ADDITIVE INJECTION

What Is Additive Injection?

In the Earth Pressure Balance (EPB) shield method, various additives are injected to stabilize the tunnel face by mixing and kneading the excavated soil with the shield cutter to achieve plastic fluidity (muck conditioning), followed by applying the required pressure.
TAC offers a comprehensive range of additives and injection systems—mineral-based, polymer-based, foam-based, and highly responsive composite types—to accommodate all soil conditions.

Principle of Additive Injection

The condition of the excavated soil after Additive Injection is as illustrated in the schematic diagram.
By injecting an appropriate amount of additives, the soil is transformed into a plastically fluidized state, enabling stable and continuous excavation.

Types and Features of Additives

Here we introduce the characteristics of excavation additives that can be selected to suit diverse construction conditions and objectives.

List of Excavation Additives

Category	Classification	Product Name	True Specific Gravity (Bulk Density)	pH Value	Main Components	Packaging	Features
Mineral-Based	Clay / Bentonite	TAC-α TAC-βⅡ TAC-β	2.6	6.9–9.2 (Neutral)	#250 (<63μm), #250 (<63μm), #200 (<75μm)	Bulk, 1t Flexible Container, 25kg Bag	Supplements the fine particles lacking in the ground to be excavated and ensures fluidity of the excavated soil. Serves as the basic material for additive quantity calculations.
Surfactant-Based	Foaming Agent	KT-10C	1.03	7.0 (Neutral)	Anionic Synthetic Surfactants	18kg Can, 200kg Drum, 1t Container	The bearing effect of fine independent foam cells ensures soil fluidity. The dispersing effect of surfactants helps prevent adhesion in clay soils. The air-pressure effect enhances water-sealing performance.
Surfactant-Based	Penetrant (Dispersing Agent)	TAC Filter	0.9	8.0–9.0 (Weak Alkaline)	Higher Fatty Acid Salts	17kg Can	Low-foaming surfactants reduce surface tension on clay surfaces and allow permeation into particles. Highly effective in loosening dense, hard clay soils (with high N-values).
Polymer-Based	Flocculant	TAC Through	1.06	7–8 (Neutral)	Sodium Polyacrylate (Anionic PAM)	18kg Can, 1t Container	Adsorbs fine particles in excavated soil and aggregates soil and water. Ensures fluidity in sandy soils and prevents excessive liquefaction in clay soils. Forms a coating on clay particles, effectively preventing adhesion.
	Composite	TAC Carry	(0.8)	6–8 (Neutral)	Composite Polymer of Super Absorbent Resin (SAP) and Nonionic Thickener (HEC)	20kg Bag, 500kg Bag	A composite polymer additive developed for soil conveying in gravelly ground. The thickening effect combined with SAP-formed granules provides high fluidity, functioning as a substitute for fine particles in the ground.
	Dispersant	TAC Palate	1.3	6–7 (Neutral)	Sodium Polycarboxylate	20kg Can	Adsorbs onto clay particle surfaces, increasing surface charge and repulsive force. Exhibits steric hindrance to prevent re-adhesion. Reduces injection rates in clayey soils.
Natural Polymer-Based	Thickener	TAC Tector P	(0.3)	8.5–9.5 (Weak Alkaline)	α-Glucose, Amylopectin	15kg Bag	A polymer additive made from plant-derived ingredients. Produces high viscosity when dissolved in water. Being naturally derived, it has no environmental impact.
Composite	Mineral-Based + Flocculant	Through Shock	1.1–1.3	10–11 (Alkaline)	Mineral-Based + TAC Through		Two components are mixed at the tunnel face and used as a highly viscous additive with strong resistance to water dilution. Also used as a backfill material for over-excavation.
Composite	Mineral-Based + Plasticity Modifier	Clay Shock	1.2–1.3	10–11 (Alkaline)	Mineral-Based (TAC-β, βⅡ) + TAC-3G (Plasticity Modifier)		Two components are mixed at the tunnel face to produce plastic clay. Exhibits excellent shear resistance and forms a plug zone. Widely used to prevent blowout in water-rich gravel layers and as various filling materials.