Abstract:The true triaxial apparatus is an ideal instrument to study the mechanical properties of soil under complex stress state, but how to keep the loading structure and soil without friction and independent loading in three directions is the technical bottleneck of the development of true triaxial apparatus. Aiming at the problem of bidirectional friction between rigid loading plate and specimen in rigid-flexible compound true triaxial apparatus, based on a new friction reduction method in which the contact between soil and loading plate is changed from whole contact to distributed contact and sliding friction to rolling friction, a bidirectional micro-friction load transfer plate for true triaxial test is developed. The structure principle and detail structure of the device are introduced in detail. The effect of the friction-reducing measures of the distributed contact instead of the integral contact and sliding friction into rolling friction is demonstrated by large-scale direct shear test and numerical calculation. The results show that: 1) The friction coefficient between the specimen and the loading plate is tested by large-scale direct shear test, and the value is as low as 0.023. Compared with the traditional friction reduction method, the friction coefficient can be reduced by more than 90%. 2) Compared with the integral contact, the distributed contact can make the stress and deformation of the sample in three directions more uniform, and reduce the friction between the sample and the loading plate to a great extent. 3) The distributed sliding blocks are overlapped with each other and the gap is reserved to meet the synchronous deformation with the sample, and the three-dimensional non-interference independent loading of true triaxial test under the condition of large deformation (the maximum vertical deformation is 90 mm, and the strain is up to 15%) is realized. The successful development of the bi-directional micro friction load transfer plate for geotechnical true triaxial test effectively eliminates the interfacial friction between the specimen and the loading plate, so that the specimen can deform freely in both directions in the tangent direction of the contact surface, and ensure that the three-dimensional loading does not interfere with each other under the condition of large deformation, solving the key technical problems in the development of true triaxial apparatus.