Geotechnical Site Investigation
Expert-defined terms from the Postgraduate Certificate in Geotechnical Engineering & Soil Mechanics course at London School of Planning and Management. Free to read, free to share, paired with a globally recognised certification pathway.
Geotechnical Site Investigation #
an organized process of obtaining and analyzing information about the physical properties and conditions of soil and rock at a specific location, to support the design and construction of structures or infrastructure. Related terms include site characterization, soil testing, and geophysical surveys. The investigation typically involves fieldwork such as drilling boreholes, collecting samples, and conducting in-situ tests, followed by laboratory testing and analysis to determine the relevant geotechnical parameters.
Borehole #
a narrow, deep hole drilled into the ground to obtain soil or rock samples or to install instruments for in-situ testing. Related terms include split spoon sampler, undisturbed sample, and continuous coring. Boreholes are typically drilled using rotary or percussion methods, and the diameter and depth vary depending on the purpose of the investigation.
Cone Penetration Test (CPT) #
a method of in-situ testing that involves pushing a cone-shaped probe into the ground at a constant rate and measuring the resistance forces. Related terms include electrical cone penetrometer and piezocone. CPT provides information on the soil stratigraphy, density, and strength, and can be used to estimate the groundwater level and the soil permeability.
Direct Shear Test #
a laboratory test used to determine the shear strength of soil or rock. Related terms include normal stress and shear stress. The sample is placed in a shear box and subjected to a known normal stress, then a horizontal force is applied until the sample fails. The shear stress and displacement are recorded, and the shear strength is calculated as the ratio of shear stress to normal stress at failure.
Dynamic Cone Penetration Test (DCPT) #
a method of in-situ testing that involves dropping a standard weight onto a cone-shaped probe and measuring the penetration depth. Related terms include California bearing ratio (CBR) and resistance value (Rv). DCPT provides information on the soil strength and stiffness, and can be used to estimate the CBR and Rv values for pavement design.
Geophysical Survey #
a non-intrusive method of investigating the subsurface using physical phenomena such as sound waves, electromagnetic fields, or gravity. Related terms include seismic refraction, ground-penetrating radar (GPR), and electrical resistivity tomography (ERT). Geophysical surveys can provide information on the soil or rock stratigraphy, thickness, and mechanical properties, and can help identify potential hazards such as sinkholes or buried objects.
In #
situ Test: a method of testing the soil or rock properties in their natural location, without removing them from the ground. Related terms include pressuremeter test and vane shear test. In-situ tests can provide information on the soil or rock stiffness, strength, and permeability, and can help estimate the in-situ stress and deformation behavior.
Laboratory Test #
a method of testing the soil or rock samples in a controlled environment, using standardized equipment and procedures. Related terms include triaxial test and consolidated-undrained test. Laboratory tests can provide information on the soil or rock index properties, such as grain size distribution, plasticity, and density, as well as the mechanical properties, such as strength, stiffness, and deformation behavior.
Permeability #
a measure of the ability of water or other fluids to flow through the soil or rock. Related terms include hydraulic conductivity and coefficient of permeability. Permeability is a key parameter for evaluating the groundwater flow and the seepage behavior of soil or rock, and is used in the design of drainage systems, foundations, and excavations.
Plasticity #
a measure of the ability of soil or rock to deform without breaking or cracking. Related terms include liquid limit and plastic limit. Plasticity is an important property for evaluating the behavior of soil or rock under loading or excavation, and is used in the design of foundations, slopes, and embankments.
Sample Disturbance #
the change in the physical or mechanical properties of soil or rock due to the sampling process. Related terms include disturbed sample and undisturbed sample. Sample disturbance can affect the accuracy and reliability of laboratory test results, and is minimized by using appropriate sampling devices and procedures, such as thin-walled tubes, piston samplers, or undisturbed block samplers.
Shear Strength #
the maximum resistance of soil or rock to shearing or sliding forces. Related terms include friction angle and cohesion. Shear strength is a key parameter for evaluating the stability and safety of slopes, foundations, and other geotechnical structures, and is determined by laboratory or in-situ tests such as direct shear test, triaxial test, or vane shear test.
Soil Classification #
the systematic identification and grouping of soil types based on their physical and mechanical properties. Related terms include Unified Soil Classification System (USCS) and British Standard Soil Classification System (BS). Soil classification provides a common language and framework for describing soil behavior and properties, and is used in the design and analysis of geotechnical structures and systems.
Standard Penetration Test (SPT) #
a method of in-situ testing that involves driving a standard sampler into the ground using a standard weight and hammer, and counting the number of blows required to achieve a certain penetration depth. Related terms include N-value and SPT blow count. SPT provides information on the soil density, strength, and stratigraphy, and is widely used in geotechnical engineering for foundation design, site investigation, and hazard assessment.
Triaxial Test #
a laboratory test used to determine the strength and deformation behavior of soil or rock under triaxial stress conditions. Related terms include deviator stress and axial strain. The sample is placed in a triaxial cell and subjected to a confining pressure, then a vertical load is applied until the sample fails. The deviator stress and axial strain are recorded, and the shear strength and deformation modulus are calculated based on the failure criterion and the stress-strain curve.
Undrained Test #
a laboratory test used to determine the undrained shear strength of soil or rock, assuming no water flow during the test. Related terms include consolidated-undrained test and unconsolidated-undrained test. Undrained tests are used to evaluate the short-term stability and deformation behavior of soil or rock, and are particularly relevant for rapid loading or dynamic conditions, such as earthquakes or pile driving.
Vane Shear Test #
a laboratory or in-situ test used to determine the undrained shear strength of soft clays or sensitive soils. Related terms include torque and shear stress. The vane shear test involves inserting a four-bladed vane into the soil, and rotating it at a constant rate while measuring the torque required to shear the soil. The undrained shear strength is calculated as the ratio of torque to the vane area and the soil height.
Young's Modulus #
a measure of the stiffness or elasticity of soil or rock, defined as the ratio of stress to strain in the linear elastic range. Related terms include secant modulus and tangent modulus. Young's modulus is a key parameter for evaluating the deformation behavior of soil or rock under loading or excavation, and is used in the design of foundations, slopes, and other geotechnical structures.
Zone of Saturation #
the layer of soil or rock