Akitoshi Mochizuki

A New Independent Principal Stress Control Apparatus

A newly designed independent principal stress control apparatus is presented together with some typical test results obtained by the apparatus. The minor principal stress on a cuboidal specimen, σ x , is loaded by air pressure in the triaxial cell, and two couples of rigid platens are used to load the major and intermediate principal stresses, σ z and σ y . This apparatus has the following features: 1. The axial stress, σ z , is applied from the underside of the specimen, the reaction being supported by a frame in the cell. It makes both the anisotropic consolidation and extension test possible; it also makes the preparation of sand or soft clay specimens very easy. 2. A new device to load intermediate stress, σ y , was developed to minimize the friction between lateral loading platens and the specimen. 3. A new system to measure the specimen deformation is also developed with a no-contact gap sensor which moves up and down during the test. It can measure the total volume change and also the change of the shape of the specimen. Some typical results of triaxial test, plane strain test, and independent stress control test on two sands are presented. Deformation or distribution of strain of the specimen observed by no-contact gap sensor is also discussed.