This document discusses rock mass structure and characterization. It defines rock material, rock mass, and rock structure. It describes major structural features like bedding planes, folds, faults, shear zones, dykes, joints, and veins. It discusses important geomechanical properties of discontinuities such as spacing, persistence, orientation, roughness, aperture, and filling. It covers approaches for collecting structural data through mapping exposures and geotechnical drilling and core logging. It also discusses presenting structural data.

1. Rock Mass Structure
and Characterization
BY: MARIA CARISSA M. LANDOY, RCE

2. Rock material is the term used to
describe the intact rock between
discontinuities; it might be
represented by a hand specimen or
piece of drill core examined in the
laboratory.

3. Rock mass is the total in situ medium
containing bedding planes, faults,
joints, folds and other structural
features.

4. The nature and
distribution of
structural features
within the rock
mass is known as
the rock
structure.

5. Major Types of Structural
Features
Bedding planes divide sedimentary
rocks into beds or strata. They
represent interruptions in the course of
deposition of the rock mass.

6. Folds are structures in which the
attitudes of the beds are changed by
flexure resulting from the application
of post-depositional tectonic forces.

9. Faults are fractures on which
identifiable shear displacement has
taken place. They may be recognized
by the relative displacement of the
rock on opposite sides of the fault
plane.

15. Shear zones are bands of material,
up to several meters thick, in which
local shear failure of the rock has
previously taken place. They
represent zones of stress relief in an
otherwise unaltered rock mass
throughout which they may occur
irregularly.

17. Dykes are long, narrow intrusions of
generally fine-grained igneous rock
with steep or vertical and
approximately parallel sides.

19. Joints are the most common and
generally the most geotechnically
significant structural features in rocks.
Joints are breaks of geological origin
along which there has been no visible
displacement.

20. Veins, or cemented joints, are mineral
infillings of joints or fissures. They may
be sheet-like or tabular or irregular.

21. Important Geomechanical
Properties of Discontinuities
Spacing is the perpendicular distance
between adjacent discontinuities, and
is usually expressed as the mean
spacing of a particular set of joints.

22. Persistence is the term used to
describe the areal extent or size of a
discontinuity within a plane. It can be
crudely quantified by observing the
trace lengths of discontinuities on
exposed surfaces.

23. Orientation, or the
attitude of a discontinuity
in space, is described by
the dip of the line of
maximum declination on
the discontinuity surface
measured from the
horizontal, and the dip
direction or azimuth of this
line, measured clockwise
from true north.

24. Roughness is a measure
of the inherent surface
unevenness and waviness
of the discontinuity relative
to its mean plane.

27. Aperture is the
perpendicular
distance separating
the adjacent rock
walls of an open
discontinuity in
which the
intervening space is
filled with air or
water.

28. Filling is the term used to describe
material separating the adjacent
rock walls of discontinuities.

29. Collecting Structural Data
Mapping Exposures
In the early stages of a mining project,
it may not be possible to gain access
underground. In this case, surface
outcrops must be utilised to obtain
information on the engineering
properties and structure of the rock
mass.

30. Approaches Used for Mapping
• spot mapping in which the observer
selectively samples only those
discontinuities that are considered to be
important;
• lineal mapping in which all discontinuities
intersecting a given sampling line are
mapped; and
• areal mapping in which all discontinuities
within a selected area of the face, often
called a window, are mapped.

31. Technique Used for Mapping
The basic technique used in mapping surface
or underground exposures is the scanline
survey. A scanline is a line set on the surface
of the rock mass, and the survey consists of
recording data for all discontinuities that
intersect the scanline along its length.

32. Geotechnical drilling and core
logging
Core drilling is the most reliable way of
exploring the interior of a rock mass prior to
mining. Downhole geophysical and other
instruments may be used in drill holes to
investigate the structure and physical
properties of the rock mass.

33. Presentation of Structural Data
Major structural features such as
dykes, faults, shear zones and
persistent joints may be depicted in a
variety of ways. Their traces may be
plotted directly on to mine plans with
the dips and dip directions marked.

34. Joints and bedding planes
The data for joints and bedding planes differ in
two significant respects from the data for
major structural features such as faults.
• They are much more numerous, giving rise
to a distribution of orientations for each set
rather than the single orientation used to
describe a major feature.
• Their spacing or frequencies are important
and must be represented in some way

35. Thank You ….