15
unit to the transfer pipe, perhaps using a high-early mix
(Type III).
Alternatively, the boot can be filled from the initial
load into/across a vacant boot. This will be a segregated mix
which will be subject to repeated impact prior to initial set,
let alone full cure. With repeated breakage of developing
cement bonds, the expected strength may be closer to a
simple gravel mass than a concrete block. The steel con-
tainment must then provide significant energy absorption
capacity, thus warranting an appropriate design.
In the case of non-cementitious dry transfer, or dry
binder transfer, it is common to fill the boot from the first
load. Subsequent loads impact the boot mass as in a rock
box, where the principal contact is rock-on-rock. Even
though the rock is degraded to an extent, it also is replen-
ished with each new load in a balance which minimizes
wear on the device interior.
If a hatched boot is used, it can be appropriate prior
to being placed in service (initial and following each clea-
nout cycle) to coat contact surfaces and bolts with form oil,
suitable grease or anti-seize compound to aid in releasing
the hatch should that be necessary. If the hatch is hinged,
the hinge pin also should be lubricated. In addition to the
concrete/shotcrete heat of hydration, the lubrication will be
subject to the mix chemistry.
System Pre-Shift
A system pre-shift inspection precedes and is fundamentally
different than individual load transfer preparation. That
especially is the case with wet transfer, where load prepara-
tion includes the initial wetting and slicking procedures.
Pre-shift essentially is a check of equipment and controls
to assure functionality prior to initiation of system opera-
tion. The complexity will reflect that of the system itself,
and will entail inspection of subsystems and components
as appropriate. Reliable communication between stations
and operators needs to be confirmed before proceeding to
transfer preparation.
Transfer Preparation
Critical first steps are to assure personnel are on station
(surface and underground), equipment (including commu-
nication and control) has been inspected and prepared or
staged for service, and loads will be delivered to or prepared
at the surface station in a timely and productive manner. As
a minimum, surface and underground stations should be in
direct contact with each other and mine dispatch.
Dry, non-cementitious transfer typically does not
require line preparation beyond assuring personnel are on
station, the line is vacant, the boot is ready to divert loads,
and the receiving mobile unit or area is prepared. These
conditions might be checked visually or with instrumenta-
tion such as densometers or lasers. Audible sounding of the
line can be effective where appropriate. A single small test
load can be effective in assessing readiness.
Dry cementitious transfer (pre-mixed concrete, shot-
crete, cement or fly ash binder) typically is into dedicated
bins or silos. Due to segregation in transfer, the concrete
or shotcrete reception vessels may include mechanical
remix such as screw conveyor or pug mill arrangements.
Fundamental to dry transfer preparations are confirm-
ing operability of dust handling provisions at surface and
underground stations.
Wet, especially cementitious transfer, requires diligent
care to prepare the line for transfer, at surface and under-
ground stations. Recommended preparation includes send-
ing a load-equivalent volume of water through the system,
with positive confirmation at the discharge area. This wet-
ting to be followed with one load of neat grout -cement &
water -to ‘milk’ or ‘grease’ the line. Alternatively, a manu-
factured slicking agent can be used, dosed appropriate to
the line length. These steps minimize the occasion of the
concrete or shotcrete loads sticking to the pipe walls and
potentially leading to a frozen or plugged line.
The local ventilation characteristics can principally
influence transfer as regards line preparation for wet mate-
rial. Airflow quantity, temperatures, humidity, downcast,
upcast, drying time all are factors in the line preparation
regimen. These may change seasonally as well as if the
overall vent network changes with new development and
mining. Components as simple as line caps or plugs (top
of system) can markedly decrease the tendency to dry, and
commensurately increase the effective utility of the system.
Transfer Execution
A few hundred feet per second are not unusual transfer
velocities, and it is critical to never spike the discharge,
which can lead to freezing (i.e., self-compacting or pile-
driving) the load in the line and transfer ELL. Establishing
sufficient reception volume primarily is a design aspect,
but can become an operational matter when loading into
transit mixers or haul trucks. That especially is an object
when there are alternative delivery conditions, such as to
the sill or into a vehicle. In either case, the discharge ori-
fice, whether rigid pipe or flexible material handling hose,
must be at sufficient height above the target surface that
the load does not occlude that orifice. The rapid buildup
and expected low slump must be considered, with a recom-
mended practice that the final discharge orifice be no lower
than the lip of the top hatch or gunwale (top rail) of the
unit to the transfer pipe, perhaps using a high-early mix
(Type III).
Alternatively, the boot can be filled from the initial
load into/across a vacant boot. This will be a segregated mix
which will be subject to repeated impact prior to initial set,
let alone full cure. With repeated breakage of developing
cement bonds, the expected strength may be closer to a
simple gravel mass than a concrete block. The steel con-
tainment must then provide significant energy absorption
capacity, thus warranting an appropriate design.
In the case of non-cementitious dry transfer, or dry
binder transfer, it is common to fill the boot from the first
load. Subsequent loads impact the boot mass as in a rock
box, where the principal contact is rock-on-rock. Even
though the rock is degraded to an extent, it also is replen-
ished with each new load in a balance which minimizes
wear on the device interior.
If a hatched boot is used, it can be appropriate prior
to being placed in service (initial and following each clea-
nout cycle) to coat contact surfaces and bolts with form oil,
suitable grease or anti-seize compound to aid in releasing
the hatch should that be necessary. If the hatch is hinged,
the hinge pin also should be lubricated. In addition to the
concrete/shotcrete heat of hydration, the lubrication will be
subject to the mix chemistry.
System Pre-Shift
A system pre-shift inspection precedes and is fundamentally
different than individual load transfer preparation. That
especially is the case with wet transfer, where load prepara-
tion includes the initial wetting and slicking procedures.
Pre-shift essentially is a check of equipment and controls
to assure functionality prior to initiation of system opera-
tion. The complexity will reflect that of the system itself,
and will entail inspection of subsystems and components
as appropriate. Reliable communication between stations
and operators needs to be confirmed before proceeding to
transfer preparation.
Transfer Preparation
Critical first steps are to assure personnel are on station
(surface and underground), equipment (including commu-
nication and control) has been inspected and prepared or
staged for service, and loads will be delivered to or prepared
at the surface station in a timely and productive manner. As
a minimum, surface and underground stations should be in
direct contact with each other and mine dispatch.
Dry, non-cementitious transfer typically does not
require line preparation beyond assuring personnel are on
station, the line is vacant, the boot is ready to divert loads,
and the receiving mobile unit or area is prepared. These
conditions might be checked visually or with instrumenta-
tion such as densometers or lasers. Audible sounding of the
line can be effective where appropriate. A single small test
load can be effective in assessing readiness.
Dry cementitious transfer (pre-mixed concrete, shot-
crete, cement or fly ash binder) typically is into dedicated
bins or silos. Due to segregation in transfer, the concrete
or shotcrete reception vessels may include mechanical
remix such as screw conveyor or pug mill arrangements.
Fundamental to dry transfer preparations are confirm-
ing operability of dust handling provisions at surface and
underground stations.
Wet, especially cementitious transfer, requires diligent
care to prepare the line for transfer, at surface and under-
ground stations. Recommended preparation includes send-
ing a load-equivalent volume of water through the system,
with positive confirmation at the discharge area. This wet-
ting to be followed with one load of neat grout -cement &
water -to ‘milk’ or ‘grease’ the line. Alternatively, a manu-
factured slicking agent can be used, dosed appropriate to
the line length. These steps minimize the occasion of the
concrete or shotcrete loads sticking to the pipe walls and
potentially leading to a frozen or plugged line.
The local ventilation characteristics can principally
influence transfer as regards line preparation for wet mate-
rial. Airflow quantity, temperatures, humidity, downcast,
upcast, drying time all are factors in the line preparation
regimen. These may change seasonally as well as if the
overall vent network changes with new development and
mining. Components as simple as line caps or plugs (top
of system) can markedly decrease the tendency to dry, and
commensurately increase the effective utility of the system.
Transfer Execution
A few hundred feet per second are not unusual transfer
velocities, and it is critical to never spike the discharge,
which can lead to freezing (i.e., self-compacting or pile-
driving) the load in the line and transfer ELL. Establishing
sufficient reception volume primarily is a design aspect,
but can become an operational matter when loading into
transit mixers or haul trucks. That especially is an object
when there are alternative delivery conditions, such as to
the sill or into a vehicle. In either case, the discharge ori-
fice, whether rigid pipe or flexible material handling hose,
must be at sufficient height above the target surface that
the load does not occlude that orifice. The rapid buildup
and expected low slump must be considered, with a recom-
mended practice that the final discharge orifice be no lower
than the lip of the top hatch or gunwale (top rail) of the