Environmental and Operational Risks in Jet Grouting: A Case-Based Source–Pathway–Receptor Framework for Monitoring and Trigger–Action Plan Development

Jet grouting (JG) is widely used for soil improvement, excavation support, and groundwater cut-off works, often under groundwater conditions and in proximity to sensitive receptors. The same high-energy erosion–mixing mechanisms that enable JG performance can also generate environmental and operational risks, including ground deformation, pore-water pressure transients, unintended hydraulic connectivity, accidental releases of grout or fluids, contaminant mobilisation, and groundwater-quality disturbance. This review synthesises field- and practice-based findings into a monitoring-oriented decision-support structure that links Source–Pathway–Receptor mechanisms with measurable early-warning indicators and predefined response actions. The study does not propose a new numerical or constitutive model; instead, it operationalises dispersed case-based evidence into a structured basis for project-specific monitoring and Trigger–Action Plan development. The analysis is organised into six recurring pathway classes: deformation response, pore-pressure and hydrogeological response, hydraulic incidents, contaminated-ground controls, barrier performance, and spoil/returns management. Across cases, escalation is rarely governed by a single absolute threshold. Instead, it is more reliably identified when an abnormal response increases with time, persists after jetting pauses, spreads beyond the expected influence zone, or is confirmed by more than one source of evidence, such as instrumentation, process behaviour, and field observations. Based on these patterns, the paper develops a generic, project-calibrated Trigger–Action Plan (TAP) structure to support risk-informed construction control, reduce environmental disturbance, protect groundwater and other sensitive receptors, and improve the environmental consistency of jet grouting practice.