UNIT 2: ENGINEERING GEOLOGY & REMOTE SENSING

Exam-Focused Short Notes | Based on RGPV Past Papers (2022-2025)

1.0 FUNDAMENTALS OF MINERALS AND ROCKS

1.1 Minerals in Engineering Geology

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

• Mode of Formation:

  • Magmatic: From cooling magma (e.g., Olivine).

  • Hydrothermal: From hot aqueous solutions (e.g., Quartz veins).

  • Sedimentary: From precipitation or accumulation (e.g., Calcite in limestone).

  • Metamorphic: From recrystallization under heat/pressure (e.g., Garnet).

• Physical Properties for Identification:

  | Property | Description | Example | | :--- | :--- | :--- | | Color | Unreliable; varies with impurities. | Quartz (clear, white, pink). | | Streak | Color of powdered mineral (on porcelain plate). | Hematite (red-brown streak), regardless of color. | | Luster | Way light reflects from surface. | Metallic (Pyrite), Vitreous (Quartz), Pearly (Mica). | | Hardness | Resistance to scratching (Mohs Scale 1-10). | Talc (1), Gypsum (2), Calcite (3), Fluorite (4), Apatite (5), Orthoclase (6), Quartz (7), Topaz (8), Corundum (9), Diamond (10). | | Cleavage | Breakage along planes of weak atomic bonding. | Mica (1 perfect), Calcite (3 perfect @ 75°), Feldspar (2 perfect @ 90°). | | Fracture | Breakage not along cleavage planes. | Conchoidal (Quartz), Hackly (native metals). | | Crystal Form | External shape of crystal. | Hexagonal (Quartz), Cubic (Halite). | | Specific Gravity | Density relative to water. | Heavy (Galena ~7.5), Light (Gypsum ~2.3). | | Tenacity | Behavior under stress (brittle, malleable, flexible). | Mica (flexible & elastic). | | Magnetism | Attraction to magnet. | Magnetite. |

• Chemical Properties: Solubility (Halite in water), Reaction with Acid (Calcite effervesces with dilute HCl).

• Rock-Forming Minerals & Engineering Significance:

  • Quartz (SiO₂): Hard, resistant, durable. Major constituent of granite, sandstone. Good construction material but can cause abrasive wear on machinery.

  • Feldspar (KAlSi₃O₈ - NaAlSi₃O₈ - CaAl₂Si₂O₈): Common in igneous/metamorphic. Weatherable to clay (kaolin), leading to reduced rock strength.

  • Mica (Muscovite/Biotite): Perfect cleavage → planes of weakness in rock mass (schist, gneiss). Affects slope stability and foundation bearing capacity.

  • Calcite (CaCO₃): Soft, soluble in acid. Forms limestone/marble. Susceptible to chemical weathering (karst), causing sinkholes and leakage in dams.

  • Olivine ((Mg,Fe)₂SiO₄): Mg-Fe silicate. Common in ultrabasic rocks (peridotite). High temperature stability, but alters easily (serpentinization) → weakness.

[!TIP] Exam Focus: Questions often ask to "explain properties for identification" or "significance of specific minerals." Always link property to engineering behavior (e.g., mica's cleavage → slope failure).

1.2 Petrology

• Definition: Branch of geology that studies the origin, occurrence, structure, and classification of rocks.

• Subdivisions:

  • Igneous Petrology: Study of rocks from solidified magma/lava.

  • Sedimentary Petrology: Study of rocks from weathered/transported/deposited/ lithified sediments.

  • Metamorphic Petrology: Study of rocks transformed by heat, pressure, and fluids.

• Importance in Engineering Geology: Determines rock strength, durability, permeability, and weathering susceptibility—critical for foundation, slope, and tunnel design.

1.3 Igneous Rocks

• Classification:

  • By Composition:

    • Acidic/Felsic: >66% SiO₂ (Granite, Rhyolite). Light color, low density, high quartz/feldspar.

    • Basic/Mafic: 52-66% SiO₂ (Diorite, Gabbro, Basalt). Dark color, high density, high Fe-Mg minerals (pyroxene, olivine).

    • Ultrabasic: <52% SiO₂ (Peridotite). Very high Fe-Mg, low Si.

  • By Texture (grain size & arrangement):

    • Phaneritic: Coarse-grained, visible crystals (intrusive/plutonic). e.g., Granite.

    • Aphanitic: Fine-grained, crystals not visible (extrusive/volcanic). e.g., Basalt.

    • Porphyritic: Large crystals (phenocrysts) in fine matrix. Indicates two-stage cooling.

    • Glassy: No crystals (rapid cooling). e.g., Obsidian.

    • Pyroclastic: Fragmental (volcanic explosion). e.g., Tuff, Agglomerate.

• Engineering Properties & Description:

  • Granite (Phaneritic, Acidic): High strength, low porosity, excellent durability. Good for foundations, aggregates, monuments. Weakness: Columnar joints can cause slope instability.

  • Basalt (Aphanitic/Phaneritic, Basic): Very high strength/density, good abrasion resistance. Excellent for road aggregates/dam foundations. Weakness: Can be vesicular (gas bubbles) → permeability; columnar joints.

1.4 Sedimentary Rocks

• Formation Process (Lithification/Diagenesis):

  1. Weathering: Breakdown of parent rock.

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

  3. Deposition: Sediment settles in basin.

  4. Lithification: Compaction + Cementation (calcite, silica, iron oxides) → solid rock.

• Classification by Origin:

  • Clastic: Fragments of pre-existing rocks (Sandstone, Shale, Conglomerate).

  • Chemical: Precipitated from solution (Limestone, Rock salt, Gypsum).

  • Organic: Accumulation of organic debris (Coal, Chalk).

• Texture & Structure:

  • Grain Size: Udden-Wentworth scale (boulder → clay).

  • Sorting: Uniformity of grain size (well-sorted = good permeability).

  • Bedding: Primary layering (most important structure).

  • Cross-bedding: Inclined layers → paleocurrent direction.

  • Ripple Marks: Indicates water movement.

• Engineering Properties & Description:

  • Limestone (Chemical/Organic): Variable (dense massive vs. porous). Reacts with acid. Forms karst (sinkholes, caves) → major foundation/leakage hazard. Good when dense.

  • Sandstone (Clastic): Strength depends on cement. Well-cemented = good foundation/aggregate; poorly cemented = weak, friable, prone to erosion.

  • Shale (Clastic): Very fine-grained, fissile (splits along bedding). Low strength, high swelling potential (when wet), poor foundation material. Major slope stability problem.

1.5 Metamorphic Rocks

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

• Texture & Structure:

  • Foliated: Minerals aligned in planes/bands.

    • Slate: Very fine, slaty cleavage (from shale). Used for roofing, flooring.

    • Schist: Medium-coarse, pronounced schistosity (platy minerals like mica). Major weakness plane.

    • Gneiss: Coarse, banded (alternating light/dark mineral layers). Strong but anisotropic.

  • Non-Foliated: No planar alignment.

    • Marble: Recrystallized calcite/dolomite (from limestone). Good for dimension stone, but soluble/effervescent.

    • Quartzite: Recrystallized quartz (from sandstone). Very high hardness & strength, excellent for aggregates, abrasion-resistant.

• Engineering Properties & Description:

  • Marble: Medium-high strength, polishable. Susceptible to acid rain and chemical weathering.

  • Quartzite: Extremely hard, strong, durable, low porosity. Excellent for heavy-duty foundations and railway ballast.

  • Slate: Good cleavage → easy splitting, but weak perpendicular to cleavage. Used for roofing, but can delaminate.

  • Schist: Very anisotropic strength. Strength along foliation >> across. Major concern for foundations/slopes on inclined foliation.

  • Gneiss: Generally strong and massive, but banding can create weakness zones.

1.6 The Rock Cycle

• Interrelationship: No rock type is permanent. Processes of weathering, erosion, deposition, lithification, melting, metamorphism, and cooling continuously transform rocks.

• Engineering Relevance: Understanding the cycle predicts potential rock quality (e.g., weathered granite → residual soil) and geological history (e.g., folded metamorphic schist indicates tectonic forces).

2.0 STRUCTURAL GEOLOGY AND GEOLOGICAL STRUCTURES

2.1 Orientation of Rock Bodies

• Outcrop: The part of a rock body visible at the Earth's surface. Factors: Topography, vegetation, soil cover, dip of beds.

• Strike: The compass direction of a horizontal line on an inclined plane (e.g., N30°E). Measured with a compass.

• Dip: The angle of inclination of a plane measured perpendicular to the strike from the horizontal (0°-90°). Dip Direction is the compass direction of maximum slope.

  • True Dip: Maximum dip angle (perpendicular to strike).

  • Apparent Dip: Dip measured in any direction other than true dip. Always < True Dip.

  • Formula: $$\displaystyle \tan(\text{Apparent Dip}) = \tan(\text{True Dip}) \times \sin(\theta) $$

  where $\theta$ = angle between apparent dip direction and strike direction.

[!TIP] Common Pitfall: Students confuse dip direction with strike. Remember: Strike is horizontal line; Dip is vertical angle down the steepest slope. Always draw a cross-section sketch.

• Engineering Importance:

  • Slope Stability: Dip direction relative to slope face is critical (planar failure if dip ≈ slope angle & into slope).

  • Tunneling: Tunnel alignment parallel to strike often avoids intersecting dipping beds.

  • Foundations: Strip foundations should be placed parallel to strike to minimize differential settlement on dipping beds.

  • Dams: Reservoir leakage along dipping permeable strata.

2.2 Folds

• Parts of a Fold:

  DiagramCANVAS: A simple anticline/syncline cross-section labeled: Limbs (two sides), Hinge (line of max curvature), Axial Plane (plane dividing fold symmetrically), Crest (top of anticline), Trough (bottom of syncline), Axis (line along hinge).

• Classification:

  1. By Mode of Occurrence:

     • Anticline: Arch, oldest rocks in core.

     • Syncline: Trough, youngest rocks in core.

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

     • Dome: Circular/elliptical anticline (all sides dip away).

     • Basin: Circular/elliptical syncline (all sides dip inwards).

  2. By Shape of Folded Layers (Interlimb Angle):

     • Gentle (<70°), Open (70°-30°), Tight (30°-0°), Overturned (<0°, one limb tilted beyond vertical), Isoclinal (limbs parallel, <10°).

  3. By Attitude of Axial Plane: Upright, Inclined, Overturned, Recumbent (axial plane nearly horizontal).

• Engineering Significance:

  • Anticlines: Often good oil/gas traps. Can cause arching effect → uplift stresses on foundations.

  • Synclines: May collect groundwater. Can be zones of weakness if filled with soft sediments.

  • Tight/Overturned Folds: Intense fracturing → high permeability/weakness.

  • Domes/Basins: Complex structural patterns; require detailed mapping for foundations/tunnels.

2.3 Joints

• Definition: A fracture along which there has been no significant displacement.

• Origin: Tectonic (stress), Cooling (columnar in basalt), Exfoliation (sheeting in granite).

• Classification:

  • By Origin: Tectonic, Non-tectonic (cooling, unloading).

  • By Orientation: Systematic (parallel sets), Random.

  • By Pattern: Columnar (hexagonal, cooling), Mural (sheet-like, parallel to surface, from exfoliation/unloading).

• Mural Joints: Major joints parallel to the ground surface, formed by expansion due to erosion/ unloading (exfoliation). Engineering Significance: Control the depth of weathering and stability of rock slopes. Can lead to toppling failures in slopes.

• General Engineering Importance:

  • Rock Mass Strength: Joints divide rock into blocks → reduce strength drastically.

  • Permeability: Joints are primary pathways for water → seepage, piping, foundation leakage.

  • Slope Stability: Provide release surfaces for planar/wedge failures.

  • Tunneling: Cause rock bursts, inflows, overbreak.

2.4 Faults

• Definition: A fracture with significant displacement.

• Components:

  • Fault Plane: Surface of rupture.

  • Hanging Wall: Block above fault plane (dip-slip faults).

  • Footwall: Block below fault plane.

  • Fault Scarp: Steep slope from displacement at surface.

  • Throw: Vertical displacement.

  • Heave: Horizontal displacement perpendicular to strike.

  • Slip: Total displacement vector.

• Classification by Relative Movement:

  DiagramCANVAS: Three simple cross-sections: 1) Normal Fault (hanging wall moves down, crust extending). 2) Reverse/Thrust Fault (hanging wall moves up, crust compressing; thrust has low angle <45°). 3) Strike-Slip Fault (horizontal movement; right-lateral if opposite side moves right).

  • Strike-Slip: Horizontal movement.

    • Right-Lateral (Dextral): Opposite side moves to right.

    • Left-Lateral (Sinistral): Opposite side moves to left.

  • Dip-Slip: Vertical component.

    • Normal Fault: Hanging wall down (tensional regime).

    • Reverse Fault: Hanging wall up (compressional regime). Thrust Fault is a low-angle (<45°) reverse fault.

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

• Recognition Features: Fault breccia/cataclasite (crushed rock), slickensides (polished/striated fault plane), fault gouge (clay), offset markers (dikes, strata), linear valleys/escarpments (lineaments).

• Engineering Significance:

  • Seismic Hazard: Active faults = earthquake risk. No critical structures (dams, nuclear plants) within fault rupture zones.

  • Foundation Weakness: Fault zones are crushed, weak, permeable → differential settlement, leakage.

  • Groundwater: Faults can be barriers (impermeable gouge) or channels (brecciated zone).

  • Slope Stability: Fault scarps are prone to landslides.

2.5 Unconformities

• Definition: A surface of non-deposition or erosion that separates younger from older rocks, representing a gap in the geological record.

• Types:

  DiagramCANVAS: Four cross-sections: 1) Angular Unconformity (tilted/folded older rocks overlain by flat-lying younger). 2) Disconformity (parallel layers, but with erosion surface/soil horizon). 3) Nonconformity (sedimentary overlying igneous/metamorphic). 4) Paraconformity (parallel layers, no obvious erosion, but time gap).

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

  • Disconformity: Parallel sedimentary layers, but with evidence of erosion (channel incisions, fossil gap).

  • Nonconformity: Sedimentary rocks overlying eroded igneous/metamorphic basement.

  • Paraconformity: Parallel layers, no obvious erosion surface, but time gap from fossil record.

• Engineering Importance:

  • Weak Zones: Unconformity surfaces are often weathered, fractured, and have low shear strength.

  • Landslide Potential: Especially angular unconformities where strong rock overlies weak weathered rock.

  • Foundation Problems: Differential settlement across unconformity.

  • Groundwater: Can act as aquiclude (impermeable) or aquifer (if weathered/permeable).

  • Leakage Paths: Under dams/reservoirs if permeable beds truncated by unconformity.

3.0 GEOLOGICAL PROCESSES AND THEIR ENGINEERING SIGNIFICANCE

3.1 Weathering

• Definition: In-situ disintegration/decomposition of rocks due to atmospheric agents. Distinguished from Erosion (removal/transport by water, wind, ice).

• Factors Controlling Weathering:

  • Climate: Most important (temperature, rainfall). Chemical weathering dominant in warm/wet; physical in cold/dry.

  • Rock Composition/Structure: Mineralogy (calcite vs. quartz), grain size, joints, faults.

  • Topography: Slope affects drainage, exposure.

  • Time: Duration of exposure.

  • Biological Activity: Plant roots, burrowing animals, organic acids.

• Types:

  | Type | Process | Example | Engineering Impact | | :--- | :--- | :--- | :--- | | Physical | Mechanical breakdown without chemical change. | Freeze-thaw (frost wedging), Thermal expansion (exfoliation), Salt crystallization, Unloading (exfoliation joints). | Creates loose, unstable material (scree). Increases porosity/permeability. Weakens rock slopes. | | Chemical | Chemical alteration of minerals. | Solution (halite, gypsum), Hydrolysis (feldspar → clay), Hydration (anhydrite → gypsum, volume increase), Oxidation (iron minerals → rust), Carbonation (calcite dissolution by CO₂). | Permanently alters mineral structure → severe strength loss. Forms clay (swelling). Karst development. | | Biological | Organic activity. | Root wedging, Burrowing, Organic acid secretion. | Accelerates both physical & chemical weathering. Localized but intense weakening. |

• Effect of Weathering on Rock Strength:

  • Massive decrease in uniaxial compressive strength (UCS) and shear strength.

  • Increase in porosity and permeability.

  • Disintegration from intact rock to soil (regolith).

  • Depth of weathering profile is critical for foundation depth.

• Impact on Structures:

  • Foundations: Settlement on weathered rock/soil.

  • Slopes: Weathered zones are failure surfaces.

  • Dams/Tunnels: Leakage through weathered zones; need for grouting.

  • Roads/Canals: Heave from swelling clays (from hydrolysis).

  • Aggregates: Weathered rock produces poor-quality, friable aggregate.

3.2 Groundwater

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

• Occurrence:

  • Zone of Aeration (Vadose): Pores partly air/water.

  • Water Table: Upper surface of saturation.

  • Zone of Saturation: All pores filled with water.

  • Perched Water Table: Local saturated zone above main water table due to impermeable layer.

• Properties Controlling Water-Bearing Capacity:

  | Rock Type | Primary Control | Key Rocks & Behavior | | :--- | :--- | :--- | | Igneous | Secondary Porosity (fractures, vesicles). | Granite: Low primary porosity, water in fractures/joints. Basalt: Vesicular top → aquifer; columnar joints → pathways. | | Sedimentary | Intergranular Porosity & Permeability. | Sandstone: High porosity/permeability → good aquifer. Limestone: Variable; fractures/karst → high secondary permeability. Shale: Low porosity/permeability → aquiclude. | | Metamorphic | Fracturing & Foliation. | Quartzite: Low unless fractured. Slate/Schist: Foliation planes can be zones of weakness/permeability. |

• Engineering Importance:

  • Seepage & Piping: Under dams, foundations, causing failure.

  • Slope Stability: Pore water pressure reduces effective stress → decreases shear strength (critical in landslides).

  • Foundation Problems: Buoyancy, softening of clays, quicksand conditions.

  • Construction Dewatering: Essential for open excavations, tunneling.

  • Water Resource: Aquifers for supply.

3.3 Earthquakes

• Definition: Sudden release of energy causing ground shaking due to rupture along a fault.

• Causes: Tectonic (plate boundaries), Volcanic, Reservoir-induced (Ris), Collapse (mining).

• Key Terms:

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

  • Epicenter: Point on surface directly above focus.

  • Magnitude: Energy released at source. Logarithmic (Richter $$\displaystyle M_L $$, Moment Magnitude $$\displaystyle M_w $$). Single value for earthquake.

  • Intensity: Shaking and damage at a location. Decreases with distance from epicenter. Measured by Mercalli (I-XII) or MSK scales. Varies with location.

[!TIP] Exam Distinction: Magnitude is about the earthquake's size (instrumental). Intensity is about the effects at a place (subjective damage). A shallow, large-magnitude quake near a city = high intensity.

• Effects on Structures: Ground shaking (inertial forces), surface rupture, liquefaction, landslides, tsunamis, fires.

3.4 Fluvial Processes (Geological Work of Rivers)

• Processes: Erosion (hydraulic action, abrasion, solution), Transportation (traction, saltation, suspension, solution), Deposition (when competence/capacity decreases).

• Depositional Landforms:

  | Landform | Process | Engineering Problem | | :--- | :--- | :--- | | Alluvial Fan | Deposition at mountain front. | Unconsolidated, variable, prone to flooding/channel shifts. Poor foundation. | | Floodplain | Overbank deposition. | High water table, soft soils, flood risk. | | Natural Levee | Coarse sediments deposited near channel. | Better foundation than floodplain, but still water issues. | | Point Bar | Deposition on inside of meander bend. | Unstable, shifting river banks. | | Oxbow Lake | Cut-off meander. | Filled with soft sediments. | | Delta | Deposition at river mouth. | Very soft, compressible, high liquefaction potential. |

• Engineering Problems: Bank erosion (undermines structures), Siltation (reduces reservoir capacity), Flooding.

3.5 Other Exogenic Processes (Brief)

• Volcanoes:

  • Types: Shield (fluid basalt), Composite/Stratovolcano (explosive, viscous andesite/rhyolite), Cinder cone.

  • Hazards: Lava flows (destroy property), Pyroclastics (ash, nuées ardentes - fast, hot, deadly), Lahars (volcanic mudflows), Volcanic gases.

• Sea and Oceans (Coastal Processes):

  • Erosion: Hydraulic action, abrasion, solution.

  • Deposition: Beaches, spits, bars.

  • Landforms: Cliffs, wave-cut platforms, sea arches, sea stacks, beaches, tidal flats.

  • Engineering Problems: Coastal erosion (undermining structures), siltation of harbors, saltwater intrusion.

4.0 ENGINEERING GEOLOGY APPLICATIONS: SITE INVESTIGATION

4.1 Dams

• Definition: Barrier across watercourse for storage (reservoir), control, or diversion.

• Purposes: Water supply, Irrigation, Hydroelectricity, Flood control, Recreation.

• Geological Investigations for Site Selection:

  DiagramCANVAS: A simple dam cross-section showing: 1) Foundation: Must be competent, impermeable rock (granite, quartzite), no faults/folds/joints. 2) Reservoir Basin: Must be impermeable (clay/shale core or groutable rock), minimal karst. 3) Alignment: Geology along dam axis and spillway must be stable. 4) Materials: Nearby sources of sand, gravel, clay for concrete/embankment.

  1. Foundation: Impermeable, strong, unweathered rock (Granite, Quartzite, Basalt). Must have no major faults, folds, or open joints. Depth to sound rock.

  2. Reservoir Basin & Rim: Geology must prevent leakage (through faults, karst, permeable strata). Sedimentation rate assessment.

  3. Dam Axis & Spillway Alignment: Must avoid geological structures. Spillway needs erosion-resistant rock.

  4. Construction Materials: Availability of aggregates (hard, durable rock), clay for core (low permeability, low swell).

• Case Studies of Failures (Examples):

  • St. Francis Dam, USA (1928): Failure due to weak, foliated schist foundation with a fault. Piping along contact.

  • Malpasset Dam, France (1959): Fault zone in gneiss foundation not properly grouted → sliding failure.

  • Teton Dam, USA (1976): Eocene volcanic rocks with permeable zones and faults in foundation. Piping through jointed rock.

4.2 Tunnels

• Site Selection Factors:

  • Rock Mass Quality: RMR/Q-system. Prefer massive, strong, low-jointed rock.

  • Groundwater: Low inflow. Faults/zones predict high water.

  • Geological Structures: Avoid faults, folds (especially tight), major joint sets. Alignment parallel to strike often favorable.

  • Overburden: Depth affects stress (rock bursts in hard rock, squeezing in weak rock).

  • Ground Conditions: Anticipate rock bursts (hard, brittle, high stress), squeezing (weak, plastic rock under pressure), swelling (shale, anhydrite), inflows (faults, karst).

• Engineering Problems During Tunneling: As above. Requires detailed geological mapping and probing ahead (TBM, pilot tunnel).

4.3 Canals

• Geological Considerations:

  • Alignment: Through stable, low-permeability materials (clay, unfractured rock). Avoid faults, steep slopes, landslide zones.

  • Seepage Control: Avoid permeable strata (sand, gravel, fractured rock). Use cut-off walls/grouting if unavoidable.

  • Slope Stability: Canal banks must be stable. Avoid seepage-prone, weak, or highly weathered materials.

  • Construction Materials: Source for embankments (clay) and lining (concrete aggregates).

4.4 Importance of Geology in Civil Engineering (General)

• Role: Provides 3D understanding of subsurface for safe, economical design.

• Applications:

  • Site Selection: Avoid hazards (faults, landslides, floodplains, karst).

  • Foundation Design: Determines type (shallow vs. deep), bearing capacity, settlement.

  • Construction Materials: Source identification/quality assessment (aggregates, clay, stone).

  • Slope Stability: Identifies weak planes (joints, foliation, faults), weathering depth.

  • Groundwater Management: Predicts seepage, dewatering needs, water pressure.

  • Natural Hazard Mitigation: Earthquake, landslide, flood risk assessment.

• Examples for Key Rock Types:

  • Granite: Excellent foundation/aggregate if massive. Problem: Joints, weathering.

  • Quartzite: Excellent for foundations/ballast. Very hard → drilling/cutting costs.

  • Shale: Poor foundation. Swells when wet, low strength. Avoid or remove/replace.

  • Slate: Good for roofing, but weak perpendicular to cleavage → foundation issues if foliation dips.

  • Schist: Highly anisotropic. Strength varies with foliation orientation. Major slope/foundation concern.

5.0 REMOTE SENSING AND GIS IN ENGINEERING GEOLOGY

5.1 Remote Sensing Fundamentals

• Definition: Science & art of acquiring information about objects/areas without physical contact, using sensors on platforms.

• Components: Energy Source (Sun/passive, own source/active) → Interaction with Atmosphere/Target → Sensor (detects & records energy) → Platform (satellite, aircraft, drone) → Data (analog/digital) → Processing → Interpretation/Application.

• Elements:

  • Energy Source: Sun (optical), own source (radar, LiDAR).

  • Sensor: Passive (detects reflected sunlight, e.g., Landsat) vs. Active (emits & detects own energy, e.g., Radar, LiDAR). Multispectral (few broad bands) vs. Hyperspectral (many narrow bands).

  • Platform: Satellite (Landsat, Sentinel), Aerial (aircraft), Ground-based.

  • Data: Digital (pixels with DN values).

  • Interpretation: Visual (analog) or Digital (using software/classification algorithms).

5.2 Remote Sensing Techniques

• Visual Interpretation Elements: Use of tone/color, texture, pattern, shape, size, shadow, association to identify features.

• Types of Remote Sensing:

  • Optical: Visible, NIR, SWIR. Best for mapping lithology, land use, vegetation, structures (lineaments).

  • Thermal: Infrared (heat). Detects geothermal anomalies, groundwater discharge.

  • Microwave (Radar): Active, penetrates clouds/clouds. Sensitive to surface roughness, moisture, topography (InSAR for deformation).

  • LiDAR (Light Detection and Ranging): Active laser. Generates high-resolution DEMs/DSMs. Excellent for terrain analysis, landslide mapping, fault scarp detection.

5.3 Practical Applications in Engineering Geology

1. Landslide Hazard Zonation & Monitoring: Identify old slides, map scarps/transverse cracks, monitor movement (InSAR, LiDAR).

2. Groundwater Potential Mapping: Lineament mapping (fractures), drainage analysis, vegetation indices (moisture), lithology mapping.

3. Geomorphological Mapping & Terrain Analysis: DEMs from LiDAR/SAR for slope, aspect, drainage, watershed delineation.

4. Identification of Geological Structures: Lineament analysis (faults, joints, fold axes) from satellite imagery (especially SAR for linear features). Mapping folds, faults, unconformities.

5. Environmental Impact Assessment & Reclamation: Land use/land cover change, mine reclamation monitoring, pollution detection.

6. Site Suitability Analysis: Overlay of slope, geology, drainage, land use for infrastructure planning (GIS+RS).

5.4 Geographic Information System (GIS)

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

• Components: Hardware, Software (ArcGIS, QGIS), Data (spatial & attribute), People, Procedures.

• Use in Resource Mapping:

  • Integration: Combine layers (geology, soil, hydrology, land use, roads, slope).

  • Overlay Analysis: Boolean logic (AND, OR) to find suitable areas. e.g., (Slope < 15°) AND (Geology = Granite/Basalt) AND (Distance to Road < 5km) for quarry site.

  • Thematic Maps & Suitability Maps: Create maps rating areas from highly suitable to unsuitable.

• Use in Engineering Geology:

  • Engineering Geological Mapping: Standardize and store map data.

  • Hazard & Risk Assessment: Landslide zonation (weighted overlay of slope, geology, rainfall, land use), flood mapping.

  • Spatial Data Management: Centralized database for borehole logs, lab tests, mapping.

  • Route Alignment: Optimal path for roads/canals considering multiple geological constraints.

[!TIP] Exam Link: Questions often ask "practical applications of RS" or "use of GIS in resource mapping." List specific examples (landslide, groundwater, dam site) and mention overlay analysis for GIS.