The granite residual soils were sieved into five groups to study their tensile mechanics. The soil mineral compositions before and after HCL treatments were measured with X-ray diffraction

and the tensile strengthes of granite residual soils were tested with the direct tension apparatus. The changes of particles before and after HCL treatments were analyzed with micro-tomography method. The results showed that α-FeO(OH)

α-Fe

2

O

3

and Fe

3

O

4

disappeared after HCL treatment. The tensile strength of different groups of soils firstly increased and then decreased with water content increasing (existing a convex peak). After HCl treatments

the iron and aluminum colloids wrapped around the basic aggregate units of the granite residual soils and the cements between the different structural units were consumed in the chemical reaction with HCl treatments

which resulted in the particle sizes of the granite residual soils decreasing. The destruction of microstructures led to the granite residual soil aggregates losing cements binding. The decreasing suctions

especially the structure suctions

between grains of the granite residual soil led to that the samples were easily broken under the direct tension effect.