Lessons Learned from Silicate Grouting in a Cofferdam Construction-Paper

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The study evaluated sodium silicate grout (MK) and colloidal silica grout (LV) for sealing a gap in the sheet-pile cofferdam built for the Tamkang Bridge pier foundations. Using the tube-a-manchette (TAM) method, MK was injected into sandy gravel and silty sand, while LV was tested in a deeper silty-sand zone.<br /><br />Both grouts reduced the soil’s permeability from approximately \(5.9 \times 10^{-4}\) cm/s before treatment to around \(10^{-6}\) cm/s afterward, demonstrating their effectiveness as water cut-off materials.<br /><br />However, the grouts behaved differently in the ground. MK showed relatively slow gel development when mixed with site soil, and its injection pressure was generally about 7–15 bar. LV gelled much faster than expected from tests on neat grout: laboratory testing indicated that in-situ soil minerals accelerated gelation, increasing viscosity and producing higher, more variable injection pressures—up to 20–35 bar in some holes. Despite this, LV remained injectable and achieved the required permeability reduction.<br /><br />A follow-up laboratory test found that diluting the LV mixture and reducing the salt concentration substantially delayed early gelation while allowing the grout to harden over time. This adjustment may improve injectability and make LV a viable, potentially more economical option for permanent waterproofing.<br /><br />The main practical lesson is to test grout with representative site soils before construction, since soil mineral composition can strongly affect gel time and injection pressure. Both grouts can provide effective seepage control, but their mix designs should be tailored to ground conditions.

Keywords

sodium silicate grout

colloidal silica grout

Tamkang Bridge

sheet-pile cofferdam

tube-a-manchette

permeability reduction

soil grouting

water cut-off

gelation behavior

injection pressure