Influence of confined water pocket in deep fill layers on cut slopes stability

Confined water pockets in deep artificial fill are commonly simplified as groundwater-level rise, although their localized pressure, uplift force, and stress-redistribution effects may control the stability of cut slopes and tunnel portals. This study examines this problem using the Tangshan Road Interchange and Connecting Road Project of Qingyin Expressway as a case study. A two-stage framework was adopted. First, Geo5 was used for code-oriented limit-equilibrium evaluation by representing the water pocket as an equivalent groundwater uplift. Second, PLAXIS 2D was used to model the water pocket explicitly and quantify the effects of pocket diameter (d) and distance to the slope face (L). In this paper, Option 1 refers to a reinforcement-dominated steep-slope design with grouting and a 1:1 slope ratio, whereas Option 2 refers to a geometry-optimized design with a gentler 1:2.5 slope ratio and extended drainage measures. The Geo5 results show that the grouted slope is acceptable when the water pocket is ignored (factor of safety = 1.08) but becomes unstable when the pocket is represented as groundwater uplift (factor of safety = 0.92). The optimized cutting Option increases the factor of safety to 1.18. The PLAXIS results further show that Option 1 is highly sensitive to pocket geometry, with the factor of safety decreasing from 1.076 to 0.459 as d increases and L decreases. Option 2 is more robust, with the factor of safety decreasing from 1.380 to 0.904 under the most adverse tested case and remaining above 1.0 in most other cases. The results demonstrate that, when the distribution of confined water pockets is uncertain, geometric optimization and drainage provide a more reliable stability reserve than reinforcement measures that rely mainly on strength enhancement.