Tensile strength is often ignored in traditional research of engineering geology and soil mechanics

however

tensile strength plays a critical role in the stability assessment of red soil collapse

soil dam

embank ment

subgrade and rubbish buried field. The tensile strength test apparatus developed by authors is used to explore two types of granite residual soil existing widely in South China

and shear strength parameters of cohesive granite residual soil are obtained through direct shear test

then the mechanism of granite residual soil's tensile strength is analysed. The results show that granite residual soil's tensile strength increases with the rising water content and dry unit weight

however the range becomes less with the rising dry unit weight and water content; the tensile of sandy granite residual soil is usually lower than that of cohesive granite residual soil

and cohesive granite residual soil's tensile strength increases with cohesion

but has little relation with angle of internal friction. The analysis of granite residual soil's tensile strength indicates that joining forces between soil particles are the main source of tensile strength

which includes joining forces with direct contact

microcosmic joining force without direct contact

and joining force aroused through cement or Gas-Liquid shrink film.