Comparative Evaluation of the Combined Effect of Stone Columns and Cement Grouting on the Shear Strength and Final Settlement of Saturated Clay Soils Using Numerical Modelling and Field Data

Abstract

Improvement of saturated clay soils in large-scale civil projects has always been one of the major challenges in geotechnical engineering. Combining different ground improvement methods, such as stone columns and cement grouting, provides an effective solution for enhancing shear strength and reducing final settlement. In this study, both field and numerical investigations were conducted to evaluate the combined effect of stone columns and cement grouting on the mechanical parameters of saturated clay soils. Field tests were carried out in Gilan Province, Iran, where 12 stone columns with a diameter of 0.8 m were constructed, followed by cement grout injection with a 35% concentration at a depth of 6 m. Results from plate load tests (PLT) and direct shear tests (DST) indicated that the undrained shear strength increased from 40 to about 86 kPa, while final settlement decreased by more than 45%. Numerical modelling using PLAXIS 3D demonstrated a strong correlation with field data (R = 0.92). Sensitivity analysis revealed that increasing grout concentration up to 40% had the greatest effect on reducing final settlement, while increasing the column diameter beyond 1 m had a limited influence on shear strength improvement. The findings of this research can serve as a practical design reference for ground improvement projects in soft clay soils, preventing costly secondary settlements in substructure systems.