Abstract：Breakage is an important factor to influence wetting deformation of coarse-grained materials；and farther study is necessary. The wetting triaxial tests under various confining pressures and wetting stress levels are carried out on a coarse-grained material with a new stress-control triaxial apparatus；and the grain grading test is done with the samples before and after wetting. According to the tests，the cause of grain breakage due to wetting is explained；and the wetting deformation and grain breakage value expressed by Hardin index are obtained. The test results indicate that the wetting deformation is related to confining pressures and wetting stress levels；the wetting induces the grain breakage；and the wetting grain breakage has obvious influence upon the grain size distribution curve. The difference of grain size distribution curve before and after wetting is like a hump；and the maximum value is located at about the grain diameter of 25% of the grain size distribution curve . The grain breakage caused by the wetting reduce the coefficient of curvature；the coefficient of uniformity and the special grain diameter of 60% of the grain size distribution curve and the grain breakage value becomes greater with the increase of confining pressure and wetting stress level. The wetting deformation has close correlation with the wetting grain breakage；and the axial wetting deformation is linear to the grain breakage approximately. It is found that the wetting deformation behaviour can be explained from the viewpoint of the wetting grain breakage.
