STRUCTURAL GEOLOGY

• Structural Geology


  The study of the three-dimensional distribution of rock units with respect to their deformational histories
• Structural Geology


  • The primary goal is to use measurements of present-day rock geometries to uncover information about the history of deformation (strain) in the rocks, and ultimately, to understand the stress field that resulted in the observed strain and geometries
  • This understanding of the dynamics of the stress field can be linked to important events in the geologic past, such as mountain building, rifting, and plate tectonics
• Attitude of Beds


  The orientation or position of rock layers or sedimentary beds in relation to the Earth's surface, including the inclination or dip of the beds and their orientation in terms of strike
• Strike


  The compass direction of a horizontal line on the inclined bed, measured in degrees clockwise from north
• Dip


  The angle of inclination of the bed from the horizontal plane, measured perpendicular to the strike and ranging from 0° (horizontal) to 90° (vertical)
• By combining the strike and dip measurements, geologists can determine the three-dimensional orientation of the beds in the subsurface
• Geologists often create geologic maps to depict the attitude of beds in an area, using symbols and lines to represent the strike and dip of rock units
• Outcrop


  A location where the bedrock or geological formation is visible at the Earth's surface, allowing direct observation and sampling of the bedrock in situ for geologic analysis and creating geologic maps
• Geological Map


  A specialized map that depicts the geological features and formations of a particular area, including the distribution of different rock types, geological structures, and other relevant features
• Types of Geological Maps

  • Bedrock maps
  • Surficial maps
  • Structural maps
  • Mineral maps
  • Geologic hazard maps
• Geological Structures


  • Observing and understanding geological structures helps us to determine the kinds of stresses that have existed within Earth in the past, which is critical to our understanding of plate tectonics, earthquakes, the formation of mountains, metamorphism, and Earth resources
• Fold


  A wavelike bend in layered rock, representing rock strained in a ductile manner, usually under compression
• Parts of Folds


  • Hinge (axis)
  • Axial plane
  • Limb
  • Crest
  • Trough
  • Crest plane
  • Trough plane
• Anticline


  An upward-arching fold
• Syncline


  A downward-arching fold
• Fault


  A fracture or crack in the Earth's crust along which there has been movement of rock masses, occurring when rocks break due to stress or strain and the blocks on either side of the fracture move relative to each other
• Types of Faults


  • Normal faults
  • Reverse faults
  • Strike-slip faults
• Joint


  A break or fracture of natural origin in the continuity of either a layer or body of rock that lacks any visible or measurable movement parallel to the surface (plane) of the fracture
• Genetic Classification of Joints

  • Tensional joint
  • Shear Joint
  • Tectonic joint
• Geometric Classification of Joints

  • Strike joint
  • Dip joint
  • Oblique/diagonal joint
• Importance of Folds, Faults, and Joints in Engineering

  • Influence the behavior and properties of rocks and soil in the subsurface, affecting the stability, strength, and deformation characteristics of the ground
  • Can have a direct impact on the structural integrity of engineered structures like buildings, bridges, and tunnels
  • Can serve as pathways for groundwater flow and impact the migration of contaminants through the subsurface
  • Can control the accumulation, concentration, and accessibility of valuable mineral resources
• Folds, faults, and joints

  • They can affect the structural integrity of engineered structures like buildings, bridges, tunnels, and other infrastructure
  • Proper consideration of them during design and construction is essential to ensure stability and durability
• Faults and joints


  • They can serve as pathways for groundwater flow, influencing water supply and management
  • They can impact the migration of contaminants through the subsurface
  • Understanding their distribution and characteristics is important in assessing and mitigating potential risks associated with groundwater contamination and resource management
• Folds, faults, and joints


  • They can have a significant impact on the extraction and utilization of mineral resources
  • They may control the accumulation, concentration, and accessibility of valuable minerals
  • Knowledge of the structural controls they provide is crucial in identifying and locating economically viable mineral deposits
• Folds, faults, and joints

  • They influence excavation and construction projects
  • They can impact the stability of excavation walls, the design of support systems, and the selection of construction methods
  • Proper assessment and understanding of these structures are necessary to ensure safe and efficient construction operations
• Rock mechanics


  • A branch of geomechanics that focuses on the behavior of rocks under various mechanical and environmental conditions
  • It involves the study of how rocks respond to forces, stresses, and deformations
  • It plays a crucial role in understanding the stability, strength, and behavior of rock masses in engineering and geotechnical applications
• Porosity


  A measure of the void spaces in a material, determined by dividing the volume of voids by the total volume
• Permeability


  • A measure of the ability of a material (such as rocks) to transmit fluids
  • It is related to the number, size, and connections of openings in the rock
• Density


  The measure of mass per unit volume of a rock, providing an indication of the rock's overall compactness
• Strength


  A rock's ability to resist deformation or failure under stress, a critical property for construction materials and stability analysis
• Hardness


  A measure of a rock's resistance to scratching or abrasion, determined by the strength of the chemical bonds within the rock's mineral constituents
• Elasticity


  A rock's ability to deform under stress and return to its original shape once the stress is released, related to the rock's elastic modulus
• Plasticity


  The property of a rock to undergo permanent deformation without fracturing under stress, influenced by factors like temperature, pressure, and mineral composition
• 1. waves (Primary waves)


  Compressional waves that cause particles in the rock to move parallel to the direction of wave propagation, traveling faster than other seismic waves and able to propagate through both solids and fluids
• 1. Waves (Shear Waves)


  Shear waves that cause particles in the rock to move perpendicular to the direction of wave propagation, propagating slower than P-waves and only able to travel through solid materials
• Factors influencing wave velocity

  • Rock type and composition
  • Porosity and saturation
  • Degree of saturation
  • Rock fabric and anisotropy
  • Stress and confining pressure
  • Temperature
  • Frequency and wave type
• Static modulus of elasticity

  Represents the rock's stiffness under static or slowly applied loads, measuring the ratio of stress to strain within the elastic deformation range
• Dynamic modulus of elasticity


  Represents the rock's stiffness under dynamic or rapidly applied loads, measuring the ratio of stress to strain when the rock is subjected to high-frequency or dynamic loading
• Grouting


  • A technique or process used in engineering and construction to improve the properties of rock or soil masses by injecting a fluid material (grout) into the subsurface to fill voids, strengthen weak zones, or control water flow
  • It can be used for ground improvement, sealing and water control, and foundation stabilization
• Common types of grouts

  • Cementitious grouts
  • Chemical grouts
  • Expansive grouts