Hybrid Grouting for Remediation of Taupo Control Gate, Waikato River-Paper

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The Taupo Control Gates remediation addressed hydraulically eroded voids behind a downstream sheet-pile wall on the Waikato River. Because the full extent of the voiding was unknown and grout migration into the turbulent river had to be avoided, Wagstaff Piling NZ and McConnell Dowell developed a controlled, rapid-setting grouting approach.<br /><br />The method combined downstage drilling, which helped identify voids through changes in drilling resistance and penetration rate, with upstage injection of a two-component grout. Cementitious grout (Part A) and a sodium-silicate activator mix (Part B) were pumped separately and combined at the drilling rig. Their flow rates were adjusted in real time to control gel time, including setting in under five seconds where highly connected pathways risked grout escape. Injection pressure was capped at 10 bar to protect the sheet-pile wall, with wall movement monitored during the work.<br /><br />More than 100 m³ of grout was placed across the 36 m treatment zone, at depths of 2–12 m below ground. The greatest uptake occurred between 4 and 12 m, near the sheet-pile toe; some injection increments accepted up to about 2,200 L, indicating large or interconnected voids. Primary holes generally took more grout than secondary verification holes.<br /><br />Pressure records commonly showed a gradual rise, a sharp drop, and a subsequent increase. These cycles, interpreted alongside grout volumes, indicated progressive void filling, breakthrough into connected pathways, and renewed confinement. Surface heave, cracking, and lateral strain during high-volume injections provided further evidence of void infilling.<br /><br />The project demonstrated that combined pressure, flow, grout-volume, drilling, and surface observations can guide treatment of complex void networks. Real-time control of grout composition and delivery helped stabilise the riverbank while limiting migration into the river. The approach may also be applicable to other critical infrastructure exposed to hydraulic erosion.

Keywords

Taupo Control Gates

grouting remediation

hydraulic erosion

sheet-pile wall

Waikato River

void filling

rapid-setting grout

sodium silicate

pressure monitoring

riverbank stabilization