In shield construction, clay strata often give rise to problems such as mud cake wrapping around the cutter head and soil in the chamber being unable to flow normally, because of their high plasticity and high water content. This not only causes boring torque to soar and thrust to increase, but also easily jams the screw conveyor and blocks muck discharge; in severe cases the machine has to be stopped for manual cleaning, and a single such treatment can cost as much as several hundred thousand yuan. Chemi Tech has worked in the field of ground conditioning for many years and, for the specific scenario of clay dispersion, has introduced a dedicated dispersant product that breaks down the clay agglomerate structure at the molecular level.
Market pain points concentrate on two areas. The first is the cutter head zone. Under high temperature and high pressure, clay particles dehydrate and harden at the cutter head openings, forming a compact mud cake, like putting a "cement coat" on the cutter head, which reduces the penetration rate. The second is inside the soil chamber. Clay particles attract one another into a three-dimensional network structure, so the soil loses its fluidity and the muck cannot be discharged continuously. Traditional methods such as dilution with water or ordinary dispersants often treat the symptom rather than the cause, and adding too much water can trigger the risk of blowouts.
The core idea of Chemi Tech's shield clay dispersant is "intercalation and deconstruction". The polymer molecular chains in the product carry a large number of negatively charged groups that can be inserted between the layers of clay minerals, propping the interlayer spacing open through electrostatic repulsion while coating the particle surfaces and blocking the van der Waals connections between particles. After verification with a laboratory rheometer and cross-checking in the field, at a dosage of 0.1%-0.3% of the muck mass it can reduce the clay plasticity index by 30%-50% and lower the hardness of the mud cake to a level that can be easily peeled off by hand.
The specific implementation steps are divided into four. Step one: entry testing. Take samples of the stratum clay and measure basic rheological parameters, including the liquid and plastic limits, zeta potential and shear strength. Step two: formula matching. Based on the test results, determine the dilution concentration and addition ratio of the dispersant. Step three: injection process. Inject the dispersant solution continuously or intermittently through the foam pipeline in front of the cutter head or the reserved holes in the soil chamber bulkhead, keeping the injection pressure at 0.2-0.5 MPa. Step four: dynamic monitoring. Use earth pressure sensors and torque meters to feed back data in real time and observe the curves of thrust and torque; when the torque drops by 15%-20% and the fluctuation of the chamber pressure is less than 0.05 bar, the dispersion effect is judged to meet the standard.
Actual cases show that a company encountered full-face hard plastic clay while constructing a metro section; by the 27th ring the torque had risen to 3800 kN·m and the thrust to 28000 kN, and the muck discharge rate was only 60% of normal. After adopting the Chemi Tech dispersant and injecting it continuously for 6 rings at a 0.15% addition ratio, the torque gradually fell back to 2200 kN·m, the thrust dropped to 18000 kN and the muck discharge rate recovered to 95%. No blowout or over-excavation occurred throughout the process, and construction efficiency rose by about 40%. When the cutter head chamber was opened for inspection, only scattered soft mud was attached, with no hard mud cake.
Chemi Tech is committed to providing its partners with full-cycle service, from product selection and injection parameter optimization to effect verification, with every decision supported by real data. If clay boring and its mud cake and adhesion problems are troubling you, you are welcome to contact our technical team for a customized solution.