High rockfill embankment for the extension of an airport main runway

The main runway of A Coruna airport in Spain is being lengthened by 400 m. The natural ground surface is sloping down gently, and this lead to a maximum height of the new embankment extension of about 35 m. The embankment has been made with a good quality granite rockfill, with slopes 1.4(H): 1(V). The foundation ground is formed by schist of weathering degree II-III, with a soil cover 5 to 12 m thick. The allowable post-construction log-term settlement was fixed as 0.20 m. Preliminary design calculations showed that this limit would be exceeded in about 30% of the area. Hence, stone columns were used, in addition to excavation and replacement of the inadequate shallow soft soils. Recorded settlements showed a rapid development during the construction period, which extended to about 2 years. The analysis pays special attention to the effect of the stone columns on the overall ground stiffness. Stability analyses are also presented. The interaction with nearby structures and facilities was also relevant, given the uncommon height of the embankment.