Stability analysis of a 9-level boulder-filled slope reinforced with anti-slide piles

The secondary excavation of existing slopes for expressway widening in mountainous regions often encounters giant boulders embedded within the slopes, posing significant stability challenges, particularly during anti-slide pile construction. This study investigates the stability of boulder-embedded slopes throughout the anti-slide pile construction process using finite element numerical simulation, based on a highway widening project. The results demonstrate that the spatial distribution of boulders is a critical factor controlling slope stability. Boulders located in the upper-middle and lower-middle parts of the slope can enhance stability during different stages of anti-slide pile drilling by increasing the shear strength of the soil mass and providing a confining effect; whereas shallow boulders adversely affect stability due to their self-weight effects. Furthermore, it was found that the presence of boulders behind the pile alignment induces significant plastic strain zones in the surrounding soil during drilling, which is detrimental to excavation stability. This investigation concludes that the influence of boulder distribution and its dynamic interaction with anti-slide pile construction phases must be carefully considered in the design and construction of slope widening works.