Comparative seismic analysis of t-shaped and conventional deep cement mixing columns in highway embankments on soft soil

Weak soils present significant challenges for highway construction in seismic regions, often leading to instability issues such as settlements and slope failures. These conditions necessitate safe, effective, and cost-efficient solutions to ensure embankment stability. Despite the critical importance of embankment stability under dynamic loading, research on soil reinforcement techniques in seismic scenarios is limited. This study evaluated the seismic performance of conventional deep cement mixing (DCM) columns versus innovative T-shaped deep mixing (TDM) columns for highway embankments on soft soil through three-dimensional finite element analysis via PLAXIS 3D. After validation, a comprehensive parametric study investigated the effects of column type, spacing (1.67 m, 2.14 m, and 3.0 m), and seismic loading on embankment response parameters, including settlement, lateral displacement, and excess pore water pressure. The results demonstrate that both reinforcement methods significantly enhance seismic stability compared with unreinforced conditions. Compared with unreinforced embankments, TDM columns achieved superior performance, with settlement reductions of 89.95% versus 36.11% for DCM columns. Under seismic loading, the TDM columns exhibited 88.31% less settlement than the DCM columns at the embankment crest. Parametric analysis revealed that closer column spacing (1.67 m) reduced settlements to 0.0032 m for TDM compared with 0.023 m at wider spacing (3.0 m). The TDM columns also demonstrated more controlled consolidation behavior with smoother settlement time histories and reduced excess pore water pressure fluctuations. The findings indicate that TDM columns provide superior seismic performance through enhanced load transfer mechanisms and improved soil‒structure interactions, making them the preferred solution for highway embankments in seismically active regions.