In shield tunnel construction, clay strata often cause mud cakes to form on the cutter head and clog the screw conveyor, which in turn makes the boring speed drop sharply and aggravates equipment wear. Traditional countermeasures often rely on increasing the volume of injected water or repeated shutdowns for cleaning, which is not only costly but may also trigger the risk of soil and water loss in the strata. Chemi Tech has launched a dedicated clay dispersant that solves the dispersion problem at the chemical level, targeting the high plasticity and high cohesion peculiar to clay minerals.
I. Pain Points and Requirements
Clay particles in a water medium readily undergo compression of the electric double layer, so that the attractive force between particles exceeds the repulsive force and they aggregate into dense clumps. Such clumps adhere to the cutter head openings, the mixing arms and the inner wall of the soil chamber, forming a compact mud cake. Once the mud cake forms, the soil cut from the face cannot be discharged smoothly and the torque rises sharply; in severe cases the chamber must be opened for treatment. The market urgently needs a dispersant that can break clay agglomeration at its source, rather than relying only on physical dilution.
II. Product Principle
Chemi Tech's clay dispersant is a polymer-based compound formulation whose main components include anionic polymers and inorganic electrolytes. Its action proceeds in two steps: first, the anionic groups are adsorbed on the edges of clay particles through charge neutralization, reducing the van der Waals force between the particles; second, the long polymer chains form a steric hindrance layer on the particle surface that keeps the particles from coming close to each other again. The whole dispersion process remains continuous and stable and does not fail as shear force decays.
III. Specific Implementation Steps
1. On-site preparation: before shield launching, pre-dissolve the Chemi Tech dispersant in the circulating grouting water tank at a mass ratio of 0.3%-0.5%, and stir evenly until it is fully dissolved.
2. Injection method: once the soil chamber pressure is stable, inject the dispersion liquid continuously through the injection ports at the center of the cutter head or on the soil chamber bulkhead at a rate of 10-15 liters per minute. The injection volume can be adjusted according to the real-time condition of the muck; the principle is to ensure full contact between the dispersant and the clay.
3. Process monitoring: for every ring advanced, record the cutter head torque, the screw conveyor speed and the muck discharge temperature. If the torque drops by more than 15%, the dispersant is working; if the discharged muck shows clumps larger than 5 mm in diameter, the injection rate needs to be increased.
4. Adjustment mechanism: for clay with a high plasticity index (Ip>30), the concentration may be raised appropriately to 0.8%, combined with short intermittent advances, so that the dispersant stays in the soil chamber and reacts for 5 minutes.
IV. Case Support
A metro section in a certain city crossed a full-face clay stratum; the original boring speed was only 6 mm per minute and the cutter head torque soared to 90% of the rated value. After the Chemi Tech dispersant was adopted and injected according to the steps above, by the third ring the torque had stabilized at 55% of the rated value and the muck changed from a pasty mass into uniform granules 1-2 cm in size. The subsequent boring speed rose to 14 mm per minute and the daily advance increased from 4 rings to 9 rings. No chamber blockage or shutdown occurred throughout the section.
V. Summary
Through precise chemical design, Chemi Tech's clay dispersant acts directly on the core of clay agglomeration and significantly reduces the construction resistance of the shield in clay strata. Combined with scientific injection parameters and real-time monitoring, it helps construction units achieve continuous, efficient and low-risk boring. If you need a tailored plan, contact our technical team for on-site trial guidance.