5
When aggregate is transferred, it can be appropriate
to incorporate spray chambers and sumps. Further to that,
direct feed into excavated bins, muck bays, or fill stopes
may forego the need for a transfer boot.
Vacuum Break/Pressure Release
Different configurations will be appropriate to different
media, and whether wet or dry. In addition to caps or plugs
for safety, they can be appropriate for assisting with ventila-
tion control, material flow, extending drying time, or dust
management.
In graded aggregates, wet or dry, a vent bypass – effec-
tively a vacuum break – at the collar can be useful to assist
full flow into the slickline. That is especially so if strong
upcast is present. In any event, a bypass provides a locus
for dust collection if that is a problem at the surface. Once
transfer is complete, the bypass and slickline are plugged to
assist in ventilation control and system safety.
Though some segregation is expected due to particle
size-and-shape drag in free-fall (Particle Size Distribution/
Particle Shape), transfers can be characterized as slug flow,
which in turn can induce a trailing vacuum behind the flow
(Appendix), with hammer, turbulence, and increased pipe
wear. In some cases, these effects can be severe. Vacuum
breaks or vent bypasses can lessen these effects.
Fine material such as sand or dry binder – cement, fly
ash – can be handled reliably with combined pressure/relief
valves (CAV) at the slickline collar, similar to the use of
CAVs for liquid transfer. These media typically can be fed
through closed silos or bins, which are further protected by
using rotary valves (rotary air locks) to avoid uncontrolled
drawdown which becomes uncontrolled charging of the
transfer line.
UNDERGROUND STATION—
TRANSFER IMPACT
The material characteristics and the system depth and con-
figuration are principal factors determining the impact force
at the diverter boot. Classical/empirical free-fall analyses
(5), computational flow dynamics (CFD), and discrete ele-
ment modeling (DEM) provide evolving methods for esti-
mating the velocities and impact forces in a given system.
The impact penetration/consolidation within the boot
is affected both by the transferring material and the mate-
rial in the boot/rockbox base. Even if the same material,
consolidation, possibly degradation, of material in the
boot will occur through subsequent impact. The direction
change and discharge port configuration affect the process
and are addressed in the boot/rockbox design.
With long drops, even wet mixes will tend toward seg-
regation, and to some extent the diverter/rockbox/energy
dissipator serves as a remix point. In placing shaft linings
and stations, that may be the extent of remix. For mine
development, construction, and ground support, it is advis-
able to discharge into transit mixers which will more com-
pletely remix the loads.
The K-2 potash mine of IMC, with a 975-m (3,200-
ft) drop of salt tailings, using a 14-cm (5.5-in) ID pipe
with a 90-degree discharge ELL, experienced considerably
lower impact stress than expected (6). The ELL was instru-
mented, with an observed loading on the order of 4.1 MPa
(600 psi), well below expected calculations on the order
of 13.8 MPa (2,000 psi). The tails were transferred with
solids content ranging between 20 and 30 percent, and
cemented or uncemented as appropriate for the immediate
fill requirements.
UNDERGROUND STATION—
BOOT/ROCKBOX
The diverter device itself can be analyzed as a pipe bend
(7) which also functions as an energy dissipator or thrust
block under complex impact. The boot below or beyond
the operating flow of material essentially is the rock ELL or
rock box component, minimizing the opportunity for pipe
wear along the sweep of the ELL. A typical hinged base
shotcrete/concrete boot is illustrated in Figure 1.
Boot Geometry
An enlarged receiving chamber can accommodate the
rebound and scatter which occurs as the material deflects
to the discharge opening. That energy dissipating chamber
-top of the boot -should be nominally 1.5 time the inlet
pipe diameter from the top of the boot to the invert of the
discharge barrel. The boot diameter should be no less than
1.5 times the inlet pipe diameter. The boot length should
be no less than three inlet pipe diameters, and should
increase with drop length, nominally 15cm (6 in) for each
additional 300m (1,000 ft) (Appendix).
The boot discharge diameter should be no less than
the diameter of the slickline/dropline. If the discharge pipe
plunges downward as in a conventional lateral, the enlarged
effective discharge area contributes to reliable operation.
Matching the discharge diameter to the diameter of the
body of the boot can be acceptable with the following
proviso.
Commonly, the boot discharge is coupled to additional
conduit lengths which feed the final target, whether static
or mobile. Material handling hoses are typical final conduits
whether filling shaft forms or loading haul trucks or transit
When aggregate is transferred, it can be appropriate
to incorporate spray chambers and sumps. Further to that,
direct feed into excavated bins, muck bays, or fill stopes
may forego the need for a transfer boot.
Vacuum Break/Pressure Release
Different configurations will be appropriate to different
media, and whether wet or dry. In addition to caps or plugs
for safety, they can be appropriate for assisting with ventila-
tion control, material flow, extending drying time, or dust
management.
In graded aggregates, wet or dry, a vent bypass – effec-
tively a vacuum break – at the collar can be useful to assist
full flow into the slickline. That is especially so if strong
upcast is present. In any event, a bypass provides a locus
for dust collection if that is a problem at the surface. Once
transfer is complete, the bypass and slickline are plugged to
assist in ventilation control and system safety.
Though some segregation is expected due to particle
size-and-shape drag in free-fall (Particle Size Distribution/
Particle Shape), transfers can be characterized as slug flow,
which in turn can induce a trailing vacuum behind the flow
(Appendix), with hammer, turbulence, and increased pipe
wear. In some cases, these effects can be severe. Vacuum
breaks or vent bypasses can lessen these effects.
Fine material such as sand or dry binder – cement, fly
ash – can be handled reliably with combined pressure/relief
valves (CAV) at the slickline collar, similar to the use of
CAVs for liquid transfer. These media typically can be fed
through closed silos or bins, which are further protected by
using rotary valves (rotary air locks) to avoid uncontrolled
drawdown which becomes uncontrolled charging of the
transfer line.
UNDERGROUND STATION—
TRANSFER IMPACT
The material characteristics and the system depth and con-
figuration are principal factors determining the impact force
at the diverter boot. Classical/empirical free-fall analyses
(5), computational flow dynamics (CFD), and discrete ele-
ment modeling (DEM) provide evolving methods for esti-
mating the velocities and impact forces in a given system.
The impact penetration/consolidation within the boot
is affected both by the transferring material and the mate-
rial in the boot/rockbox base. Even if the same material,
consolidation, possibly degradation, of material in the
boot will occur through subsequent impact. The direction
change and discharge port configuration affect the process
and are addressed in the boot/rockbox design.
With long drops, even wet mixes will tend toward seg-
regation, and to some extent the diverter/rockbox/energy
dissipator serves as a remix point. In placing shaft linings
and stations, that may be the extent of remix. For mine
development, construction, and ground support, it is advis-
able to discharge into transit mixers which will more com-
pletely remix the loads.
The K-2 potash mine of IMC, with a 975-m (3,200-
ft) drop of salt tailings, using a 14-cm (5.5-in) ID pipe
with a 90-degree discharge ELL, experienced considerably
lower impact stress than expected (6). The ELL was instru-
mented, with an observed loading on the order of 4.1 MPa
(600 psi), well below expected calculations on the order
of 13.8 MPa (2,000 psi). The tails were transferred with
solids content ranging between 20 and 30 percent, and
cemented or uncemented as appropriate for the immediate
fill requirements.
UNDERGROUND STATION—
BOOT/ROCKBOX
The diverter device itself can be analyzed as a pipe bend
(7) which also functions as an energy dissipator or thrust
block under complex impact. The boot below or beyond
the operating flow of material essentially is the rock ELL or
rock box component, minimizing the opportunity for pipe
wear along the sweep of the ELL. A typical hinged base
shotcrete/concrete boot is illustrated in Figure 1.
Boot Geometry
An enlarged receiving chamber can accommodate the
rebound and scatter which occurs as the material deflects
to the discharge opening. That energy dissipating chamber
-top of the boot -should be nominally 1.5 time the inlet
pipe diameter from the top of the boot to the invert of the
discharge barrel. The boot diameter should be no less than
1.5 times the inlet pipe diameter. The boot length should
be no less than three inlet pipe diameters, and should
increase with drop length, nominally 15cm (6 in) for each
additional 300m (1,000 ft) (Appendix).
The boot discharge diameter should be no less than
the diameter of the slickline/dropline. If the discharge pipe
plunges downward as in a conventional lateral, the enlarged
effective discharge area contributes to reliable operation.
Matching the discharge diameter to the diameter of the
body of the boot can be acceptable with the following
proviso.
Commonly, the boot discharge is coupled to additional
conduit lengths which feed the final target, whether static
or mobile. Material handling hoses are typical final conduits
whether filling shaft forms or loading haul trucks or transit