PVA 섬유보강 시멘트-점토 혼합토의 강도특성에 관한 실험적 연구

Abstract

Currently, the stability analysis of embankments founded on soft ground stabilized with DCM (Deep Cement Mixing) columns has been performed based on a limit equilibrium analysis by using a composit shear strength. Recent research efforts based on centrifuge tests, numerical analyses, and case studies revealed that the group of DCM columns might fail by several failure modes governed not only by shear failure but also by bending or tilting failure. So, the applicability of current practice for the stability analysis of embankments founded on soft ground stabilized with DCM columns is uncertain. Therefore, the bending capacity of DCM columns needs to be incorporated in the stability analysis. In this study, PVA (Polyvinyl alcohol) fiber has been added to improve the bending capacity of DCM columns. This thesis presents the effects of cement contents, PVA fiber contents and lengths, and curing periods on the stress-strain behavior and the strength characteristics of PVA fiber reinforced cement-clay mixtures through a series of unconfined compressive strength test, third-point bending test, splitting tensile strength test, and flexural performance test. Test specimens were prepared with a variety of cement contents, fiber contents, fiber lengths, and curing periods to investigate the effect of these parameters on the behavior and the strength characteristics of PVA fiber reinforced clayey soil-cement mixture. In addition, a compresso-meter has been revised to measure the internal strain of test specimen during the process of loading. The internal strain was used to evaluate the secant moduli (E50) of soil-cement mixtures. The PVA fiber reinforced clayey soil-cement mixture showed a ductile failure whereas the unreinforced clayey soil-cement mixture showed a brittle failure. The inclusion of PVA fiber in clayey soil-cement mixtures improved the compressive strength, the flexural strength, and the tensile strength of clayey soil-cement mixtures in several aspects. As the cement content and the amount of PVA fibers in the mixture increases, the strength of the mixture increases. As the curing period is increased, the unconfined compressive strength is increased irrespective of fiber inclusion. But, the effect of curing period on the long-term flexural strength is minimal. In addition, it has been proved that the inclusion of PVA fiber in clayey soil-cement mixtures can effectively control the growth of crack after the initial crack has been developed and thereby preventing an abrupt failure of mixtures. This might be attributed to the increased energy absorption capacity of PVA fiber reinforced cement-clay mixtures.