Analysis and interpretation of joint system

1. SEMINARSEMINAR
onon

2. Introduction
Terminology
Classification
Origin of joints
Occurrence of joints
Fractography
Conclusion
Reference

3. Most rocks are broken by relatively smooth fractures known as
joints.
We may find quite a large proportion of outcrop of any of these
rocks practically free from joints at some places, but at other places
the same type of rock may be heavily jointed, showing cracks of a
greater variety .
Hence it is not only the genesis of the rocks which is responsible for
these structures but also the forces to which these rocks have been
subjected to after their formation.

4. JOINTSJOINTS:
Are fractures along which there has been no appreciable displacement
parallel to fracture and only slight movement normal to the fracture plane.
Joints are most common of all structures present in all settings in all
kind of rocks as well as consolidated and unconsolidated sediment .
Joints may be open or closed in nature.
Open joints are those in which the blocks have been separated or opened
up for small distances in a direction at right angles to the fracture surface.
These may be gradually enlarged by weathering processes and develop
into fissure in rocks.
In closed joints , there is no such separation. Even then these joints may
be capable of allowing fluid is(gases and water) to pass through the rock.

6. 1. Spatial relationships
2. Geometry
3. Genesis (origin)

7.  All joints are divided in to two main groups on the basis of presence or otherwise of some
regularity in their occurrence:
 Systematic joints (regular joints)
 Non-systematic (irregular joints)
 Systematic joints-These show a distinct regularity in their occurrence which can be measured
and mapped easily. Such joints occur in parallel or sub parallel joint sets that are repeated in
the rocks at regular intervals. eg: columnar joints and mural joints.
.
 Non-systematic joints-as the name implies these joints do not possess any regularity in their
occurrence and distribution. They appear at random in the rocks and may have incompletely
defined surfaces. In many cases these are related to the systematic joints in that these occur
between them. At other times, the non systematic joints may show no relationship with the
systematic joints and their curved and rough surfaces may even cut across the former.

8. SYSTEMATIC JOINTS
NON-SYSTEMATIC JOINTS

9.  In stratified rocks, joints are generally classified on the basis of relationship of their attitude
with that of the rocks in which they occur. Three types recognized on this basis are
 Strike joints - Strike joints in which the joints sets strike parallel to the strike of the rocks.
 Dip joints -Dip joints in which the joints sets strike parallel to the dip direction of the rocks.
 Oblique joints - Oblique joints are those joints where the strike of joints is at any angle
between the dip and the strike of the layers. These are also called diagonal joints when they
occur midway between the dip and strike of the layers.
Strike joints Dip joints Oblique joints

11. In igneous and metamorphic rocks the joints may be classified on the basis of
their geometric relations with planar structures of those rocks such as
lineation or cleavage etc. Two terms are commonly used in such cases;
Bedding joints
In stratified rocks, some joints may develop essentially parallel to the bedding planes.
These are simply referred as bedding planes. These are simply referred as bedding joints.
Cross or Q joints
Cross joints are the joints
traversing the linear
structures at right angles
Longitudinal or S joints
Longitudinal or s joints are joints traversing parallel to
the linear structure. In these rocks all the joint
system traversing at any other angular inclination with
the linear structures are described diagonal joints.

13.  Joints are very common and at the same time very complex structures in rocks.
 As regards their origin it is often very difficult to attribute a particular type or
group or system of joints to an exact cause of origin. Only in a few cases , the
predominant force (compression or shear or tension)that has been responsible for
the development of joints in the rocks can be established easily.
Tension joints Shear joints Compression joints
In such cases, joints are classified in to 3 types

14. Tension joints are those, which have developed due to the tensile forces acting
on the rocks. The most common location of such joints in folded
sequence is on the outer margins of crests and troughs. They are
also produced in igneous rocks during their cooling
.Shear joints are commonly observed in the vicinity of the fault planes and shear
zones where the relationship with shearing forces is clearly
established. In folded rocks, these are located in axial regions.
Rocks may be compressed to crushing and numerous joints may
result due to the compressive forces in this case. In the core
regions of folds where compressive forces are dominant, joints
may be related to compressive forces.
Compression
joints

15.  Joints are caused in different rocks due to different reasons.
 No single theory can explain origin of all types of joints .
 At present it is agreed that there are at least 3 principal processes due to which joints may
be caused in different rocks. These are outlined as follows
;
Contraction during Formation
Expansion and Contraction
Crustal Disturbances

16.  Sedimentary rocks especially those of plastic nature and rich in moisture in the initial stages
(clay, shale's, limestone's and dolomites) undergo some contraction on drying up which might
have resulted into irregular jointing
 Similarly igneous rocks which form by cooling and crystallisation from an originally hot and
molten material, during the cooling process giving rise to tensile forces strong enough to
break the congealing masses in to jointed blocks . Such contraction or shrinkage is generally
accepted to be the cause of the vertical type joints in granites and columnar joints of basalts.

17. Vertical joints in granite due to contraction Columnar joints in basalt due to contraction
Joints in sedimentary rock due to
compaction and drying
Vertical joints in dolomite due to contraction

18.  Rocks ,like many other solids, expand with rise in temperature and contract on
cooling.
 Such repeated expansion and contraction is characteristic of regions with dry hot
climates where day and night temperatures on the one hand and summer and
winter temperatures on the other hand vary with in a very wide range.
 The outer parts of rocks exposed to direct sun heat may develop cracks and
fissures due to such repeated expansion and contraction

19.  Many jointed types, especially those associated with folded and faulted rocks are
clearly related to the processes of crustal disturbances that are responsible for
building of mountains and continents.
 Sudden seismic shocks have also been suggested by some as a possible cause for
the development of joints in many rocks
Joints in tectonically disturbed
rock strata.

20. (A) IGNEOUS ROCKS
Columnar joints
Mural joints

21.  Sheet joints - A horizontal set of joints
often divides the rock mass in such away as
to give it an appearance of a layered
sedimentary structure, called in this case as a
sheeting structure.
Mural joints – They may occur 3 sets of
joints in such a way that one set is horizontal
and other 2 sets are vertical, all the 3 sets
being mutually at right angles to each other.
This sort of geometrical distribution of joints
dividing the rock mass into cubical blocks or
murals ..
Sheet joints
Mural joints (horizontal & vertical) in
granite , on Summit of Cadillac Mountain,
US

22. Columnar joints(prismatic joints)- The joints divide the rock mass into
polygonal blocks, each block being bounded by 3 to 8 sides.
Normally the main joints are vertical or perpendicular to the
cooling surface and may extend to varying depths ranging
from a few centimeters to many meters.
Columnar joints
Gilbert hill, Mumbai
Columnar basalt
Malwa Island, Mumbai

23.  Most sedimentary rocks are generally profusely jointed.
 Joints may be systematic and non systematic classes.
 These joints may be closely and regularly spaced sets, parallel or sub parallel to each
other and bearing varying relationship with the attitude of the rock
(C) METAMORPHIC ROCKS
 These tock types are heavily jointed in many cases, the joints being of irregular or non-
systematic types.
 These joints are often the result of local and regional stresses acting on rocks as a
source of metamorphism.

24.  Joint propagation can be studied using the techniques of fractography in which
characteristic marks such as hackles and plumose structures can be used to determine
propagation directions and, in some cases, the principal stress orientations
Importance to soil and rock mass strength
 In geotechnical engineering a joint forms a discontinuity that may have a large influence on
the mechanical behavior (strength, deformation, etc.) of soil and rock masses in, for example,
tunnel, foundation, or slope construction.
Importance in the production of geofluids
 It is long been recognized that joints (fractures) play a major role in the subsurface fluid flow
of water in aquifers and petroleum in oil fields. Major industry research projects have been
dedicated during the last decades to the study of faulted and fractured reservoirs.

25. Plumose structure on the
exposed surface of a joint in the
Passaic Formation of the Newark
basin, North America
Plumose structure(South Atlantic
region of United States)
Hackles
RIBs are the large curved surface.

26.  Joints are defined as divisional planes or fractures along which there has been no relative
displacement.
 Joints may be open or closed in nature.
 Systematic joints occur in parallel or sub parallel joint sets that are repeated in the rocks at
regular intervals. Non-systematic joints appear at random in the rocks and may have
incompletely defined surfaces
 Joints are originated by the process of expansion and contraction and crustal disturbances
 Joints are of great practical importance for all those dealing with the rocks as sites,
materials of construction, in prospecting for minerals, groundwater and oil and gas
reservoirs. Hence elementary knowledge about their geometry, classification and style of
occurrence in different rocks is important.

27.  Bruce E. Hobbs, Winthrop D. Means and Paul F. Williams (1976). An
outline of Structural Geology, International Edition, pp.289-300.
 George A., Davis Stephen and J .Reynolds(1977). Structural Geology
Second Edition, pp.204-67.
 Lu de Sitter(1956).Structural geology, First edition, pp.122-132.
 Marland P. Billings(1982). Structural Geology, Third Edition, pp.140-173.
 www.bgu.ac.il/geol/classes/structural/Front/lec00
 www.geo.wvu.edu/~jtoro/structure