DEVELOPMENT ON LARGE DIRECT SHEAR EQUIPMENT FOR SOIL-ROCK MIXTURE AND EXPERIMENTAL STUDY ON STRENGTH CHARACTERISTICS OF STRAIN LOCKING

As a special engineering geological material between homogeneous soil mass and cataclastic rock mass,soil and rock mixture(SRM) is widely distributed in China. This paper summarizes the design parameters and functional advantages of the main large direct shear apparatus at home and abroad. It researches the SRM-1000 type large geotechnical shear strength experiment equipment with motor servo control. It realizes the direct shear test,the oblique shear test and shear test,freeze-thaw cycling test,based on multi-scale,creep,freezing-thawing and seepage control conditions of more physical field. The new apparatus solves the problems including that the normal stress is not constant,the vertical load cannot be aligned to the sample center,the shear failure surface is unique and fixed,and the hydraulic system is unstable. Samples with different stone contents(0,30%,50%,70%) and particle sizes(L1,L2,L3,L4)are used to test the direct shear deformation and strength characteristics under different vertical pressures(50 kPa,200 kPa,300 kPa,400 kPa). The structural characteristics of force chain between block stones in shear zone are monitored by aluminum wires. The variation rules of bulk shrinkage and expansion caused by compaction,slip and dislocation of block stones are studied. The characteristics of strain hardening and strain locking strength of SRM under different conditions are revealed.