Risk control of deep permeation grouting by determination of grout volumes based on the monitoring and observational engineering-Paper

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The paper presents an observational-engineering approach to designing and quality-controlling a deep, grout-based water barrier for the Muiden aqueduct, part of the Schiphol–Amsterdam–Almere motorway project. The aqueduct’s construction pits required excavation below the water table, while large-scale groundwater extraction was restricted. Low-pressure silica grouting (“softgel”) was therefore used to create a horizontal seal at depths of up to 24 m.<br /><br />At these depths, installation deviations can leave gaps between neighboring grout spheres, causing significant leakage. The authors measured deviations in element position, inclination, and depth, then incorporated their statistical characteristics into a probabilistic model. The model also accounts for how overlap between adjacent grout spheres can enlarge them. Multiple simulations visualize potential gaps and assess how grout volumes and installation sequence affect leakage risk.<br /><br />The analysis highlights a balance: insufficient grout may leave holes, while excessive grout can create a rapidly advancing grout front, cause fracturing, increase leakage risk, and waste time and materials. Simulations informed a strategy using larger volumes near the retaining wall—0.9 m³ per element in the first two rows, 0.8 m³ in the next two, and 0.675 m³ elsewhere.<br /><br />The softgel barrier generally performed adequately during dewatering and excavation, despite local leakage and penetration by more than 4,000 piles. Actual dewatering quantities remained within permitted limits.<br /><br />The authors conclude that probabilistic, visualized field modelling can improve understanding of grouting risks and support better choices of grout volumes and sequence. They note that future improvements depend on more comprehensive measurements of individual element deviations and better knowledge of grout behavior and soil permeability.

Keywords

grout barrier

softgel grouting

waterproofing

probabilistic model

aqueduct construction

groundwater extraction

silica grouting

leakage risk

installation deviations

dewatering