Innovative Design and Quality Control of Single Stage High Pressure Injection Micropiles, Waal-Compact-Piles-Paper

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The paper presents the Waal-Compact-Pile, a single-stage high-pressure injection micropile system designed for installation in restricted spaces. A steel tube is drilled into the ground using low-pressure grout; at the required depth, denser grout is injected at pressures of 8.5–10 MPa. The pressure forms a hardened grout bulb whose diameter is typically 1.4–1.5 times the drill-head diameter.<br /><br />Bulb formation pushes against and deforms the surrounding soil, increasing horizontal stress and improving its strength and stiffness. Load tests at Wijdewormer and Betuwelijn indicate that pile capacity is predominantly provided by shaft friction, with low toe displacement. At Wijdewormer, shaft resistance accounted for about 88% of the measured capacity. The piles’ behavior was comparable to that of micropiles installed using the more time-consuming, multistage IRS method.<br /><br />Finite element modelling (FEM) incorporated the grout bulb and resulting soil improvements. It reproduced the observed load–deformation behavior and estimated pile capacity with acceptable accuracy, suggesting FEM may support future design. Its use, however, depends on consistently achieving the assumed bulb dimensions.<br /><br />The proposed quality-control system monitors drilling depth and force, grout composition, flow, pressure, and total grout volume. The most important indicator is the ratio of injected grout volume to the expected grout-bulb volume. Further field measurements are needed to establish acceptable confidence limits for this ratio across different pile dimensions and soil conditions.

Keywords

Waal-Compact-Pile

micropile

high-pressure grouting

grout bulb

shaft friction

soil improvement

finite element modelling

load test

quality control

ground engineering