Grouting design for shield tunnels in strong karst areas

Abstract:

Karst geology has negative impact on subway tunnel construction， and may bring potential safety hazards and increase construction difficulty. Based on the exploration data of the Nanjing to Jurong intercity rail project， the karst caves in the interval are classified， the karst treatment experience of similar strong karst formations are summarized， and the relevant treatment principles are proposed. The three-dimensional finite element simulation is used to determine the karst treatment range with the corresponding treatment measures proposed. Sleeve valve tube grouting was used to treat caves within 3m of the outer contour of the tunnel with the deployment of the grout holes reaching the cave boundary as the criteria. The dual-fluid slurry of cement-water glass was injected from the peripheral holes， while plain cement slurry was injected from the central holes use. The grouting pressure and the grouting amount were taken as the final injection index， and grouting effect was checked by using the drilling core method to meet the requirements on strength， compactness and permeability. The core samples were found to be complete and continuous after treatment， and the cement-soil mixture was dense， which verified the feasibility of the grouting design.