GeoTech Explained…

A

Adhesion
The force that causes soil to stick to another surface.

Air Voids Ratio
The volume of air within soil voids expressed as a proportion of the total soil volume.

Allowable Bearing Capacity
The maximum load the ground can safely support without failure.

Alluvial Soils
Soils deposited by rivers, streams, or flooding.

Angle of Shearing Resistance
The angle that represents a soil’s resistance to shear due to friction between particles, commonly denoted as φ (phi).

Aquifer
A layer of soil or rock that stores and transmits groundwater.

Artesian
Groundwater under pressure that rises naturally in a borehole or well.

Atterberg Limits
Tests used to determine how clay soils behave at different moisture levels.

B

Bearing Capacity
The ability of soil or rock to safely support loads from structures without shear failure or excessive settlement.

Bearing Pressure
The pressure applied to the ground by a structure.

Bedrock
The solid rock beneath soil and loose materials.

Bentonite
A swelling clay commonly used for drilling and sealing works.

Borehole
A drilled hole used to investigate ground conditions.

British Soil Classification System (BSCS)
A system used in the UK to classify soils by their properties.

Bulk Density
The total mass of soil divided by its total volume.

C

Cable Percussive
A drilling method that breaks soil and rock using a heavy falling tool.

California Bearing Ratio (CBR)
A test that measures the strength of subgrade soils for roads and pavements.

Clay
A very fine-grained soil that becomes sticky when wet.

Coarse-grained Soils
Soils mainly made up of sand and gravel particles.

Coefficient of Active Earth Pressure
A coefficient used to calculate the lateral earth pressure exerted by soil when it is free to deform sufficiently behind a retaining structure.

Coefficient of Compressibility
A parameter that quantifies the amount of volume change in soil resulting from an increase in effective stress.

Coefficient of Consolidation
A measure of how quickly a soil settles as water is squeezed out.

Coefficient of Curvature
A number used to assess how well-graded a soil is.

Cohesionless Soils
Soils such as sand and gravel that derive their strength primarily from friction between particles rather than cohesion.

Cohesive Soils
Soils such as sand and gravel that derive their strength primarily from friction between particles rather than cohesion.

Compaction
The process of densifying soil by reducing air spaces.

Compression Test
A test that measures how a material behaves under crushing loads.

Cone Penetration Test (CPT)
An in-situ test where a cone is pushed into the ground to assess soil strength.

Confined Aquifer
An aquifer trapped between impermeable layers.

Consolidation
The gradual settlement of soil caused by water being squeezed out.

Consolidation Test
A laboratory test used to measure how much and how quickly soil compresses and settles when a load is applied.

D

Density
The mass of a material per unit volume, including solids, water and air where applicable.

Desk Study
A review of existing information about a site before investigations begin.

Desiccation
The drying out of soil, often causing shrinkage and cracking.

Direct Shear Test
A laboratory test used to determine the shear strength of soil.

Dry Density
The density of soil excluding the weight of water.

E

Effective Stress
The stress carried by the soil skeleton, equal to total stress minus pore water pressure.

F

Field Density Test
A test used to measure soil density on site.

Fine-grained Soils
Soils made mainly of silt and clay-sized particles.

Friction Angles
Values that represent the frictional resistance between soil particles and contribute to shear strength.

G

Geotechnical Engineer
An engineer who studies soil, rock, and ground conditions.

Geotextiles
Permeable fabrics used in construction to separate, reinforce, or drain soil.

Grain Size Distribution Curve
A graph showing the range and proportion of particle sizes in soil.

Ground Movement Monitoring
Measuring and tracking movement of soil or structures.

Groundwater Monitoring
Measuring groundwater levels and conditions over time.

H

Hydrometer Test
A laboratory test used to determine the size of fine soil particles.

I

In-situ
Testing or measuring something in its natural position in the ground.

L

Liquid Limit
The moisture content at which soil changes from plastic to liquid behaviour.

Liquidity Index
A measure of the consistency of a fine-grained soil relative to its plastic and liquid limits.

M

Maximum Dry Density (MDD)
The highest dry density achievable through compaction.

Moisture Content
The amount of water present in soil.

N

N-Value
The number of hammer blows needed in an SPT test to drive a sampler a set distance.

Negative Skin Friction
Additional load on a pile caused by surrounding soil settling.

O

Oedometer Test
A laboratory test used to measure soil compression and consolidation.

One-dimensional Compression
Compression that occurs in only one direction, usually vertically.

Overburden Pressure
The pressure exerted by the weight of soil and rock above a point.

Overconsolidation Ratio (OCR)
A measure comparing a soil’s past maximum pressure to its current pressure.

P

Particle Size Distribution (PSD)
The range and percentage of different particle sizes within a soil.

pH Value
A measure of acidity or alkalinity.

Piezometer
An instrument used to measure groundwater pressure or level.

Plastic Limit
The moisture content at which soil changes from semi-solid to plastic.

Plasticity
The ability of a soil to be moulded without breaking.

Plasticity Index (PI)
The numerical range over which a soil remains plastic.

Plate Bearing Test
A test used to determine the bearing capacity and stiffness of the ground.

Pore Pressure
Pressure exerted by water within soil voids.

Porosity
The proportion of a soil’s volume made up of void spaces.

Primary Consolidation
Settlement caused by the expulsion of water from soil pores.

Proctor Test
A laboratory test used to determine optimum moisture content and maximum dry density.

R

Remolded Swell Test
A test measuring how much disturbed soil expands when wetted.

Rotary Bored
A drilling method using a rotating cutting tool to create boreholes.

S

Sensitivity
The loss of strength a soil experiences when disturbed.

Setting Out
Marking positions and levels on site before construction starts.

Settlement
The downward movement of the ground due to loading.

Shear Modulus
A measure of how stiff a soil or material is when it is twisted or pushed sideways.

Shear Strength
The ability of soil to resist sliding or shearing.

Shear Stress
A force acting parallel to a surface.

Sieve Analysis Test
A test used to determine the particle size distribution of coarse soils.

Site Investigation
The process of assessing ground conditions on a site.

Soil Classification
The grouping of soils based on their characteristics.

Standard Penetration Test (SPT)
An in-situ test used to assess soil strength by driving a sampler into the ground.

Stiffness
The resistance of soil or a material to deformation.

Strain
The amount of deformation caused by stress.

Stress
Force applied per unit area.

Subgrade Modulus
A measure of how much the ground deflects under load.

T

Topographical Survey
A survey showing ground levels and surface features.

Total Stress
The combined stress carried by soil particles and pore water.

Trial Pit
An excavation used to inspect near-surface ground conditions.

Triaxial Stress Test
A laboratory test used to determine soil strength under different stress conditions.

U

Utility Survey
A survey used to locate underground services such as pipes and cables.

Ultimate Bearing Capacity
The maximum load the ground can support before failure occurs.

Unconfined Compressive Stress Test
A laboratory test measuring the compressive strength of cohesive soil without confinement.

Unit Weight
The weight of a material per unit volume.

V

Vane Shear Test
An in-situ test used to measure the shear strength of soft clays.

Void Ratio
The ratio of void space volume to solid particle volume.

Volume of Solids
The volume occupied by soil particles only.

Volume of Voids
The total volume of air and water spaces in soil.

Volume of Water
The volume of water contained within the soil.

Volumetric Strain
The change in volume of soil divided by its original volume.

W

Water Content
The amount of water in soil expressed as a percentage of dry soil weight.

Weight of Soil Grains
The weight of the solid soil particles only.

Weight of Water
The weight of water contained within the soil.

Window Sample
A ground investigation method that pushes a sampling tube into the ground to obtain soil samples.

Y

Yield Point
The stress level at which a material begins to deform permanently.

Yield Stress
The minimum stress required to cause permanent deformation.

Z

Zero Air Voids Curve
A line on a compaction graph showing the theoretical maximum density with no air in the soil voids.