HGE PART II

Void Ratio

Void Ratio

The ratio of the volume of void space to the volume of solid substance

Porosity

The ratio of the volume of voids to the volume of the soil sample or specimen. It is simply the open space between the soil grains.

Degree of Saturation

The ratio of the volume of water in the void spaces to the volume of the voids. It is simply the measure of the void volume that is filled by water, expressed as a percentage ranging from 0 to 100.

Moisture Content

The ratio of weight of water to the weight of solids in a given volume of soil.

Unit Weight

the weight of soil per unit volume

Dry Unit Weight

the weight per unit volume of soil, excluding water

Saturated Unit Weight

unit weight of a soil when it is 100 percent saturated.

Bulk unit weight

known as total, wet or moist unit weight. It is the total weight divided by the total volume

Critical hydraulic gradient

the hydraulic gradient that brings a soil (essentially, Coarse-grained soils) to static liquefaction

Density

The ratio of the total mass to the total volume of a unit of soil. Usually expressed as a unit weight where weight is interchanged with mass.

Dry density

The ratio of the mass of the solids (soil grains) to the total unit volume of soil.

Submerged Density

Also, buoyant density. Difference between the total density and the density of water

Density index

Also, relative density. The density of a granular soil relative to the minimum and maximum densities achieved for that particular soil

Consistency

used to describe the degree of firmness of soil

Cohesion

the attraction of one water molecule to another resulting from hydrogen bonding (water-water bond).

Adhesion

It involves the attraction of a water molecule to a non-water molecule (water-solid bond)

Stickiness

The capacity of soil to adhere to other objects. It is estimated at moisture content that displays maximum adherence between thumb and forefinger

Rupture Resistance

a field measure of the ability of the soil to withstand an applied stress or pressure as applied using the thumb and forefinger.

Atterberg’s Limit

the limits of water content used to define soil behavior

Liquid Limit

The moisture content in percent required to close a distance of 12.7mm along the bottom of the groove after 25 blows.

Liquid Limit

defined as the moisture content at which soil begins to behave as a liquid material and begins to flow

Cup Method To Determine Liquid Limit

the device used in this method consists of a brass cup and a hard rubber. The brass cup is dropped onto the base by a cam operated by a crank.

Plastic Limit

The moisture content at which the transition from Semi-Solid to Plastic state.

Shrinkage Limit

The moisture content at which the transition from Solid to Semi-Solid takes place defined as the moisture content at which no further volume change occurs with further reduction in moisture content.

Liquidity Index

ratio which signifies the relative consistency of a cohesive in the natural state

Plasticity

Degree a soil can be molded or reworked causing permanent deformation without rupturing.

Consistency Index

The ratio of the difference between the liquid limit and water content to the difference between the liquid limit and the plasticity index

Plasticity index

difference between the liquid limit and plastic limit of a soil.

Shrinkage index

The difference between the plastic and shrinkage limits

Residual Soil

Soils formed by the weathered products at their place of origin

Lacustrine Soil

Soils formed by deposition of quiet lakes

Alluvial Soil

Soils transported by running water and deposited along streams

Glacial Soil

Soils formed by the transportation and deposition of glaciers

Marine Soil

Soils deformed by deposition in the seas

Gravel Soil

Soil with occasional particles of quartz, feldspar and other minerals

Aelian Soil

Soils transported and deposited by wind:

Skempton

defined the ratio of the plasticity index to the percent of clay size fraction , by weight as Activity

Sieve Analysis

used to determine the grain size distribution of coarse-grained soil.

Hydrometer Analysis

used to determine the grain size distribution of the soils passing the No. 200 sieve.

Effective Size

this diameter in the particle size distribution curve corresponding to `10% finer. It is used to measure the hydraulic conductivity and drainage through the soil

Effective Size

the grain size corresponding to 10 percent passing on a grain-size distribution curve.

Particle-Size Distribution Curve

sed to determine the following four) parameters for a give soil:

Coefficient of Uniformity

defined as the ratio between the grain diameter (in millimeters) corresponding to 60 percent passing on the curve (D60) divided by the diameter of the 10 percent (D10) passing.

Coefficient Gradation

is defined as the ratio between the square of the grain diameter (in millimeter) corresponding to 30 percent passing on the curve (D30) divided by the product of the grain diameter of the 60 percent (D60) passing and the grain diameter of the 10 percent (D10) passing.

Coefficient of curvature

Also curvature coefficient. A measure of the shape parameter obtained from a grain size distribution curve. CD=(D30)2/D10D60.

Poorly Graded

A type of soil in the particle size distribution curve in which most of the soil grains are the same size

AASHTO System

was originally proposed by the a Highway Research Board’sCommittee on Classification of Materials for Subgrades and Granular Type Road. According to the present form of the system, soil can beclassified according to eight major groups, A-1 through A-8, based on the grain size distribution, liquid limit and plasticity indices.

USCS System

soil classification system used in engineering and geology to describe the texture and grain size of a soil. The classification system can be applied to most unconsolidated materials, and is represented by a two-letter symbol.

Coarse-grained soils

Soils with more than 50% by weight of grains retained on the #200 sieve (0.075mm).

Fine-grained soils

Silt and clay soils. Soils containing particles smaller than No. 200 sieve or 0.075 mm in size according to the Unified Soil Classification System

Cobbles

According to the USCS Soil Classification of a soil particle whose size is greater than 75 mm is called___.

USDA System

also called as Textural classification system

Clay

Soil particles which are finer (smaller) than 0.002 mm in size

Soil Compaction

Volume change in soils which air is expelled from the voids, but with the water content remaining constant. Compaction may occur due to vibration, and self-weight. In construction, compaction is achieved by rolling, tamping or vibrating fill soils

1. To increase shear strength

2. To decrease future settlements

3. To decrease permeability

4. To increase the stability of slopes of embankments

Reasons why soil, when placed in a dense state is to be compacted

a. Nuclear method

b. Sand cone method

c. Rubber ballon method

The standard procedure for determining the filed unit weight of compacted soil include:

Optimum moisture content

the moisture content at which the maximum dry unit weight is attained

Proctor Compaction Test

The laboratory test generally used to obtain the max dry unit weight of compaction and the optimum moisture content

Permeability

the property of soil which permits flow of water or other liquids through or it is the case with which water can flow through it.

Maximum dry density

A soil property obtained in the laboratory from a Proctor test. Density of soil at 100% compaction

Coefficient of Permeability

the constant of permeability, a factor that indicates if the volume of flow is to be great or small, relatives to the ease or difficulty with which water moves through the soil.

Hydraulic conductivity

Also, coefficient of permeability. The constant average discharge velocity of water passing through soil when the hydraulic gradient is equal to 1.0. Clays are considered relatively impervious, while sands and gravels are considered pervious.

Transmissivity or Transmissibility

the ability of an aquifer to transmit water through its entire thickness.

Discharge velocity

quantity of water flowing in unit time through a unit gross cross sectional area of soil at right angles to the direction of flow

Constant head test

this is used to determine the coefficient of permeability of coarse-grained soil.

Falling Head Test

this is used to determine the coefficient of permeability of fine grained soil

a. fluid viscosity and pore size distribution

b. grain size distribution and degree of saturation

c. roughness of soil particles and degree of saturation

The coefficient of permeability of soil depends on

Drawdown

The magnitude of the lowering of a water table, usually near a well being pumped

Effective Stress

The sum of the vertical components of the forces developed at the points of contact of the solid particles per unit cross sectional area of the soil mass.

Pore water pressure

stress induced by water pressure

Intergranular Stress

stress resulting from particle to particle contact of soil

Total Stress

sume of effective and neutral stress

Capillary rise

The height to which water will rise above the water table due to negative pore water pressure or capillary action of the soil.

Capillary stresses

Pore water pressures less than atmospheric values produced by surface tension of pore water acting on the meniscus formed in void spaces between soil particles.

Piezometer

An instrument used to measure in-situ pore water pressures

Equipotential line

a line along which the potential head at all points is equal

Flow Line

a line along which a water particle will travel from upstream to the down stream side in the permeable soil medium

Flow Net

a combination of a number of flow line and equipotential line

Boussinesq equation

An equation used to determine the increase in vertical pressure at a particular depth that is caused by an application of a point load at a given surface. See Boussinesq Theory for equations and calculations.

1. Deformation of soil particles

2. Relocations of soil particles

3. Expulsions of water on air from the void spaces

The increase in stress caused by foundation and other loads compresses a soil layer

Primary consolidation settlement

The result of volume change in saturated cohesive soils because of the expulsion of water that occupies the void spaces.

Normally Consolidated

Type of clay whose present effective BURDEN pressure is the maximum pressure that the soil was subjected to in the past

Over Consolidated

Type of clay whose present effective OVERBURDEN pressure is the maximum pressure that the soil was subjected to in the past.

Secondary consolidation settlement

The result of the plastic adjustment of soil fabrics

Immediate settlement

Caused by the elastic deformation of dry soil and of moist and saturated soils without any change in the moisture content.

Compression index

(Also, compressibility index) The logarithmic slope of the primary consolidation curve. The slope of the normal compression line and critical state line of the Casagrande Method of consolidation curves.

Swell Index

smaller in magnitude than the compression index

Coefficient of Consolidation

Generally decreases as the liquid limit of soil increases and its range of variation is rather wide.

Overconsoldation ratio

Ratio of preconsolidation pressure to present effective overburden pressure.

Shear

Soil derives its strength from it capacity to resist

Direct Shear Test

It is the oldest and simplest form of shear test arrangement. The test equipment consist of a metal shear box in which the soil specimen placed

Direct shear test

Laboratory test used to determine the relationship of shear strength to consolidation stress. Strength characteristics that are estimated from this test includes cohesion and angle of internal friction

Triaxial Shear Test

It is one of the most reliable methods available for determining the shear strength parameters. It is used widely for both research and conventional testing.

Confined aquifer

An aquifer that is contained between two stratifications of low permeability soil or rock.

Unconfined Compressive Strength Test

Laboratory test similar to the unconsolidated-undrained test performed on plastic soils, usually clay. From this test, the undrained shear stregth is calculated as 1/2 of the unconfined compressive strength.

Cohesion

considered to be equal to the undrained shear strength.

Undrained shear strength

(Also undrained strength) The shear strength of a saturated soil at a given water content (or voids ratio, or specific volume) under loading conditions where no drainage of pore water can take place. The undrained shear strength of soil is independent of applied stresses and therefore can be measured at any level of stress, provided the void ratio remains constant. The undrained Mohr-Coulomb envelope will be horizontal.

Coulomb's equation

Named after Charles Augustin Coulomb, (1736-1806) An equation relating the shear strength of soil to the normal effective stress on the failure plane

Deviator stress

The difference between the axial and radial stresses of a triaxial test sample

Triaxial shear strain

A strain parameter used in the interpretation of triaxial stress test results.