The compressive strength of a soil bag pile when compressed vertically and the shear strength when sheared laterally were evaluated by performing a series of full-scale loading tests. The effects of soil bag material, backfill soil type, number of soil bags in a pile and associated effects of the end restraint at the top and bottom ends of a soil bag pile were evaluated. The results of vertical compression tests showed that initial compaction of the backfill in the soil bags is effective in increasing the initial stiffness at small deformation, and that preloading is even more effective in increasing the overall stiffness and decreasing the creep deformation. The shear strength of a soil bag pile subjected to lateral shear is substantially smaller as compared with a high compressive strength when compressed vertically. It was found that the shear strength of well-graded granular backfill was partially mobilised in vertical compression tests but the mobilisation was even lower in the lateral shear tests. The soil bag pile showed highly anisotropic strength characteristics, resulting from no or negligible complementary shear stresses acting at the vertical interface between the horizontally adjacent soil bags and highly anisotropic reinforcing effects of geosynthetic cover sheets of soil bags.
A series of consolidated drained triaxial compression tests were performed on recycled concrete aggregates to investigate the feasibility of their use as a backfill material for geotechnical engineering structures requiring a high stability while allowing a limited amount of deformation, such as embankments and conventional type and geosynthetic-reinforced soil retaining walls supporting highway and railway. The experimental results showed the following. The compressive strength max when well compacted at water content in the vicinity of the optimum water content wopt is similar to that of typical well graded gravelly soil that is categorized as the highest class backfill material. When well compacted at the same energy level, the peak strength and pre-peak stiffness of recycled concrete aggregate is insensitive to changes in the moulding water content relative to wopt. When well compacted around wopt, the effect of confining pressure on max is similar to the one of typical well graded gravelly soil, while confined saturation does not have any detrimental effects on the max and pre-peak stiffness. With a decrease in the compacted dry density from the maximum dry density at fixed water content around wopt for a given compaction energy level, the max and pre-peak stiffness decreases at a very high rate. The viscous property of the recycled concrete aggregate is similar to the one of ordinary type backfill materials. When well compacted around wopt, residual strains by sustained and cyclic loading are not significant.
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