Advance in research on shear strength of unsaturated soil

The shear strength of unsaturated soil is one of the important engineering properties. On the basis of referring to the Chinese and foreign literatures, mainly from the theories and formulas, instruments as well as the specific aspects of the experimental research results to summarize, the paper outlines the advance in research on shear strength of unsaturated soil. Although different scholars have carried out extensive studies and obtained certain research results, also, the view of the difference between shear strength of unsaturated soil and shear strength of saturated soil is the matrix suction's contribution to the strength is approved by academia now. There are still some problems that the scope of shear strength formulas of unsaturated soil, the difficulty of measuring matrix suction and the experimental conditions can't reflect the real stress state of unsaturated soil. Therefore, the further researches are needed to improve the shear strength theory system of unsaturated soil.