<p>Jet grouting is widely employed as a ground improvement technique in seismic regions due to its ability to enhance soil strength, reduce liquefaction potential, and improve the performance of deep or shallow foundations. However, despite its increasing use, the post-earthquake integrity of jet-grout columns remains insufficiently understood, particularly regarding the potential for hidden discontinuities, internal cracking, or reductions in apparent column length. This study investigates the condition of jet-grout columns constructed in 2018, affected by the 2023 Kahramanmaraş earthquakes, and re-evaluated in 2025 through Pile Integrity Tests (PIT), coring, and uniaxial compressive strength (UCS) analyses. PIT results indicated an approximately 16.6% reduction in apparent PIT reflection depth, suggesting reduced low-strain wave transmissibility and possible stiffness discontinuity in the lower column segments rather than direct geometric shortening. UCS tests showed a 30.1% reduction in compressive strength over seven years, consistent with the combined effects of aging, environmental exposure, sustained service conditions, and possible earthquake-induced microcracking. This deterioration increased the design cyclic stress ratio (CSR_design) by 9.4% and reduced the liquefaction safety factor (FS) by 8.6%, leading to an overall rise of about 7% in the Liquefaction Potential Index (LPI) and 8.4% in the Liquefaction Severity Index (LSI). Additionally, elastic shortening analyses indicated a 19.6% increase in vertical deformation, suggesting greater settlement potential. These findings highlight that even moderate strength loss can significantly affect the seismic performance and reliability of jet-grouted foundations. Therefore, post-earthquake reassessment and design frameworks should incorporate time-dependent stiffness and strength degradation, while explicitly considering the interpretation limits of PIT-derived apparent reflection depths.</p>