Abstract: For interlayer staggered zones revealed in Baihetan large-scale hydropower station, a preparation method of reconstituted specimens is explored to reflect in-situ stress of these zones with an alternative method of super particle processing. Meanwhile, the pre-consolidation pressure and consolidation time are controlled by the static loading. Based on unconsolidated and undrained triaxial tests on reconstituted specimens from the interlayer staggered zone under either different pre-consolidation pressures or different high confining pressures, in combination with tests of mineral composition analysis and scanning electron microscopy (SEM). The mechanical deformation characteristics of interlayer staggered zones under different pre-consolidation pressures are discussed in detail. Under different confining and pre-consolidation pressures, deviatoric stress-axial strain curves of interlayer staggered zones reconstituted specimens exhibit strain hardening, and the plastic failure shows as the waist-drum shape. Under the same pre-consolidation pressure conditions, the failure stress, deformation modulus and Poisson’s ratio increase with the increase of confining pressure, and the expansion effect is highly obvious. However, under the same confining pressure, the failure stress, deformation modulus and Poisson’s ratio gradually increase with the increase of pre-consolidation pressure, while the Poisson’s ratio decreases slightly. The cohesion decreases and the internal friction angle increases respectively, with consolidation pressure enhancing. The qualitative and quantitative microstructure analysis further reveal that the plastic deformation of the interlayer staggered zone, as rock materials containning fragments, mainly resulted from particle breakage and directional arrangement under high stress. Therefore, the pre-consolidation pressure is an important factor affecting the characteristics of the interlayer staggered zone.

Key words: interlayer staggered zone, pre-consolidation pressure, particle crushing