Geological & Geophysical Investigations

• Geological and geophysical investigations are important in civil engineering

Geological Investigation

• Geological investigation is the first and most important step in building completion
• Geological investigation identifies area feasibility for construction
• Geological investigation determines building foundations
• Geological investigation sets up preventative measurements for a building

Site Investigation

• Site investigation assesses site suitability for the proposed structure
• Site investigation explores ground conditions at and below the surface
• Site investigation involves collecting all necessary information for:
  • Safe and economic design
  • Construction and maintenance of civil engineering structures
  • Environmental management
  • Extraction and development of resources

Stages of Site Investigation

• Desk study
• Site reconnaissance
• Ground investigation
• Sampling
• Reporting

Remote Sensing

• Remote sensing identifies and analyzes phenomena on Earth's surface
• Remote sensing uses devices borne by aircraft or spacecraft
• Information from remote sensing is transposed to a base map, which is checked during fieldwork
• Remote sensing data is used in geographical information systems

Aerial Photography

• Aerial photography allows division of the concerned area into topographical and geological units.
• Aerial photography enables engineering geologists to plan fieldwork and select locations for sampling

Geological Methods

• Geological methods assess data on topographic, geologic, tectonic, and geophysical aspects.
• Geological methods are applied in site investigations to study outcrops and landforms
• Geological methods include the study of geological and tectonic structures and solve problems of stratigraphy

Classification of Geological Methods

• Surface investigation
• Subsurface investigation

Surface Investigation: Aerial Surveying

• Aerial survey is a method of collecting geomatics or other imagery
• Aerial survey uses airplanes, helicopters, UAVs, balloons, or other aerial methods
• Aerial surveying, aka photogrammetry, surveys land that would be impossible or impractical to survey on the ground
• Aerial surveying helps with forest inventory, land surveying, land reclamation, railway, highway planning, power lines, and various explorations

Surface Investigation: Hydrogeological Surveying

• Hydrogeology studies groundwater and its impact on the subsurface environment
• Hydrologists study the impact of groundwater on surface water
• Hydrogeologists study the impact of surface water on groundwater
• A hydrogeological survey investigates hydrologic and geologic parameters at the subsurface level

Subsurface Investigation: Test Pit Excavation

• Test pits are holes dug prior to construction to ensure ground conditions are suitable
• Test pits average a depth of 3-15 feet deep
• Test pits allow geotechnical engineers to assess soil composition before breaking ground

Subsurface Investigation: Boring

• Soil boring tests examine soil subsurface solidity and properties
• Soil boring reviews soil by removing a few shallow centers from the silt
• The soil can then be tried to be certain it contains no risky pollutants like oil

Subsurface Investigation: Electrical Resistivity Method

• Electrical resistivity techniques are a type of geophysical reviewing that guides in imaging the subsurface
• Electrical resistivity techniques use contrasts in electric potential to distinguish subsurface material

Subsurface Investigation: Seismic Refraction Method

• Seismic refraction/reflection line uses seismographs
• Seismographs are lined up along the Earth's surface to record seismic waves
• The method generates seismic waves by explosion.
• Seismic refraction records reflections and refractions of waves from velocity discontinuities

Exploration Techniques

• Exploration searches for mineral, coal, oil, and gas deposits
• Information gathered during exploration assesses location, size, and quality of the deposit
• Exploration helps determine if a deposit can be recovered economically
• Exploration searches for worthwile mineral or petroleum deposits to extract, process, and sell

Types of Exploration Techniques

• Geophysical surveys
• Geological mapping
• Desktop surveys
• Geochemical surveys

Geophysical Survey: Airborne Geophysical Surveys

• Airborne geophysical surveys measure various physical or geochemical parameters
• Airborne geophysical surveys are conducted using fixed-wing aircraft or helicopters
• The parameters measured include:
  • conductivity
  • magnetic susceptibility
  • rock density
  • radioactive element concentration
  • reflectance spectra

Geophysical Survey: Ground Based Surveys

• A survey can range from a single geophysicist to a team of geophysicists and technicians
• Ground-based geophysical surveys range from walking surveys to the use of quadbikes, light cars, or seismic trucks
• Seismic, magnetic, radiometric, gravitational and electromagnetic surveys are examples of ground-based geophysical surveys

Geophysical Survey: Magnetic Geophysical Surveys

• Magnetic surveys track changes in the Earth's magnetic field
• Surveys are delicate enough to pick up on small changes in the amount of magnetic minerals present

Geophysical Survey: Gravity Surveys

• Gravity surveys quantify rock density changes in the Earth's crust
• A gravimeter measures the gravity field
• Surveys are sensitive enough to detect minute changes in the field
• Gravity surveys map various rocks or geological formations

Geophysical Survey: Electromagnetic(EM) Surveys

• Electromagnetic (EM) surveys generate an electromagnetic field
• Electromagnetic (EM) surveys measure changes in conductivity in the near-surface soil and rock in three dimensions

Geophysical Survey: Seismic Surveys

• Seismic surveys track vibration as it travels across the Earth's crust
• Seismology fundamentals are used in ground based seismic surveys
• Seismic surveys make a picture of geology undeneath the surface

Geophysical Survey: Induced Polarization(IP) Surveys

• IP surveys establishes an electric field in the ground
• IP surveys measures chargeability and resistivity of the region beneath the surface

Geophysical Survey: Drillhole Surveys

• Drillhole surveys entail the use of a thin wire rope to lower a variety of scientific insturments
• Drillhole surveys go down exploration drillholes or boreholes
• Sondes may measure rock properties by measuring magnetic, radiometric, or electrical information from the rocks inside the borehole

Deskstop and Geological Surveys

• Geological mapping locates and identifies rock types and geological structures in relation to landforms and topography
• Geological mapping can be the first method of exploration used on the ground
• Geological mapping may take place at either a local or regional scale
• Desktop surveys study available geological information for a particular area of interest
• Desktop surveys investigate and analyze previous company exploration reports, exploration data, and published geological information

Geochemical Survey

• Geochemical surveys identify areas for further investigation
• Soil, rock, and/or sediment samples are typically collected as part of the surveys.
• Samples are sent to a laboratory for analysis to determine prospective mineralization zones.

Types of Geochemical Surveys

• Soil Sampling
• Stream Sediment Sampling
• Channel Sampling
• Costeaning
• Bulk Sampling

Seismic and Electrical Methods

• Seismic Methods
• Resistivity Methods
• Electromagnetic Methods.

Seismic Methods

• Seismic methods involve measuring seismic wave propagation through earth materials.
• Seismic surveys involve seismic waves which radiate outward from a sound source
• This sound source on the surface,
  • An explosive charge
  • A mechanical impact
• Seismic analysis generates an ultrasound image of the earth

Basic Principles of Seismic Methods

• Seismic Wave Generation: Waves are generated by a controlled disturbance that produces waves capable of penetrating earth
• Propagation of Seismic Wave: Seismic waves travel through the Earth and reflect upon changes in subsurface properties.
• Recording Seismic Waves: Recorded by ground motion on the earth's surface
• Travel Time Analysis, arrival times are analyzed to determine travel times and velocity, geophysicists infer structure properties
• Seismic waves travel at different speeds and velocity for properties, used to analyse structure
• Reflections occur betwen two layers of acoustic properties, refactions occus when waves change direction, crucial data needed to construct detailed images of subsurface
• Data processing and imaging, Seismic data is extensive processing, used to reduce noice, meaningful representaiton of subsurface
• Interoretation, valuble info, and map areas to determine applications

How to Produce Sound Waves

• Vibroseis
• Explosive Detonation

Resistivity Method

• Based on the principle that the distribution of electrical potential in the ground around a current-carrying depends on the electrical resistivities and distribution

Resistivity

• Electrical resistance of a conductor of unit area and unit length
• Electrical resistance is use comparing various materials on electric current
• Higher ratings for poor conducters

Priniples of Reisitivty in GeoPhyisical Investigation

• Resistivity of rocks in soils in variable
• Mineral and Water can vary in the Earth
• Electric current is only conducted because they contain water.

Electromagnetic Method

• This method detects the electrical properties of the subsurface by inducing Electromagnetic energy within the subsurface and measuring the of earth materials.

Primary Field

• Is produced but soruces in nature and below and above grand that create circuits in conductors called conductors.

Secondary Field

• Secondary Field is produced by the circuits that distort the primary feild.
• When primary is distorded the fade will switch off slowly.

Very-Low-Frequency Method

• The most common soruce of the soruce metjod in the frequencies.

Ground Probing Radar Method

• Based upon the transmission of pulsed electromagnetic waves in the frequency range 1 to 1000 MHz. • In this method, the travel times of the waves reflected from subsurface interfaces are recorded as they arrive at the surface, and the depth to an interface. • Ground probing radars have been used for a variety of purposes in geotechnical engineering, for example, the detection of fractures and faults in rock masses, the location of subsurface voids and the delineation of contaminated plumes.

Direct Pantrations.

• Description of underground conditions at specific locations are revealed by physically sampling or testing soil, rock and
• Groundwater, make actual excavation.

Two Types of Derict Panration

• Standard and Cone Test

Civil Engineering in Geology

• Civil engineering designs infrastructure like roads, bridges, buildings, and water systems
• Civil engineering geology focuses on how soil, rocks, and geological conditions affect construction projects
• Civil engineering geology includes site investigations, foundation design, slope stability, and managing hazards

Important fields

• Structures
• Geotechnical
• Transpotations
• Water
• Enviromental
• Costructuions