Monitoring and analysis of excess pore water pressure response during jet grouting installation in liquefiable silty sand soils

The Yellow River floodplain, characterized by poor geotechnical properties and high liquefaction potential, is commonly treated using double-fluid and triple-fluid system jet grouting. However, poor column quality is often encountered due to complex hydrogeological conditions and highly permeable soil characteristics. This study investigates the failure mechanisms of jet grouting column formation through pore pressure monitoring and comprehensive quality evaluation. Furthermore, a parametric study was conducted by varying key construction parameters, including grouting pressure in the double-fluid system, as well as grouting pressure and nozzle spacing in the triple-fluid system. For this purpose, field tests were performed on nine columns constructed using double and triple-fluid jet grouting techniques. The accumulation and dissipation of excess pore water pressure (EPWP) govern both the liquefaction extent and the resulting column quality. In the double-fluid system, the liquefaction extent increases with grouting pressure, leading to a larger column diameter but a reduction in unconfined compressive strength (UCS). In the triple-fluid system, besides grouting pressure, nozzle spacing plays a critical role in controlling liquefaction; increasing the spacing from 0.3 m to 0.7 m decreases the liquefaction extent and enhances UCS by 2.81 MPa by minimizing overlap of the disturbance zones. The difference between liquefaction extent and column radius ( Δ l ) exhibits a linear negative correlation with UCS in the double-fluid system, whereas a nonlinear correlation is observed in the triple-fluid system. Furthermore, in both cases, EPWP decays exponentially with an influence range of about 10 times the column diameter. An energy waste assessment framework is developed by quantifying over-liquefied zones relative to the final pile structure, enabling systematic evaluation of energy waste rate (EWR) across different construction configurations. Additionally, this study proposes a novel strategy for liquefiable silty sand foundations by linking EPWP to column quality, enabling optimization of construction parameters. The findings highlight that increasing nozzle spacing in the triple-fluid system can effectively improve column integrity by reducing the affected zone.