SELF-HARDDENINGNG SLURRY FILTRATION AND THE END OF THE API TEST DEAD END .-Paper

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The study develops a modified filter-press test to assess filtration and filter-cake formation in self-hardening slurry (SHS) cutoff walls. The standard API test—30 minutes at 100 psi—does not represent field conditions: its small cell and high pressure can cause SHS to lose nearly all its water, making the results unsuitable for design.<br /><br />The proposed approach uses a 12-inch cell, a representative pressure of 20 psi, and an eight-hour test. Samples are cured, sliced, and measured to profile density. Three binder formulations were tested, with and without added silty sand representing suspended soil solids.<br /><br />The tests recorded slurry losses of roughly 30% of the initial volume and filter cakes several inches thick. Filtration concentrated solids not only at the ground interface but across much of the sample, potentially increasing wall strength and reducing permeability. Added soil solids also affected cake density. Using sand rather than filter paper as the interface increased measured filtrate volume by about 20%, underscoring the need for a test surface representative of site soils.<br /><br />These changes can influence cutoff-wall properties, material quantities, cost, and construction performance. Denser, stronger interfaces may be beneficial, but high binder concentrations can increase brittleness and the risk of cracking. Filtration and cake development also depend on mix design, hydrostatic head, soil conditions, suspended solids, and trenching equipment.<br /><br />The method is useful for design studies, not routine quality control, because meaningful testing takes many hours. The results are preliminary and conservative: the cell was too short, the test did not span the full workable period before setting, and refilling distorted measurements. The authors recommend longer-duration tests in taller cells with more realistic interfaces. Overall, the study argues that filtration must be considered in SHS wall design and that the API test is inadequate for this purpose.

Keywords

self-hardening slurry

cutoff wall

filter-press test

filtration

filter cake

binder formulation

silty sand

density profile

permeability

wall design