Based on a self-made constant-stiffness direct shear instrument designed by Qingdao University of Technology

direct shear tests were conducted on four types of clayey soil-concrete interface with water contents of 18%

20%

25%and 28%.The shear stress-strain response was analyzed under different water contents and normal stresses

and the effect of water content on the properties of the clayey soil-concrete interface was discussed.Test results showed that water content affected the shear deformation of the clayey soil-concrete surface.When the water content was high

shear deformation exhibited a typical elasto-plastic deformation after the peak interface shear stress was reached.In contrast

when the water content was low the curve of interface shear stress versus shear displacement showed a shape of fold line.The interface shear strength decreased with the increase of water content

but a linear relationship held between shear strength and normal stress.The cohesion was affected by the critical water content of 25%;it increased with increasing water contents when the water content was less than the critical value.However

it decreased with increasing water contents while the water content was more than the critical value.Water contents exerted a limit impact on the frictional coefficient

whose variation was merely 5.5%.