Shotcrete Pump Selection for Underground Mining

The wet mix determines how the material enters the pump, moves through the delivery line, and responds to changes in pressure. Engineers should review the complete mix design rather than treating shotcrete as a uniform pumping medium.

Relevant properties include:

• Cement content
• Water-to-cement ratio
• Aggregate grading
• Maximum particle size
• Admixtures
• Mix consistency
• Fiber type and dosage
• Temperature
• Expected delivery and working time

A mix must be cohesive enough for spraying but sufficiently workable for pumping. Small changes in water content, aggregate distribution, admixture dosage, or temperature can alter its behavior.

Pump selection should account for the expected operating range, not only the properties of an ideal laboratory or trial mix. This is particularly important underground, where transport time, ambient conditions, and changing production schedules may affect the material before it reaches the pump.

Aggregates make shotcrete abrasive. As the material passes through the pump and pipeline, it continuously contacts internal components.

The severity of wear depends on several factors, including aggregate hardness, grading, particle shape, material velocity, pressure, and operating hours. Pump construction and component selection must reflect this abrasive duty.

Wear should also be considered over the full service cycle. A pump may initially meet the required performance, but progressive wear can affect clearances, pressure capability, and delivery consistency. Inspection intervals, component access, replacement procedures, and spare-parts planning should therefore influence the selection decision.

The objective is not to eliminate wear. It is to manage wear predictably without allowing routine maintenance to create disproportionate underground downtime.

Steel or synthetic fibers can make the shotcrete more difficult to transfer. Their influence depends on fiber material, dimensions, shape, dosage, and distribution within the mix.

A pump intended for fiber-reinforced shotcrete must allow the material to enter and move through the pumping elements without unnecessary restriction. The complete transfer path also matters. Narrow passages, unfavorable transitions, and inconsistent feeding can encourage fibers to accumulate or orient in ways that disrupt flow.

Evaluating fiber content requires more than confirming that a pump can handle solids. Engineers should consider how the combined mix behaves during feeding, pumping, and pressure changes.

Testing with the actual shotcrete mix may be appropriate when fiber characteristics or material behavior fall outside established operating experience.

The required pump capacity should reflect the demands of the spraying process. A nominal maximum flow rate does not show how the pump will perform across the full operating range.

Shotcrete delivery may need to change as the spraying unit moves between surfaces, builds layers, or responds to different excavation profiles. The pump should provide controlled adjustment without creating unstable flow.

A pump that is unnecessarily large may operate outside its preferred range or make fine control more difficult. An undersized pump may be unable to maintain the required supply when system resistance increases.

Selection should therefore consider the normal operating point, expected variations, starting conditions, and peak requirements rather than relying on maximum capacity alone.

The pump must overcome resistance throughout the transfer system. This includes friction within the pipeline, elevation differences, fittings, hose sections, transitions, and resistance associated with the shotcrete itself.

Longer transfer distances and vertical lifts generally increase the pressure demand. Pipeline diameter also affects resistance. A smaller line may be easier to route underground but can increase pressure losses and material velocity.

Shotcrete consistency adds another variable. A change in mix behavior can increase the pressure required to maintain the same delivery rate. The selected pump must therefore provide sufficient pressure for the anticipated operating range without treating maximum pressure as the normal duty point.

Pressure calculations should be based on the complete installation. Evaluating the pump separately from the delivery system can result in an incomplete selection.

Reliable discharge begins with consistent pump feeding. Dense shotcrete must reach the pumping elements without bridging, air pockets, or an interrupted material supply.

The arrangement of the hopper, mixer, transfer equipment, and pump inlet affects how well the material is presented to the pump. Inadequate feeding can reduce output even when the pump has sufficient theoretical capacity.

High suction capability is valuable when handling viscous shotcrete, but inlet conditions still require careful design. The pump cannot compensate indefinitely for poor material flow upstream.

Engineers should examine the complete route from material delivery to the pump inlet, including hopper geometry, fill level, agitation, inlet dimensions, and the possibility of material remaining stationary.

The spraying process benefits from uniform shotcrete delivery. Flow variations can complicate nozzle control, layer build-up, and coordination between pumping and spraying equipment.

Progressive cavity pumps transfer material through cavities that move continuously from the suction side to the discharge side. This positive-displacement principle produces uniform flow without pulsing.

The conveying action also supports low-shear handling of viscous and fiber-reinforced mixes. Limiting unnecessary mechanical stress helps reduce the risk of disrupting the mix or encouraging segregation during transfer.

These characteristics make progressive cavity technology suitable where the shotcrete requires controlled handling, high suction capability, and stable delivery under changing pressure conditions.

A suitable pump must also fit the mine. Space restrictions, access routes, power supply, pipeline connections, ventilation, equipment mobility, and proximity to the spraying area all affect the installation.

Maintenance access deserves the same attention as the pump footprint. Enough space must remain for inspection, component replacement, cleaning, and safe handling of service parts.

Equipment that fits into the available space but cannot be serviced efficiently may create avoidable downtime. Pump orientation and connection points should therefore be reviewed before the final configuration is approved.

Shotcrete cannot remain stationary in the pump and delivery system indefinitely. Cleaning procedures, planned interruptions, shift changes, and unexpected stoppages should be considered during selection.

The pump configuration should support inspection and service under underground conditions. SEEPEX BNM pumps can be equipped with Drive Joint Access and Rotor Joint Access to simplify access to relevant components without unnecessarily disturbing adjacent equipment.

These features can support a Maintain in Place approach where the installation and service conditions allow it. Their value should be assessed against the mine’s maintenance strategy, available working space, lifting arrangements, service intervals, and downtime tolerance.

Shotcrete pump selection brings the material, pumping duty, installation, operation, and maintenance strategy together.

The final evaluation should confirm:

• Shotcrete consistency and workable range
• Aggregate grading and maximum particle size
• Fiber type, dimensions, and dosage
• Required delivery rate and control range
• Transfer distance and elevation
• Pipeline layout and anticipated pressure
• Feeding conditions
• Available installation and service space
• Cleaning procedures
• Operating hours and interruption tolerance
• Wear-part access and maintenance requirements

A progressive cavity pump is well suited to demanding shotcrete transfer when high suction capability, low-shear handling, uniform flow, and pressure stability are required. The final pump configuration should be selected against the actual mix and complete system duty. When those requirements are defined accurately, the pump becomes an integrated part of a reliable underground shotcreting process.