Low Transport Efficiency: Overly wet spoil is difficult to handle and transport. It does not meet solid waste standards, leading to high logistics costs and potential spillage during haulage.

Environmental Compliance Issues: Regulations require all discharged material to meet specific solid content and stability criteria. Untreated slurry cannot be directly disposed of in standard landfill sites.

Complex On-Site Treatment: Traditional stabilization methods—such as adding lime, sawdust, or other bulk agents—are labor‑intensive, time‑consuming, and generate excess waste volume, while also altering soil properties and requiring additional space.

Additionally, in water-bearing sand or gravel layers, excessive groundwater infiltration into the excavation chamber dilutes the excavated soil into a fluid slurry that cannot maintain pressure balance in the chamber. This condition can cause face instability, equipment wear, ground settlement, or even blowouts — posing serious risks to construction safety and efficiency.

Application of SAP in TBM Tunneling

Super Absorbent Polymers (SAP) play a transformative role in TBM and EPB projects by turning “water into soil.” When mixed into the spoil, SAP particles absorb free water within seconds, expanding many times their original volume and converting the slurry into a plastic, manageable paste.

In tunneling operations, SAP is applied in three main areas:

1. Soil Conditioning in EPB Operations

SAP is often used in combination with foam agents to stabilize unstable or high‑permeability strata. The treated soil forms a cohesive “plug” within the screw conveyor, maintaining effective face pressure, sealing groundwater entry, and preventing accidents such as spewing or washouts.

2. Muck Management and Transportation

At the screw conveyor outlet or muck pit, granular or powdered SAP can be directly added to the discharged spoil. Within minutes, it absorbs excess moisture and transforms the slurry into a stackable, non‑flowing material suitable for conveyor transport and compliant disposal. This technique eliminates the need for bulky cement or lime stabilization and greatly improves the efficiency and cleanliness of muck handling operations.

3. On-Site Slurry Dewatering and Emergency Treatment

When space is limited—especially in urban tunneling sites—large physical dewatering systems are often impractical. SAPs offer a rapid, chemical dewatering solution that solidifies waste slurry on-site. The treated material meets disposal requirements, minimizing water content and environmental impact without additional equipment or waiting time.

✅ Effective Moisture Control: SAP instantly captures free water and converts fluid spoil into a plastic mass, maintaining pressure balance and preventing face instability.

✅ Improved Safety: Stabilized spoil prevents flooding, spewing, and handling risks, ensuring worker and equipment protection.

✅ High Efficiency: The required dosage is very low (approx. 0.5%–1.5%), minimizing material costs while reducing spoil volume increase to less than 1%.

✅ Simplified Operations: SAP can be integrated directly into belt conveyors or muck systems without infrastructure changes, ensuring smooth and continuous processing.

✅ Environmental Compliance: SAP-treated materials are inert, non-toxic, and meet landfill standards, supporting sustainable tunneling practices.

✅ Reduced Site Footprint: Unlike mechanical dewatering systems, SAP requires no large equipment or additional ground space—ideal for urban or space‑constrained sites.

✅ Lower Logistics Costs: Solidified spoil is easier and safer to transport, reducing truck trips and overall disposal expenses.

In Summary

SAP technology provides a simple, safe, and eco‑friendly solution to one of the toughest challenges in TBM tunneling—handling high‑water‑content spoil. By enhancing soil stability, improving transport efficiency, and ensuring environmental compliance, SAP serves as an essential additive for modern tunneling operations, ultimately enabling a cleaner, faster, and more sustainable construction process.