Two different collapse models are developed for predicting the collapse resistance of encased pipes for pipe rehabilitation applications. One model corresponds to an unsymmetrical collapse mode and the other one corresponds to a symmetrical collapse mode. Attention is focused here on modeling the effect of the small radial gap between the encased pipe and the host pipe on encased pipe collapse resistance. This small radial gap is assumed to have developed when installing the encased pipe into the host pipe. It increases in size when subjected to temperature change, swelling, and application of external hydrostatic pressure. The predictions by the models correlate well with some collapse test results on encased pipes.

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This study treated the surface of ultra-high molecular weight polyethylene (UHMWPE) fibres with plasma and optimized the parameters of plasma treatment. On this basis, UHMWPE fibre composites reinforced with carbon nanotubes (CNTs) were prepared, and the changes of UHMWPE fibres before and after modification in the chemical composition, surface morphology, and mechanical properties were studied. The results showed that oxygen-containing functional groups and active free radicals on the surface of plasma treated UHMWPE fibres increased. Tensile strength and modulus of UHMWPE fibre composites reinforced with CNTs increased by 16.3% and 21%.