Abstract: The organic content in the red clay is an important factor affecting the engineering performance of cement treated soils. By testing the mechanical strength of the treated red clay with different organic content, the effect of organic matter on the deformation and strength properties of the treated red clay was evaluated. The mechanism of organic matter in the cement-treated red clay was analyzed by the Scanning Electronic Microscope (SEM) and X-Ray Diffraction tests. The results show that, within the organic content studied, the tested sample cohesion increases with the organic content, while the unconfined compressive strength and internal friction angle of the sample continue to decrease until close to the critical value of organic content. At the microscopic level, the organic content affects the mechanical properties of the cement treated red clay by inhibiting the formation of hydration products and inducing the transformation of its structure and morphology.

Key words: red clay, cement treated soil, organic matter, mechanical property, microstructure