Rock Mechanics

Rock Mechanics

The theoretical and applied science of the mechanical behaviour of rock and rock masses in response to force fields of their physical environment.

Engineering Rock Mechanics

Geological Rock Mechanics

2 Kinds of Rock Mechanics

Minimum risks during construction.

Speed of construction.

Long-term quality of infrastructure.

The importance of opportunities depends on these 3

Physical Properties

Mineralogical composition - mineral structure, texture

Specific gravity, density, unit weight

Porosity, void ratio

Moisture content, degree of saturation

Permeability

Swelling properties

Anisotropy

Electrical properties

Thermal properties

Velocity of Elastic waves

Durability

Mechanical Properties

Elastic Modulus/ Deformation modulus and Poisson's ratio

Uniaxial compressive strength

Tensile strength

Shear strength Properties

Point load strength

Rock hardness

True

Strength of the rock is dependent on its physico-chemical composition.

True

Physico-mechanical characteristics of same rock type may vary

True

Rocks are strong in taking compressive load but relatively weak in taking tensile load

True

Rocks behave mostly as brittle material but may behave as ductile/plastic

Basalt

Rock with highest Average Bulk unit weight (kN/m³) which is 30

Hard coal

Rock with lowest Average Bulk unit weight (kN/m³) which is 15

Porosity

intrinsic property

Porosity

the storage capacity of the geologic material

Primary Porosity

______ Porosity ranges from < 1% in crystalline rocks like granite to over 55% in some soils.

Secondary Porosity

______ Porosity - porosity of some rock is increased through fractures or solution of the material itself

0-2%

porosity of igneous or metamorphic rocks

up to 40%

porosity of sedimentary rocks

Void Index

mass of water contained in a rock sample after one hour period of immersion

Void Index

ratio of difference between the saturated and dry weight of rock to dry weight of rock

Permeability

relative interconnection of pores

Permeability

"If the material has high ____ than pore spaces are connected to one another allowing water to flow from one to another, however, if there is low ____ then the pore spaces are isolated and water is trapped within them.

Sonic Velocity

evaluates the degree of fissuring

Uniaxial Compressive Strength (UCS) testing

used in estimating situ rock strength in coal mines

Durability

inverse of the alterability of rocks

Durability

controlling not only the stability of slopes, surface and underground excavations but also that of a great number of stone structures, buildings and monuments.

Elastic

change is reversible

shale, milestone

Ductile

change is not reversible

clay, mica

Fracture

change is irreversible and the rock breaks

brittle

quartz, feldspar

Rate of Stress

Temperature

Confining Pressure

Other factors of Deformation

Compression

Pressed together

Tension

Stretched apart

Shear

Slips horizontally

Stress

____ cause Strain

Strain

_____ results in Fracture

Strain

amount of deformation

Strength

existing competency of the rock fabric binding components

Laboratory Tests

Unconfined Compression Tests

Triaxial Compression Test

Splitting Tension Test

Beam Bending Test

Ring Shear test

Uses of Rocks

Blocks of stones are used in foundations, walls, bridge pier, abutments, lighthouses, aqueducts, and retaining walls.

Uses of Rocks

Rocks are used for masonry work, lintels, and vertical columns, covering floors of the building

Uses of Rocks

Flags or thin slabs are used for paving, roofing, etc

Uses of Rocks

Broken or crushed rocks are used as aggregates in concrete, in road constructions

Uses of Rocks

Broken or crushed rocks are also used as railway ballast.

Uses of Rocks

Stone screenings are used as a natural substitute for sand

Uses of Rocks

Limestone is the basic material for the manufacture of lime concrete and cement

Uses of Rocks

Rocks are used as blocks along the river and canal banks for preventing erosion called riprap.

Uses of Rocks

Base material for water and sewage filters, in case of waterworks and sewage treatment plants.

Uses of Rocks

Limestone is also used as a flux in the blast furnaces.

Uses of Rocks

In the construction of the masonry dam, stones of good quality and durability are of vital importance.

Uses of Rocks

For ornamental works in and outside the buildings, like blocks, slabs and chips

Compressive Strength of rock

Drill core quality

Joint spacing

Joint characteristics

Ground water conditions

Joint Orientation

Properties of Rocks for Engineering Purposes