Abstract:

During tunnel excavation in a filled karst cavity, slope landslides easily occur. Therefore, field investigation and MultiFracS fracture analysis software are used to analyze the causes of crack development in the slope and the deformation of the surrounding rock, reinforcement measures for the slope are proposed, and reinforcement effects are evaluated. The following conclusions are drawn: (1) Continuous rainfall is the direct cause of the landslide of the slope. With an increase in the water content, the shear strength of the filled gravel decreases, causing considerable displacement of the karst cavity and cracks. When the water content increases to 20%, cracks in the cavity area develop further, local cracks appear, and the surface sliding displacement continues to increase. (2) The tunnel excavation disturbance accelerates the formation of through cracks between the surface cover and underlying bedrock, and the slope exhibits an overall sliding trend. Based on the field investigation and numerical analysis, the slope protection form of the "gentle slope + steel anchor pipe/anchor cable frame beam" is adopted and the anchor rod and part of the anchor cable are replaced with the grouting steel anchor pipes, which could help prevent the deformation and damage of the gravel soil in the cavity during the infiltration by rain. The fieldmeasured data demonstrate that the reinforced slope remains stable during the secondary tunneling process, thereby effectively controlling the deformation in the tunnel and the surface settlement.

Key words:  karst tunnel; filled karst cavity, gravel soil, slope landslide, crack, reinforcement measures