Proposed Improvements to Laboratory Testing Programs For The Design Of Self-Hardening Slurry Cutoff Walls-PPT Presentation

PPT Presentation

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The presentation proposes improving laboratory testing of self-hardening slurry (SHS) used in cutoff walls. SHS must remain fluid during trenching before hardening into the finished wall, but conventional tests—often based on simple mixes, room-temperature curing, and strength and permeability measurements at 14–56 days—may not represent field conditions.<br /><br />Testing should better account for site water and soil chemistry, different bentonite products, soil incorporation, mixing sequence, fluidizer dosage, curing temperature, and the time slurry remains workable. Current programs often overlook workability, filtrate loss, gel strength, and the temperature sensitivity of high-slag mixes. Standard filtration tests may also use unrealistic pressures and durations.<br /><br />Seven proposed improvements are:<br /><br />1. Measure filter-cake formation and filtration under realistic conditions, including expected soil content.<br />2. Measure gel strength directly to assess whether soil particles remain suspended and settle.<br />3. Extend curing measurements beyond 90 days to understand long-term performance.<br />4. Set bentonite hydration requirements based on relevant properties—such as viscosity, gel strength, and filtrate loss—rather than a fixed hydration time.<br />5. Reproduce field mixing and construction timelines, including agitation, warming, fluidizer variation, and soil additions.<br />6. Use more representative strength and strain tests, including long-term testing beyond 12 months.<br />7. Determine the hydraulic gradient below which flow through the wall does not occur.<br /><br />The authors argue that better testing will require additional time and funding, and that complex projects may need extensive or academic studies. They encourage sharing results, involving geochemists, and prioritizing sustainable mixes made with local materials.

Keywords

self-hardening slurry

cutoff walls

laboratory testing

filtrate loss

gel strength

bentonite hydration

workability

curing temperature

hydraulic gradient

sustainable mixes