EPB Tunnelling Spoil Solidification

Control free liquid in variable EPB spoil and create a more consistent material for conveyor transfer, loading, haulage and disposal.

EPB tunnelling spoil can change continuously with geology, groundwater and the conditioning program. AuraChem tests suitable superabsorbent polymers against representative spoil samples and develops a practical product, application rate and dosing method around the project’s muck-handling system.

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EPB tunnelling spoil in the North East Link spoil handling facility

From Screw Conveyor to Spoil Pit

As an earth pressure balance TBM excavates, conditioned spoil is extracted through the screw conveyor. It then travels through belt conveyors and transfer points before being discharged into a spoil pit, muck bin or spoil shed. From there, the material is loaded into trucks and transported to an approved receiving facility.

If the spoil contains excessive free water, it may become difficult to load, release liquid during transport or fail a Paint Filter Liquids Test or similar receiving criterion. This can create spill and work health and safety risks, disrupt truck loading and reduce available spoil-pit capacity.

Spoil must be removed continuously to support tunnelling. If wet material cannot be loaded and transported efficiently, a full spoil pit or muck bin can slow or stop TBM production.

Why EPB Spoil Is Variable

EPB spoil may contain changing proportions of clay, sand, rock flour, groundwater and excavated fines. Foams, surfactants, polymers and other conditioning agents can also influence how water is held within the spoil and how a particular SAP grade performs.

Changes in geology, groundwater, TBM operation or conditioning dosage can alter the required product and application rate. Salinity, dissolved ions, pH, solids content and available mixing must also be considered.

For this reason, clean-water absorption figures alone are not a reliable basis for field selection.

How SAP Captures Free Water in Spoil

A compatible cross-linked superabsorbent polymer is distributed through the spoil, where it absorbs available water into a swollen gel structure. With adequate distribution and contact time, this can reduce mobile liquid and create a more consistent material for conveyor transfer, loading and transport.

Selected SAP grades can absorb many times their mass in water. Some products may absorb approximately 100 times their own mass under suitable clean-water test conditions. Actual absorption in EPB spoil is usually lower and depends on geology, groundwater chemistry, conditioning agents and mixing.

Indicative SAP application rates may fall between approximately 0.1% and 0.5% by weight of total wet spoil. The operating rate must be established through representative sample testing and field validation.

SAP Compared with Lime

Lime is commonly used on Australian tunnelling projects to treat wet EPB spoil. Depending on moisture content, geology and the required consistency, typical lime addition rates may range from approximately 10–30% by weight of wet spoil.

Adding lime at these rates can substantially increase the mass and volume of treated material. This may result in:

More material requiring handling and disposal
Additional truck movements
Higher transport and disposal costs
Increased fuel consumption and associated emissions
More product storage and dosing infrastructure
A significant increase in spoil pH
Potential changes to disposal acceptance or available receiving facilities

By comparison, SAP is typically applied at approximately 0.1–0.5% by weight of wet spoil, subject to representative testing and field validation.

A suitable SAP absorbs available water without introducing the large quantity of mineral solids associated with lime treatment. It can therefore improve spoil consistency while minimising additional treatment mass and avoiding the significant pH increase commonly associated with lime.

Indicative Treatment Comparison

Consideration

Lime Treatment

SAP Treatment

Indicative addition rate

Approximately 10–30% of wet spoil

Approximately 0.1–0.5% of wet spoil

Treatment mechanism

Adds mineral solids and chemically reacts with moisture

Absorbs available water into a gel structure

Added material mass

High

Very low by comparison

Effect on pH

Can substantially increase spoil pH

Generally avoids the large pH increase associated with lime

Transport impact

Added treatment mass may increase truck movements

Lower addition mass may avoid additional truck movements

Storage requirements

Larger treatment-product volumes required

Considerably smaller product-storage footprint

Indicative addition rate

Lime Treatment

Approximately 10–30% of wet spoil

SAP Treatment

Approximately 0.1–0.5% of wet spoil

Treatment mechanism

Lime Treatment

Adds mineral solids and chemically reacts with moisture

SAP Treatment

Absorbs available water into a gel structure

Added material mass

Lime Treatment

High

SAP Treatment

Very low by comparison

Effect on pH

Lime Treatment

Can substantially increase spoil pH

SAP Treatment

Generally avoids the large pH increase associated with lime

Transport impact

Lime Treatment

Added treatment mass may increase truck movements

SAP Treatment

Lower addition mass may avoid additional truck movements

Storage requirements

Lime Treatment

Larger treatment-product volumes required

SAP Treatment

Considerably smaller product-storage footprint

Actual treatment rates and outcomes depend on the project material and operating conditions. Representative testing should be completed before comparing consumption, cost or performance.

SAP treatment does not automatically determine or preserve the regulatory classification of the spoil. Classification and disposal acceptance must be confirmed for the treated material under the applicable project, regulatory and receiving-facility requirements.

Selecting AuraSorb 4000 or 8000 for Spoil

AuraSorb 4000 Series

The primary AuraSorb series for EPB tunnelling spoil.

Standard profile

Suited to dependable general-purpose treatment where sufficient mixing and contact time are available.

Rapid profile

Can be evaluated where faster interaction with available liquid is required.

AuraSorb 8000 Series

Can be evaluated where enhanced liquid retention, improved stackability or a drier-feeling treated material is required.

Final product selection depends on spoil composition, conditioning chemistry, treatment speed and the required handling outcome.

Discuss the Appropriate AuraSorb Series

What Drives the Required Dose in EPB Spoil

Variable

Why it matters

Free-water and solids content

Influences the initial product addition required to reach the target consistency

Ground conditions and particle size

Clay, sand, rock flour and fines affect mixing and water availability

Conditioning chemistry

Foams, surfactants and polymers may change absorption response and gel strength

pH, salinity and dissolved ions

Ionic content can reduce the capacity of some SAP grades

Addition point and mixing energy

Determine how evenly the product reaches available water

Required handling outcome

The target may differ for conveyor transfer, loading, haulage or disposal

Dosing at the Spoil Pit or on the Conveyor

Direct Spoil-Pit Addition

SAP can be applied directly to a spoil pit, muck bin or treatment area and mixed using suitable site equipment. This method may suit batch treatment where sufficient mixing and contact time are available before loading.

Controlled Conveyor Dosing

For continuous operations, SAP can be dosed onto a belt conveyor before a transfer point. The movement of the spoil through the transfer point assists product distribution before the material reaches the spoil pit.

An automated dosing system may include:

Bulk SAP storage
Level sensors for inventory monitoring
Dry-product screw feeder
Variable-speed dose control
Conveyor load cells
Moisture or free-water measurement
Product consumption monitoring

The dosing rate can be adjusted according to conveyor throughput and changing spoil conditions. Final system design must consider calibration, dust control, safe access and reliable product distribution.

Benefits for Spoil Logistics and TBM Uptime

These benefits remain subject to representative testing and field validation.

Free-Liquid Control

Reduces mobile and drainable liquid within the spoil.

More Consistent Loading

Creates a more manageable material for continuous truck loading and haulage.

Reduced Spill Risk

Helps limit liquid release or spoil liquefaction during transport.

Support for TBM Production

Faster treatment and spoil removal can help maintain spoil-pit capacity and reduce the risk of interrupting excavation.

Lower Treatment Addition

SAP is normally applied at substantially lower rates than lime and other mineral bulking agents.

Reduced Added Transport Mass

Avoiding large lime additions may reduce additional truck movements, fuel consumption and associated emissions. SAP does not reduce the original quantity of excavated spoil.

From Sample to Field Method

01
Review the Process
Confirm the TBM discharge arrangement, conveyor route, transfer points, spoil storage and required handling outcome.
02
Test Representative Spoil
Screen suitable grades using spoil that reflects the project’s geology, groundwater and conditioning program.
03
Establish an Initial Dose Range
Assess free-liquid control, response time, final consistency and sensitivity to changing moisture conditions.
04
Select the Addition Point
Consider the screw-conveyor discharge, belt conveyor, transfer point, spoil pit or another controlled treatment location.
05
Validate and Optimise
Confirm distribution, contact time and acceptance criteria under actual production conditions, then adjust the dose as drive conditions change.

What a Spoil Test Report Includes

Testing can provide:

An initial product recommendation
Indicative application-rate range
Observed response time
Target material description
Suggested addition point
Initial mixing and dosing approach

These findings provide a starting point for field validation rather than a guaranteed operating dose.

EPB Spoil Treatment FAQs

How much SAP is required for EPB spoil?

Indicative rates may fall between approximately 0.1% and 0.5% of total wet spoil. The actual rate depends on free water, geology, groundwater chemistry, conditioning agents, mixing and the required consistency.

How much lime is normally used for wet EPB spoil?

Depending on the moisture content, geology and required outcome, typical lime addition rates may range from approximately 10–30% by weight of wet spoil. The actual requirement must be determined for the project material.

Can SAP help spoil pass a Paint Filter Liquids Test?

A suitable SAP can reduce mobile liquid and may help treated spoil meet the relevant free-liquid criterion. Compliance must be confirmed using the project or receiving facility’s required test method.

Does SAP change the spoil classification?

SAP primarily changes the physical handling condition of the spoil. It does not automatically determine or preserve its regulatory classification. Classification and disposal acceptance must be confirmed for the treated material.

Can conditioning foam affect SAP performance?

Yes. Surfactants, polymers, salinity and dissolved ions can affect absorption and gel behaviour. Testing should use spoil produced with the actual conditioning program where practical.

Can the SAP dose be automated?

Yes. A dry-product screw feeder can be linked to conveyor load cells and suitable process measurements to adjust the dose according to spoil throughput and changing conditions.