No abstract

This paper discusses the multi-level cyclic triaxial testing of bimsoils (block-inmatrix soils), which are chaotic, mechanically and/or spatially heterogeneous geological masses in geotechnical construction. The cyclic triaxial tests simulate the behavior of bimsoil material under varying number of passing vehicle wheels. It is found that the applied confining pressure alters the stress state of the tested bimsoil and a transmission from strain softening to strain hardening occurs. The bimsoil deformation, strength, fatigue life, and stiffness are improved as the ambient pressure increases. The strain rate analysis reveals that the strong volumetric dilatancy occurs earlier for a bimsoil under relatively low confining pressure. Post-test CT scanning shows the mesoscopic structural changes inside the bimsoil, including the multiple interface cracking behaviors and crack propagation surrounding the rock blocks. It is suggested that the contact, interlocking, occlusion, and separation among the existing blocks greatly contribute to the volume dilatancy characteristics of bimsoil under high ambient pressure.

Exfoliated poly(ethylene terephthalate) (PET)/organoclay nanocomposites were prepared by extrusion blending method with different clay contents and molecular weights of raw PET. Pyromellitic dianhydride (PMDA) was extruded, together with PET and clay, to introduce long-chain branching to PET backbone and delaminate the clay layers. Although the molecular weights and viscoelastic properties of nanocomposites were much lower than those of foamable PMDA-modified PET, the melt foamability of nanocomposites was significantly improved by the well-dispersed clays due to the heterogeneous nucleation effect, enhanced nonisothermal crystallization rate, and so on. Foaming temperature windows with a width of 20−60°C were explored for PET/clay nanocomposites with intrinsic viscosities of 0.67−0.94 dL/g, in which nanocomposites foams with cell diameters of 29−53 μm, cell densities of 6.5 × 10 7 −6.9 × 10 8 cells/cm 3 , and expansion ratio of 10−50 could be controllably produced using supercritical CO 2 as a blowing agent.

In this study, we experimentally investigated the mechanical behaviors of a fault unwelded bimrock exposed to first freeze-thaw weathering and then disturbed stress conditions. The impact of freeze-thaw damage on volumetric deformation, damage propagation, and mesoscopic instability mode was studied. Test results show that the block-matrix interface cracking easily occurs after freeze-thaw treatment. The strain rate increases with the increase of the freeze-thaw cycle, and an early instability precursor is issued from the evolution of volumetric strain rare. In addition, a coupled evolution model considering the mechanical damage and the freeze-thaw weathering damage was defined, and it was suggested that the model pattern has obviously correlation with the occurrence of freeze-thaw damage. Moreover, posttest CT scanning revealed the influence of freeze-thaw on meso-cracking and volumetric dilatancy pattern. It is found that the block contact, interlocking, occlusion, and separation contribute a lot to bimrock volumetric expansion.