Hybrid Injections – Laboratory Testing and Field Experience During Tunnel Excavation-PPT Presentation

PPT Presentation

Pdf Summary

The presentation describes hybrid injection, a computer-controlled grouting method that combines cement suspension with two-component polyurethane resin in a single injection process. Unlike staged injections or fixed pre-mixed grouts, the method automatically adjusts the polyurethane dosage as conditions change.<br /><br />The system mixes cement grout at a plant, combines the polyurethane components in a static mixer near the borehole, and then blends the resin with the cement grout shortly before injection. A control system monitors and records flow rates and pressure, varying polyurethane content—typically from 0% to 40%—during injection.<br /><br />Laboratory testing examined viscosity and compressive strength at different resin contents and curing times. The injection approach can begin with cement grout and add polyurethane when needed, helping address large, water-bearing fissures while limiting resin use and targeting the areas that require treatment. The presentation highlights flexibility in grout properties, reduced leakage and waiting times, and the ability to seal and consolidate in one process. Hybrid injection can be applied in rock and loose soil.<br /><br />A case study at the Ritom hydropower project in Switzerland involved a 2,300 m headrace tunnel, where excavation of the lower section encountered water inflows of 135 L/s. The adopted solution was to construct a concrete plug to enable work in dry conditions, supported by pre- and post-excavation injections. The injection plan used 20 m boreholes with 5 m overlap, packers at 10 m and 5 m depth, pressure up to 30 bar, and staged water-flow targets.<br /><br />Overall, hybrid injection offers adaptable grout design and can combine sealing and consolidation within a controlled injection process.

Keywords

hybrid injection

grouting

cement suspension

polyurethane resin

computer-controlled

flow rate

pressure monitoring

viscosity

compressive strength

Ritom hydropower project