Lecture 1 Rock Mech

Ground

is any natural material present at the site where engineering structures are laid. It is divided into “soil” and “rock”.

Soils

consists of loose particles not cemented together

Rocks

consist of consolidated particles cemented together resulting in a tensile strength

Rock Mass

The whole array of blocks of rock and the discontinuity planes are called

Soil Mechanics

It is defined as the study of the physical properties of soil that will have a direct impact on the design of structures to be built on it.

Rock Mechanics

It is characterized by the fact that rock is not a continuum but a regulated discontinuum; It deals w/ the theoretical & applied behavior of rocks; the branch of mechanics concerned w/ the response of rock to the loads applied into it;It deals primarily with the changes in mechanical behavior in rock such as stress, strain and motion of rocks brought by engineering activities.

Engineering Geology

applies to geological sciences to engineering practice to ensure that geological factors affecting location, design, and construction engineering works are recognized and adequately provided for a sound and stable engineering structure.

Engg Geology Geology

1. Limited up to 300ft Covers 10-20 miles depth below surface or more

2. Had a specific area of Study cover large areas study

Geotechnics

is the civil engineering discipline containing element of engineering geology fortified with pertinent knowledge from other earth sciences such as foundation engineering, soil mechanics, rock mechanics, earthworks, hydraulics, hydrology tunnels, etc.

Theoretical Basis of Rock Mechanics

The ultimate understanding of the strength of the rock and its performance in-situ.

Importance of Rock Mechanics to Engineering Practice

To avoid hazard

To reduce hazard

To eliminate hazard

Theory of Elasticity

rocks have elastic properties whereby all strains created by externally applied loads are instantaneously and totally recoverable upon removal of all external loads. A material is perfectly elastic if it recovers completely upon removal of external loads.

Theory of Plasticity

To study, mathematically the stresses and displacement in plastically deforming rock materials. When rock mass will be under the action of large enough stresses, there is strain permanent deformations which remain after the removal of the externally applied load.

Rock Mass

It consists of intact rock but is more commonly formed from an array of intact rock blocks with boundaries formed by discontinuities.

Intact Rock

are blocks of rock that do not contain mechanical discontinuities and do have tensile strength

Discontinuities

is a plane or surface that marks a change in physical and chemical characteristics in rock material.

Discontinuity

is a plane that marks an interruption in the continuity and normally has low or zero tensile strength.

Discontinuous rock mass

is a rock mass containing discontinuities.

Igneous Rocks

forms when hot molten silicate materials called magma coming from beneath the earth’s crust solidifies.

Sedimentary Rocks

forms by deposition & accumulation of sediments of other rocks, plant and animal remains, by wind or water at earth surface and their later solidification or cementation into rock.

Metamorphic Rocks

forms when already existing rocks undergo changes by recrystallization into solid state at high pressure, temperature and chemical actions.

7 Rock Properties

1) physical 5) elastic

2) mechanical 6) plastic

3) electrical 7) strength

4) thermal

10 Physical Properties

1. Mineralogical Composition, Structure & Texture

2. Specific Gravity

3. Unit Weight

4. Porosity

5. Void Ratio

6. Natural Moisture Content

7. Saturation Moisture Content

8. Degree of Saturation

9. Permeability to Water

10. Chemical Effects