3.4 Site investigation techniques (boring, sampling, in-situ tests)
5 min read•august 16, 2024
Site investigation is crucial for understanding subsurface conditions in geotechnical projects. It involves desk studies, site reconnaissance, geophysical surveys, and through borings and .
methods, soil techniques, and in-situ tests provide essential data for soil classification, strength, and deformation properties. These techniques help engineers assess potential hazards and develop cost-effective design solutions for construction projects.
Site Investigation for Geotechnical Projects
Objectives and Importance
Top images from around the web for Objectives and Importance
Integrating Geotechnical Investigation with Hydrological Modeling for Mitigation of Expansive ... View original
Is this image relevant?
Importance of Geotechnical Investigation for Design and Construction of Shafts over 1000 m Deep View original
Is this image relevant?
Chamine: Site appraisal in fractured rock media: coupling engineering geological mapping and ... View original
Is this image relevant?
Integrating Geotechnical Investigation with Hydrological Modeling for Mitigation of Expansive ... View original
Is this image relevant?
Importance of Geotechnical Investigation for Design and Construction of Shafts over 1000 m Deep View original
Is this image relevant?
1 of 3
Top images from around the web for Objectives and Importance
Integrating Geotechnical Investigation with Hydrological Modeling for Mitigation of Expansive ... View original
Is this image relevant?
Importance of Geotechnical Investigation for Design and Construction of Shafts over 1000 m Deep View original
Is this image relevant?
Chamine: Site appraisal in fractured rock media: coupling engineering geological mapping and ... View original
Is this image relevant?
Integrating Geotechnical Investigation with Hydrological Modeling for Mitigation of Expansive ... View original
Is this image relevant?
Importance of Geotechnical Investigation for Design and Construction of Shafts over 1000 m Deep View original
Is this image relevant?
1 of 3
- Site investigation provides essential information about subsurface conditions for design and construction purposes
- Primary objectives encompass determining , groundwater conditions, and engineering properties of soil and rock
- Assesses potential geotechnical hazards (soil liquefaction, expansive soils, karst topography)
- Scope and extent depend on project type, size, complexity, and variability of subsurface conditions
- Leads to cost-effective design solutions, reduced construction risks, and improved project performance
- Inadequate investigation may result in unforeseen ground conditions, causing project delays, cost overruns, and potential failures
- Typically involves desk studies, site reconnaissance, geophysical surveys, and subsurface exploration through borings and in-situ tests
Investigation Process and Components
- Desk studies analyze existing geological maps, aerial photographs, and historical records
- Site reconnaissance involves visual inspection and surface mapping of the project area
- Geophysical surveys (seismic refraction, electrical resistivity) provide non-invasive subsurface information
- Subsurface exploration includes borings, test pits, and trenches for direct observation and sampling
- determines physical and mechanical properties of soil and rock samples
- Data interpretation and reporting synthesize findings for engineering design and decision-making
- Iterative process may require additional investigations based on initial findings
Boring Methods for Soil and Rock
Common Boring Techniques
- boring uses continuous or hollow-stem augers for shallow depths in cohesive soils
- Suitable for depths up to 30 meters in stable soil conditions
- Provides disturbed samples and allows for installation of monitoring wells
- Wash boring utilizes circulating fluid to remove cuttings, effective in granular soils and weathered rock
- Can reach depths of 60 meters or more
- Allows for Standard Penetration Testing (SPT) at regular intervals
- Rotary drilling employs rotating bit and circulating fluid for deep borings in various soil and rock conditions
- Capable of reaching depths over 100 meters
- Suitable for obtaining rock cores and installing deep foundations
Specialized Boring Methods
- Percussion drilling uses heavy chisel-like tool, effective in hard soils, boulders, and rock formations
- Can penetrate through cobbles and boulders that may obstruct other methods
- Relatively slow but useful in difficult ground conditions
- Core drilling specifically designed for obtaining intact rock samples using diamond-tipped core barrels
- Provides continuous rock cores for geological and geotechnical analysis
- Essential for characterizing rock mass properties and discontinuities
- Sonic drilling utilizes high-frequency vibrations to advance the borehole
- Minimizes disturbance to surrounding soil and produces high-quality continuous core samples
- Effective in a wide range of soil types, including gravels and cobbles
Selection Criteria and Considerations
- Choice of boring method depends on soil type, depth of investigation, groundwater conditions, and required sample quality
- Each method has advantages and limitations in terms of speed, cost, sample disturbance, and applicability to different ground conditions
- Environmental considerations (noise, drilling fluid disposal) may influence method selection
- Equipment availability and site accessibility affect the feasibility of different boring methods
- Multiple boring techniques may be employed on a single project to address varying subsurface conditions
Soil Sampling Techniques
Disturbed Sampling Methods
- Auger sampling collects soil cuttings from auger flights during drilling
- Provides bulk samples for soil classification and index property tests
- Not suitable for strength or consolidation testing due to significant disturbance
- Split-spoon sampling used in (SPT)
- Obtains representative samples at regular intervals during drilling
- Allows for visual classification and basic laboratory testing
- Bulk sampling involves collecting large volumes of soil from test pits or excavations
- Useful for compaction testing and aggregate evaluation
- Provides insight into soil variability and presence of cobbles or boulders
Undisturbed Sampling Techniques
- Thin-walled tube sampling (Shelby tubes) obtains relatively undisturbed samples in cohesive soils
- Suitable for soft to medium stiff clays and silts
- Samples used for strength, consolidation, and permeability testing
- Piston sampling employs a fixed or free piston to reduce sample disturbance
- Effective in soft soils and below the water table
- Provides high-quality samples for sensitive clays and organic soils
- Block sampling involves cutting out large, undisturbed soil blocks
- Yields highest quality samples for research and critical projects
- Limited to shallow depths and requires careful excavation and handling
Sample Quality and Handling
- Quality of soil samples categorized into five classes (A to E) based on degree of disturbance
- Class A represents highest quality (e.g., block samples)
- Class E represents completely remolded samples
- Proper sample handling, transportation, and storage crucial to maintain sample integrity
- Use of appropriate containers (tubes, jars, bags) for different sample types
- Sealing and labeling samples to prevent moisture loss and ensure traceability
- Sampling procedures must adhere to standardized methods (ASTM D1587, D1586)
- Choice of sampling technique depends on soil type, required sample quality, depth of sampling, and intended laboratory tests
In-Situ Tests for Site Characterization
Penetration Tests
- Standard Penetration Test (SPT) measures soil resistance by driving split-spoon sampler
- N-value (blows per 30 cm penetration) used to estimate soil density and strength
- Widely used due to simplicity and extensive empirical correlations (liquefaction potential, bearing capacity)
- (CPT) pushes instrumented cone into ground at constant rate
- Measures tip resistance and sleeve friction for continuous soil profiling
- Particularly useful in stratified soils and soft deposits
- Pore pressure measurements (CPTu) provide additional data on soil behavior
Strength and Deformation Tests
- Vane shear test determines undrained of soft to medium stiff clays
- Directly measures soil strength in-situ, minimizing disturbance effects
- Useful for sensitive clays and organic soils where sampling is difficult
- Pressuremeter test evaluates soil deformation characteristics and lateral earth pressure
- Applies pressure to borehole walls using inflatable membrane
- Provides stress-strain data for various soil types and rock
- Dilatometer test assesses soil stiffness and stress history using flat plate device
- Particularly effective in profiling sand and clay deposits
- Yields data on lateral stress, overconsolidation ratio, and soil type
Geophysical Methods
- Seismic refraction measures velocity of seismic waves through soil and rock layers
- Useful for determining depth to bedrock and soil stiffness profiles
- Covers large areas efficiently but requires careful interpretation
- Electrical resistivity imaging maps subsurface resistivity variations
- Identifies soil and rock types, groundwater conditions, and contamination plumes
- Non-invasive method suitable for environmental and hydrogeological investigations
- Ground-penetrating radar (GPR) detects subsurface features using electromagnetic waves
- Effective for locating utilities, voids, and shallow stratigraphic boundaries
- Limited depth penetration in conductive soils
Key Terms to Review (21)
ASTM D1586: ASTM D1586 is a standard test method used to determine the density of soil and the resistance of soil to penetration by a standard split-barrel sampler during a boring operation. This test is crucial for site investigations as it helps in understanding soil conditions and the potential settlement behavior of shallow foundations, allowing engineers to make informed decisions during construction projects.
ASTM D421: ASTM D421 is a standard test method established by ASTM International for the determination of the particle-size distribution of soils. This method is crucial in geotechnical engineering as it helps identify soil characteristics essential for site investigations, which influence decisions on design and construction practices.
Auger: An auger is a drilling device used to bore holes into the ground, typically for soil sampling or site investigation. It consists of a helical screw blade that helps in removing material while creating a cylindrical hole, allowing engineers to gather important information about subsurface conditions, which is crucial for assessing the suitability of a site for construction or other purposes.
Boring: Boring is a technique used in geotechnical engineering to create holes in the ground for the purpose of site investigation and foundation design. This process allows engineers to gather important information about soil and rock properties, which is essential for assessing the suitability of a site for construction projects. By obtaining samples from various depths, engineers can analyze the ground conditions and make informed decisions regarding the type of foundations to use, whether it's piles, drilled shafts, or caissons.
Cone Penetration Test: The cone penetration test (CPT) is a sophisticated in-situ testing method used to determine the geotechnical properties of soil. It involves pushing a cone-shaped probe into the ground at a constant rate and measuring the resistance of the soil against the cone. This test provides valuable information about soil stratigraphy, strength, and compressibility, which are essential for foundation design and other engineering applications.
Disturbed Sampling: Disturbed sampling refers to the collection of soil or rock samples that have been altered or disturbed during the process of obtaining them. This type of sampling is crucial when exploring site conditions, as it helps in understanding the existing materials and their properties, even though the samples may not fully represent the in-situ conditions. Factors like drilling techniques and handling can cause these disturbances, affecting the physical characteristics and moisture content of the samples collected.
Field Testing: Field testing refers to the process of assessing the physical properties and behavior of soil and rock materials at the site where construction or engineering projects will take place. This hands-on approach allows engineers and geotechnical professionals to gather real-time data about the conditions of the site, which is essential for making informed decisions about design and construction methods. By using various techniques like boring, sampling, and in-situ tests, field testing ensures that the materials' characteristics are accurately represented for the project's requirements.
Geological Mapping: Geological mapping is the process of creating visual representations of the distribution and relationships of geological features in a specific area. This technique is essential for understanding subsurface conditions and aids in the identification of resources, hazards, and environmental impacts. By combining field observations with data from site investigation techniques, geological mapping provides a comprehensive overview of the geology that informs decision-making in various applications, including construction and land use planning.
Geotechnical Borehole: A geotechnical borehole is a cylindrical hole drilled into the ground to investigate subsurface conditions and gather data about soil and rock properties. This process is essential for understanding the geology of a site, enabling engineers and geologists to assess factors such as soil strength, groundwater levels, and material composition, which are crucial for safe construction and site development.
Geotechnical Report: A geotechnical report is a comprehensive document that presents the findings of a site investigation, including soil and rock properties, groundwater conditions, and engineering recommendations. This report is crucial for informing design and construction decisions in civil engineering projects. By synthesizing data from various investigation techniques, the report ensures that any potential risks associated with the site conditions are identified and managed appropriately.
In-situ tests: In-situ tests are field tests conducted on soil or rock at the actual location where the material is found, allowing for direct assessment of its physical and mechanical properties. These tests provide valuable data on how soil behaves under natural conditions, which is crucial for making informed decisions in construction and engineering projects. By examining the material in its natural environment, in-situ tests help to minimize uncertainties that may arise from laboratory testing or sampling techniques.
Laboratory testing: Laboratory testing refers to the systematic examination of soil samples in controlled environments to determine their physical and engineering properties. This testing is essential for evaluating soil behavior, classifying soil types, and assessing their suitability for construction projects. By providing precise data on soil characteristics, laboratory testing informs decisions related to site investigation techniques, soil classification systems, and reinforcement techniques.
Moisture Content: Moisture content refers to the amount of water present in a soil sample, expressed as a percentage of the dry weight of the soil. It plays a crucial role in understanding soil behavior and properties, influencing the results of site investigations, strength assessments, and stability analyses. Knowing the moisture content helps in determining the effective stress within the soil and is essential for accurate engineering applications.
Sampling: Sampling is the process of collecting representative portions of soil or rock from a specific site for analysis and testing. This technique is crucial in understanding the geotechnical properties of the materials present, guiding design and construction decisions. Accurate sampling methods help ensure that the information gathered reflects the true conditions of the site, which is essential for evaluating stability, load-bearing capacity, and other important factors in engineering projects.
Shear Strength: Shear strength is the maximum resistance of a soil or rock to shear stress, which is critical in understanding how materials behave under loading conditions. This concept is essential in various aspects of geotechnical engineering, as it influences stability, load-bearing capacity, and the overall performance of structures in contact with soil.
Soil Investigation Report: A soil investigation report is a comprehensive document that outlines the findings from an assessment of subsurface soil conditions at a specific site. It typically includes data from site investigations such as boring, sampling, and in-situ tests, providing critical information about soil properties, composition, and behavior, which are essential for the design and construction of foundations and other structures.
Soil Stratigraphy: Soil stratigraphy is the study of soil layers and their characteristics, which helps in understanding the vertical arrangement of soil materials and the historical development of a site. It provides crucial insights into how different soil types interact with one another, their properties, and how they can affect engineering and construction projects. This understanding is essential for accurately assessing soil conditions, which is particularly important for various techniques used in site investigation, the design of deep foundations, and considerations related to seismic stability.
Split Spoon Sampler: A split spoon sampler is a cylindrical device used to collect soil samples during drilling operations, primarily for geotechnical investigations. This tool consists of two halves that can be separated to retrieve the soil sample after penetration into the ground. It allows for effective sampling of cohesive and granular soils, providing crucial data about subsurface conditions.
Standard Penetration Test: The Standard Penetration Test (SPT) is a widely used in-situ testing method for assessing the geotechnical properties of soil. It involves driving a split barrel sampler into the ground at the bottom of a borehole using a hammer to measure resistance. The results help in determining soil strength, stratification, and index properties, which are crucial for evaluating the suitability of sites for shallow foundations and other structures.
Subsurface exploration: Subsurface exploration is the process of investigating and assessing the physical properties and conditions of soil and rock beneath the Earth's surface. This process is crucial for understanding ground conditions, which informs the design and construction of structures. It involves various methods like boring, sampling, and in-situ tests to gather essential data about subsurface materials, groundwater levels, and other geotechnical properties that influence engineering projects.
Undisturbed sampling: Undisturbed sampling refers to the process of collecting soil samples in a way that preserves the natural structure and moisture content of the soil. This method is crucial for obtaining accurate data regarding the engineering properties of soil, as it minimizes any alterations that might occur during the sampling process. Maintaining the integrity of the soil sample is essential for effective site investigation techniques like boring, sampling, and in-situ tests, allowing engineers to make reliable assessments of ground conditions.