Influence of eggshell powder on the unconfined compressive strength and compressibility behavior of clay soil

In this study, the influence of eggshell powder on soil strength and compressibility behavior was investigated using unconfined compressive strength and oedometer tests. Soil specimens were prepared with different eggshell powder contents and tested after 7 and 28 days of curing. Eggshell powder produced a significant difference in soil behavior based on dosage. At appropriate contents, eggshell powder improved strength and decreased compressibility through filling voids, packing particles more effectively, and transferring stress within the soil matrix. However, excessive eggshell powder content led to lower strength due to disturbance of the soil skeleton and reduction in interparticle friction. At 10% eggshell powder, the maximum dry density increased from 1.656 to 1.683 g/cm3 while the optimum moisture content from 18% to 16%. The 7-day compressive strength increased about 28.4%, and compressibility decreased by approximately 7% as the final void ratio decreased from 0.45 to 0.42. Overall, eggshell powder acted mainly as a microstructural modifier rather than a strong cementing agent, and its effectiveness depended on the optimum content. The study confirms that eggshell powder is a promising sustainable physical soil modifier additive for improving selected soil engineering properties of clay soil.