Numerical and experimental investigation of pillar reinforcement with pressurized grouting and pre-stress

To prevent and/or minimize flood-induced damage in metropolitan cities like Seoul, South Korea, construction of an underground rainwater storage cavern becomes an alternative to other conventional countermeasures. In this paper, a new pillar-reinforcement method was developed to improve pillar stability that is crucial for the successful construction of the rainwater storage cavern. Three pillar-reinforcing scenarios were compared numerically: (1) shotcrete installation only, (2) shotcrete installation and pillar-reinforcement with radially pressurized grouting and pre-stress, and (3) shotcrete installation and pillar-reinforcement with vertical upward pressurized grouting and pre-stress. The third pillar-reinforcement readily made the stress condition return to an elastic state showing superior performance to the other methods. In addition, two pillar widths of 800 mm and 1200 mm were considered to investigate the effects of pillar width on pillar reinforcement by carrying out a small-scale model test, in which the three pillar-reinforcement scenarios can be modeled step-by-step. The pillar width of 1200 mm resulted in smaller major principal stresses, representing better reinforcing performance than that of 800 mm. Moreover, it was shown that the pressurized grouting enhances the ground strength and more importantly lessened stress concentration in the pillar. However, applying pre-stress further increased ground strength because of the increase in internal pressure.