Abstract: The effect of sample preparation methods on the shear strength of Ningming expansive soils is investigated by using direct shear tests. Three different sample preparation methods were explored: fresh water prepared submerged in salt water; salt water prepared sample submerged in salt water and fresh water prepared sample leached by salt water. The effect of different concentration of the salt water are also investigated. The results indicate that, the concentration of fluid in the soil as well as the sample preparation methods have effects on the shear strength. With the increase of the salt concentration, the cohesion as well as internal friction angle decrease in samples prepared by all three different methods. The shear strength values are different in samples prepared with different methods. Sample prepared by the salt water leaching has the largest influence on the shear strength.

Key words: compacted samples, sample preparation methods, direct shear tests