The treatment approaches for weathered residual soil of granite and alluvial-diluvial，which are the most widespread excavated soils in South China，were put forward． After the processing procedures，the usable excava-ted soils were utilized to partially or fully replace the river sand to prepare cement mortar，and the water-reducing admixture demand for suitable working performance of the cement mortar was investigated． The compressive and flexural tensile tests were carried out to examine the influence of the replacement ratio of excavated soil on the me-chanical behavior of cement mortar containing excavated soil． The results show that: (1) on the premise of ensu-ring good working performance of the cement mortar，water-reducing admixture demand increases with the increase of the replacement ratio of excavated soil，but its largest dosage (calculated by solid content) accounts for only 1. 1% of the binding material; (2) the compressive strength，flexural tensile strength and elastic modulus of the
cement mortar prepared partially or fully with the usable content of alluvial-diluvial soil are roughly equivalent to those of the cement mortar containing no alluvial-diluvial soil，so it is practicable to fully replace the river sand with the usable content of alluvial-diluvial soil in actual practice; (3) replacing 30% of the river sand with the us-able content of weathered residual soil of granite has no significant adverse effects on the mechanical behaviors of the cement mortar，but when the replacement ratio increases to 50%，the 28d flexural tensile strength，compres-sive strength and elastic modulus of the cement mortar maximally drop by 6%，15% and 10%，respectively，compared with those of the cement mortar without weathered residual soil of granite． It is suggested that the re-placement ratio of such soil should not exceed 50% in practice．