Hydraulics and Geotechnical Definitions

• These are study notes covering questions about hydraulics and geotechnical engineering, focusing on definitions of terms.

Key Definitions

• Surface Tension: The elastic tendency of liquids minimizing surface area; allows denser objects/insects to float or run on water.
• Soil Components: Include minerals, gas, and organic materials.
• Soft Cohesive Soil Deposit: Has an unconfined compression strength between 0 to 24 kPa.
• USCS Soil Grain Size: Gravel is greater than 4.75 mm but less than 75 mm.
• Sieve Analysis: Used to determine the particle size distribution of granular materials.
• Effective Stress: The weight and pressure that keeps sand grains together, preventing them from spreading like a liquid; primarily from static friction.
• Liquefaction: The phenomenon where soil strength and stiffness reduce due to earthquake shaking or rapid loading.
• Steady Flow: A flow where the velocity of the fluid at a fixed point does not change with the time.
• Pascal's Principle: Pressure exerted on a liquid is transmitted equally in all directions.
• Bernoulli's Principle: In steady flow without friction, total energy is constant along the flow path.
• Void Ratio: The ratio of the volume of voids to the volume of solids.
• Degree of Saturation: The ratio of the volume of water to the volume of voids.
• Cohesionless Soil: Is difficult to compact, and prone to settlement due to vibrating loads.
• Practically Impermeable Soil: Has very low permeability for water flow.
• Medium Dense Sand: Has a number of blows of 10 to 30 in the standard penetration test.
• Groundwater Table Rise: Reduces the bearing capacity of the soil.
• Discharge: The volume of liquid passing through a cross-section of a stream.
• Metacentric Height: A ship is stable if the metacentric height is above the center of gravity.
• Soil Maximum Dry Density: Increases with increased compaction pressure.
• Water Table Rise: Decreases effective stress.
• Hydraulic Grade Line: Represents the points of highest water elevation in a series of open pipes rising from a pressurized pipeline.
• Water Hammer: A pressure surge caused by sudden stoppage or change in fluid direction.
• National Structural Code: States cut surfaces should be no steeper than 1 to 1.
• Porosity: The ratio between the volume of voids and the total volume of the soil mass.
• Dry Air Unit Weight: Approximately 10.6 N/m^3 at standard temperature and pressure.
• Mercury Pressure: Is about 13.6 times greater than water pressure.
• Hydrodynamics: Study of forces exerted by liquids in motion.
• Soil Properties: The most used property is the moisture content.
• Shear Vane: Used to determine the undrained shear strength of the soil
• Hydraulic Jump: An abrupt rise in the water surface.
• Gradation: Distribution in the particle size of the soil.
• Coefficient of Gradation: Ratio involving grain diameters at 30%, 60%, and 10% passing on a particle size distribution curve.
• Bulk Unit Weight: Also known as total, wet, or moist unit weight representing total weight divided by the total volume.
• Relative Density: Ratio comparing void ratios of cohesionless soil in its loosest, natural, and densest states.
• Soil Consistence: Describes the degree and kind of cohesion/adhesion between soil particles, relating to soil's resistance to deformation.
• Cohesion: Attraction of water molecules due to hydrogen bonding.
• Stickiness: Capacity of soil to adhere to other objects; maximum adherence between thumb and forefinger.
• Plastic Limit: Moisture content at which soil starts behaving like a plastic material, crumbles at 3.18 mm diameter
• Shrinkage Limit: Moisture content with no further volume change upon moisture reduction.
• Plasticity Index: Difference between the liquid limit and plastic limit of a soil.
• AASHTO System: Originally proposed by the Highway Research Board for classifying materials for subgrades and granular roads.
• Soil Classification System: The USCS system is used in engineering and geology and is represented by a two-letter symbol.
• USDA System: Also known as Textural classification.
• Compaction: Densification of soil by removing air, requiring mechanical energy.
• Optimum Moisture Content: Moisture content at which maximum dry unit weight is achieved.
• Vibroflotation: A technique for in situ densification of thick layers of loose granular soil.
• Hydraulic Conductivity: Also referred to as the coefficient of permeability.
• Soil Permeability: Depends on fluid viscosity, pore size distribution, grain size, saturation, and roughness of soil particles.
• Flow Line: Path of water particle from upstream to downstream in permeable soil.
• Equipotential Line: A line along which the potential head is equal at all points.
• Flow Nets: Combine flow lines and equipotential lines to calculate groundwater flow.
• Effective Stress: Sum of vertical forces at solid particle contacts per unit area.
• Immediate Settlement: Caused by elastic deformation without moisture content change.
• Primary Consolidation Settlement: Volume change in saturated cohesive soils due to water expulsion.
• Over-Consolidation Ratio: Ratio of previous maximum pressure to present effective overburden pressure.
• Shear Strength: Internal resistance per unit area to resist failure and sliding.
• Triaxial Shear Test: Reliable method for determining shear strength parameters, for research and conventional testing.
• Direct Shear Test: Oldest and simplest form, a metal shear box contains the soil specimen.
• Slope Stability Analysis: Analysis comparing shear stress and strength to determine slope stability.
• Base Failure: Sliding surface passes at a distance below the toe.
• Slope Failure: Sliding surface intersects the slope above the toe.
• Toe Circle: Failure circle passing through the toe of the slope.
• Auger Boring: Simplest method using hand tools for exploratory boreholes.
• Wash Boring: Method using casing and chopping bit to advance boreholes.
• Rotary Drilling: Uses rotating bits to cut and grind soil and rock.
• Percussion Drilling: An alternative method for hard soil and rock, requires casing.
• Split-Spoon Sampler: Obtains generally disturbed but representative soil samples.
• Spring Core Catcher: eases sample recovery of the fine sand below the water surface.
• Cone Penetration Test: Versatile method to determine material in a soil profile and estimate engineering properties.