Rehabilitation of Overdeformed Metro Tunnel in Shanghai by Multiple Repair Measures

摘要

This paper presents a case study describing the effectiveness of multiple measures implemented to repair overdeformed metro shield tunnels in Shanghai. The changes in horizontal diameter were up to 3.6% of the tunnels' diameters due to unexpected surcharge at the ground surface. The surcharge was removed, and then structural reinforcements were added. The tunnel sections that had extremely large convergences were reinforced by bonding aromatic fiber-reinforced plastic sheets to the tunnel crown and bonding steel plates to the inner surface of the full lining rings. The tunnel sections that had relatively large convergences were reinforced only by bonding fiber-reinforced plastic sheets. In addition, instead of installing steel plates at these sections, cement-sodium silicate grouting was performed at the two sides of the tunnel springline three years after reinforcement by fiber-reinforced plastic sheets, because a gradual increase in convergence was observed at these sections. The grouting resulted in a 30% reduction in horizontal convergence. However, less than 5% of the grouted volume contributed to the horizontal movement of the tunnel cross sections. Cone penetration tests were conducted at the grouted sections as well as at green field sections. The results showed an increase in cone tip resistance of about 110%-130% in the grouted zones compared to the nongrouted zones. However, the increase was localized and had a high coefficient of variance, indicating that the improvement from grouting was highly variable.