Direct shear test is a traditional method for the measure of coarse grained soils strength indexes, but the testing apparatus has significant technical defects,which not only cause shear area gradually reducing, the center position of shear surface gradually offsetting, with the occurrence and development of shear displacement, but also normal stress increasing and irregularly distributing on shear surface. In order to overcome these defects, a new direct shear testing apparatus for large coarse grained soils was developed, by using the framework of gear and rack to fix the position of shear area, and by using equalizing technic of linear ratio pressure adjustment to keep the normal stress from varying.
