This document discusses techniques for measuring the index properties of rocks, which are relatively easy to measure properties that provide valuable information about rock specimens. It describes five key index properties: porosity, density, sonic velocity, permeability, and strength. Porosity identifies the proportion of voids in a rock. Density provides information about mineral and grain constituents. Sonic velocity evaluates the degree of fissuring. Permeability assesses the interconnectivity of pores. And strength determines the competency of the rock fabric. Equations are provided for calculating each of these index properties.

1. TOPIC: TECHNIQUES FOR MEASUREMENT OF IN-SITU STRESSES

2. INDEX PROPERTIES OF
ROCK
Because of vast range in the properties of rocks &due to certain
properties that are relatively easy to measure are valuable & may be
designated index properties for rock specimens.
• POROSITY
• DENSITY
• SONIC VELOCITY
• PERMEABILITY
• STRENGTH

3. 1 Porosity identifies the relative proportion of solids and voids.
2 Density adds the information about the minerals and grain
constituents.
3 The sonic velocity evaluate the degree of fissuring (planar
cracks in igneous & metamorphic rocks).
4 Permeability evaluate the relative interconnection of pores.
5 Strength determine the present competency of rock fabric to
bind the component together.

4. Porosity
Porosity is the ratio or fraction b/w the proportion of void spaces & the total spaces in the rock
n= vp /vt
Vp = volume of pores
Vt = total volume
Sedimentary rocks are formed by the accumulation of grains . rock fragments & shells.
Porosity varies from 0% to 90 % with 15% as a typical value for an average sandstone
Porosity generally decreases with age & depth below the surface.
A typical cambrian sandstone has 11% porosity & cretaceous sandstone has 34 % porosity
Chalk is most porous among all the rocks its porosity is 50%.

5. Porosity can be determined from the following
calculations
• Measured density.
• Measured water content after saturation in water
• Mercury content after saturation with mercury using pressure injector.
• Measured solid volume & pore air volume using boyles law.

7. DENSITY
Density is the mass per unit volume.
Density = M/V
It is stated previously that the porosity of rock can be calculated from the knowledge of its
weight density.
Density tell about the porosity & permeability .
At 20 °C in the rock the volume of water is 62.4 𝑔/𝑐𝑚3
.
If the percentage of different mineral can be estimated under a binocular microscope or
from the thin section , the specific gravity of the part of the rock can be calculated as
the weighted average of solid specific gravities of component grains & crystal.

8. G𝑖 = Specific gravity of component 𝑖
𝑉𝑖 = volume percentage in the solid part of the
rock
The relationship b/w porosity &dry density is

9. The dry density is related with wet density by relationship
W= water content of rock (dry weight basis)
Water content &porosity are related by

10. In case of mercury content
Specific gravity of mercury =13.5

12. SONIC VELOCITY
Sonic velocity evaluate the degree of fissuring( planar cracks in igneous and
metamorphic rock)
SONIC VELOCITY AS AN INDEX TO DEGREE OF FISSURING:
The velocity with which stress waves are transmitted. First calculate the longitudinal
wave velocity that the specimen would have,if it lakcked pores or fissures.
If the mineral composition is known longitudinal wave velocity can be calculated as

13. Where the v1 𝑖 is the longitudinal wave velocity in mineral constituent 𝑖
which have volume proportion C𝑖 in the rock.
Now measure the actual velocity of the longitudinal waves in th rock
specimen & form the ratio
As a quality index define
Where np% is the porosity of non fissured rockas a
percentage.

16. PERMEABILITY
Permeability evaluate the relative interconnection of
pores.
Fluid mechanics depend upon permeability.
Shale is porous ,not permeable &fluid mechanics is not
involved
Sandstone is porous ,permeable & fluid mechanics is
involved,

17. STRENGTH
Strength determine the present competency of rock fabric
to bind the component together.
Strength determination of rock usually required carefull
test setup & specimen preparation & result are highly
sensitive to the method & style of loading.
Strength index is now available using the point load test
describe by “BROCH & FRANK”.

18. Where P is the load of rupture & D is the
distance b/w the point loads
Test are done on pieces of drill core at atleast .4 times as long
as the diameter

19. THANK YOU