Subsurface Exploration Techniques

To gather information for foundation design, bearing capacity assessment, settlement prediction, ground water analysis, lateral earth pressure estimates, suitable construction techniques, potential problem identification, material analysis, and existing structure safety evaluation.

Type of structure, soil variability, and investigation cost.

Initial site visit and map/record study to plan further subsurface investigations, choosing the appropriate methods, materials and laboratory/in-situ tests.

Information collected during the initial site visit about topography, settlement cracks, landslides, and other features.

Balancing the cost of the investigation with the project's cost.

More variable soil conditions demand more detailed subsurface investigation, increasing costs. Uniform soil conditions allow for less extensive exploration.

To obtain the maximum useful information for design and construction while minimizing costs.

A phased approach to subsurface investigations, starting with site reconnaissance to gather data for detailed planning, drilling, sampling, testing, and reporting.

A step after site reconnaissance, aiming to identify soil depth, thickness, extent, and composition. It uses a few borings and tests like cone penetrometers, and sounding rods to understand soil strength and compressibility.

The final stage of exploration, determining engineering properties of different soil layers. It involves extensive borings, sampling, and laboratory testing, and potentially field tests like vane shear, plate load, and permeability tests.

Different layers of soil with varying composition and properties.

Device used during preliminary exploration to determine the strength and compressibility of soils.

A field test to assess the shear strength of soil in its natural state.

A field test used to determine the load-bearing capacity of soil.

A test to determine how easily water flows through a soil.

Grouping soil based on particle size. Coarse-grained soils have particles larger than 0.075mm, while fine-grained soils have particles smaller than 0.075mm.

Collecting soil samples that maintain the original structure and conditions found in the ground.

Collecting soil samples that change the original structure, but maintain the proportions of different components.

These samples represent the soil's composition but not its original structure.

Samples that preserve the soil's original structure for tests like shear strength and consolidation.

Tests conducted on undisturbed samples, such as shear strength, consolidation, density, water content and permeability.

Elements that influence sampling, including time constraints, terrain, costs and the purpose of the investigation.

Tools used to collect disturbed samples from depth, such as split-spoon samplers, Shelby tubes and macrocore push samplers.

Used to drill boreholes up to 10m deep in various soil types. Best suited for soils above the water table, but can also work in clayey soils below the water table. Uses a string of drill rods for advancement.

Not suitable for very stiff clays, hard clays, granular soils below the water table, and sand mixed with gravel. The type and depth of the soil layer limit its application.

Used in all types of soil, including sandy soils below the water table. The flights of the auger convey soil to the surface. Hollow stem allows for sampling and testing.

A power-driven auger with a hollow stem, enabling sampling and testing without lifting the auger. The hollow stem can be plugged or removed for these operations.

The hollow stem can be plugged when advancing the auger. This plug can be removed to collect soil samples or conduct standard penetration tests.

Faster drilling, deeper boreholes (up to 60m), versatile for different soil types, and allows for sampling and tests without lifting the auger.

Soil samples can be collected and standard penetration tests can be conducted through the hollow stem without lifting the auger from its position. This saves time and effort.

The helical blades of the auger, responsible for conveying soil to the surface. These flights can also act as a casing for the borehole.

A method for drilling exploratory borings using a heavy-duty pipe with a cutting edge and a flat valve. It's effective in dense sandy deposits, stiff to hard clay soils, and even sandy soil mixed with gravel.

A method for drilling holes primarily for obtaining undisturbed samples for analysis. It's suitable for sand, silt, or clay, but not soil mixed with gravel or boulders.

A method that uses rotating bits attached to drilling rods to cut and grind soil, creating a borehole. It's commonly used for sand, clay, and rocks (unless highly fractured).

A slurry of water and bentonite used in rotary drilling to lubricate the drill bits, remove cuttings, and prevent borehole collapse.

A method that utilizes a heavy chisel repeatedly dropping onto the surface to create holes in rocks and hard strata.

A soil sample obtained from a borehole using a technique that preserves the natural structure and properties of the soil for accurate analysis.

The Shell Method is effective for drilling through soil containing gravel due to its robust cutting edge and ability to handle denser materials.

A test to measure soil density and strength by driving a split-spoon sampler into the ground using a hammer. The number of blows to drive the sampler 30 cm is recorded as the SPT N-value.

Measures soil resistance to penetration by pushing a cone-shaped probe into the ground at a constant rate.

Measures the in-situ stress-strain behavior of soils by applying pressure radially to a cylindrical probe inserted into a borehole.

Assesses how easily water flows through soil or rock by injecting or pumping water into a borehole and measuring the flow rate.

Evaluates soil strength, especially for road construction, by driving a cone into the soil using a hammer and recording the penetration per blow.

Determines soil moisture content, salinity, and structure by measuring the resistance to electrical current flow through the soil.