Field measurement and failure forecast during the remediation of a failed cut slope

A large number of deep cuts are formed during the construction of expressways in mountainous areas. Inadequate interpretation of ground conditions is a major contributing factor to the failure of cut slopes. This study focuses on the Hongyan landslide along the S26 expressway. Due to lack of an adequate pre-construction investigation, a landslide was triggered by small-scale excavation at the toe part of the slope. The potential slip surface was incorrectly located; consequently, two rows of stabilizing piles were not long enough to reach stable rocks. To overcome the mistake, two additional rows of piles were installed. During construction, both slope deformation and the stress of reinforced bars in piles were monitored for safety considerations. A Verhulst model-based failure forecast was also utilized to insure the stability of the slope during remedial works. Reviewing this landslide reveals a number of lessons. First, sufficient geological investigation and careful interpretation of ground conditions are mandatory prior to the design of a cut slope. Second, systematic field monitoring is strongly recommended, especially when the geology of the slope is complex and it is difficult to determine failure patterns. Third, the failure forecast can serve as a supplementary measure to insure the safety of workers and slopes. Last, it always takes some time for stabilizing piles to mobilize.