Theoretical and Practical Aspects of Jet Grout Plug and Cut-Off Design-Paper

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The paper examines how jet-grouted cut-offs and base plugs can be designed to control groundwater and ground movement. Their effectiveness depends on column diameter, spacing, drilling deviation, and achieved strength, but untreated gaps are the main cause of leakage.<br /><br />Statistical analyses assess the likelihood and size of gaps. Linear cut-offs are more robust than base plugs because water must pass through several aligned gaps to penetrate a double-row wall. Even a small ungrouted area can substantially increase overall permeability. Random column-diameter variation has relatively little effect, while drilling deviation is a major risk; consistently undersized columns, however, can also compromise performance. Base plugs are particularly difficult to make watertight, especially when excavation reaches the plug and groundwater pressure or piping could cause instability.<br /><br />The paper recommends careful column layout and construction sequencing. Initial columns should be installed before adjacent work can shadow them, while selected closure columns can be jetted at higher energy or extended slightly below the plug to improve overlap. Measuring drilling deviation and using three-dimensional modelling can help identify and address potential gaps. Site plans should also be prepared to manage unexpected leakage.<br /><br />Base plugs may serve to reduce excavation movements, control groundwater, and improve the working surface. For structural design, the paper distinguishes design strength, characteristic or representative strength, and field strength, emphasizing that their relationships and required acceptance criteria must be specified correctly.<br /><br />Overall, reliable performance requires statistical consideration of construction variability, close control of drilling accuracy, suitable sequencing, and practical measures to achieve and verify overlap.

Keywords

jet grouting

cut-off walls

base plugs

groundwater control

ground movement

column diameter

drilling deviation

construction variability

permeability leakage

three-dimensional modelling