Abstract: It is of vital importance to study the mechanical response of sand in strain-path controlled tests during which the ratio of lateral to axial strain increments is kept constant.By employing a transducer for measuring the volumetric strain of the sample and adjusting the lateral stress in axial strain controlled tests,a conventional triaxial test apparatus is improved to control the strain increment ratio,defined as the ratio of lateral to axial strain increments,constant in the strain path test.The device can be applied in the investigation of stress-strain behavior of sand loaded along constant strain increment ratio paths.In addition,the constant strain path tests are conducted for sand.Comparison and analysis of the test results indicate the satisfactory experimental precision of the apparatus,thus showing its effectiveness.