<p>Secondary excavation of existing cutting slopes is a cost-effective option in mountainous highway expansion projects and attracts the interest of engineers because it may induce tensile cracks. Thus, in this study, the impact of cracks on excavated slopes with reinforcements was investigated. A validated extended finite element method (XFEM) model, based on Shantou-Meizhou highway expansion project, analyzed the slope stability and lateral stress along the stabilizing pile under varying crack properties (i.e., locations and length) and slope ratio of the trailing edge (<i>α</i>). Additionally, further analyses were performed which considered the hydraulic properties of carbonaceous mudstone (i.e., natural water content and groundwater level). The results indicate that: (1) Longer cracks induce the discontinuity of the soil stress and the closer distance of the crack from cutting slope leads to a shallower slip plane, which result in smaller stress on the pile and factors of safety (FOS); (2) The increasing <i>α</i> reduces the FOS, but the change in lateral stress is nonlinear; (3) The decline in natural water content increases FOS, while the rise of groundwater impacts it significantly. The results demonstrate that the location and length of cracks are critical factors for the stability of excavated slopes. Besides, the hydraulic conditions should be controlled in carbonaceous mudstone slopes to maintain safety margins. This study could provide guidance for similar projects.</p>