Abstract: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.