Geotechnical Investigation Study Notes

Identify stages of geotechnical investigation: Understanding the different phases involved in assessing soil and rock for engineering projects.
Explain various in-situ geotechnical investigation methods: Analyzing methods employed directly on site to examine soil characteristics.
Determine soil parameters from in-situ test methods for foundation designs: Identifying and quantifying factors critical for constructing stable foundations.

Identify type and source of materials: Recognizing the composition of the ground material relevant to engineering applications.
Plan and design of foundations: Developing an appropriate strategy for building foundations based on soil conditions.
Evaluate soil bearing capacity: Assessing the maximum load the soil can support without failure.
Evaluate lateral earth pressure: Understanding the forces exerted by the ground on a structure.
Estimate probable settlement: Predicting how much the ground will compress or yield under loads over time.
Determine potential foundation problems: Identifying possible future issues that could arise from soil properties.
Planning for construction technique: Formulating construction strategies based on the geotechnical data gathered.

Assessment: Initial evaluation of project requirements and site conditions.
Preliminary Information (Desk Study): Gathering relevant data from various sources to understand the site context.
- Sources include:
- Aerial photographs
- Geological maps and memoirs
- Mining and mineral records
- Public records and utility maps
Site Inspection: Observing the physical site including land use and access to services.

Main Ground Investigation: Conducting comprehensive testing with various specialized methods:
- Field Tests:
- Special field tests (e.g. vane tests, plate bearing, Dutch cone, pressuremeter, pumping tests)
- In situ shear and stress testing
- Further Boreholes and Excavations: Extending the depth and range of investigations.
Laboratory Testing: Analyzing samples collected to determine their physical and chemical properties.
Instrumentation: Installing instruments to monitor conditions over time (e.g. for settlement or pore pressure).

Final report: Compiling all findings and recommendations based on the investigation.
Investigation during construction: Continuous assessment as construction proceeds, ensuring no unexpected issues arise.
Investigation during operation: Monitoring conditions after construction to ensure longevity and safety of the structure.

Major Functions:
- Site Assessment: Collecting and interpreting data from soil and rock properties.
- Foundation Design: Selecting the suitable foundation type and construction method based on analysis.
Importance of Early Involvement: Engaging geotechnical engineers early can lead to cost savings and enhanced project understanding, minimizing redundancy.

Antecedent Investigation: Collecting historical data and existing site information.
Field Tests: Conducting tests on-site to evaluate soil properties in real conditions.
Laboratory Tests: Analyzing samples in a controlled environment for detailed insights.
Geotechnical Report: Comprehensive documentation covering all aspects of the investigation.

Purpose: To gather preliminary information about the site.
- Considerations:
- Previous investigations and construction performances in the area.
- Sources of information to consult:
  - USGS topographic maps
  - Aerial photos (e.g., from USGS, DOT's)
  - LANDSAT data
  - State geological maps
  - FEMA flood zone maps
Site Visit Prior to Field Work: Important for ascertaining the general site conditions, including:
- Geologic reconnaissance
- Geomorphology and topography
- Access restrictions and environmental issues

Geophysical Investigations: Using techniques such as:
- Surface resistivity
- Ground-penetrating radar
- Electromagnetic conductivity
- Seismic tests (refraction, reflection)
Boring and Excavation:
- Disturbed and Undisturbed Sampling: Ensuring the integrity of soil samples for analysis.
In Situ Testing: Techniques used directly within the ground for real-time data collection.

Visual Inspection of Subsurface: Essential for understanding local geology.
Hand-operated and Machine Drilling: Differences in equipment types affect sampling integrity.
Disturbed Samples (SPT and Split Spoon Sampler): Common method for obtaining in-situ data by Standard Penetration Test.
Undisturbed Samples (Shelby Tubes): Used for analyzing soil without changing its structure.

Purpose: To investigate soil formations beneath the groundwater table (GWT).
Key Components:
- Borehole supported by casing and/or drilling fluid (water, bentonite, etc).
- Techniques for cleaning and sampling below GWT.

SPT (Standard Penetration Test): Utilizes a split spoon sampler driven into the ground to determine soil resistance.
CPT (Cone Penetration Test): Measures resistance of soil to penetration by a cone.
DMT (Flat Plate Dilatometer Test): Assesses soil properties using a dilatometer.
PMT (Prebored Pressuremeter Test): Measures soil pressure response in a borehole.
VST (Vane Shear Test): Evaluates in-situ shear strength of cohesive soils.

Equipment: A 140 lb hammer used to spur the sampler.
Data Collection: The number of blows to penetrate specified distances is recorded.
N-value: Defined as the number of blows required to drive the sampler into undisturbed soil. Adjustments are made based on hammer type and efficiency:
- N60: Normalized SPT value adjusted for hammer efficiency for meaningful correlations to soil strength.

Different hammers have varying efficiencies impacting data:
- Donut Hammer: 45% efficiency
- Safety Hammer: 60% efficiency
- Automatic Hammer: 75-95% efficiency
The majority of correlations are based on results from the Safety Hammer, hence adjustments are necessary when using different types.

Correcting for borehole diameter (B) and rod length (L) to calibrate test results for accurate interpretation:
- C_b (Borehole correction)
- C_r (Rod length correction)
Additional lateral stress due to overburden is also factored into SPT results, adjusting values for density effects and expected soil behavior under load.