What are joints? •Terminology related to joints •Classification •Engineering considerations Strike joints Dip joint: Oblique joint: bedding joints. Tension joints: Shear joints: Compression joints:

1. By
Rahul sinha

2. •What are joints?
•Terminology related to joints
•Classification
•Engineering considerations

3. What are joints?
•Joints may be defined as the fractures that divide the rocks into parts or blocks which have not been suffered any relative motion along that fracture.
•Joint set: it may be defined as group of or more joint surfaces trending in the same direction with almost the same dip.
• Joint system: A joint system is a group of two or more joint sets. (May have two or three intersecting sets)

4. Terminology related to joints
•Nature: joints may be open or closed.
•Open joints: open joints are the joints in which the blocks have been separated for the small distance to right angles to the fracture surface.
•Closed joints: closed joints are the joints in which the blocks are not separated from each other but allow the fluids(water and gases) to pass through the rocks.
•Veins: generally open joints gets filled up by secondary materials which crystallize or precipitate there forming thin or thick steaks of material. These steaks are called veins when thin and fissure veins when there thickness is greater than 20 cm.

5. Classification
•Joints are classified on the basis of
I.Spatial relationship
II.Geometry
III.Genesis(origin)

6. On the basis of spatial relation
•Systematic joints: joints that shows distinct regularity in the occurrences which can be easily measured or mapped. Such joints occur in parallel joint set that are repeated in the rocks at the regular intervals.
•Non-systematic joints: the joints that don’t posses any regularity in their occurrence and distribution.
On the basis of geometry
There are three types of joints on the basis of geometry:
1.Strike joints
2.Dip joints
3.Oblique joints

7. •Strike joints: the joints which are parallel to the strike of the rock.
•Dip joint: the joints which are parallel to the dip of the rock.
•Oblique joint: joints which are neither parallel to the strike nor to the dip of the layer in which they occur.
•In stratified rocks some joints may develop essentially parallel to the bedding planes. These are called bedding joints.

8. On the basis of origin of joints
1.Tension joints: joints which are developed due to the tensile force acting on the rocks. The ,most common location of such joints are the outer margins of crests and troughs in the folding.
2.Shear joints: these joints are commonly observed in the vicinity fault planes and shear zones where shearing stress prevails. In folds they occur in axial regions.
3.Compression joints: rocks may be compressed too crushing and numerous joints may result due to compressive forces. These occur in the compressive regions of the folds like on in innermost margin of the axis of folds.

9. Engineering considerations
DISAVANTAGES
a.joints are important because they split the rocks into a number of pieces which, in turn, reduce the competence of rock mass, increase the porosity and permeability and make them (rocks) susceptible to quick decay and Weathering.

10. b. Joints become avenues for the leakage of water in case of reservoirs. If they are closely spaced in the upstream side, silting problems also arise in reservoirs.
c. The incompetence, leakage and other effects introduced by joints in rocks may create foundation problems at dam sites.
d. Joints may pose ground water problems in tunnelling.
e. Depending on the relation of the dip of joints in rocks with reference to the surface slope, they may pose problems in laying roads and railways along hill slopes.
ADVANTAGES
1.Increase the ground water potentiality in any place.
2.Suitable spaced joints (i.e., with neither very close nor very wide joint intervals) not only facilitate the quarrying process or tunnelling process but also reduce the cost by decreasing the use of explosives.

11. •What are unconformity?
•Origin of unconformity
•Classification
•Engineering considerations

12. What is unconformity?
•An unconformity may be defined as surface of the erosion on non-deposition occurring within the sequence of rocks. An unconformity is developed due to the change in the process of deposition of sedimentary rocks.

13. Origin of unconformity
•If the process of deposition remain uninterrupted for considerable time then layer will be deposited in order. Older beds occupy the position at the base of the sequence and younger beds are on the top. The sequence of deposition is called conformable.
•But if in any case the deposition is interrupted at a certain stage and exposed to erosion, then top layers will be eroded. This is followed by the phase of deposition of new beds over eroded surface. The sequence so formed is not conformable.

14. Types of unconformities?
•Angular unconformity: it is characterized by different inclinations and structural features above and below the surface unconformity. The sequence below the unconformity may be steep, faulted or folded and sequence above may be horizontal or inclined.
•Disconformity: it is the type of unconformity in which the beds below and above the surface of erosion are almost parallel.
Angular unconformity and disconformity

15. Nonconformity
Non-conformity: it is the term used for unconformity in the sequence of the rocks composed of plutonic igneous or metamorphic rocks as older and sedimentary rocks as younger or newer.

16. Engineering consideration
•Unconformity indicates the discontinuity in the sequence of the rocks. The behavior of the rocks above and below the unconformity shows the variation in their mechanical properties and hence affect the stability of the project.
•Unconformity marks the a weak contact which can allow percolation of water and can also act as fault plane towards forces imposed from above.

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