Bentonite slurry moves through several different conditions during diaphragm-wall construction. It begins as a freshly mixed suspension, takes on excavated material in the trench, passes through separation equipment and may return for another cycle. Selecting bentonite for diaphragm walls therefore requires attention to how the slurry behaves throughout that journey.
A laboratory trial can establish whether a candidate grade develops suitable fresh-slurry properties. The next question is whether those properties remain manageable when the fluid encounters site water, excavated solids and the proposed recycling process.
In cutter-based diaphragm-wall construction, bentonite suspension supports the open trench and carries excavated material to the surface. The charged slurry passes to a separation plant, and treated fluid returns to the trench. BAUER describes this arrangement in its trench cutter systems brochure.
For material evaluation, it helps to follow four connected stages:
The equipment also needs to suit the work. BAUER identifies soil conditions and cutter performance as factors in matching treatment capacity to the excavation process. A bentonite comparison should therefore include information about the proposed slurry plant.
Begin with representative mixing water. Record its source, pH, hardness and conductivity, together with the water temperature. The EFFC/DFI support fluids guide discusses how water chemistry can affect bentonite dispersion and swelling.
Compare candidate grades at recorded concentrations using the same preparation procedure. Note the mixing equipment, powder-addition sequence, mixing duration, hydration period and measurement time. These details make the results easier to reproduce when a sample moves from laboratory assessment to site trials.
Evaluate hydration behavior, density, viscosity and filtration characteristics together. A higher viscosity reading alone does not establish better excavation support or more efficient recycling. The fresh-slurry results should provide a baseline for tracking later changes.
For more on preparing comparable samples, read our article on water quality and bentonite hydration. Diaphragm-wall slurry should still be evaluated against its own project requirements.
Used slurry contains both bentonite and particles introduced by excavation. Removing sand does not necessarily remove the finer soil fraction. The EFFC/DFI guide distinguishes sand removal from the more demanding task of separating suspended fines.
BAUER also describes additional treatment options, including desilters and centrifuges, within its slurry-handling systems. The appropriate arrangement depends on the material entering the circuit and the treatment required.
When recycled slurry differs from the fresh baseline, investigate the operating history before changing the bentonite dosage. Review the excavated material, water additions, separation performance and any recorded contamination. Increasing the powder concentration does not remove accumulated soil particles.
A result is more useful when its sampling point is clear. As a practical recording approach, distinguish samples from the fresh-slurry tank, the return line before treatment, the treated-slurry outlet and the reuse tank.
Each record should identify:
Agree the sampling locations, test frequency and action criteria within the project quality plan. Acceptance requirements should follow the applicable specification and approved construction procedure. Industry guidance supports those decisions; it does not replace them.
A useful supply specification connects the delivered powder with slurry prepared under agreed conditions. Request representative samples, grade and batch identification, and test results that state the methods used.
Include the intended water source, expected temperature range, excavation method and recycling equipment in the evaluation brief. Where practical, extend the comparison to a controlled trial with representative excavated material. This helps address questions that a clean-water test leaves unanswered.
HERMANO supplies civil engineering bentonite for construction-slurry evaluation. To discuss candidate materials, share your project requirements, water information and slurry-plant details. An existing slurry test report can also provide a useful starting point.
