volcanic gases.

Sea & Oceans (Coastal Processes):

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

• Depositional: Beaches, spits, bars, barrier islands, lagoons.

• Importance: Coastal erosion threatens structures; sediment transport affects ports.

8. Engineering Geology Applications

Dam Engineering:

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

• Geological Investigations:

  1. Foundation: Sound rock (granite/gneiss), no faults/weak zones, low permeability.

  2. Reservoir: No soluble rocks (limestone/dolomite → leakage), no active faults, adequate capacity.

  3. Spillway/Tunnels: Stable slopes, no landslide zones.

  4. Seismic: Distance from active faults, foundation rock response.

• Case Studies of Failures:

  • Malpasset Dam (France, 1959): Fault in gneiss foundation, excessive water pressure → breach.

  • Teton Dam (USA, 1976): Built on loess/sand with basaltic core, internal erosion (piping).

Tunnel Engineering:

• Site Selection Factors:

  • Rock Mass Quality: RMR/Q-system (joints, strength, groundwater).

  • Geological Structures: Avoid faults, shear zones, major folds.

  • Groundwater: Low inflow preferred; hydrogeological mapping.

  • Overburden: Depth affects stress, squeezing/swelling conditions.

  • Alignment: Minimize crossing of weak zones.

Canal Engineering:

• Selection Steps:

  1. Alignment: Short, gentle curves, stable slopes.

  2. Geology: Avoid landslides, fault zones, expansive soils.

  3. Slope: Stable cut/fill slopes (consider bedding/foliation).

  4. Soil: Low permeability (clay linings), low shrink-swell.

  5. Water Availability: Source reliability, sedimentation.

Rock Properties for Engineering (Description & Properties):

Effect of Weathering on Structures:

• Foundations: Reduced bearing capacity, settlement (especially in clay-rich weathered rock).

• Slopes: Weathered zones become failure surfaces (landslides).

• Infrastructure: Road cuts in weathered rock degrade; aggregates soften.

• Underground: Increased seepage, squeezing in tunnels.

9. Remote Sensing & GIS in Engineering Geology

Remote Sensing (RS):

• Definition: Acquisition of information about Earth's surface without physical contact, using sensors on platforms (satellites, aircraft).

• Principle: All objects emit/reflect electromagnetic (EM) radiation; sensors detect specific wavelengths.

• Types:

  | Type | Wavelength | Penetration | Use | |----------------|-------------------|---------------------|----------------------------------| | Optical | Visible, NIR | Surface only | Land use, lithology mapping | | Thermal | Mid-IR (heat) | Surface | Heat discharge, groundwater seepage | | Microwave (SAR)| cm to m | All-weather, day/night | Surface deformation, soil moisture | | LiDAR | Laser (near-IR) | Vegetation penetration | High-res DEM, fault scarp mapping |

• Components: Energy Source (Sun/sensor), Atmosphere, Target, Sensor, Processing, Interpretation.

• Elements (Resolution):

  • Spatial: Pixel size (e.g., 30m for Landsat).

  • Spectral: Number/width of bands (multispectral vs hyperspectral).

  • Radiometric: Sensitivity to brightness levels.

  • Temporal: Revisit time (frequency).

• Visual Interpretation Elements: Tone, texture, shape, size, pattern, shadow, association.

Applications in Engineering Geology:

• Site Selection: For dams, roads, urban expansion (slope, geology, land use).

• Landslide Mapping: Identify scarps, tension cracks, displaced material.

• Groundwater Exploration: Lineaments (fractures), vegetation patterns (seepage zones).

• Mineral Exploration: Alteration halos, structural controls.

• Environmental Assessment: Land degradation, pollution, post-disaster mapping.

Geographic Information System (GIS):

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

• Components: Hardware, Software, Data, Procedures, People.

• Use in Resource Mapping & Site Selection:

  • Multi-Criteria Analysis (MCA): Overlay thematic maps (geology, slope, drainage, land use) with assigned weights to find suitable zones.

  • Example for Dam Site: Combine layers: bedrock type, fault buffer zone, slope < 20°, seismicity, land cover → suitability map.

• Integration with RS: RS provides input spatial data (e.g., satellite imagery) for GIS analysis.

[!TIP] Exam Focus: Past papers frequently ask for RS applications and GIS use in site selection. Always link to engineering geology context (e.g., "GIS integrates geological, topographic, and hydrological data to evaluate dam site stability").