Remedial Base Grouting of Caissons under Artesian Conditions-PPT Presentation

PPT Presentation

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The Forest Hill Station project is part of Toronto’s Eglinton Crosstown Light Rail Transit system. Its top-down construction used secant piles for temporary shoring and king piles to support the permanent structure.<br /><br />During installation of a king pile, ground disturbance led to approximately 25 m³ of additional concrete—about 63% above the theoretical volume. Subsequent geotechnical investigations indicated reduced soil density and consistency. Keller selected permeation grouting to stabilize potentially disturbed soils and verify conditions beneath the pile bases.<br /><br />Work was carried out beneath a steel-filled roof slab and under artesian conditions, with groundwater about 2 m above the drill-hole collars. Crews installed standpipes and a work platform, then drilled battered holes using casing and mud slurry. The holes passed through the tunnel, king-pile concrete and steel, and continued approximately 3 m below the pile tips.<br /><br />Low-strength cement-bentonite grout was placed by tremie, followed by installation of multiple-port sleeve pipes (MPSPs). The casing was withdrawn while the holes were pressure-grouted. Water was used to open each port, and grout was injected until target refusal pressures were reached. Targets varied by port elevation, from 330 psi at the lowest port to 560 psi at the upper port.<br /><br />Quality control included hole-alignment checks, daily grout-strength testing, specific-gravity checks, drilling and grouting logs, and real-time pressure and flow monitoring.<br /><br />The program used nine MPSPs across four piles, including a verification MPSP. Grout was injected through 41 ports, with pressure refusal achieved at 37. Injection pressures reached 600 psi, and total grout volume was 7.9 m³.

Keywords

Forest Hill Station

Eglinton Crosstown

Light Rail Transit

permeation grouting

geotechnical investigation

king pile

secant piles

artesian conditions

multiple-port sleeve pipes

quality control