This document discusses several index tests used by engineers and geologists to determine the strength and deformation properties of soils and rocks in the field. It describes the Brazilian test, point load index test, impact test, and Schmidt hammer rebound test. The Brazilian test measures tensile strength. The point load index test uses a handheld device to apply a compressive force and induce tensile cracking. The impact test evaluates coal degradation. The Schmidt hammer rebound test measures surface hardness in a non-destructive manner using rebound value correlations. These index tests provide immediate preliminary results without extensive preparation and can be correlated to laboratory strength tests.

2. TOPIC:

3. INTRODUCTION
Engineers or geologists determine index
properties:
 At the field site.
 By hand held or portable equipment.
 Index properties correlated to strength and
deformation properties for design

4. Reasons for Developing Index
Tests
 1 Laboratory testing elaborate & time
consuming
 2 Delay in assessment
 3 Field tests immediate results
requiring
 Not much specimen preparation
 Use of portable equipment for testing
 Correlated to strength & design properties
 Representing in situ properties
 Borehole logging can be related to index
tests

5. Brazilian Test
σt = 2P / πDt
 σt= Uniaxial tensile strength
 P = Load at failure on a
portable machine MPa
 D = diameter of the core (m)
 t = Thickness of core (m)

6. Idealised Condition for Brazilian Test
 Minimum core diameter 54 mm
 Diameter to height ratio1 to 2
 Minimum number tests –5
 Loading rate- 6.5 mm/minute
 Loading through curve jig
 Failure of specimen across loading platen

7. Point load Index Test
 The point load test was developed by Broch and
Franklin in 1972.
 It is a small hand-portable test apparatus used to
provide an index for the strength classification of
hard rocks in the field; it allows a quick and non-
expensive on-site evaluation of strength of hard
rocks.
 The test consists of squeezing pieces of
rock diametrically between two hardened steel
cones

9. Point load Index Test:
 Basically, the test method relies on the
principle of inducing tensile stress into the rock
by the application of a compressive force.
 Rock specimens break since tensile cracks
develop parallel to the loading direction.
 The cylindrical rock samples can be loaded
diametrically or axially whereas irregular rock
pieces can also be loaded

10. Idealised Condition for Point Load Index
Test
 Portable loading machine
 Calibration chart for size correction
 Minimum core diameter 50mm
 L/d ratio = 1.5:1
 Number samples-10-15
 No standard rate of loading
 Platen 60 degree cone with 5mm curvature

11. Point load Strength Test
 The maximum tensile stress at the centre
of the specimen may be related to the
applied load and to the distance between
the point loads according to the equation:
Is= P/D2
Where,
Where P is the load (MN) at rupture and
D is the core diameter (meters).

12. Point load Strength Test:
 For irregular rock pieces, an equivalent
diameter should be recorded.
 In general, it has been found that the
value of the
load P at failure depends largely on the core
diameter.
 Hence, the results of point load tests are
usually presented in terms of a reference
diameter equal to 50 mm.
 The unconfined compressive strength σc
is related to the point load
index with 50 mm cores Is50 as follows:

13. Point load Strength Test:
σc =24Is

14. MRDE Impact Test
 Test to estimate degradability of coal.
 Face conveyor, transfer points, storage bin,
screening and washing.
 1.8kg standard plunger (42mm diameter) is
dropped.
 on coal by standard distance.
 20 blows on 100 gm of coal.
 One impact every 2 seconds.
 Weight of coal remaining on 3mm sieve is
impact index.

15. Standard test conditions:
 Specimen diameter > 32 mm
 Number of sample 5 or 6
 Impact rate not faster than 1 to 2 per
second

16. Schmidt Hammer Rebound Test
 Portable inexpensive
 devise.
 Rock joints or rock
 surface or lab specimen.
 Amount of rebound of
 hammer on the prepared
 surface.
 Rebound number on the
scale can be correlated to UCS.

17. Schmidt Hammer Rebound Test:
 ISH= 0.5 σc
 ISH= Schmidt rebound number
 σc = UCS MPa
 Coefficient of Correlation = 0.86

18. Schmidt Hammer Test
 A Schmidt hammer, also known as a Swiss
hammer or a rebound hammer, is a device to
measure the elastic properties or strength of
concrete or rock, mainly surface hardness and
penetration resistance.
 It was invented by Ernst Schmidt, a Swiss
engineer