An experimental study on the development of high performance shotcrete for permanent tunnel support

摘要

Recently, the study of high performance shotcrete as a permanent tunnel support has gained an increasing amount of attention in Korea. However, several attempts to adapt permanent shotcrete lining tunnel with PCL(Precast Concrete Lining) instead of conventional in-situ concrete lining, have been abolished due to the lack of trust on the performance of rock bolt and shotcrete as a permanent tunnel support. Therefore, in this study, target performance levels of shotcrete (compressive strength over 40MPa, flexural strength over 4.5 MPa) were set up to achieve long-term durability for the life-time of tunnel. The maximum size of aggregate was 10 mm and hooked-ends type steel fiber were used for mix design. The alkali free accelerator was mainly utilized for the test, and the aluminate and the silicate accelerators were used for comparison. The silica fume of 4, 7, 10% was added substituting the same amount of cement. 987 test samples consisting of cylinder, beam, round panel(by RTA, Australia) and square panel(by EFNARC) were prepared using a shotcrete machine, Meyco Suprema. Several tests on the samples were carried out by the elapsed time of 3, 7,28 days and 3 months and will be continued to the elapsed time of 6, 12 and 24 months. The compressive strength, the flexural strength and the flexural toughness were measured to monitor the performance of shotcrete according to each elapsed time. Finally, the optimum mix composition was proposed to meet the target performance level of the shotcrete as a tunnel support.