Back-calculation of pillar foundation for Skjeggestad Bridge

Abstract

In 2015, a landslide incapacitated the expressway E18 in southern Norway because one of the large foundation pillars of the southern lane of Skjeggestad Bridge near Mofjellbekken failed. This accident immobilised throughway traffic between Oslo and southern Norway for 17 months until the bridge became fully operational again. This paper focuses on the adjacent bridge pillar of the northern lane which experienced substantial displacements during the landslide. The paper presents the back-calculated reserve capacity of the pile foundation immediately after the landslide occurred. This was essential to establish the impact of the slide on the foundation capacity and evaluate the safety of the northern lane for traffic. The paper is a companion of the paper presenting the two-and three-dimensional analyses of the landslide that occurred in Mofjellbekken. The software Trimble NovaPoint Geosuite was used for an integrated design approach examining the soil layering, selecting the soil parameters and doing capacity calculations on the pile foundation (and calculating the stability analyses in the companion paper). The soil parameters were selected based on a statistical analysis of the key parameters and for cases with insufficient information correlations on similar soils are used. Two modelling approached were investigated to simulate the slide impact on the piles. The sensitivity of the lateral performance of the piles to soil stiffness was investigated based on recommendations from different guidelines. The implication of these analyses on pile cross-sectional utilization is discussed.