Jungjoo Kim

Evaluation of rock load based on critical shear strain concept on tunnels

After studying the characteristics of three different evaluation methods of rock load; namely theoretical method, empirical method and numerical method, there were too many limitations for them to be applied on tunnels. Therefore, in this research paper, the method based on numerical analysis is selected to use as this method is the most reasonable one since it considers all parameters that are necessary for rock load estimations, and it also considers the interaction between ground and tunnel support. The critical shear strain concept formulated by Sakurai (1981) was used in order to measure exact rock load values based on numerical analysis. Evaluation on a Level 1 rock load height, which is depicted by the stable region in the graph shows that rock load is not affecting between ground grade 1~3, and it was evaluated that the fourth and fifth grades show less values of rock load height which led to the conclusion of a more economical design of concrete lining.

Stability analysis of an existing utility tunnel due to the excavation of a divergence tunnel emerging from double-deck tunnel

Government plans to construct a double-deck tunnel under a portion of Gyeongbu Expressway that will solve traffic problems and could also be used as a flood storage facility. Divergence tunnels connect the main tunnel to the urban areas and their construction effects on adjacent structures at shallow depth need to be analyzed. This study primarily includes the numerical analysis of construction effects of divergence tunnels on utility tunnels. The utility tunnel was analyzed for three cases of volume loss applied to the divergence tunnel and two cases of the angle between main tunnel and divergence tunnel (36° and 45°). The results show that the more the volume loss was applied and the shorter the distance was between utility tunnel and divergence tunnel, the more the utility tunnel was affected in terms of induced displacements, angular displacement and stability. The worst scenario was found out to be the one where the angle between main tunnel and divergence tunnel was 36° and the distance between divergence tunnel and utility tunnel was 10 m, resulting in the largest displacement and differential settlement at the bottom of the utility tunnel. A relationship between the angular displacement and the distance to diameter ratio was also established.

3-Dimensional numerical analysis on support performance of early-high-strength shotcrete

Now-a-days, the trend in constructing tunnels is to build more deeper, more longer tunnels of greater cross-sections. That’s why, the demand of “Early-high-strength shotcrete” is very high because of their advantage of attaining higher strength immediately after excavation, which controls the ground subsidence. So, this study reveals the supporting phenomena of early-high-strength shotcrete, using three-dimensional numerical analysis. The crux of this study can be applied practically in construction sites also. Support Performance of two different qualities of shotcrete was checked out, by keeping the general shotcrete’s thickness constant and comparing it with early-high-strength shotcrete’s thickness decreasing it gradually in five steps, and analysing/comparing the support performance in all cases. Effect of using early-high-strength shotcrete was analysed to save the cost of steel sets, which are widely used for supporting the ground before the hardening of general shotcrete. The results of numerical analysis on the performance of early-high-strength shotcrete show that, it behaves more effectively under worse ground conditions and it can support the ground more conveniently than steel sets, before the shotcrete is hardened.