Causes of Landslides in Road Embankment with Retaining Wall and Pile Foundation: A Case Study of National Road Project in Porong-Sidoarjo, Indonesia

This study was conducted to determine the cause of landslides in the toll road embankment of the national road project in the Porong-Sidoarjo area. The landslide was observed only on the north side of the embankment, with a maximum height of 7.8 meters from the subgrade despite the reinforcement with a retaining wall and pile foundation. The land shift and subsidence on the Northside led to a decline in the embankment elevation and the displacement to a maximum depth of 3.50 m. Back analysis through the limit equilibrium method was used to determine the strength of the existing reinforcement against the landslide. The results showed that the heavy rain was indeed one of the causes of landslides in the location, while the main cause was the depth of soft soil, much deeper than those in the surrounding locations. This is why a severe landslide was recorded on one side of the embankment. Moreover, the existing anti-slide pile reinforcement was discovered not to be sufficient due to its shallower length compared to the area of the landslide, and this was associated with the absence of overall stability analysis in this design. The findings showed that it is necessary to conduct a comparative study between the overall stability and the active and passive forces analyses for the soil to produce the safest design required to avoid landslides.