Types of pillars used in the mining sector

2.  Rock support is the term widely used to describe the
procedures and materials used to improve the stability and
maintain the load bearing capacity of rock near to the
boundaries of an underground excavation.
 The primary objective of a support system is to mobilize
and conserve the inherent strength of the rock mass so
that it becomes self-supporting.
 Rock support generally combines the effects of
reinforcement, by such elements as dowels, tensioned
rock bolts and cables, and support, with shotcrete, mesh
and steel sets which carry loads from individual rock
blocks isolated by structural discontinuities or zones of
loosened rock.

3.  In an underground mine (E.g. room-and-pillar mining), the
pillars are required to provide global stability which can be
defined as supporting the overlying strata up to the
surface. In addition, local stability in the form of stable
pillar ribs and roof are required to provide safe working
conditions.
 However regardless of which mining method is used,
every mine must leave pillars to stabilize underground
structures. The variation of the ground conditions, stress,
the multiple pillar applications related to the mining
methods and ore body geometry results in pillars being
non identical.
 The pillar shape, the load acting on the pillar, and the
strength of the pillar material are the three most important
factors to be considered when designing a pillar.
 pillars can be grouped into three groups namely; support
pillars,stabilising pillars and protection pillars.

4. Sill Pillar
Horizontal pillars that separate levels or stopes, often used when multiple levels
are mined concurrently.
Room
and pillar
Pillars are left in place in a predetermined and calculated pattern as rooms are
mined out.
Yield
Pillars
Pillars are designed to fail by going past peak load carrying capacity. Roof-strata
is maintained by relieving pressure in working areas and controlling transference
of load to abutments that are clear of working areas and road ways. Yielded pillars
still carry load.
Post
Pillars
Room and pillar variation where ore is mined out in a series of horizontal slices.
Barrier
Pillars
Solid blocks left between two mines or sections of a mine. Provides regional
support in large mines to prevent accidents due to inrushes of water, gas, or
explosions or a mine fire.
Bracket
Pillars
Slip on discontinuities may cause rock burst within stopes, which can cause
equipment damage and injury or loss of life. Ore immediately adjacent to these
geological structures is left unmined to protect the structure from mining induced

5. Shaft
Pillars
A large area that is left unworked around the shaft bottom to protect the shaft and
the surface building from damage due to subsidence. Protects the shaft itself.
Crown
Pillars
A rock mass of variable geometry, mineralized or not, situated above an
uppermost stope of the mine, which serves to permanently or temporarily ensure
the stability of surface elements. Surface elements include bodies of water and
soil.
Barrier
Pillars
Solid blocks left between two mines or sections of a mine. Provides regional
support in large mines to prevent accidents due to inrushes of water, gas, or
explosions or a mine fire.
Bracket
Pillars
Slip on discontinuities may cause rock burst within stopes, which can cause
equipment damage and injury or loss of life. Ore immediately adjacent to these
geological structures is left unmined to protect the structure from mining induced

6.  Support pillar – is an in stope pillar left out in
production areas, used in massive deposits
like coal,chrome and iron minning.
 Protective – a pillar that is used to protect
structures such as shafts, crusher chambers
 Control – Are Pillars used to control mining
hazards like rock bursts, and tremors. The
width to height ratio is generally more than
10

9. introduction

11.  A triaxial shear test is a common method to measure
the mechanical properties of many deformable solids,
especially soil (e.g., sand, clay) , rocks, and
other granular materials or powders.
 In a triaxial shear test, stress is applied to a sample of
the material being tested in a way which results in
stresses along one axis being different from the
stresses in perpendicular directions.
 This is typically achieved by placing the sample
between two parallel platens which apply stress in one
(usually vertical) direction, and applying fluid pressure
to the specimen to apply stress in the perpendicular
directions

12.  The application of different compressive stresses in the test apparatus
causes shear stress to develop in the sample; the loads can be
increased and deflections monitored until failure of the sample.
 During the test, the surrounding fluid is pressurized, and the stress on
the platens is increased until the material in the cylinder fails and forms
sliding regions within itself, known as shear bands
 The geometry of the shearing in a triaxial test typically causes the
sample to become shorter while bulging out along the sides. The
stress on the platen is then reduced and the water pressure pushes
the sides back in, causing the sample to grow taller again.
 This cycle is usually repeated several times while collecting stress and
strain data about the sample.
 During the test the pore pressures of fluids (e.g., water, oil) or gasses
in the sample may be measured using Bishop's pore pressure
apparatus.

13.  In general conventional triaxial test involves
subjecting a cylindrical soil sample to radial
stresses (confining pressure) and controlled
increases in axial stresses or axial displacements.
 Triaxial test data, in general, include evolution of
axial and volumetric strain, deviatoric and isotropic
stress, and pore pressure evolution a
 from the triaxial test results, it is possible to deduce
the shear strength parameters, namely friction
angle, cohesion, dilatancy angle and the other
dependent parameters.

16.  Triaxial cell –this is where the specimen is
placed and is covered by specimen
membrane.
 Load frame- its purpose is to apply to the
specimen.
 Load cell-its purpose is measuring the
applied load.
 Pressure and volume control modules –
these control amount of pressure applied to
the specimen and volume .
 Data acquisition system –records data as the

18.  There are two phases in a triaxial test which are
consolidation phase and shear phase
 During the consolidation phase there is increase in
pressure in the cell which provides a uniform
confining stress all the specimen equal to minor
principal stress (Q3) it may be allowed to
consolidate or not.
 During the shear phase load is applied to the top of
the specimen and increases shear stress at the top
(Q1) as shown in the diagram
 Stress gradually increases until the specimen
 fails.
 There is also another phase called the saturation
phase.

20.  Pressure is added and Q3 increases
 Two drainage conditions : drained(drainage
valve is open) and undrained ( drainage
valve is closed).
 UNSOLIDATED TEST (symbol U)-when
valve is closed.
 No volume change and excess pore
pressure is generated.
 CONSOLIDATED (symbolC)-Drainage vailve
is open and volume change is allowed and
no excess pore pressure

21.  Drained ( symbol D)- drainage valve is open
and no excess pore pressure generated
during shearing.
 Undrained(symbol U)-drainage valve closed
and no volume change
 Excess pore pressures generated.
 Often measure pore pressure.

23.  The cylindrical soil specimen used is usually of the dimension of 100
mm diameter and 200 mm height.
 The specimen preparation depends on the type of the soil. Samples of
cohesive soils are often prepared directly from saturated compacted
samples, either undisturbed or remolded.
 For cohesion-less soils, however, the specimen is prepared with the
help of a mold that maintains the required shape of the specimen.
 The specimen is vertically enclosed with a thin rubber membrane and
placed between two rigid ends inside a pressure chamber.
 The upper plate can move vertically and apply vertical stresses to the
specimen. The axial strain/stress of the sample is controlled through
the movement of this vertical axis

24.  In case of consolidated drained (CD) the test
sample is consolidated and sheared in
compression slowly to allow pore pressures
build up by shearing to dissipate, the rate of
axial deformation is kept constant that is strain
is controlled.
 The idea is that the test allows the sample and
the pore pressures to fully adjust to surrounding
stress.
 The test may take a long time to allow sample
to adjust, in particular low permeability samples
need long time to drain and adjust strain to
stress levels.

25.  in case of an unconsolidated undrained (UU) test the loads are
applied quickly and the samples are not allowed to consolidate
during the test.
 the sample is compressed at a constant rate ,stain controlled.
 In case of consolidated undrained (CU) the sample is not
allowed to drain ,the shear characteristics are measured under
undrained conditions and assumed to be fully saturated
 Measuring the pore pressures in the sample allows
approximating the consolidated-drained strength .
 Shear speed is often calculated based on the rate of
consolidation under a specific confining pressure
 Confining pressure can vary anywhere from 1psi to 100psi or
greater , sometimes requiring special load cells capable of
handling higher presures.

26.  effect of rubber membrane on the measured deviatoric stress i.e. the
rubber membrane used to enclose the soil sample in undrained
triaxial compression test results in apparent increase in the
measured strength, depending up on the stiffness, thickness, and
diameter of the membrane
.
 bedding Error and Effects of Specimen Boundaries
 volume Change during Saturation
 volume Change due to Membrane Penetration: In triaxial tests on
granular soils, volume change due to membrane penetration occurs
when the latex membrane penetrates into the surface irregularities
of the specimen with increasing of the effective minor principal
stress, while the membrane tends to return to its original position
when the principal stress is reduced