Rock Mechanics Notes

Rock Mechanics

is the theoretical and applied science of the mechanical behavior of rock. It is the branch of mechanics concerned with the response of rock to the force fields of its physical environment.

Structural rock mechanics

which is concerned with the stability of engineering structures in which the material is predominantly rock.

Comminution

which is concerned with the reduction of rock to small fragments by the application of external forces as in drilling, blasting, cutting and grinding.

Intact rock or rock material

in-situ material

Lithology

Geology

Discontinuities

any opening in the rock

Rock mass

intact rock + discontinuities

Active support

Timbering, cable bolt, shotcrete, cable slings, poured in situ & pre cast concrete

Passive support

rock bolt, screens, grouting, pillars

Grouting

Injecting cement at a high pressure

Cement and water

the grout is composed of ______.

Rock bolting

inserting steel bolts ar rods with grouted ends.

Shotcrete/Sprayed concrete

concrete is pneumatically sprayed onto a surface to create a structural layer.

Plane failure,wedge failure, circular failure, toppling/ rotational failure

Modes of failure

Plane failure

striking parallel to the slope

Wedge failure

slide simultaneously on 2 discontinuity planes.

striking obliquely across the slope face.

Circular failure

slides on a single cylindrical face into free space/excavation

Toppling/Rotational failure

multiple rock columns/layers caused by a steeply dipping….

Block toppling

Types of Toppling failure when the rock block is already detached from the rock mass of the slope.

Flexural toppling

Types of Toppling failure when the rock block remains attached from the rock mass of the slope.

Block flexural toppling

simultaneous failure of individual blocks and the flexural failure of a larger rock mass or slab.

Rockbursts

is a sudden energy release at a free face of a rock structure resulting to a failure or collapse characterized by a violent ejection of rock,accompanied by significant vibrations and noise.

Kolar gold mine in India

earliest rock burst in the world.

Indirect Tensile/ Brazilian

a laboratory test used to determine the tensile strength of a cylindrical rock specimen having the shape of a disc.

Slickensides

is the standard term used for smooth and stick, shiny surfaces that look polished.

Factor of safety

Fr (resistive force) /Fi (inducive force)

Specific gravity

the ratio of the weight of a substance to the weight of an equal volume of a standard substance.

Youngs modulus of elasticity/elastic modulus/ tensile modulus

Physical properties of rocks

is a measure of the rock stiffness or ability to deform elastically under an applied load.

compressive stress/axial strain

Poissons Ratio

Lateral strain/longitudinal strain or axial strain

Shear Modulus (Modulus of rigidity)

a measure of the materials stiffness in shear.

ability of a material to resist transverse deformations.

Bulk modulus (volume modulus)

ability of a substance to withstand changes in volume when under compression on all sides.

Lame’s constant/ moduli (lambda)

measures of a rocks brittleness, which is a function of both Young’s modulus and poissons ratio.

Hookes law of elasticity

stress is proportional to the strain in a linear elastic material

Mohr-Coulomb failure criterion

failure across when the shear stress exceeds the shear strength of the material on the failure plane.

represented by a linear failure

Hoek- Brown failure criterion

represented by non linear failure.